CBSE Class 10 Science Chapter 8 How do Organisms Reproduce

Sexual Reproduction In Humans:

CBSE Class 10 Science Chapter 8 How do Organisms Reproduce Short Question And Answers

Question 1. What is the importance of DNA copying in reproduction?
Answer:

Reproducing organisms create new individuals that look very much like themselves. The daughter organisms and their parents look similar because their body design is similar.

• Reproduction at its most basic level involves making copies or the blueprint of the body design. The chromosomes in the nucleus of a cell contain information for the inheritance of features from parents to the next generation in the form of DNA (Deoxyribonucleic Acid, molecules).
• So, reproducing cells prepare copies of DNA molecules to keep one DNA copy with the parent cell and other copy/copies to pass on to the next generation/daughter cells.

Read and Learn More CBSE Class 10 Science Short Answer Questions

Question 2. Why is variation beneficial to the species but not necessary for the individual?
Answer:

A variation may not be beneficial for an individual that is not suitable for the niche. In this case, an individual or a few variants may not survive. This does not affect the existence of a species.

• Variations are useful for the survival of species in changed environmental situations.
• For example, if a population of reproducing organisms were suited to a particular niche (well-defined place of abode) and if the niche is drastically changed, the population could be wiped out.
• However, if some variations were to be present in a few individuals in these populations, there would be some chance for them to survive.

Question 3. How does binary fission differ from multiple fission?
Answer:

Question 4. How will an organism be benefited if it reproduces through spores?
Answer:

The nuclei in the hypha of fungus like Mucor and Rhizopus, get surrounded by a bit of cytoplasm and get a thick wall. This wall protects the spore during unfavourable conditions.

When the favourable conditions return, the spores develop into new hyphae. Thus, spores help the fungus tide over unfavourable conditions.

Question 5. Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?
Answer:

In highly developed multicellular organisms, different cell types perform different specialised functions. Reproduction in such organisms is also the function of a specific cell type.

• If the organism itself consists of many cell types, reproduction by regeneration or fragmentation cannot be achieved.
• In multicellular organisms like Hydra and Planaria regeneration is carried out by specialised cells.
• These cells proliferate and make large numbers of cells. From this mass of cells, different cells change to become various cell types and tissues.
• Such specialised cells which can regenerate or develop a new individual from their body part do not exist in complex organisms.

Question 6. Why is vegetative propagation practised for growing some types of plants?
Answer:

Reasons for growing some types of plants by vegetative propagation:

1. Plants raised by vegetative propagation can bear flowers and fruits earlier than those produced from seeds.
2. Such methods also make possible the propagation of plants such as bananas, oranges, roses and jasmine that have lost the capacity to produce seeds.
3. All plants produced by this method are genetically similar enough to the parent plant to have its all characteristics.

Question 7. Why is DNA copying an essential part of the process of reproduction?
Answer:

Reproducing organisms create new individuals that look very much like themselves. They look similar because their body designs are similar.

• The DNA present in chromosomes located in the nucleus of a cell contains information for the inheritance of features from parents to the next generation.
• So, reproducing cells creates two copies of the DNA. One copy of DNA remains in the reproducing original cell. The other copy of DNA is passed to the daughter cell formed by the parent having additional cellular apparatus.

Question 8. How is the process of pollination different from fertilisation?
Answer:

Pollination is the process by which the pollen from another reaches the stigma of the flower of the same species. Fertilisation is the process in which the male gamete fuses with the egg to form a zygote.

Question 9. What is the role of the seminal vesicles and the prostate gland?
Answer:

Seminal vesicles secrete a viscous fluid which forms most of the part of semen. It also lubricates the passage through which the sperms travel.

• This fluid also protects the sperm from the acids normally present in the urethra and female reproductive duct. The prostate gland produces prostatic fluid which is discharged into the urethra through more than two dozen fine ducts.
• There is more secretion during sexual act when they are forcefully ejected by contraction of muscular and elastic tissues.

Question 10. What are the changes seen in girls at the time of puberty?
Answer:

The females show development of breasts, darkening of nipples, menstruation and growth of public hair.

Question 11. How does the embryo get nourishment inside the mother’s body?
Answer:

After fertilisation, the lining of the uterus thickens and is richly supplied with blood to nourish the growing embryo.

• The embryo gets nutrition from the mother’s blood with the help of a special tissue called the placenta. This is disc-shaped tissue which is embedded in the uterine wall.
• The placenta contains villi on the embryo’s side of the tissue and blood spaces on the mother’s side surrounding the villi. This provides a large surface area for food and oxygen to pass from the mother to the embryo and waste products from the embryo to the mother’s diseases.

Question 12. If a woman is using a copper-T, will it help protect her from sexually transmitted
Answer:

Copper-T is a contraceptive method which prevents implantation of the zygote inside the uterus. It cannot prevent a woman from sexually transmitted diseases (STDs). STDs are transmitted by contact which cannot be prevented by copper-T.

Question 13. What are the advantages of sexual reproduction over asexual reproduction? Answer:

Sexual reproduction incorporates the process of combining DNA from two different individuals during reproduction.

• Sexual reproduction promotes variation among the offspring of the same parents and provides opportunities for new combinations of characters, thus playing an important role in the origin of new species.
• Asexual reproduction does not require a combination of DNA from two different individuals. So, it does not create variations and does not help in creating new species and evolution.

Question 5. What are the functions performed by the testes in human beings?
Answer:

Testes are the sites for the formation of sperms. They also produce a hormone named testosterone which is responsible for secondary sex characteristics in males.

Question 14. Why does menstruation occur?
Answer:

The ovary releases one egg every month and the uterus prepares for the implantation of the zygote by thickening its walls which are richly supplied by blood vessels.

If the egg is not fertilised, the uterine lining slowly breaks down and comes out through the vagina as blood and mucus. This cycle takes place regularly every month and is known as menstruation and lasts for about two to eight days.

Question 15. Draw a labelled diagram of the longitudinal section of a flower.
Answer:

Question 16. What are the different methods of contraception?
Answer:

The methods used for the regulation of childbirth are:

1. Barrier method: In this method, physical devices like condoms, cervical caps and diaphragm are used to prevent sperm from reaching upto the ovum.
2. Chemical method: In this method, specific drugs are used by females. These drugs may be (a) oral pills or (b) vaginal pills. Oral pills mainly contain hormones and are called oral contraceptives.
3. Intrauterine contraceptive devices (IUCDs): IUCDs like Copper-Tis are placed safely in the uterus by a skilled doctor. IUCDS prevent implantation of the fertilized ovum inside the uterus.
4. Surgical method: This method applies to both males and females. In males, a small portion of vas deferens and in females the fallopian tube is surgically removed or ligated (tied). It is known as vasectomy in males which prevents the release of sperm from the testis. In females, it is called tubectomy.

Question 17. How are the modes of reproduction different in unicellular and multicellular organisms?
Answer:

The modes of reproduction in unicellular organisms are:

1. Binary fission is found in unicellular animals like Amoeba, Paramecium, Euglena, etc. After attaining an optimum size the adult individual undergoes a simple division into two daughters of equal size. It consists of the division of the nucleus followed by the cleavage of cytoplasm into equal parts, each having a daughter nucleus. Binary fission can occur in any place in Amoeba.
2. Multiple fission is also a mode of asexual reproduction found in unicellular animals or protozoans, e.g., Plasmodium, and Monocystis. The nucleus of the parent cell undergoes repeated divisions to produce several daughter nuclei. The cytoplasm cleaves around each nucleus to form many daughter cells. Ultimately under favourable conditions, the parent cell membrane ruptures and daughter individuals are released. Sometimes, the daughter cells derived from multiple fission develop resistant coverings to produce spores. The process is called sporulation.
3. Budding: Some unicellular organisms such as yeast can put out small buds that separate and grow further.

The mode of reproduction in multicellular organisms

1. Fragmentation: Simple multicellular organisms such as spirogyra simply break up into smaller pieces upon maturation. These pieces, known as fragments, grow into new individuals.
2. Regeneration: In some fully differentiated organisms—an individual, such as Hydra and Planaria, if somehow cut or broken up into many pieces, many of these pieces grow into separate individuals, Regeneration is carried out by specialised cells.
3. Budding: Organisms, such as Hydra use regenerative cells for reproduction in the process of budding. In Hydra, an outgrowth, called bud, develops at a specific site. When their buds mature, they detach from the parent body and become new independent individuals.
4. Sexual reproduction: This mode of reproduction is common in complex multicellular organisms. In this mode of sexual reproduction, both sexes-males and females- are needed to produce a new generation. Thus, the sexual mode of reproduction involves two individuals.

Question 18. How does reproduction help in providing stability to populations of species?
Answer:

Variations in the population that help the population of a species to tide over adverse environmental conditions are induced by reproduction, especially by sexual reproduction. These variants are adapted to the changing environment of the niche. Reproduction also helps generate copies of individuals that are suited to a particular environment which is existing.

Question 19. What could be the reasons for adopting contraceptive methods?
Answer:

Reasons for adopting contraceptive methods

1. The sexual act always has the potential to lead to pregnancy. If a woman (mother) is not in good health or mentally unprepared, it will cause adverse effects on the mother and the foetus.
2. There are many diseases such as AIDS, gonorrhoea, and syphilis which are transmitted through sexual acts. These can be prevented by the use of contraceptives.
3. The reproduction process causes an increase in population if adequate measures are not taken to prevent pregnancy. The increase in population in our country is increasing exponentially. This puts strains on the natural resources of the country and is a major cause of poverty in our country.

Thus, adopting contraceptives can prevent:

1. Unwanted pregnancies.
2. Spread of sexually transmitted diseases (STDs) and lethal diseases like AIDS and HIV.
3. Frequent pregnancies may cause health hazards to the mother and her infant.

Question 20. List any two modes of asexual reproduction in animals. Under which mode of reproduction is vegetative propagation placed and why? List two advantages of vegetative propagation.
Answer:

Two asexual modes of reproduction in animals are:

Fission/Fragmentation/Budding/Regeneration (Any Two) Vegetative propagation is under an asexual mode of reproduction.

Reasons: Reproductive part of the plant not involved/Single parent involved.

Advantages of vegetative propagation (Any two)

1. Plants raised can bear flowers and fruits earlier than those produced from seeds.
2. Plants that have lost the capacity to produce seeds can be produced.
3. All plants produced are genetically similar to the parent plant.

Question 21. State two examples of each of the following:

1. Plants having unisexual flowers
2. Agents of pollination
3. Physical changes that are common to both boys and girls.

Answer:

1. Papaya, watermelon
2. Wind, water, air, insects (any two)
   1. Increase in height and weight. (Body becomes larger)
   2. Thinner hair appears on the legs, arms as well as on the face.
   3. Skin becomes oily and pimples develop.

Question 22. What is the placenta? State its function in human females.
Answer:

Placenta: A special tissue embedded in the uterus wall with the help of which the human embryo gets nutrition from the mother’s blood.

Functions:

1. To provide a large surface area for glucose and O2 to pass through the mother’s blood to the embryo.
2. To metabolic waste generated by the embryo is removed through the placenta into the mother’s blood.

Question 23. Variations are important for the survival of species over time. Justify this statement with reasons.
Answer:

Variations help the individuals to survive even after the drastic changes occur in nature. These changes may be in the niche, temperature, salinity water levels, etc.

Question 24. Mention the changes seen in the girls that depict the aspect of the sexual maturation of the body.
Answer:

1. Growth of pubic hair. (armpits and the genital area)
2. Breast size begins to increase with darkening of the skin of the nipples at the tips of the breast.
3. The hips widen.
4. Menstruation starts.

Question 25. Justify the following statements:

1. Variations are beneficial for the species over some time.
2. New offspring produced are similar to their parents but not identical.
3. Binary fission is different in Amoeba and Leishmania.

Answer:

1. Variations are beneficial for species because they give survival advantages even in adverse environmental conditions.
2. Similar-Same DNA Not identical-Due to variation during DNA copying
3. Amoeba-Any plane; Leishmania-definite orientation.

Question 26. Name and explain the method by which rhizopus reproduces.
Answer:

Rhizopus reproduces by spore formation.

Method:

It is a method of asexual reproduction. Spores are produced in a structure called sporangium. The nucleus divides several times within the sporangium and each nucleus with a bit of cytoplasm, develops into a spore.

Question 27. What is the effect of DNA copying, which is not perfectly accurate, on the reproduction process? How does the amount of DNA remain constant though each new generation is a combination of DNA copies of two individuals?
Answer:

1. DNA copying leads to more variations in the offspring.
2. Sexually reproducing organisms have a special lineage of cells which have only half the amount of DNA/half the number of chromosomes as the parent cell.
3. When such germ cells fuse, a new individual is formed with the same amount of DNA as that of a parent.

Question 28. Explain how organisms create an exact copy of themselves.
Answer:

To build the copies of DNA or the genetic material, the cells use biochemical reactions. Additional cellular apparatus along with the DNA copies are separated and so a cell divides to give rise to two almost identical cells.

Question 29. State the changes that take place in the uterus after the implantation of a young embryo. How does this embryo get nourishment inside the mother’s body?
Answer:

1. The uterine wall thickens, i.e., richly supplied with blood.
2. A special tissue called the placenta develops which connects the embryo to the uterine wall that provides nutrients and oxygen to it.
3. The placenta is a disc which is embedded in the uterine wall. It contains villi on the embryo’s side of the tissue. On the mother’s side are blood spaces, which surround the villi. This provides a large surface area for glucose and oxygen to pass from the mother to the embryo.

Question 30.

1. What is the location of the following:
   1. DNA in a cell
   2. Gene
2. Expand DNA.

Answer:

1. 1. In the nucleus of a cell.
   2. Located on the chromosomes.
2. Deoxyribonucleic acid

Question 31. What are chromosomes? Explain how in sexually reproducing organisms, the number of chromosomes in the progeny is maintained.
Answer:

1. Chromosomes are thread-like structures made up of DNA found in the nucleus.
2. The original number of chromosomes becomes half during gamete formation. Hence, when the gametes combine, the original number of chromosomes gets restored in the
   progeny.

Question 32.

1. What are sexually transmitted diseases? Name anyone who is caused by bacteria
   and one caused by viral infection.
2. Mention any two methods to avoid such diseases.

Answer:

1. Diseases that spread through sexual contact are called sexually transmitted diseases.
   1. Gonorrhoea or syphilis
   2. Warts, HIV, AIDS
   1. Use of condoms on the penis.
   2. Use covering on a vagina.

Question 33. Differentiate between plumule and radicle.
Answer:

Question 34. Explain the process of regeneration in planaria. How is this process different from reproduction?
Answer:

1. Planaria gets cut into many pieces, each piece grows into separate individuals, and specialized cells proliferate. The mass of cells gets differentiated into various cells and tissues.
2. Regeneration is not the same as reproduction as most of the organisms would not normally depend on being cut up to be able to reproduce. (It is normally for repair of the damaged part.)

Question 35. Distinguish between the functions of the ovary and testis.
Answer:

Question 36. Differentiate between the following:

1. Placenta and uterus
2. Unisexual and bisexual flowers
3. Fertilization and germination

Answer:

Question 37. A part of the male reproductive system is shown below. Study the diagram and answer the questions that follow.

1. Two parts have been incorrectly labelled. Identify them.
2. State the function of the urethra.
3. Which hormone is released by the testis?

Answer:

1. Testis, Penis
2. It serves as a common passage for both sperm and urine.
3. Testosterone

Question 38. How can pregnancy be prevented surgically?
Answer:

1. When vas deferens in males are blocked surgically, sperm transfer will be prevented.
2. When fallopian tubes are blocked, eggs will not be able to reach the uterus.

Question 39.

1. State, in brief, the functions of the following parts of the human female reproductive system:
   1. Ovary
   2. Fallopian tube
   3. Uterus
2. State, in brief, the functions of the following parts of the human male reproductive system:
   1. Scrotum
   2. Testes
   3. Vas deferens

Answer:

1. 1. Ovary-Production of ova and sex hormones
   2. Fallopian tube-Site of fertilization
   3. Uterus-Keeps the foetus till complete development.
   1. Scrotum–Protects testes outside the abdominal cavity.
   2. Testes-Produces male gametes called sperms.
   3. Vas deferens-Delivers sperms from the testes to the urethra.

Question 40. What is the function of copper-T used by some women? What is its side effect?
Answer:

It prevents pregnancy as it prevents implantation in the uterus. It can cause side effects due to irritation of the uterus.

Question 41.

1. How do organisms reproduce by fission?
2. Write the names of any two organisms which reproduce by this method.
3. Differentiate between the fission of Leishmania and Plasmodium.

Answer:

1. Cell division takes place which leads to the creation of new individuals.
2. Bacteria, Protozoa
3. Leishmania-binary fission occurs in a definite orientation. Plasmodium undergoes multiple fission.

Question 42. Differentiate between binary fission and multiple fission.
Answer:

Question 43. State the importance of chromosomal differences between sperms and eggs of humans.
Answer:

1. Eggs always contain the same type of sex chromosomes (both X). Sperms contain X or Y sex chromosomes. Thus, sperm containing the X chromosome when combines with the X chromosome of the egg results in a female child.
2. Whereas sperm containing the Y chromosome when combines with the X chromosome of the egg results in a male child.

Question 44. What happens to the following parts after fertilization?

1. Ovum
2. Ovary
3. Ovule
4. Sepals and petals

Answer:

1. Forms zygote
2. Forms fruit
3. Forms seed
4. Shrivel and fall off

Question 45. Differentiate between self-pollination and cross-pollination.
Answer:

Question 46. Which kind of contraceptive method prevents STDs and how?
Answer:

1. Barrier method
2. Because by this method there is no direct contact between the genital organs of male and female and thus it prevents transmission of any infection.

Question 47.

1. Identify the asexual methods of reproduction in each of the following organisms:
   1. Rose
   2. Yeast
   3. Planaria
2. What is fragmentation? Name a multicellular organism which reproduces by this method.

Answer:

1. 1. Vegetative propagation by stem
   2. Budding
   3. Regeneration
2. Fragmentation is an asexual method of reproduction in which an organism simply breaks up into smaller pieces upon maturation. These pieces or fragments grow into new individuals.

Spirogyra is a multicellular organism with a relatively simple body organisation which reproduces through this simple method of reproduction, i.e., fragmentation.

Question 48. List four points of significance of reproductive health in a society. Name any two areas related to reproductive health which have improved over the past 50 years in our country.
Answer:

Significance:

• Prevents STDs
• Advantages of small family
• Less mortality among newborns
• Reduces the cases of maternal mortality

Areas which have improved: Family planning, decrease in STD cases.

Question 49. In a bisexual flower despite the young stamens being removed artificially, the flower produces fruit. Provide a suitable explanation for the above situation.
Answer:

The pistil is intact. Cross-pollination has occurred leading to fertilisation and formation
of fruit.

Question 50. Can you consider cell division as a type of reproduction in unicellular organisms? Give one reason.
Answer: Yes, because it results in the formation of two daughter cells, that is, it results in the production of more individuals of the organism.

Question 51. What is a clone? Why do offspring formed by asexual reproduction exhibit remarkable similarity?
Answer: Clone refers to the offspring of an organism formed by the asexual method of reproduction. Since they possess exact copies of the DNA of their parent, clones exhibit remarkable similarity.

Question 52. Explain how offspring and parents of organisms reproducing sexually have the same number of chromosomes.
Answer:

Reduction division (meiosis) during gamete formation halves the chromosome number in both male and female gametes. Since these two gametes fuse during fertilisation, the original number of chromosomes (as in the parent) is restored in the offspring.

Question 53. Colonies of yeast fail to multiply in water but multiply in sugar solution. Give one reason for this.
Answer:

Sugar provides energy for sustaining all life activities in yeasts. In water, it fails to
reproduce because of inadequate energy in its cells.

Question 54. Why does bread mould grow profusely on a moist slice of bread rather than on a dry slice of bread?
Answer:

Moisture is an important factor in the growth of hyphae. Moistened bread slice offers both moisture and nutrients to the bread mould, hence it grows profusely. A dry slice of bread offers nutrients but not moisture hence hyphae fail to grow.

Question 55. Give two reasons for the appearance of variations among the progeny formed by sexual reproduction.
Answer:

1. Sexual reproduction involves two parents with different sets of characters.
2. The gene combinations are different in gametes.

Question 56. Would a Planaria cut vertically into two halves regenerate into two individuals? Complete the figure by indicating the regenerated regions.

Answer:

Yes, the shaded part in the figures represents the regenerated halves.

Question 57. From the internet, gather information about the chromosome numbers of five animals and five plants. Correlate the number with the size of the organism and answer the following questions.

1. Do larger organisms have more number of chromosomes cells?
2. Can organisms with fewer chromosomes reproduce more easily than organisms with more chromosomes?
3. The more the number of chromosomes/cells, the greater the DNA content. Justify.

Answer:

1. No, there is no relationship between the size of the organism and its chromosome number.
2. No, the process of reproduction follows a common pattern and is not dependent on the number of chromosomes.
3. Yes, since the major component of chromosomes is DNA, if there are more chromosomes in a cell, the quantity of DNA will also be greater.

Question 58. In tobacco plants, the male gametes have twenty-four chromosomes. What is the number of chromosomes in the female gamete? What is the number of chromosomes in the zygote?
Answer:

1. The number of chromosomes in the female gamete is 24.
2. Number of chromosomes in zygote is 48.

Question 59. Why cannot fertilisation take place in flowers if pollination does not occur?
Answer:

1. In a flower, fertilisation requires both male and female gametes.
2. If pollination does not occur, male gamete is not available hence fertilisation cannot take place.

Question 60. Is the chromosome number of zygote, embryonal cells and adult of a particular organism always constant? How is the constancy maintained in these three stages?
Answer:

Yes, the constancy is maintained because cells in all these three structures undergo only mitotic divisions.

Question 61. Where is the zygote located in the flower after fertilization?
Answer: Zygote is located inside the ovule which is present in the ovary.

Question 62. Reproduction is linked to the stability of the population of a species. Justify the statement.
Answer:

In reproduction, DNA passes from one generation to the next. Copying of DNA takes place with consistency but with minor variations. This consistency leads to the stability of species.

Question 63. How are general growth and sexual maturation different from each other?
Answer:

General growth refers to different types of developmental processes in the body like an increase in height, weight gain, and changes in shape and size of the body, but sexual maturation is specific to changes reflected at puberty like cracking of voice, new hair patterns, development of breasts in females etc.

Question 64. Trace the path of sperm during ejaculation and mention the gland and its functions associated with the male reproductive system.
Answer:

Sperm comes out from the testis into the vas deferens and then passes through the urethra before ejaculation. The secretions of seminal vesicles and prostate glands provide nutrition to the sperms and also facilitate their transport.

Question 65. What changes are observed in the uterus if fertilisation does not occur?
Answer:

The thick and spongy lining of the uterus slowly breaks and comes out through the vagina as blood and mucus.

Question 66. What changes are observed in the uterus after the implantation of the young embryo?
Answer:

The uterine wall thickens and is richly supplied with blood. A special tissue called the placenta develops which connects the embryo to the uterine wall that provides nutrients and oxygen to it.

Question 67. What are the benefits of using mechanical barriers during sexual acts?
Answer:

Mechanical barriers like condoms prevent the sperm from reaching the egg. Thus it is an effective method to avoid pregnancy. It also prevents the transmission of infections during sexual acts.

Question 68. In the given figure label the parts and mention their functions.

1. Production of egg
2. Site of fertilisation
3. Site of implantation
4. Entry of the sperms
5. Answer:

1. Ovary (production of egg)
2. Oviduct (site of fertilisation)
3. Uterus (site of implantation)
4. Vagina (entry of the sperm)

Question 69. What would be the ratio of chromosome number between an egg and its zygote? How is the sperm genetically different from the egg?
Answer:

The ratio is 1: 2. Sperms contain either X or Y chromosome whereas an egg will always have an X chromosome.

Question 70. Green and red-coloured seeds are recessive and dominant traits respectively. Out of F₁ and F_2, in which generation will the green seed appear, if both parents are not hybrid?
Answer: F₂ generation.

Question 71. What is self sterility mechanism in flowers which allows only cross-pollination?
Answer:

In self-sterility, pollen grains of the same flower are not capable of fertilising that flower, e.g. potato, tea etc. Hence, cross-pollination is the rule applied.

Question 72. Colonies of yeast fail to multiply in water but multiply in sugar solution. Give one reason for this.
Answer:

Sugar provides energy for sustaining all life activities in yeast. In water, it fails to reproduce because of inadequate energy in its cells.

Question 73. What is the main cause of variations among organisms during sexual reproduction?
Answer:

During sexual reproduction, the DNA copying mechanism is not accurate, and the resultant errors are a source of variations in populations of organisms.

Question 74. What is the advantage of reproduction through spores in the case of rhizopus?
Answer:

1. The spores are covered by thick walls that protect them until they come into contact
   with another moist surface and can begin to grow.
2. Spores being lighter easily get dispersed to distant places and provide better chances of survival.

Question 75. We hear and read about female foeticide, which is a wrong practice. In some families, be it rural or urban, females are tortured for giving birth to a girl child. They do not seem to understand the scientific reason behind the birth of a boy or a girl.

Answer the following questions based on the information given above.

1. In your opinion, is the approach of society towards the mother in this regard correct? Explain the scientific reason.
2. How can you promote awareness among people?
3. What values will you be promoting by doing so?

Answer:

1. In my opinion approach of society is baseless. The sex of the child is determined by the type of chromosome present in sperm (X or Y) that fuses with the ovum at the time of fertilisation.
2. By organising poster-making, debates and seminars.
3. Spreading social awareness against various social malaise, viz. gender, inequality female foeticide etc.

Question 76. Seeds have some food stored in the cotyledons that are helpful during the process of germination. A small seed can grow into a giant tree when allowed to grow in the right conditions/environment.

Answer the following questions based on the above passage:

1. How is the food stored in the cotyledons helpful during the process of germination?
2. List four values acquired by a student in the early stages of his/her growth which can
   enable him/her to achieve great heights in life.
3. Write any two environmental conditions to be provided by the parents/family to help the child’s personality grow in the right direction.

Answer:

1. Cotyledons contain food in the form of bio-chemical energy which is used in the process of germination.
2. Hard work, passion for learning and knowledge, similarity, thinking skills and originality.
3. Providing opportunities for a variety of learning experiences, motivation and freedom to experiment.

Question 77. In a certain village, the sex ratio is very low due to a large number of cases of female infanticide. A man from the same village takes his pregnant wife to the doctors to find out whether the foetus is a girl or a boy. The doctor performs a test and tells them that it is a girl.

Answer the following:

1. Name the technique used by the doctor to determine the type of sex of the foetus.
2. Which values are disrespected by doctors?
3. Suggest two actions to be taken by the administration to promote desired related values.

Answer:

1. The technique used to determine the type of sex of the foetus is called amniocentesis.
2. Value for life, professional ethics, gender bias.
3. Enactment of law.
   1. Awareness campaigns about the declining sex ratio and its ill effects.
   2. Education of women.

Question 78. Mr Sharma was suffering from various types of diseases presently. He went for thorough health check-ups and was diagnosed to be HIV+. Soon this news spread in his neighbourhood and on account of this, he faced social isolation.

Answer the following questions based on the information given above.

1. Do you think people’s indifference towards HIV+ people is justifiable? What kind of approach should we have toward the persons suffering from AIDS?
2. How can one protect oneself from this disease?
3. What values are not promoted by Mr Sharma’s neighbours?

Answer:

1. Not. We should exhibit a humane approach/behaviour and should not treat them as isolated.
2. One should be aware of the mode of transmission of disease, the danger of sharing needles, transfusion of contaminated blood, etc.
3. Sympathy for fellow human beings, care, humane nature.

Question 79. List any two reasons why the Government has banned prenatal sex determination by law.
Answer:

1. People may get female foetus absorbed.
2. Reckless female foeticide has disturbed the male-female ratio in society.

How do Organisms Reproduce Multiple Choice Questions and Answers

Question 1. In the list of organisms given below, those that reproduce by the asexual method are

1. Banana
2. Dog
3. yeast
4. Amoeba

1. (2) and (4)
2. (1), (3) and (4)
3. (1) and (4)
4. (2), (3) and (4)

Answer: 2. (1), (3) and (4)

Question 2. In a flower, the parts that produce male and female gametes (germ cells) are

1. Stamen and anther
2. Filament and stigma
3. Anther and ovary
4. Stamen and style

Answer: 3. Anther and ovary

Question 3. Which of the following is the correct sequence of events of sexual reproduction in a flower?

1. Pollination, fertilisation, seedling, embryo
2. Seedling, embryo, fertilisation, pollination
3. Pollination, fertilisation, embryo, seedling
4. Embryo, seedling, pollination, fertilisation

Answer: 3. Pollination, fertilisation, embryo, seedling

Question 4. Offsprings formed by an asexual method of reproduction have greater similarities among themselves because

1. Asexual reproduction involves only one parent
2. Asexual reproduction does not involve gametes
3. Asexual reproduction occurs before sexual reproduction
4. Asexual reproduction occurs after sexual reproduction

1. (1) and (2)
2. (1) and (3)
3. (2) and (4)
4. (3) and (4)

Answer: 1. (1) and (2)

Question 5. Characters transmitted from parents to offspring are present in

1. Cytoplasm
2. Ribosome
3. Golgi bodies
4. Genes

Answer: 4. Genes

Question 6. Characters that are transmitted from parents to offspring during reproduction show

1. The only similarities between parents
2. Only variations with parents
3. Both similarities and variations with parents
4. Neither similarities nor variations

Answer: 3. Both similarities and variations with parents

Question 7. A feature of reproduction that is common to Amoeba, Spirogyra and Yeast is that

1. They reproduce asexually
2. They are all unicellular
3. They reproduce only sexually
4. They are all multicellular

Answer: 1. They reproduce asexually

Question 8. In Spirogyra, asexual reproduction takes place by

1. Breaking up of filaments into smaller bits
2. Division of a cell into two cells
3. Division of a cell into many cells
4. Formation of young cells from older cells.

Answer: 1. Breaking up of filaments into smaller bits

Question 9. The ability of a cell to divide into several cells during reproduction in Plasmodium is called

1. Budding
2. Reduction division
3. Binary fission
4. Multiple fission

Answer: 4. Multiple fission

Question 10. The correct sequence of reproductive stages seen in flowering plants is

1. Gametes, zygotes, embryos, seedlings
2. Zygote, gametes, embryo, seedling
3. Seedling, embryo, zygote, gametes
4. Gametes, embryos, zygotes, seedlings

Answer: 1. Gametes, zygote, embryo, seedling

Question 11. The number of chromosomes in parents and offsprings of a particular species remains constant due to

1. Doubling of chromosomes after zygote formation
2. Halving of chromosomes during gamete formation
3. Doubling of chromosomes after gamete formation
4. Halving of chromosomes after gamete formation

Answer: 2. Halving of chromosomes during gamete formation

Question 12. In Rhizopus, tubular thread-like structures bearing sporangia at their tips are called

1. Filaments
2. Hyphae
3. Rhizoids
4. Roots

Answer: 2. Hyphae

Question 13. Vegetative propagation refers to the formation of new plants from

1. Stem, roots and flowers
2. Stem, roots and leaves
3. Stem, flowers and fruits
4. Stem, leaves and flowers

Answer: 2. Stem, roots and leaves

Question 14. Factors responsible for the rapid spread of bread mould on slices of bread are

1. A large number of spores
2. Availability of moisture and nutrients in bread
3. Presence of tubular branched hyphae
4. Formation of round-shaped sporangia

1. (1) and (3)
2. (1) and (2)
3. (2) and (4)
4. (3) and (4)

Answer: 3. (2) and (4)

Question 15. The length of the pollen tube depends on the distance between

1. Pollen grain and the upper surface of the stigma
2. Pollen grain on the upper surface of the stigma and ovule
3. Pollen grain in anther and the upper surface of the stigma
4. The upper surface of the stigma and the lower part of the style

Answer: 2. Pollen grain on the upper surface of stigma and ovule

Question 16. Which of the following statements is true for flowers?

1. Flowers are always bisexual
2. They are the sexual reproductive organs
3. They are produced in all groups of plants
4. After fertilisation, they give rise to fruits

1. (1) and (4)
2. (2) and (3)
3. (1) and (3)
4. (2) and (4)

Answer: 4. (2) and (4)

Question 17. Which among the following statements is true for unisexual flowers?

1. They possess both stamen and pistil
2. They possess either stamen or pistil
3. They exhibit cross-pollination
4. Unisexual flowers possessing only stamens cannot produce fruits

1. (1) and (4)
2. (2), (3) and (4)
3. (3) and (4)
4. (1), (3) and (4)

Answer: 2. (2), (3) and (4)

Question 18. Which among the following statements is true for sexual reproduction in flowering plants?

1. It requires two types of gametes
2. Fertilisation is a compulsory event
3. It always results in the formation of a zygote
4. Offspring formed are clones

1. (1) and (4)
2. (1), (2) and (4)
3. (1), (2) and (3)
4. (1), (2) and (4)

Answer: 3. (1), (2) and (3)

Question 19. Offsprings formed as a result of sexual reproduction exhibit more variations because

1. Sexual reproduction is a lengthy process
2. Genetic material comes from two parents of the same species
3. Genetic material comes from two parents of different species
4. Genetic material comes from many parents

Answer: 2. Genetic material comes from two parents of the same species

Question 20. Reproduction is essential for living organisms to

1. Keep the individual organism alive
2. Fulfill their energy requirement
3. Maintain growth
4. Continue the species generation after generation

Answer: 4. Continue the species generation after generation

Question 21. During adolescence, several changes occur in the human body. Mark one change associated with sexual maturation in boys

1. Loss of milk teeth
2. Increase in height
3. Cracking of voice
4. Weight gain

Answer: 3. Cracking of voice

Question 22. In human females, an event that reflects the onset of the reproductive phase is

1. Growth of body
2. Changes in hair pattern
3. Change in voice
4. Menstruation

Answer: 4. Menstruation

Question 23. In human males, the testes lie in the scrotum, because it helps in the

1. Process of mating
2. Formation of sperm
3. Easy transfer of gametes
4. All the above

Answer: 2. Formation of sperm

Question 24. Which among the following are not the functions of testes at puberty?

1. Formation of germ cells
2. Secretion of testosterone
3. Development of placenta
4. Secretion of estrogen

1. (1) and (2)
2. (2) and (3)
3. (3) and (4)
4. (1) and (4)

Answer: 3. (3) and (4)

Question 25. The correct sequence of organs in the male reproductive system for the transport of sperm is

1. Testis → vas deferens → urethra
2. Testis → ureter → urethra
3. Testis → urethra → ureter
4. Testis → vas deferens → ureter

Answer: 1. Testis → vas deferens → urethra

Question 26. Which among the following diseases is not sexually transmitted?

1. Syphilis
2. Hepatitis
3. HIV-AIDS
4. Gonorrhoea

Answer: 2. Hepatitis

Question 27. Asexual reproduction takes place through budding in

1. Amoeba
2. yeast
3. Plasmodium
4. Leishmania

Answer: 2. Yeast

Question 28. Which of the following is not a part of the female reproductive system in human beings?

1. Ovary
2. Uterus
3. Vas deferens
4. Fallopian tube

Answer: 3. Vas deferens

Question 29. The anther contains

1. Sepals
2. Ovules
3. Carpel
4. Pollen grains

Answer: 4. Pollen grains

CBSE Class 10 Science Chapter 7 Control and Coordination

Hormones In Animals:

CBSE Class 10 Science Chapter 7 Control and Coordination Short Question And Answers

Question 1. What is the difference between a reflex action and walking?
Answer:

Question 2. What happens at the synapse between two neurons?
Answer:

At the synapse at the end of the axon of the neuron carrying information, the electrical impulse sets off the release of some chemicals, known as neurotransmitters. These chemicals cross the gap (synapse) reach the dendrites of the next neuron and start electrical impulses there.

Read and Learn More CBSE Class 10 Science Short Answer Questions

Question 3. Which part of the brain maintains posture and equilibrium of the body?
Answer: A part of the hindbrain known as the cerebellum maintains posture and equilibrium of the body.

Question 4. How do we detect the smell of an agarbatti (incense stick)?
Answer: The smell of an agarbatti is sensed by the olfactory receptor present in the nose. They send information to the olfactory lobe, located in the forebrain, which interprets the data.

Question 5. What is the role of the brain in reflex action?
Answer:

Nerves from all over the body meet in a bundle in the spinal cord on their way to the brain. Reflex arcs are formed in the spinal cord itself. So the input (stimulus) and output (response) actions are completed quickly, although the information input also reaches the brain. The brain may store the experience for the future.

Question 6. What are plant hormones?
Answer:

Plant hormones are special chemical compounds released by different parts of the plants. They help to coordinate growth, development, and responses to the environment. They are synthesized at places away from the site where they act. They diffuse to the area of action.

Question 7. How is the movement of leaves of the sensitive plant different from the movement of a shoot toward light?
Answer:

Differences between the movements of the leaves of the sensitive plant and the movement of the shoot toward light are as follows:

• The movement of leaves of the sensitive plant is not directional to the stimulus of touch. But the movements of the shoot are directional towards the light.
• The movement of leaves (drooping down) of sensitive plants is due to changes in the amount of water present in them. The movement of the shoot towards light is due to growth controlled by a growth hormone called auxin.

Question 8. Give an example of a plant hormone that promotes growth.
Answer:

Auxin promotes the growth of the cell, gibberellins help in the growth of the stem, and cytokinin promotes cell division (any of them).

Question 9. How do auxins promote the growth of a tendril around a support?
Answer:

The tendrils are sensitive to touch. When a part of the tendril comes in contact with a support, the growth hormone auxin diffuses from the site. This causes growth in the part of the tendril away from the support. This causes the tendril to circle the support. Thus, the tendril clings to the support.

Question 10. Design an experiment to demonstrate hydrotropism.
Answer:

Experiment to demonstrate hydrotropism: Growth movements in response to the stimulus of moisture (water) are termed hydrotropic movements (Hydrotropism).

Experiment: Place some ready-to-germinate seeds of pea/gram/beam in moist sawdust in a shallow box whose bottom has been replaced by a wire gauze.

Keep the apparatus undisturbed for 2-3 days. Keep the sawdust moist. After some time radicles will pass through the sieves. Then the radicles curve upward again to enter into the moist sawdust.

The roots are positively hydrotropic and the curvature is more than that due to the geotropic effect.

Question 11. How does chemical coordination take place in animals?
Answer:

In animals, chemical coordination is carried out by hormones secreted by endocrine glands. Hormones are secreted by ductless glands placed far away from the site of action of the secreted hormone.

1. Hormones are directly secreted into the blood that carries them to different parts of the body and also to tissues/organs where they are required.
2. The body cells have special molecules on their plasma membrane for recognition of information a hormone carries. After receiving hormonal information the organ/tissues/cells act accordingly.

Question 12. Why is the use of iodized salt advisable?
Answer:

Iodine is necessary for the synthesis of the thyroid glands’ thyroxin hormone. Thyroxin regulates carbohydrates, fat, and protein metabolism in the body to maintain the best balance for growth.

1. The deficiency of iodine may cause a decrease in the production of thyroxine resulting in goiter disease and other metabolic disorders. The main symptom of goiter is a swollen neck.
2. As a preventive measure, people are advised to use iodized common salt.

Question 13. How does our body respond when adrenaline is secreted into the blood?
Answer: Adrenaline is secreted by the adrenal gland directly into the blood. The target organs or the specific tissues on which it acts include the heart.

Response due to secretion of adrenaline

1. The heart beats faster, resulting in a supply of more oxygen to our muscles.
2. The blood to the digestive system and skin is reduced and diverted to our skeletal muscles.
3. Breathing rate increases because of contraction of the diaphragm and the rib muscles. All these responses together enable our body to be ready to deal with the adverse situation.

Question 14. Why are some patients with diabetes treated by giving injections of insulin?
Answer:

Insulin is a hormone secreted by the pancreas. It helps in regulating blood sugar levels. It is not secreted in proper amounts, and the sugar level in the blood rises causing many harmful effects. Doctors treat diabetic patients with high blood sugar levels with insulin injections to keep blood sugar levels under control.

Question 15. What is the function of receptors in our body? Think of situations where receptors do not work properly. What problems are likely to arise?
Answer:

Receptors are specialized tips of some nerves that are located in our sense organs such as skin, tongue, etc.

• They detect information from the environment and pass on the information to the spinal cord and brain for proper response. If receptors do not work properly, there will be a delay in responding to a stimulus.
• This sometimes becomes dangerous. For example, touching a hot object is an urgent and dangerous situation for us. We need to detect it and respond to it immediately.

Question 16. Draw the structure of a neuron and explain its function.
Answer:

Diagram of a neuron to show its structure:

The function of neurons is to carry messages over long distances in the body of a person quickly. The message that neurons transmit in the nervous system is in the form of electrical impulses. Neurons make the whole nervous system work efficiently.

For example, the sensory neurons transmit impulses from the sensory cell towards the central nervous system and the motor neurons transmit impulses from the central nervous system towards the muscle cells for taking appropriate action.

Question 17. How does phototropism occur in plants?
Answer:

The directional (or tropic) movements due to light, in plants are called phototropic movements. In this case shoot of the plant grows towards the direction of light whereas roots grow away from the light stimulus.

Question 18. Why does the shoot bend toward the light?
Answer:

The growth hormone, auxin, is not able to promote growth in the plant part which is well-illuminated, from one side. So, the hormone auxin diffuses toward the shady side of the shoot.

• The increased concentration of growth hormone auxin in the shaded part of the shoot causes an increase in the growth of cells in that region.
• The enhanced growth of the shaded side of the shoot i.e., one side of the shoot, causes the bending of the shoot towards the source of light.

Question 19. Which signals will get disrupted in case of a spinal cord injury?
Answer:

1. Reflex action, as information detected from the environment, will be conveyed late to the reflex arc and response to the signal may be delayed to reach the effector organ/tissues. They may lead to dangerous situations. The signal of touching a hot object, if delayed, may lead to delayed response and we may get hurt.
2. Information detected by nerves from various parts of the body may reach the spinal cord/brain late.
3. Message from the brain will not be conducted to various organizers: This will lead to disturbed control and coordination of the organism.

Question 20. How does chemical coordination occur in plants?
Answer:

Plants do not have a nervous system for control and coordination. They may have the following system:

1. By making movements dependent on growth such as bending of the shoot towards the source of light. For such actions, plants produce hormones, such as auxins, cytokinins, etc.
2. Movements that are independent of growth like shrinking or swelling as happens in touch-me-not plants.
3. The plants also use electrical-chemical means to convey information from cell to cell, as happens in the drooping of leaves on touch.

Question 21. What is the need for a system of control and coordination in an organism?
Answer:

Living organisms make many movements, which may be due to growth, in response to changes in the environment or to procure food. Each kind of change in the environment evokes an appropriate movement in response.

In multicellular organisms, different body parts or body organs must work in unison for the survival of the individual. In other words, living organisms must use systems providing control and coordination.

Question 22. How are involuntary actions and reflex actions different from each other?
Answer:

Question 23. Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.
Answer:

Question 24. What is the difference between how movement takes place in a sensitive plant and the movement in our legs?
Answer:

The difference between movement in a sensitive plant and the movement in our legs

Question 25. State the functions of any three of the structural and functional units of the nervous system.
Answer:

The structural and functional unit of the nervous system is a neuron. Its functions are as follows:

1. Cell body: Stimulus received from dendrite is changed into an impulse in the cyton.
2. Dendrites: They receive sensation or stimulus, which may be physical, chemical, mechanical, or electrical. They pass the stimulus to cyton.
3. Axon: It conducts impulses away from the cell body.

Question 26.

1. Which plant hormone is present in greater concentration in the areas of rapid cell division?
2. Give one example of a plant growth promoter and a plant growth inhibitor.

Answer:

1. Cytokinin is present in greater concentration in the areas of rapid cell division.
2. An example of a plant growth promoter is gibberellins and an example of a plant growth inhibitor is abscisic acid.

Question 27. Suggest proof that even unicellular organisms like amoeba respond to stimuli. Justify by giving two examples that even plants respond to stimuli.
Answer:

Amoeba moves towards food and tends to aggregate in moderately warm water. Amoeba and other protozoa avoid mechanical obstacles.

Thus, unicellular organisms respond to stimuli. Roots of plants move downward in response to gravitational force and shoots of plants move towards light. This shows that plants respond to stimuli.

Question 28.

1. Name the part of the brain that controls:
   1. Voluntary action.
   2. Involuntary action.
2. What is the significance of the peripheral nervous system? Name the components of this nervous system and distinguish between the origin of the two.

Answer:

1. 1. Voluntary action – cerebellum;
   2. Involuntary action – medulla oblongata.
2. The communication between the central nervous system and the other parts of the body is facilitated by the peripheral nervous system. Cranial nerves arise from the brain; spinal nerves arise from the spinal cord.

Question 29. State how the concentration of auxin stimulates the cells to grow longer on the side of the shoot which is away from light.
Answer:

When a growing plant detects light, auxin synthesizes at the shoot tip to help the cell to grow longer. When light comes from one side, auxin diffuses towards the shady side of the shoot.

This concentration of auxin stimulates the cells to grow longer on the side of the shoot which is away from light and the plant appears to bend towards light.

Question 30.

1. Explain any three directional movements in plants.
2. How are the brain and spinal cord protected in humans?
3. Name the master gland present in the brain.

Answer:

1. Three directional movements in plants are:
   1. Phototropism: It is the movement of a part of a plant towards light, e.g., the movement of the stem towards light.
   2. Geotropism: The upward and downward growth of shoots and roots in response to gravity is called geotropism.
   3. Chemotropism: It is the movement of a part of a plant in response to a chemical stimulus, e.g., the growth of a pollen tube towards a chemical produced by an ovule.
2. The brain and spinal cord are protected by a skeleton – the brain by the cranium and the spinal cord by the vertebral column.
3. The master gland present in the brain is called the pituitary gland.

Question 31.

1. An old man is advised by his doctor to take less sugar in his diet. Name the disease from which the man is suffering. Mention the hormone due to imbalance of which he is suffering from this disease. Which endocrine gland secretes this hormone?
2. Name the endocrine gland which secretes growth hormone. What will be its effect on a person of:
   1. Deficiency of growth hormones?
   2. Excess secretion of growth hormone?

Answer:

1. The man is suffering from the disease Diabetes. Insulin is the hormone that is responsible for this disease. The pancreas secretes this hormone.
2. The gland that secretes the growth hormone is the pituitary gland.
   1. Deficiency of growth hormone causes Dwarfism.
   2. Excess secretion of growth hormone causes Gigantism in a person.

Question 32. Distinguish between estrogen and progesterone.
Answer:

Question 33.

1. Identify the phytohormone used by plants while performing the following functions:
   1. Cell division in shoot tip.
   2. Inhibiting growth on the approach of unfavorable conditions.
2. List in tabular form two differences between the movement in the ‘touch-me-not’ plant and the movement of the shoot towards the light.

Answer:

1. Auxin,
2. Abscisic acid.

Question 34. How does chemical coordination occur in plants? Explain with the help of three examples.
Answer:

In plants, chemical coordination occurs through various phytohormones.

1. Auxins are secreted by growing tissues. They provide growth of plants.
2. Gibberellins cause stem elongation, seed germination, and flowering.
3. Cytokinins are present in areas of actively dividing cells like fruits and seeds. Promote cell division.
4. Abscisic acid inhibits growth and responds to environmental stress. (any three)

Question 35. Draw a neat diagram of the human brain and label it the following parts:

1. Midbrain
2. Pituitary gland

Answer:

Question 36. Illustrate with the help of a diagram, the effect of auxins in different parts of a plant.
Answer:

Question 37. List the names of hormones secreted by the following endocrine glands and mention their functions:

1. Thyroid gland
2. Adrenal gland
3. Pituitary gland

Answer:

Question 38. Write one example of each of the following tropic movements:

1. Positive phototropism
2. Negative phototropism
3. Positive geotropism
4. Hydrotropism
5. Negative geotropism
6. Chemotropism

Answer:

1. Positive phototropism: Movement of the stem of a plant towards light.
2. Negative phototropism: Movement of roots away from light.
3. Positive geotropism: Movement of roots towards gravity.
4. Negative geotropism: Upward movement of shoots.
5. Hydrotropism: Growth of roots of a plant towards the water in the soil.
6. Chemotropism: Growth of pollen tubes towards ovule.

Question 39. Describe an activity to illustrate the phenomenon of phototropism and explain why this occurs.
Answer:

Activity:

Take a plant and make such an arrangement that it receives the light coming from a window as shown in the figure and observe it for a few days.

• Now, turn the flask so that the shoots are away from light and the roots towards light. Leave it undisturbed in this condition for a few days.
• Again observe to find the difference in the movement.
• When growing plants detect light, auxin, synthesized at the shoot tip, helps the cells to grow longer; auxin always diffuses towards the shady side of the shoot. This concentration of auxin stimulates the cells to grow longer on the side of the shoot which is away from light. Thus, the plant appears to bend towards light.

Question 40. What is a cerebrospinal fluid? What is its function?
Answer:

The fluid which fills the space between the membranes which cover the brain is called cerebrospinal fluid.

Function: It protects the brain from mechanical shocks.

Question 41. What is a reflex arc?

1. What are the components of the reflex arc?
2. How do muscle cells move?

Answer:

1. The process of detecting the signal or the input and responding to it by an output action might be completed quickly. Such a connection is commonly called a reflex arc.
2. Stimulus → Receptors → Sensory neurons → Spinal cord → Motor neurons → Effector.
3. Muscle cells have special proteins that change their shape and arrangement in the cell in response to electrical impulses. This leads the muscle cells to shorten.

Question 42. Write the difference between the cerebellum and cerebrum.
Answer:

Question 43. ‘Brain and spinal cord are two vital organs of our body’. How is our body designed to protect them?
Answer:

The brain is inside a bony box contained in a fluid-filled balloon which protects it from shocks. The vertebral column protects the spinal cord. Both are protected by protective layers called meninges, protective fluid (CSF→ cerebrospinal fluid).

Question 44.

1. How does the tendril coil around the support?
2. Define phototropism.

Answer:

1. Tendrils are sensitive to touch. When they come in contact with any support, the part of the tendril in contact with the object does not grow as rapidly as the part of the tendril away from the object. This causes the tendril to coil around the support.
2. Movement of plants in response to light.

Question 45. List the sequence of events that occur when a plant is exposed to unidirectional light, leading to the bending of a growing shoot. Also, name the hormone and the type of movement.
Answer:

1. Auxin diffuses towards the shady side.
2. Causes elongation on one side (shady side) resulting in bending of the growing shoot.
3. The hormone responsible for bending is auxin and the movement is phototropic.

Question 46.

1. Name the diseases by which a person is likely to suffer due to the deficiency of:
   1. Iodine
   2. Insulin
2. How is the timing of secretion and amount of hormone secretion regulated in the human system? Explain with an example.

Answer:

1. 1. Goitre
   2. Diabetes
2. The timing and amount of hormone released are regulated by feedback mechanisms, e.g., if the sugar levels in the blood rise, they are detected by the cells of the pancreas which respond by producing more insulin. As the blood sugar level falls, insulin secretion is reduced.

Question 47.

1. Name the hormone that is injected into a diabetic patient.
2. Why should we use iodized salt in our diet?
3. If iodine is insufficient in one’s diet, what might be the deficiency disease and its symptoms?

Answer:

1. Insulin.
2. Iodine is necessary for the thyroid gland to secrete thyroxine hormone. Thyroxine regulates carbohydrates, proteins, and fat metabolism in the body, to provide the best balance for growth.
3. If iodine is insufficient in one’s diet, an iodine deficiency disease called goiter occurs. The symptom is a swollen neck.

Question 48.

1. If the cerebellum is not functioning properly, what are the activities of our body that will be affected?
2. How do muscle cells move?

Answer:

1. If the cerebellum is not functioning properly, voluntary action of our body will be affected by maintaining the posture and balance of the body.
2. Muscle cells move by changing their shape so that they get shortened.

Question 49. Name a hormone secreted by:

1. Pancreas
2. Pituitary
3. Thyroid. Write one function of each of the hormones.

Answer:

1. Insulin – controls blood sugar levels.
2. The pituitary – growth hormone regulates growth and development.
3. Thyroxine – regulates the metabolism of carbohydrates, fats, and proteins.

Question 50. Define reflex action. Give one example. Show with the help of a flow diagram the path of the reflex action.
Answer:

Reflex action is a sudden action in response to something in the environment. e.g., pulling out a hand from the flame if accidentally touched. The path of the reflex action is as follows:

Receptors Sensory neuron → Spinal cord → Effector → Motor neuron

Question 51. Name the hormone synthesized at the shoot tips. How does it help plants to respond to light?
Answer:

Auxin is synthesized at the shoot tips when a growing plant detects light and helps the cells to grow longer.

When light is coming from one side of the plant, auxin diffuses towards the shady side of the shoot. This concentration of auxin stimulates the cells to grow longer on the side of the shoot which is away from light. Thus, the plant appears to bend towards light.

Question 52.

1. Differentiate between sensory neurons and motor neurons.
2. How is the brain protected in our body?
3. Name the part of the brain responsible for the precision of voluntary actions and maintaining body posture and balance of the body.

Answer:

1. Sensory neurons carry impulses from receptors to the brain. Motor neurons carry impulses from the brain to effectors.
2. The brain is kept inside a bony box (skull). Inside the box, the brain is contained in a fluid-filled balloon which provides further shock absorption. This fluid is known as cerebrospinal fluid (CSF).
3. These are possible due to a part of the hindbrain called the cerebellum.

Question 53. Name and explain the functions of the hormones secreted by the pituitary gland in humans
Answer:

Hormones secreted by the pituitary gland along with their function are as follows:

1. Growth hormone: It regulates the growth and development of bones and muscles.
2. Trophic hormone: It regulates the secretion of hormones from other endocrine glands.
3. Prolactin hormone: It regulates the function of mammary glands in females.
4. Vasopressin hormone: It regulates water and electrolyte balance in the body.
5. Oxytocin hormone: It regulates the ejection of milk during lactation.

Question 54. How do you support the statement the pancreas’ are the overall controller of the blood glucose level?
Answer:

The pancreas releases insulin which lowers blood glucose. Moreover, it also releases glucagon which increases blood glucose. Therefore, the pancreas is the overall controller of blood glucose levels.

Question 55. Name the two main organs of our central nervous system. Which one of them plays a major role in sending commands to muscles to act without involving the thinking process? Name the phenomenon involved.
Answer:

The two main organs of the CNS are the brain and spinal cord. The spinal cord plays a major role in sending commands to muscles to act without involving the thinking process. This phenomenon is called reflex action.

Question 56. Label the parts (a), (b), and and show the direction of the flow of electrical signals in the figure given below:

Answer:

1. Sensory neuron
2. Spinal cord
3. Motor neuron
4. Effector = Muscle in the arm

Question 57. Name the plant hormones responsible for the following

1. Elongation of cells
2. Growth of stem
3. Promotion of cell division
4. Falling of senescent leaves.

Answer:

1. Auxin
2. Gibberellin
3. Cytokinin
4. Abscisic acid.

Question 58. Label the endocrine glands in the figure given below:
Answer:

1. Pineal gland
2. Pituitary gland
3. Thyroid
4. Thymus.

Question 59. In figure (a), and given below, which appears more accurate and why?

Answer:

The figure is more appropriate because in a plant shoot is negatively geotropic and hence grows upward while roots are positively geotropic, so grow downward.

Question 60. Label the parts of a neuron in the figure given below:

Answer:

1. Dendrite
2. Cell body
3. Axon
4. Nerve ending.

Question 61. Match the terms of Column (A) with those of Column (B)

Answer: 1-C, 2-D, 3-A, 4-B

Question 62. What is a tropic movement? Explain with an example.
Answer:

The directional growth movements of plants due to external stimuli are called tropic movements. These can be either towards the stimulus, or away from it. For example, in the case of phototropic movement, shoots respond by bending toward light while roots respond by bending away from it.

Question 63. What will happen if the intake of iodine in our diet is low?
Answer:

1. When iodine intake is low, the release of thyroxin from the thyroid gland will be less, by which protein, carbohydrate, and fat metabolism will be affected.
2. A person might suffer from goiter in case of iodine deficiency in the body.

Question 64. What happens at the synapse between two neurons?
Answer:

When an electrical signal reaches the axonal end of one neuron, it releases certain chemical substances that cross the synapse and move towards the dendritic end of the next neuron generating another electrical signal.

Question 65. Answer the following:

1. Give the names of hormones responsible for the physical changes in a boy and a girl.
2. Name the element of the halogen family required for the proper functioning of the thyroid gland.
3. Name the stress and fear hormones.

Answer:

1. Boy – Testosterone Girl – Oestrogen.
2. Iodine.
3. Adrenaline.

Question 66. What is a cerebrospinal fluid? What is its function?
Answer:

The fluid which fills the space between the membranes which cover the brain is called cerebrospinal fluid.

Function: It protects the brain from mechanical shocks.

Question 67. Define ‘nerve impulse’. Which structure in a neuron helps to conduct a nerve impulse?

1. Towards the cell body?
2. Away from the cell body?

Answer:

The pieces of information passing through neurons are in the form of chemical are electrical signals called nerve impulses.

1. Nerve impulses are carried by dendrites towards the cell body.
2. The axon is a highly specialized nerve fiber that conducts nerve impulses away from the cell body.

Question 68. ‘Brain and spinal cord are two vital organs of our body’. How is our body designed to protect them?
Answer:

The brain is inside a bony box contained in a fluid-filled balloon which protects it from shocks. The vertebral column protects the spinal cord. Both are protected by protective layers called meninges, protective fluid (CSF → cerebrospinal fluid).

Question 69. Give reasons:

1. The pituitary is often termed as a master endocrine gland.
2. The pancreas helps in digestion and also regulates blood sugar levels.
3. Adrenals are known as glands of emergency.

Answer:

1. The pituitary is often called the master endocrine gland because it controls and coordinates the secretion of all the other endocrine glands.
2. The pancreas secretes pancreatic juice as well as a hormone called insulin. Pancreatic juice helps in digestion whereas insulin regulates blood sugar levels.
3. Adrenalin is secreted directly into the blood and is carried to different parts of the body. It acts on the heart. As a result, the heart beats faster to supply more oxygen to our muscles. The blood to the digestive system and skin is reduced due to the contraction of muscles around.

Question 70. Answer the following:

1. Name the endocrine gland associated with the brain.
2. Which gland secretes digestive enzymes as well as hormones?
3. Name the endocrine gland associated with the kidneys.
4. Which endocrine gland is present in males but not in females?
5. Which hormone is responsible for changes in females during puberty?
6. Iodine is necessary for the synthesis of which hormone?

Answer:

1. Pituitary gland
2. Adrenal gland
3. Oestrogen
4. Pancreas
5. Testes
6. Thyroxin

Question 71. Vijay’s friend has diabetes and every day after her meal in the recess she had to check her sugar level. To monitor it at times she used to take injections also. Vijay was very fond of sweets but she never carried any sweets in her tiffin.

1. What is the cause of diabetes?
2. What helps in the digestion of sugars?
3. What value of Vijay is reflected in the above act?

Answer:

1. Deficiency of an enzyme that can digest the sugar.
2. Insulin hormone.
3. Sympathy, empathy, and kindness.

Question 72. Akash and Tarun planned to visit a nursery to purchase seasonal flowering plants. While walking in the nursery, Prakash saw a Mimosa pudica (sensitive plant). He asked Akash to touch the leaflets of the Mimosa plant. The leaflets of the plant closed up. Answer the following questions based on the above information:

1. What do you infer from this activity?
2. What would you do based on your inference?

Answer:

1. Mimosa pudica (touch-me-not or sensitive plant) responds to the stimulus of touch by closing of leaflets.
   • Like animals, plants are also living and show movement and response to stimuli.
2. We would organize campaigns to create awareness amongst the masses that plants are living things.

Question 73. Ram and Shyam were doing their homework when Ram’s mother called Ram. She asked Ram to bring a packet of common salt from the market. She asked him to check that the packet bears the label ‘Iodised salt’ or ‘enriched with Iodine’. Shyam also accompanied Ram to bring the packet.

1. Ram asked Shyam, why is it important for us to have iodized salt in our diet? Ram said iodine is necessary for the formation of thyroxin hormone.
2. Answer the following questions based on the above information:
3. Which endocrine gland secretes thyroxin hormone?
4. Which disease can occur in case iodine is deficient in our diet?
5. What will you do to spread awareness among other community members about the use of iodized salt?

Answer:

1. Thyroid gland.
2. Goitre may occur.
3. Organizing awareness programs among society.

Question 74. Tarushi’s mother always kept bananas in polybags and found them to be spoiled. Tarushi suggested her mother not keep the banana in a polybag.

1. Why should we not keep bananas in polybags?
2. Name the hormone present at the root and shoot of the plants.
3. What value of Tarushi is found in this case?

Answer:

1. Ethylene is released from polybag that helps in the ripening of fruits.
2. Auxin hormone.
3. Showed the value of a concerned and responsible child.

Control and Coordination Multiple Choice Questions

Question 1. Which of the following statements is correct about receptors?

1. Gustatory receptors detect taste while olfactory receptors detect smell
2. Both gustatory and olfactory receptors detect smell
3. Auditory receptors detect smell and olfactory receptors detect taste
4. Olfactory receptors detect taste and gustatory receptors detect smell

Answer: 1. Gustatory receptors detect taste while olfactory receptors detect smell

Question 2. The electrical impulse travels in a neuron from

1. Dendrite → axon → axonal end → cell body
2. Cell body → dendrite → axon → axonal end
3. Dendrite → cell body → axon → axonal end
4. Axonal end → axon → cell body → dendrite

Answer: 3. Dendrite → cell body → axon → axonal end

Question 3. In a synapse, a chemical signal is transmitted from

1. The dendritic end of one neuron to the axonal end of another neuron
2. Axon to the cell body of the same neuron
3. Cell body to the axonal end of the same neuron
4. Axonal end of one neuron to dendritic end of another neuron

Answer: 4. Axonal end of one neuron to dendritic end of another neuron

Question 4. In a neuron, the conversion of the electrical signal to a chemical signal occurs at /in

1. Cell body
2. Axonal end
3. Dendritic end
4. Axon

Answer: 2. Axonal end

Question 5. Which is the correct sequence of the components of a reflex arc?

1. Receptors → Muscles → Sensory neuron → Motor neuron → Spinal cord
2. Receptors → Motor neuron → Spinal cord → Sensory neuron → Muscle
3. Receptors → Spinal cord → Sensory neuron → Motor neuron → Muscle
4. Receptors → Sensory neuron → Spinal cord → Motor neuron → Muscle

Answer: 4. Receptors → Sensory neuron → Spinal cord → Motor neuron → Muscle

Question 6. Which of the following statements is true?

1. Sudden action in response to something in the environment is called reflex action
2. Sensory neurons carry signals from the spinal cord to muscles
3. Motor neurons carry signals from receptors to the spinal cord
4. The path through which signals are transmitted from a receptor to a muscle or a gland is called reflex arc
   1. 1 and 2
   2. 1 and 3
   3. 1 and 4
   4. 1, 2 and 3

Answer: 3. 1 and 4

Question 7. Which of the following statements are true about the brain?

1. The main thinking part of the brain is the hindbrain
2. Centers of hearing, smell, memory, sight, etc., are located in the forebrain
3. Involuntary actions like salivation, vomiting, and blood pressure are controlled by the medulla in the hindbrain
4. The cerebellum does not control the posture and balance of the body
   1. 1 and 2
   2. 2 and 3
   3. 1, 2 and 3
   4. 3 and 4

Answer: 3. 1, 2 and 3

Question 8. Posture and balance of the body is controlled by

1. Cerebrum
2. Cerebellum
3. Medulla
4. Pons

Answer: 2. Cerebellum

Question 9. The spinal cord originates from

1. Cerebrum
2. Medulla
3. Pons
4. Cerebellum

Answer: 2. Medulla

Question 10. The movement of the shoot towards light is

1. Geotropism
2. Hydrotropism
3. Chemotropism
4. Phototropism

Answer: 4. Phototropism

Question 11. The main function of abscisic acid in plants is to

1. Increase the length of cells
2. Promote cell division
3. Inhibit growth
4. Promote the growth of stem

Answer: 3. Inhibit growth

Question 12. Which of the following is not associated with ith growth plant slant?

1. Auxin
2. Gibberellins
3. Cytokinins
4. Abscisic acid

Answer: 4. Abscisic acid

Question 13. Iodine is necessary for the synthesis of which hormone?

1. Adrenaline
2. Thyroxin
3. Auxin
4. Insulin

Answer: 2. Thyroxin

Question 14. Choose the incorrect statement about insulin

1. It is produced by the pancreas
2. It regulates the growth and development of the body
3. It regulates blood sugar level
4. Insufficient secretion of insulin will cause diabetes

Answer: 2. It regulates the growth and development of the body

Question 15. Select the mismatched pair

1. Adrenaline: Pituitary gland
2. Testosterone : Testes
3. Estrogen: Ovary
4. Thyroxin: Thyroid gland

Answer: 1. Adrenaline: Pituitary gland

Question 16. The shape of guard cells changes due to changes in the

1. Protein composition of cells
2. Temperature of cells
3. Amount of water in cells
4. Position of the nucleus in the cells

Answer: 3. Amount of water in cells

Question 17. The growth of tendrils in pea plants is due to

1. Effect of light
2. Effect of gravity
3. Rapid cell divisions in tendrillar cells that are away from the support
4. Rapid cell divisions in tendrillar cells in contact with the support

Answer: 3. Rapid cell divisions in tendrillar cells that are away from the support

Question 18. The growth of pollen tubes towards ovules is due to

1. Hydrotropism
2. Chemotropism
3. Geotropism
4. Phototropism

Answer: 2. Chemotropism

Question 19. The movement  of sunflobywith path path path that the sun is due to

1. Phototropism
2. Geotropism
3. Chemotropism
4. Hydrotropism

Answer: 1. Phototropism

Question 20. The substance that triggers the fall of mature leaves and fruits from plants is

1. Auxin
2. Gibberellin
3. Abscisic acid
4. Cytokinin

Answer: 3. Abscisic acid

Question 21. Which of the following statements bathe the out transmission of neimpulsesulse is incorrect nerve

1. the nerve impulse travels the rom dendritic end to the rds axonal end
2. At the dendritic, end electrical impulses bring about the release of some chemicals which generate an electrical impulse at the axonal end of another neuron
3. The chemicals released from the axonal end of one neuron cross the synapse and generate a similar electrical impulse in a dendrite of another neuron
4. A neuron transmits electrical impulses not only to another neuron but also to muscle and gland cells

Answer: 2. At the dendritic end electrical impulses bring about the release of some chemicals which generate an electrical impulse at the axonal end of another neuron

Question 22. Involuntary actions in the body are controlled by

1. Medulla in forebrain
2. Medulla in midbrain
3. Medulla in hindbrain
4. Medullathe  in the spinal cord

Answer: 3. Medulla in hindbrain

Question 23. Which of the following is not an involuntary action?

1. Vomiting
2. Salivation
3. Heartbeat
4. Chewing

Answer: 4. Chewing

Question 24. When a person is suffering fa from a severe cold, he or she cannot

1. Differentiate the taste of an apple from that of an ice cream
2. Differentiate the smell of a perfume from that of an agarbatti
3. Differentiate red light from green light
4. Differentiate a hot object from a cold object

Answer: 2. Differentiate the smell of a perfume from that of an agarbatti

Question 25. What is the correct direction of the flow of electrical impulses?

Answer: 3

Question 26. Which statement is not true about thyroxin?

1. Iron is essential for the synthesis of thyroxin
2. It regulates carbohydrates, pro,tein, and fat metabolism in the bThe thyroidroid gland requires iodine to synthesize thyroxin
3. Thyroxin is also called thyroid hormone

Answer: 1. Iron is essential for the synthesis of thyroxin

Question 27. Dwarfism results due to

1. Excess secretion of thyroxin
2. Less secretion of growth hormone
3. Less secretion of adrenaline
4. Excess secretion of growth hormone

Answer: 2. Less secretion of growth hormone

Question 28. Dramatic chains of body features associated with puberty are mainly because  of the secretion of

1. Oestrogen in the rom testes and testosterone in the rom ovary
2. Oestrogen the the rom adrenal gland and testosterone the the pituitary gland
3. Testosterone the rom testes” estrogenogen the rom ovary
4. Testosterone the thyroid gland estrogenogen from the pituitary gland

Answer: 3. Testosterone the testes estrogenogen from the ovary

Question 29. A doctor advised a person to take an injection of insulin because

1. His blood pressure was low
2. His heart was beating slowly
3. He was suffering from fgoiteritre
4. His sugar levels  in his blood were high

Answer: 4. His sugar levels  in his blood were high

Question 30. The hormone which increases the fertility in males is called

1. Oestrogen
2. Testosterone
3. Insulin
4. Growth hormone

Answer: 2. Testosterone

Question 31. Which of the following endocrine glands is unpaired?

1. Adrenal
2. Testes
3. Pituitary
4. Ovary

Answer: 3. Pituitary

Question 32. The junction between two neurons is called

1. Cell junction
2. Neuromuscular junction
3. Neural joint
4. Synapse

Answer: 4. Synapse

Question 33. In humans, life processes are controlled and regulated by

1. Reproductive and endocrine systems
2. Respiratory and nervous systems
3. Endocrine and digestive systems
4. Nervous and endocrine systems

Answer: 4. Nervous and endocrine systems

Question 34. Which of the following is a plant hormone?

1. Insulin
2. Thyroxin
3. Oestrogen
4. Cytokinin

Answer: Cytokinin

Question 35. The gap between two neurons is called a

1. Dendrite
2. Synapse
3. Axon
4. Impulse

Answer: Synapse

Question 36. The brain is responsible for

1. Thinking
2. Regulating the heartbeat
3. Balancing the body
4. All of the above

Answer: All of the above

Question 37. Answer the following:

1. Which hormone is responsible for the changes noticed in females at puberty?
2. Dwarfism results due to deficiency of which hormone?
3. Blood sugar level rises due to deficiency of which hormone?
4. Iodine is necessary for the synthesis of which hormone?

Answer:

1. Oestrogen
2. Growth hormone
3. Insulin
4. Thyroxin.

Question 38. Answer the following:

1. Name the endocrine gland associated with the ith b.ain.
2. Which gland secretes digestive enzymes as well as hormones?
3. Name the endocrine gland associated with the ith kid. eys?
4. Which endocrine gland is present in males but not in females?

Answer:

1. Pituitary
2. Pancreas
3. Adrenal
4. Testes.

CBSE Class 10 Science Chapter 6 Life Processes

Respiration:

CBSE Class 10 Science Chapter 6 Life Processes Short Question And Answers

Question 1. How are the lungs designed in human beings to maximise the area for the exchange of gases?
Answer:

1. The lungs are paired, and elastic respiratory organs are placed in the thoracic cavity.
2. The trachea divides in the thoracic cavity into bronchi-the right and the left. Each bronchus divides into very small tubes called bronchioles.
3. Each bronchiole terminates in balloon-like structures called alveoli.
4. Each alveolus is thin-walled and is richly supplied by blood capillaries. Alveoli also provide maximum surface area for the exchange of gases.

Read and Learn More CBSE Class 10 Science Short Answer Questions

Question 2. What are the components of the transport system in human beings? What are the functions of these components?
Answer:

The transport system, called the circulatory system in human beings, mainly consists of the heart (pumping station), blood (fluid connective tissue) and blood vessels (in which blood flows).

1. Heart: The heart is a muscular organ which is as big as our fist. The heart is a pumping organ to push blood around the body.
   1. It receives deoxygenated blood from the body parts and pumps it to lungs for to lungs for enriching with oxygen. It receives purified. blood from the lungs and pumps it around the body.
2. Blood: Blood is fluid connective tissue. It consists of a fluid medium known as plasma in which the cells are suspended, such as white blood cells and red blood cells.
   1. Plasma transports food, carbon dioxide and nitrogenous wastes (urea and uric acid) in dissolved form.
   2. Red blood cells transport oxygen. Blood also transports many other Von substances like hormones, salt, etc. Platelets present in the blood stop bleeding from injuries by forming blood clots.
3. Blood vessels: Blood vessels form a closed network of tubes to reach all the tissues. Thus, the blood pushed by the heart flows in the blood vessels (arteries) and also comes back to the heart back to the heart in the blood vessels (veins).

Question 3. Why is it necessary to separate oxygenated and deoxygenated blood in mammals and birds?
Answer:

The separation of oxygenated and deoxygenated blood from mixing allows a highly efficient supply of oxygen to the body. This is useful in animals that have energy needs such as efficient mams and birds. They constantly use energy to maintain their body temperature.

Question 4. What are the components of the transport system in highly organised plants?
Answer:

In higher plants transport system consists of vascular bundles which contain complex conducting tissues:

1. Xylem which contains vessels tracheids, sclerenchyma (all dead tissues) and living xylem parenchyma. Vessels and tracheids form tubular structures and conduct water and dissolved minerals from roots to other parts.
2. Phloem which contains sieve tubes, companion cells, phloem sclerenchyma and phloem parenchyma. Sieve tubes and companion cells conduct prepared food from leaves to other parts of the plant.

Question 5. How are water and minerals transported in plants? Lean abortion
Answer:

1. The xylem conducts water and dissolved minerals through channels formed by tracheids. and vessels from roots to all parts of the plant body.
2. The root cells actively take up ions from the soil causing steady movement of water into the root xylem. This inward flow of water pushes water upward with pressure, called root pressure. Transport of water by root pressure is more important at night, to log especially in small plants.
3. Evaporation of water molecules from the cells of a leaf, called transpiration, creates a suction which pulls water from the xylem of roots. Thus, transpiration helps in the absorption and upward movement of water and dissolved minerals from the roots to the leaves in tall plants.

Question 6. How is food transported in plants?
Answer:

Transportation of prepared food such as carbohydrates, amino acid, etc., through the phloem from leaves to all parts of plants, is called translocation. Companion cells and sieve boron tubes conduct prepared food.

The mechanism of translocation is an active process and utilizes energy. Material like sucrose is transferred from leaf cells or the site of storage into phloem tissue. This process requires energy which is provided by ATP (adenosine triphosphate) molecules.

• Entry of sucrose into phloem tissue causes an increase in osmotic pressure. As a result water from outside moves into the phloem. The osmotic’ pressure moves the dissolved material in the phloem to tissues which have less pressure.
• Thus, material moves in phloem, mainly in sieve tubes, to the place of need in the plant body. For example, sugar is translocated from its storage organ, root or stem to growing buds which need energy.

Question 7. Describe the structure and functioning of nephrons.
Answer:

Structure of nephron: A nephron is the basic unit of filtration. A large number of nephrons are closely packed in the kidney.

• Each nephron consists of a cluster of very thin-walled blood capillaries called Glomerulus. Glomerulus is associated with the cup-shaped structure present at the end of a tubule.
• Thus, a nephron consists of a cluster of glomerulus which is a cluster of blood capillaries, a thin-walled Bowman’s capsule to collect the suig of sto filtrate and a long tubule which reabsorbs useful substances and also carries remaining urine to the collecting duct.

1. Remove excess water, wastes and other substances from your blood.
2. Return substances like sodium, potassium or phosphorus whenever only of these substances run low in our body.

Question 8. What are the differences between the transport of materials in the xylem and phloem?
Answer:

Question 9. Compare the functioning of alveoli in the lungs and nephrons in the kidneys concerning their structure and functioning.
Answer:

Question 10.

1. What happens to the heart when muscles work harder?
2. Which body system is directly affected when a person has heart disease?
3. Which cells increase in number during infection?

Answer:

1. When muscles work harder, they need more oxygen. So, the heart begins to pump blood faster to overcome that need.
2. The circulatory system is directly affected when a person has heart disease.
3. The number of white blood corpuscles (WBCs) increases during infection.

Question 11.

1. Label any 4 parts in the given diagram.
2. What are the two functions represented in this diagram?

Answer:

1. 1. Pulmonary artery to lungs
   2. Lung capillaries
   3. Pulmonary vein from lungs
   4. Aorta to body
   5. Capillaries in body organs
   6. Vena cava from the body.

1. The two functions represented are:
   1. Transport of oxygen and carbon dioxide
   2. Exchange of oxygen and carbon dioxide

Question 12. What is blood pressure? How is it measured? Give one difference between systolic pressure and diastolic pressure.
Answer:

Blood Pressure: It is the force that blood exerts against the wall of a vessel. This pressure is much greater in arteries than in veins.

• It is measured using an instrument called a sphygmomanometer.
• The pressure of blood inside the artery during contraction or ventricular systole is called systolic pressure and pressure in the artery during relaxation or ventricular diastole is called diastolic pressure.
• The normal systolic pressure is about 120 mm of Hg and diastolic pressure is 80 mm of Hg.

Question 13. Draw a diagram of the human excretory system and label kidney and ureters on it.
Answer:

Question 14. Explain the mechanism of gaseous exchange between tissues and blood.
Answer:

The exchange of respiratory gases, i.e., oxygen and carbon dioxide, occurs between the blood and tissues.

• In tissues, oxygen is used up for their activities and carbon dioxide is released. The blood from the lungs has a high concentration of oxygen and a low concentration of carbon dioxide.
• Due to this difference in concentration of oxygen and carbon dioxide, the exchange of gases takes place between tissue and blood.

Question 15. Draw a schematic diagram to show the opening and closing of the stoma.
Answer:

Question 16.

1. Write the balanced chemical equation for the process of photosynthesis.
2. When do the desert plants take up carbon dioxide and perform photosynthesis?

Answer:

1. 6CO₂ + 6H₂O→ C₆H₁₂O₆ + 6O₂
2. Desert plants take up CO₂ during the night. The CO₂ is stored in organic acid at night and photosynthesis takes place during day time in the presence of sunlight.

Question 17. State in brief the function of:

1. Renal artery
2. Ureter
3. Kidney
4. Urinary bladder

Answer:

1. Renal artery: It brings blood to the kidney for filtering waste.
2. Kidney: It filters the blood and forms urine.
3. Ureter: It passes urine from the kidneys to the urinary bladder.
4. Urinary bladder: It stores the urine until it is released through the urethra.

Question 18. Draw a neat labelled diagram of the structure of a chloroplast.
Answer:

Question 19. What will happen if:

1. Peristaltic movements do not occur all along the oesophagus.
2. There are no platelets in the blood.
3. Rings of cartilage are not present in the trachea.

Answer:

1. If peristaltic movements do not occur, the food will not be able to be pushed forward, into the stomach.
2. In case of no platelets, blood will not clot during bleeding.
3. In the absence of rings of cartilage, air passage will collapse.

Question 20.

1. Name the following:
   1. The part where the air is filtered by fine hair and mucus.
   2. The part which terminates in balloon-like structures.
   3. Balloon-like structures where the exchange of gases takes place. part which separates the chest cavity from the abdominal cavity.
2. Why is the rate of breathing in aquatic organisms much faster than in terrestrial organisms?

Answer:

1. 1. Nasal passage
   2. Bronchioles
   3. Alveoli
   4. Diaphragm.
2. Since the amount of dissolved oxygen is fairly low compared to the amount of oxygen in the air, the rate of breathing in aquatic organisms is much faster than that in terrestrial organisms.

Question 21. What is lymph? How is the composition of lymph different from blood plasma? What is the direction of its flow? List two functions of the lymphatic system.
Answer:

Lymph is a circulatory fluid which flows in the lymphatic capillaries which join to form large lymph vessels.

Composition of Lymph:

Lymph is colourless and contains less protein than plasma.

Lymph flows from tissues to the heart.

Functions:

1. Lymph carries digested and absorbed fat from the intestine.
2. It drains excess fluid from extracellular space back into the blood.

Question 22.

1. Why does a piece of bread taste sweet when chewed for some time?
2. Cellulose acts as roughage in man but serves as a source of nutrients in cows. Justify the statement.

Answer:

1. The saliva present in the mouth contains an enzyme called salivary amylase which breaks down starch present in the bread into sugar. That is why, a piece of bread tastes sweet when chewed for some time.
2. Cellulose requires time to digest. Herbivore animals like cows have longer intestines which allows cellulose to be digested whereas human beings have comparatively short intestines. Thus, it is not digested and serves merely as roughage.

Question 23. List the three kinds of blood vessels of the human circulatory system and write their functions in tabular form.
Answer:

Question 24.

1. A product is formed in our muscles due to the breakdown of glucose when there is a lack of oxygen. Name the product and also mention the effect of the build up of this product.
2. Differentiate between fermentation in yeast and aerobic respiration based on end products formed.

Answer:

1. Lactic acid is formed. The formation of lactic acid in the muscles causes cramps.
2. During fermentation in yeast, ethanol is formed while in aerobic respiration, carbon dioxide and water are formed. The energy (ATP) released in the process of fermentation is also very low compared to aerobic respiration.

Question 25. Name the glands associated with the digestion of starch in the human digestive tract and mention their role. How is the required pH maintained in the stomach and small intestine?
Answer:

1. Salivary glands – salivary amylase breaks starch into sugar.
2. Pancreas – pancreatic amylase (juice) digests starch.
3. Intestinal glands – intestinal amylase – digests starch.
4. Acidic pH in the stomach – due to Hydrochloric acid secreted by the stomach.
5. Alkaline pH in small intestine – due to bile (liver)/pancreatic juice (pancreas).

Question 26. Name the two glands associated with the digestive system in humans Name their secretion also.
Answer:

1. Gastric glands: These are present in the walls of the stomach. These release HCl, a protein-digesting enzyme called pepsin and mucus.
2. Pancreatic enzymes: The pancreas secretes pancreatic juice which contains enzymes like trypsin for digesting proteins and lipase for breaking down emulsified fats.

Question 27. What are the final products produced after digestion of carbohydrates, proteins and fats?
Answer:

1. Carbohydrates – glucose
2. Proteins – amino acid
3. Fats glycerol + fatty acid

Question 28. Name the following concerning the alimentary canal:

1. 1. The largest gland.
   2. The gland secretes digestive enzymes as well as hormones.
   3. The part where digested food is absorbed.
2. What are villi? Mention their function.

Answer:

1. 1. Liver
   2. Pancreas
   3. Small intestine
2. Numerous finger-like projections present in the inner lining of the intestine which increase the surface area for absorption.

Function: These absorb digested food in the small intestine and absorb water in the large intestine.

Question 29. What are the common features of the respiratory organs in aquatic and terrestrial animals?
Answer:

• Large surface area
• Thin-walled
• Richly supplied with blood
• Well protected.

Question 30. Where do the following processes take place?

1. Filtration of blood
2. Reabsorption of glucose and water
3. Secretion of salts to make final filtrate
4. Collection of the final filtrate.

Answer:

1. Glomerulus
2. Renal tubules
3. Tubular cells
4. Collecting duct

Question 31. Explain how Paramecium obtains its food.
Answer:

In Paramecium, the food is taken in at a specific spot and is moved to this spot by the movement of cilia which covers the entire surface of the cell.

Question 32. Assume that you are a veterinary surgeon and you have removed a good length of the small intestine of a bear that was suffering from an intestinal tumour. Now, would you suggest a plant-based or a meat-based diet for the bear after its recovery? Give reasons for your answer.
Answer:

I would suggest a meat-based diet. Because to digest a plant-based diet, the bear will need a longer small intestine, since the cellulose present in the plant diet requires a longer time for digestion.

Question 33.

1. Name the following:
   1. Part in which urine is produced
   2. The part which stores the urine
   3. The part which connects 1 and 2
   4. A part from which urine is passed out.
2. Name the factors on which the amount of water reabsorbed along the tubular part of the nephron depends.

Answer:

1. 1. Kidney
   2. Ureter
   3. Urinary bladder
   4. Urethra,
2. The amount of water reabsorbed depends on how much excess water there is in the body and on how much-dissolved waste there is to be excreted.

Question 34. State two functions of stomata.
Answer:

A massive amount of gaseous exchanges takes place in leaves through stomata. Large amounts of water can be lost through stomata (transpiration).

Question 35.

1. Name the following:
   1. The organ which stores bile
   2. The organ which produces bile
2. Name one enzyme present in pancreatic juice and write its functions.
3. What are peristaltic movements?

Answer:

1. 1. Gall bladder
   2. Liver
2. 1. Trypsin: Digests proteins into amino acids.
   2. Amylase: Digests carbohydrates into simple sugars.
   3. Lipase: Digests fats into fatty acids and glycerol.
3. The lining of the alimentary canal has muscles that contract rhythmically to push food forward. These are known as peristaltic movements.

Question 36. Define transpiration. State its two functions.
Answer: The loss of water in the form of vapour from the aerial parts of the plant is known as transpiration.

Functions:

1. It helps in the absorption and upward movement of water and minerals dissolved in it from roots to the leaves.
2. It also helps in temperature regulation.

Question 37. How would digestion of food be affected if the bile duct is completely blocked?
Answer: If the bile duct is completely blocked, bile juice will not reach the small intestine and the digestion of fats will be affected.

Question 38. What is saliva? State its role in the digestion of food.
Answer:

Saliva is a watery fluid secreted by the salivary glands in the mouth. In the mouth, food gets mixed up with saliva secreted by salivary glands. Saliva contains an enzyme called salivary amylase which breaks polysaccharide starch into disaccharide maltose (sugar).

Question 39. Distinguish between saprozoic and holozoic nutrition.
Answer:

Question 40. What are the final products after the digestion of carbohydrates and proteins?
Answer:

The final product produced after digestion of carbohydrates is glucose and that of proteins is amino acid.

Question 41. Explain the process of nutrition in Amoeba.
Answer:

The mode of nutrition in Amoeba is holozoic. It feeds on unicellular plants or animals. The various steps of nutrition are ingestion, digestion, assimilation and egestion.

• When Amoeba comes in contact with food particles, they send out pseudopodia, which engulf the prey by forming a food cup, which is known as ingestion.
• When the tips of the encircling pseudopodia touch each other, the food is encaptured into a bag called a food vacuole. Various enzymes from the cytoplasm enter the food vacuole and break them down into simple soluble molecules.
• This food is then absorbed by the cytoplasm of Amoeba through the process of diffusion. Amoeba cell obtains energy from the absorbed food. The undigested food is thrown out from its cell membrane.

Question 42. Name the following

1. The process in plants that links light energy with chemical energy
2. Organisms that can prepare their food
3. The cell organelle where photosynthesis occurs
4. Cells that surround a stomatal pore
5. Organisms that cannot prepare their food
6. An enzyme secreted from gastric glands in the stomach that acts on proteins.

Answer:

1. Photosynthesis
2. Autotrophs
3. Chloroplast
4. Guard cells
5. Heterotrophs

Question 43. “All plants give out oxygen during the day and carbon dioxide during the night”. Do you agree with this statement? Give reason.
Answer:

During this time, as the rate of photosynthesis is more than the rate of respiration, the next result is the evolution of oxygen. At night there is no photosynthesis, so, they give out carbon dioxide due to respiration.

Question 44. How do the guard cells regulate the opening and closing of stomatal pores?
Answer:

The swelling of guard cells due to the absorption of water causes the opening of stomatal pores while the shrinking of guard cells closes the pores. Opening and closing of stomata occurs due to turgor changes in guard cells.

When guard cells are turgid, the stomatal pore is open while in flaccid conditions, the stomatal aperture closes.

Question 45. Two green plants are kept separately in oxygen-free containers, one in the dark and the other in continuous light. Which one will live longer? Give reasons.
Answer:

Plants kept in continuous light will live longer because they will be able to produce the oxygen required for their respiration through the process of photosynthesis.

Question 46. If a plant is releasing carbon dioxide and taking in oxygen during the day, does it mean that there is no photosynthesis occurring? Justify your answer.
Answer:

Release of CO₂ and intake of O₂ gives evidence that either photosynthesis is not taking place or its rate is too low. Normally during the daytime, the rate of photosynthesis is much more than the rate of respiration. So, CO₂ produced during respiration is used up for photosynthesis hence CO₂ is not released.

Question 47. Why do fishes die when taken out of water?
Answer:

Fishes respire with the help of gills. Gills are richly supplied with blood capillaries and can readily absorb oxygen dissolved in water. Since fishes cannot absorb gaseous oxygen they die soon after they are taken out of water.

Question 48. Differentiate between an autotroph and a heterotroph.
Answer:

Question 49. Is ‘nutrition’ a necessity for an organism? Discuss.
Answer:

Food is required for the following purposes:

1. It provides energy for the various metabolic processes in the body.
2. It is essential for the growth of new cells and the repair or replacement of worn-out cells.
3. It is needed to develop resistance against various diseases.

Question 50. What would happen if green plants disappeared from Earth?
Answer:

Green plants are the sources of energy for all organisms. If all green plants disappear from the earth, all the herbivores will die due to starvation and so will the carnivores.

Question 51. Leaves of a healthy potted plant were coated with Vaseline. Will this plant remain healthy for long? Give reasons for your answer.
Answer:

This plant will not remain healthy for a long time because

1. It will not get oxygen for respiration.
2. It will not get carbon dioxide for photosynthesis.
3. The upward movement of water and minerals would be hampered due to lack of transpiration.

Question 52. How does aerobic respiration differ from anaerobic respiration?
Answer:

Question 53. Match the words of Column with that of Column

Answer:

1. 2
2. 1
3. 4
4. 3

Question 54. Differentiate between an artery and a vein.
Answer:

Question 55. What are the adaptations of leaves for photosynthesis?
Answer:

1. Leaves provide a large surface area for maximum light absorption.
2. Leaves are arranged at right angles to the light source in a way that causes overlapping.
3. The extensive network of veins enables quick transport of substances to and from the mesophyll cells.
4. Presence of numerous stomata for gaseous exchange.
5. The chloroplasts are more in number on the upper surface of leaves.

Question 56. Why is the small intestine in herbivores longer than in carnivores?
Answer:

Digestion of cellulose takes a longer time. Hence, herbivores eating grass need a longer small intestine to allow complete digestion of cellulose. Carnivorous animals cannot digest cellulose, hence they have a shorter intestine.

Question 57. What will happen if mucus is not secreted by the gastric glands?
Answer:

Gastric glands in the stomach release hydrochloric acid, enzyme pepsin and mucus. The mucus protects the inner lining of the stomach from the action of hydrochloric acid and enzyme pepsin.

If the mucus is not released, it will lead to erosion of the inner lining of the stomach, leading to acidity and ulcers.

Question 58. What is the significance of the emulsification of fats?
Answer:

Fats are present in food in the form of large globules which makes it difficult for enzymes to act on them. Bile salts present in bile break them down mechanically into smaller globules which increases the efficiency of fat digesting enzymes.

Question 59. What causes the movement of food inside the alimentary canal?
Answer:

The wall of the alimentary canal contains muscle layers. Rhythmic contraction and relaxation of these muscles push the food forward. This is called peristalsis, which occurs all along the gut.

Question 60. Why does absorption of digested food occur mainly in the small intestine?
Answer:

Maximum absorption occurs in the small intestine because

1. Digestion is completed in small intestine
2. The inner lining of the small intestine is provided with villi which increases the surface area for absorption.
3. The wall of the intestine is richly supplied with blood vessels (which take the absorbed food to every cell of the body).

Question 61. Match Group (A) with Group (B)

Answer:

1. D
2. C
3. A
4. B

Question 62. Why is the rate of breathing in aquatic organisms much faster than in terrestrial organisms?
Answer:

Aquatic organisms like fishes obtain oxygen from water present in a dissolved state through their gills. Since the amount of dissolved oxygen is fairly low compared to the amount of oxygen in the air, the rate of breathing in aquatic organisms is much faster than that seen in terrestrial organisms.

Question 63. Why is blood circulation in the human heart called double circulation?
Answer:

The blood circulation in the human heart is called double circulation because the blood passes through the heart twice in one complete cycle of the body – once through the right half in the form of deoxygenated blood and once through the left half in the form of oxygenated blood.

Question 64. What is the advantage of having a four-chambered heart?
Answer:

In a four-chambered heart, the left half is completely separated from the right half by septa. This prevents oxygenated and deoxygenated blood from mixing.

This allows a highly efficient supply of oxygenated blood to all parts of the body. This is useful in animals that have high energy needs, such as birds and mammals.

Question 65. Mention the major events during photosynthesis.
Answer:

The major events during photosynthesis are:

1. Absorption of light energy by chlorophyll
2. Conversion of light energy to chemical energy
3. Splitting of H₂O into H₂, O₂ and eTM
4. Reduction of CO₂ to carbohydrates

Question 66. In each of the following situations, what happens to the rate of photosynthesis?

1. Cloudy days
2. No rainfall in the area
3. Good manuring in the area
4. Stomata get blocked due to dust

Answer:

1. Decreases.
2. Decreases.
3. Increases.
4. Decreases.

Question 67. Name the energy currency in the living organisms. When and where is it produced?
Answer:

Adenosine triphosphate (ATP) is produced during respiration in living organisms and also during photosynthesis in plants.

Question 68. What is common for Cuscuta; ticks and leeches?
Answer:

All are parasites, they derive nutrition from plants or animals without killing them.

Question 69. Explain the role of the mouth in the digestion of food.
Answer:

1. Food is crushed into small pieces by the teeth.
2. It mixes with saliva and the enzyme amylase (found in saliva) breaks down starch into sugars.
3. The tongue helps in the thorough mixing of food with saliva.

Question 70. What are the functions of gastric glands present in the wall of the stomach?
Answer:

1. Production of pepsin enzyme that digests proteins
2. Secretion of mucus for protection of the inner lining of the stomach.

Question 71. Match the terms in Column (A) with those in Column (B)

Answer:

1. A
2. D
3. B
4. C

Question 72. Name the correct substrates for the following enzymes:

1. Trypsin
2. Amylase
3. Pepsin
4. Lipase

Answer:

1. Protein
2. Starch
3. Protein
4. Fats

Question 73. Why do veins have thin walls as compared to arteries?
Answer:

Arteries carry blood from the heart to various organs of the body under high pressure so they have thick and elastic walls. Veins collect the blood from different organs and bring it back to the heart.

The blood is no longer under pressure so the walls are thin with valves to ensure that blood flows only in one direction.

Question 74. What will happen if platelets are absent in the blood?
Answer: In the absence of platelets, the process of clotting will be affected.

Question 75. Plants have low energy needs as compared to animals. Explain.
Answer: Plants do not move. In a large plant body, there are many dead cells like sclerenchyma, as a result, it requires less energy as compared to animals.

Question 76. Why and how does water enter continuously into the root xylem?
Answer:

Cells of the root are in close contact with soil and so actively take up ions. The ion- concentration increases inside the root and hence osmotic pressure increases the movement of water from the soil into the root which occurs continuously.

Question 77. Why is transpiration important for plants?
Answer:

Transpiration is important because

1. It helps in the absorption and upward movement of water and minerals from roots to leaves.
2. It prevents the plant parts from heating up.

Question 78. How do the leaves of plants help in excretion?
Answer:

Many plants store waste materials in the vacuoles of mesophyll cells and epidermal cells. When old leaves fall, the waste materials are excreted along with the leaves.

Question 79. What is the functional difference between the four chambers of the heart?
Answer:

Question 80. Give one structural and one functional difference between an artery and a vein.
Answer:

Question 81. Give the role of the following in plants and animals:

1. Guard cells
2. Hymph
3. Bio catalyst
4. Phloem

Answer:

1. Stomatal opening
2. Fat transport
3. Speeding up the digestive process
4. Transport of food

Question 82. Name the excretory wastes of the following:

1. Lungs
2. Kidney
3. Skin
4. Leaves.

Answer:

1. CO₂
2. Urea
3. Sweat
4. O₂, H₂O and CO₂

Question 83. After a vigorous exercise, you may experience cramps in your leg muscles. Why does this happen?
Answer:

This happens due to the build-up of lactic acid in our muscles. During heavy exercise, there is a lack of oxygen in our muscle cells and therefore, another pathway for the breakdown of pyruvate of lactic acid takes place.

Question 84. Which organ secretes a hormone when the blood sugar rises? Name the digestive enzymes released by this organ.
Answer:

The pancreas secretes the hormone insulin which regulates the blood sugar level. Digestive enzymes secreted by the pancreas are trypsin and lipase.

Question 85. Explain the assimilation of carbohydrates, proteins and fats inside the cells.
Answer:

1. Carbohydrates: Glucose is used to release energy. Excess of glucose is brought to the liver and converted to glycogen (glycogenesis) and stored there. As the need arises the glucose is reformed from glycogen (glycogenolysis) and released into the bloodstream.
2. Proteins: Most of the amino acids are used in protein synthesis which helps in the growth and repair of body tissues. Proteins may act as structural proteins or act as enzymes and thus control various metabolic activities of the body.
   1. Amino acids which are not used as such, are deaminated in the liver i.e., the amino group (-NH₂) is removed. The amino group forms ammonia (NH₃) which is highly toxic and must be removed. This is done by liver cells which convert it to harmless urea, which is then a Diagram showing absorption of food in the intestine excreted by the kidneys. Urea is formed only in the liver.
3. Fats: Fats release energy. Excess fats are stored in the liver and the form of adipose tissue. Some fats enter into the composition of cell organelles.

Question 86. For the last few days Rakesh has started cycling long distances. But on his way back he feels cramps in his calf muscles.

1. What can be the possible cause of it?
2. Name the process involved and its equation.
3. How can Rakesh have quick relief from muscle cramps?

Answer:

1. Accumulation of lactic acid in the muscles.

2. Anaerobic respiration.

3. By having lots of water baths and a massage.

Question 87. During sports practice in the school, many students got tired very soon and were found to be anaemic. Health and Wellness group students made a presentation on the ‘right diet for right health’ and uploaded it on school website.

1. What causes anaemia?
2. Name two foods that can help to overcome the problem of anaemia.
3. What value of Health and Wellness group students is displayed in the above act?

Answer:

1. A deficiency of haemoglobin in red blood cells leads to anaemia.
2. Spinach and beetroot.
3. Health and Wellness group students showed the value of group work and being responsible citizens.

Question 88. A group of students from class X were given the project on ‘respiratory diseases’. The students spread an awareness camp on how to overcome respiratory problems.

1. What are the causes of respiratory diseases?
2. Name two respiratory diseases.
3. What value of students of class X is displayed in the above act?

Answer:

1. Too small and suspended particles inhaled causing respiratory diseases.
2. Asthma and bronchitis.
3. Students of class X showed the value of group work, being cooperative learners and responsible citizens.

Life Processes Multiple Choice Questions

1. Which of the following statements about the autotrophs is incorrect?

1. They synthesise carbohydrates from carbon dioxide and water in the presence of sunlight and chlorophyll
2. They store carbohydrates in the form of starch
3. They convert carbon dioxide and water into carbohydrates in the absence of sunlight
4. They constitute the first trophic level in food chains

Answer: 3. They convert carbon dioxide and water into carbohydrates in the absence of sunlight

2. In which of the following groups of organisms, food material is broken down outside the body and absorbed?

1. Mushrooms, green plants, Amoeba
2. Yeast, mushroom, bread mould
3. Paramecium, Amoeba, Cuscuta
4. Cuscuta, lice, tapeworm

Answer: 2. Yeast, mushroom, bread mould

3. Select the correct statement

1. Heterotrophs do not synthesise their food
2. Heterotrophs utilise solar energy for photosynthesis
3. Heterotrophs synthesise their food
4. Heterotrophs are capable of converting carbon dioxide and water into carbohydrates

Answer: 1. Heterotrophs do not synthesise their food

4. Which is the correct sequence of parts in the human alimentary canal?

1. Mouth → stomach → small intestine → oesophagus → large intestine
2. Mouth → oesophagus → stomach → large intestine → small intestine
3. Mouth → stomach → oesophagus → small intestine → large intestine
4. Mouth → oesophagus → stomach → small intestine → large intestine

Answer: 4. Mouth → oesophagus → stomach → small intestine → large intestine

5. If salivary amylase is lacking in the saliva, which of the following events in the mouth cavity will be affected?

1. Proteins breaking down into amino acids
2. Starch breaking down into sugars
3. Fats breaking down into fatty acids and glycerol
4. Absorption of vitamins

Answer: 2. Starch breaking down into sugars

6. The inner lining of the stomach is protected by one of the following from hydrochloric acid. Choose the correct one

1. Pepsin
2. Mucus
3. Salivary amylase
4. Bile

Answer: 2. Mucus

7. Which part of the alimentary canal receives bile from the liver?

1. Stomach
2. Large intestine
3. Small intestine
4. Oesophagus

Answer: 2. Large intestine

8. A few drops of iodine solution were added to rice water. The solution turned blue-black. This indicates that rice water contains

1. Complex proteins
2. Simple proteins
3. Fats
4. Starch

Answer: 4. Starch

9. In which part of the alimentary canal food is finally digested?

1. Stomach
2. Mouth cavity
3. Large intestine
4. Small intestine

Answer: 4. Small intestine

10. Choose the function of the pancreatic juice from the following

1. Trypsin digests proteins and lipase carbohydrates
2. Trypsin digests emulsified fats and lipase proteins
3. Trypsin and lipase digest fats
4. Trypsin digests proteins and lipase-emulsified fats

Answer: 4. Trypsin digests proteins and lipase-emulsified fats

11. When air is blown from the mouth into a test tube containing lime water, the lime water turns milky due to the presence of

1. Oxygen
2. Carbon dioxide
3. Nitrogen
4. Water vapour

Answer: 2. Carbon dioxide

12. The correct sequence of anaerobic reactions in yeast is

Answer: 4.

13. Which of the following is most appropriate for aerobic respiration?

Answer: 4.

14. Which of the following statement(s) is (are) true about respiration?

1. During inhalation, ribs move inward and the diaphragm is raised
2. In the alveoli, an exchange of gases takes place i.e., oxygen from alveolar air diffuses into blood and carbon dioxide from blood into alveolar air
3. Haemoglobin has a greater affinity for carbon dioxide than oxygen
4. Alveoli increase surface area for the exchange of gases

1. 1 and 4
2. 1 and 3
3. 2 and 3
4. 2 and 4

Answer: 4. 2 and 4

15. Which is the correct sequence of air passage during inhalation?

1. Nostrils → larynx → pharynx → trachea → lungs
2. Nasal passage → trachea → pharynx → larynx → alveoli
3. larynx → nostrils → pharynx → lungs
4. Nostrils → pharynx → larynx → trachea → alveoli

Answer: 4. Nostrils → pharynx → larynx → trachea → alveoli

16. During respiration exchange of gases takes place in

1. Trachea and larynx
2. Alveoli of lungs
3. Alveoli and throat
4. Throat and larynx

Answer: 2. Alveoli of lungs

17. Which of the following statement(s) is (are) true about heart?

1. The left atrium receives oxygenated blood from different parts of the body while the right atrium receives deoxygenated blood from the lungs
2. The left ventricle pumps oxygenated blood to different body parts while the right ventricle pumps deoxygenated blood to the lungs
3. The left atrium transfers oxygenated blood to the right ventricle which sends it to different body parts
4. Right atrium receives deoxygenated blood from different parts of the body while the left ventricle pumps oxygenated blood to different parts of the body

1. 1
2. 2
3. 2 and 4
4. 1 and 3

Answer: 3. 2 and 4

18. What prevents the backflow of blood inside the heart during contraction?

1. Valves in heart
2. Thick muscular walls of ventricles
3. Thin walls of atria
4. All of the above

Answer: 1. Valves in the heart

19. Single circulation i.e., blood flows through the heart only once during one cycle of passage through the body, is exhibited by

1. Labeo, Chameleon, Salamander
2. Hippocampus, Exocoetus, Anabas
3. Hyla, Rana, Draco
4. Whale, Dolphin, Turtle

Answer: 2. Hippocampus, Exocoetus, Anabas

20. In which of the following vertebrate groups/groups, the heart does not pump oxygenated blood to different parts of the body?

1. Pisces and amphibians
2. Amphibians and reptiles
3. Amphibians only
4. Pisces only

Answer: 4. Pisces only

21. Choose the correct statement that describes arteries.

1. They have thick elastic walls, blood flows under high pressure; collect blood from different organs and bring it back to the heart
2. They have thin walls with valves inside, blood flows under low pressure and carry blood away from the heart to various organs of the body
3. They have thick elastic walls, blood flows under low pressure; and carry blood from the heart to various organs of the body
4. They have thick elastic walls without valves inside, blood flows under high pressure and carries blood away from the heart to different parts of the body.

Answer: 4. They have thick elastic walls without valves inside, blood flows under high pressure and carries blood away from the heart to different parts of the body.

22. The filtration units of kidneys are called

1. Ureter
2. Urethra
3. Neurons
4. Nephrons

Answer: 4. Nephrons

23. Oxygen liberated during photosynthesis comes from

1. Water
2. Chlorophyll
3. Carbon dioxide
4. Glucose

Answer: 1. Water

24. The blood leaving the tissues becomes richer in

1. Carbon dioxide
2. Water
3. Haemoglobin
4. Oxygen

Answer: 1. Carbon dioxide

25. Which of the following is an incorrect statement?

1. Organisms grow with time
2. Organisms must repair and maintain their structure
3. The movement of molecules does not take place among cells
4. Energy is essential for life processes

Answer: 3. Movement of molecules does not take place among cells

26. The internal (cellular) energy reserve in autotrophs is

1. Glycogen
2. Protein
3. Starch
4. Fatty acid

Answer: 3. Starch

27. Which of the following equations is the summary of photosynthesis?

1. 6CO₂+ 12H₂O → C₆H₁₂O₆+ 6O₂+ 6H₂O
2. 6CO₂ + H₂O + Sunlight → C₆H₁₂O₆ + O₂+ 6H₂O
3. 6CO₂ + 12H₂O + Chlorophyll + Sunlight → C₆H₁₂O₆ + 6O₂+ 6H₂O
4. 6CO₂ + 12H₂O + Chlorophyll + Sunlight → C₆H₁₂O₆+6CO₂+ 6H₂O

Answer: 3. 6CO₂ + 12H₂O + Chlorophyll + Sunlight → C₆H₁₂O₆ + 6O₂+ 6H₂O

28. Choose the event that does not occur in photosynthesis

1. Absorption of light energy by chlorophyll
2. Reduction of carbon dioxide to carbohydrates
3. Oxidation of carbon to carbon dioxide
4. Conversion of light energy to chemical energy

Answer: 3. Oxidation of carbon to carbon dioxide

29. The opening and closing of the stomatal pore depends upon

1. Oxygen
2. Temperature
3. Water in guard cells
4. The concentration of CO₂ in stomata

Answer: 3. Water in guard cells

30. Choose the forms in which most plants absorb nitrogen

1. Proteins
2. Nitrates and Nitrites
3. Urea
4. Atmospheric nitrogen

1. 1 and 2
2. 2 and 3
3. 3 and 4
4. 1 and 4

Answer: 2. 2 and 3

31. Which is the first enzyme to mix with food in the digestive tract?

1. Pepsin
2. Cellulase
3. Amylase
4. Trypsin

Answer: 3. Amylase

32. Which of the following statement(s) is (are) correct?

1. Pyruvate can be converted into ethanol and carbon dioxide by yeast
2. Fermentation takes place in aerobic bacteria
3. Fermentation takes place in mitochondria
4. Fermentation is a form of anaerobic respiration

1. 1 and 3
2. 2 and 4
3. 1 and 4
4. 2 and 3

Answer: 3. 1 and 4

33. Lack of oxygen in muscles often leads to cramps among cricketers. This results due to

1. Conversion of pyruvate to ethanol
2. Conversion of pyruvate to glucose
3. Non-conversion of glucose to pyruvate
4. Conversion of pyruvate to lactic acid

Answer: 4. Conversion of pyruvate to lactic acid

34. Choose the correct path of urine in our body

1. Kidney → ureter → urethra → urinary bladder
2. Kidney → urinary bladder → urethra → ureter
3. Kidney → ureters → urinary bladder → urethra
4. Urinary bladder → kidney → ureter → urethra

Answer: 3. Kidney → ureters → urinary bladder → urethra

35. During deficiency of oxygen in tissues of human beings, pyruvic acid is converted into lactic acid in the

1. Cytoplasm
2. Chloroplast
3. Mitochondria
4. Golgi body

Answer: 1. Cytoplasm

CBSE Chapter 13 Magnetic Effects Of Electric Current Short Question And Answers

Question 1. List the properties of magnetic lines of force.
Answer: Those are closed curves that start in the air from the N-pole end at the S-pole and then return to the N-pole through the interior of the magnet.

1. No two magnetic lines of force can intersect each other.
2. The field lines are closer together in the regions of strong fields.
3. The field lines tend to contract lengthwise and expand sidewise.

Question 2. Why don’t two magnetic lines of force intersect each other?
Answer: If two lines of force intersect, then there will be two directions of the magnetic field at the point of intersection and a magnetic needle placed at this point should point towards these two directions, which is not possible.

Read and Learn More CBSE Class 10 Science Short Answer Questions

Question 3. Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply the right-hand rule to find out the direction of the magnetic field inside and outside the loop.
Answer: Each section of wire produces its concentric set of lines of force. By applying the right-hand thumb rule, we find that all the sections produce a magnetic field directed downward at all points inside the loop while at the outside points, the field is directed upwards. Hence, the magnetic field acts normally into the plane of paper at the points inside the loop and normally out ofthe plane of paper at points outside the loop.

Question 4. The magnetic field in a given region is uniform. Draw a diagram to represent it.
Answer: The uniform magnetic field B can be represented by equidistant parallel lines of force, as shown in the figure.

Choose the correct option.

1. The magnetic field inside a long straight solenoid-carrying current Is zero.
2. Decreases as we move towards its end
3. Increases as we move towards its end.
4. Is the same at all points.

Answer: 4. It is the same at all points

Question 5. In Activity 7.7, how do we think the displacement of rod AB will be affected if current in rod AB is increased; a stronger horse-shoe magnet is used; and the length of the rod AB is increased?
Answer: When the current in the red AB is increased, the force exerted on the conductor increases, so the displacement of the rod increases.

When a stronger horse-shoe magnet is used, the magnitude of the magnetic field increases. This increases the force exerted on the rod and the displacement of the rod. (Hi) Displacement of the rod is directly proportional to its length. Hence, there would be a larger displacement if the length of the rod AB is increased.

Question 6. State Fleming’s left-hand rule.
Answer: According to Fleming’s left-hand rule, if we stretch the forefinger, the middle finger and the thumb of our left hand are mutually perpendicular to each other and if the forefinger points in the direction ofthe magnetic field, the middle finger in the direction of current, then the thumb will point in the direction of motion or the force on the conductor.

Question 7. What is the principle ofan electric motor?
Answer: A current-carrying conductor when placed in a magnetic field experiences a force. The direction ofthis force is given by Fleming’s left-hand rule. This is the basis of an electric motor.

Question 8. What is the role ofthe split ring in an electric motor?
Answer: The split ring reverses the direction of current in the armature coil after every half rotation, i.e., it acts as a commutator. The reversed current reverses the direction ofthe forces acting on the two arms of the armature after every half rotation. This allows the armature coil to rotate continuously in the same direction.

Question 9. Explain different ways to induce a current in a coil.
Answer: A current can be induced in a coil by

1. If moving a magnet towards or away from the coil or vice versa, and
2. Changing current in the neighboring coil

Question 10. State the principle ofan electric generator.
Answer: An electric generator works on the principle of electromagnetic induction. When a closed coil is rotated in a uniform magnetic field with its axis perpendicular to the direction of the field, the magnetic field lines passing through the coil change and induce potential difference and hence a current is set up.

Question 11. Name some sources of direct current.
Answer: Some of the sources of direct current are dry cells, button cells, lead accumulators, etc.

Question 12. Which sources produce alternating current?
Answer: Alternating current is produced by A.C. generators of nuclear power plants, thermal power plants, hydroelectric power stations, etc.

Question 13. An electric oven with a kW power rating is operated in a domestic electric circuit (220 V) that has a current rating of 5 A. What result do you expect? Explain.
Answer: The electric oven draws a current given by

⇒ \(\begin{aligned}
& \mathrm{I}=\frac{\mathrm{P}}{\mathrm{V}}=\frac{2 \mathrm{~kW}}{220 \mathrm{~V}} \\
& \mathrm{I}=\frac{2000 \mathrm{~W}}{220 \mathrm{~V}} \\
& \mathrm{I}=9.09 \mathrm{~A}
\end{aligned}\)

Thus, the electric oven draws current much more than the current rating of A. That is the circuit is overloaded. Due to excessive current, the fuse wire blows, and the circuit is broken.

Question 14. What precautions should be taken to avoid the overloading of domestic electric circuits?
Answer: As a result of overloading, the connecting wires get overheated and the appliances may get damaged.

To avoid this, the following safety measures must be taken:

The wires used in the circuit must be coated with good insulating materials like PVC, etc.

The circuit must be divided into different sections and a safety fuse must be used in each section. High-power appliances like air-conditioners, refrigerators, water heaters, etc., should not be used simultaneously.

Question 15. How does a solenoid behave like a magnet? Can you determine the north and south poles of a current-carrying solenoid with the help of a bar magnet1? Explain.
Answer: The magnetic field pattern produced by a solenoid is similar to that of a bar magnet.
Like a bar magnet, one end of the solenoid has N-polarity and the other end has Spolarity.

We bring the N-pole of the bar magnet near one end of the solenoid. If there is an attraction, then that end of the solenoid has south polarity and the other has north polarity. If there is a repulsion, then that end ofthe solenoid has north polarity and the other end has south polarity.

Question 16. When is the force experienced by a current-carrying conductor placed in a magnetic field largest?
Answer: When the conductor carries current in a direction perpendicular to the direction of the magnetic field, the force experienced by the conductor is largest.

Question 17. Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from the back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of the magnetic field?
Answer: According to Fleming’s left-hand rule, the magnetic field acts in a vertically downward direction. Note that the direction of the current will be opposite to that ofthe electron beam.

Question 18. Name some devices in which electric motors are used.
Answer: Electric motor is used ’n appliances like electric fans, washing machines, mixers, grinders, blenders, computers, MP3 players, etc.

Question 19. A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is pushed into the coil, withdrawn from inside the coil, or held stationary inside the coil?
Answer: An electric current is induced in the coil and the galvanometer shows a deflection.

An electric current is induced in the coil but in the opposite direction. The galvanometer shows a deflection in the reverse direction.

No current is induced in the coil. The galvanometer shows no deflection.

Question 20. Two circular coils A and B are placed close to each other. If the current in coil A is changed, will some current be induced in the coil B? Give a reason.
Answer: Yes. When the current in coil A is changed, some current is induced in the coil B. Due to the change in current in coil A, the magnetic field lines linked with coil A and coil B get changed. This sets up induced current in coil B.

Question 21. State the rule to determine the direction of a magnetic field produced around a straight conductor-carrying current, the force experienced by a current-carrying straight conductor placed in a magnetic field that is perpendicular to it, and the current induced in a coil due to its rotation in a magnetic field.
Answer: Right-hand thumb rule: If the current-carrying conductor is held in the right hand such that the thumb points in the direction of the current, then the direction of the curl of the fingers will give the direction of the magnetic field.

Fleming’s left-hand rule: Stretch the forefinger, the middle finger and the thumb ofthe left hand mutually perpendicular to each other. The forefinger points in the direction ofthe magnetic field, the middle finger in the direction of the current, then the
thumb points in the direction of force in the conductor.

Fleming’s right-hand rule: Stretch the thumb, forefinger, and middle finger of the right hand mutually perpendicular to each other.If the forefinger points in the direction of the magnetic field, the thumb in the direction of motion of the conductor, then the middle finger points in the direction of the current induced in the conductor.

Question 22. When does an electric short circuit occur?
Answer: As a result of the live wire touching the neutral wire, the resistance offered to the flow of current becomes almost zero and this is called short-circuiting. In this situation, a large current flows through the circuit, causing a spark or damage to the appliance.

Question 23. What is the function of an earth wire? Why is it necessary to earth metallic appliances?
Answer: The earth wire connects the metallic body ofthe high-powered appliance to the earth. It is a safety measure that ensures any leakage of current of the metallic body of the appliance as it keeps its potential equal to that ofthe earth (zero volts) and the user may not get a severe electric shock.

Question 24. The horizontal component of Earth’s magnetic field at a place is uniform and its direction is south to north. A high current through a horizontal power line flows at this place from west to east. Consider two points A and B at equal distances from the wire, respectively above and below it. Giving reason explains where the fields are A and B.
Answer: According to the right-hand thumb rule, the direction of the magnetic field due to the current at A is from north to south and at B from south to north.

Therefore, at A earth’s field and field due to current are in opposite directions whereas at B they are in the same direction. So the field is more at B.

Question 25. Give some advantages of electromagnets over permanent magnets.
Answer: An electromagnet has the following advantages over a permanent magnet:

1. An electromagnet can produce a very strong magnetic field.
2. The strength of the magnetic field of an electromagnet can be increased/decreased by increasing/decreasing the strength of the current or the number of turns in the solenoid.
3. The polarity of an electromagnet can be reversed by sending the current in the reverse direction.

Question 26. Name and state the rule to determine the direction of force experienced by a straight conductor carrying current placed in a magnetic field that is perpendicular to it. Or State Fleming’s left-hand rule with a labeled diagram.
Answer: Fleming’s left-hand rule: Stretch the forefinger, the central finger, and the thumb of the left hand mutually perpendicular to each other. The forefinger points in the direction of the magnetic field, the central finger in the direction of current, and then the thumb points in the direction of force on the conductor.

Question 27. Two long parallel wires are hanging freely. If they are connected to a battery (i) in series and 2 in parallel, what would be the effect on their positions?
Answer: In series: The current flowing in them will be in the opposite direction. Hence, they will repel each other.

In parallel: The current flowing in them will be in the same direction. Hence, they will attract each other.

Question 28. What is the role of the fuse, used in series with any electrical appliance? Why should a fuse with a defined rating not be replaced by one with a larger rating?
Answer: Fuse is used for protecting appliances due to short-circuiting or overloading. The fuse is rated for a certain maximum current and blows off when a current more than the rated value flows through it.

If a fuse is replaced by one with larger ratings, the appliances may get damaged while the protecting fuse does not burn off.

Question 29. A current through a horizontal power line flows in an east-to-west direction. What is the direction magnetic field at a point directly below it and a point directly above it?
Answer: The current is in the east-west direction. Applying the right-hand thumb rule, we get that the direction of the magnetic field at a point below the wire is from north to south. The direction of the magnetic field at a point directly above the wire is from south to north.

Question 30. Explain why a fuse should be joined with the live wire and not with the neutral wire in a domestic circuit.
Answer: In a domestic circuit, the phase wire always has a much higher potential than the neutral wire. Moreover, the neutral wire is connected to the earth at the substation. Thus, during a short circuit, the fuse will break the connection with the neutral wire and not the live wire.

Question 31. A current I passes through a circular loop C and a solenoid AB as shown below:

1. What is the polarity of (a) the force ofthe loop you are looking at? (b) the end of the solenoid?
2. What is the direction ofthe magnetic field at the center ofthe loop?

Answer: The face of the loop will behave as a North Pole.

1. End B will also behave as a North Pole.
2. Straight and parallel to the axis of the solenoid.

Question 32. Can two magnetic lines of force intersect? Justify your answer.
Answer: No, if two magnetic lines of forces intersect, then there will be two tangents and hence two directions of the magnetic field at the point of intersection. This is not possible.

Question 33. Define a solenoid. How is it different from a coil? 
Answer: A coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder is called a solenoid. The strength of the magnetic field inside a coil varies while in the solenoid case, it is the same.

Question 34. State Faraday’s Laws of electromagnetic induction.
Answer: Faraday put forward the following laws: Faraday’s laws of electromagnetic induction.

1. Whenever the magnetic field (flux) linked with a coil changes, an induced EMF is produced.
2. The induced emflasts as long as the change in magnetic field (flux) continues.
3. The induced emf in the closed loop equals the negative rate of change of magnetic field (flux) through the loop.

Question 35. State Oersted observation. How can it be shown that a magnetic field exists around a wire through which a direct electric current is passing?
Answer: A magnetic needle brought close to a straight current-carrying wire aligns itself perpendicular to the wire, reversing the direction of current reverses the direction of deflation. This shows that the current-carrying wire is associated with a magnetic field.

Question 36. Draw the patterns of magnetic field lines due to a bar magnet. The magnetic field lines
are closed curves. Why?
Answer: Inside the magnet, the direction of field lines is from its south pole to its north pole. So the magnetic field lines are closed curves

Question 37. An alpha particle (+ve charged particle) enters a magnetic field at a right angle as shown in the figure. Explain with the help of a relevant rule, the direction of force acting on the alpha particle.

Answer: According to Fleming’s left-hand rule, if the forefinger points in the direction ofthe magnetic field and the central finger points in the direction of a current, the thumb gives the direction of the force acting on the conductor. So the force will act in the upward direction of the alpha particle.

Identify the type of magnetic field represented by the magnetic field lines given below and name the type of conductors that can produce them.

Answer: It represents the magnetic field lines produced by a current-carrying circular loop.

It represents the magnetic field lines produced by a solenoid

Question 38. Explain the right-hand thumb rule and cork and screw rule to find the magnetic field due to a current-carrying conductor.
Answer: Imagine a current-carrying conductor held in your right hand such that the thumb points in the direction of current, then the curl of your fingers encircling the conductor will give the direction of magnetic field lines around the conductor. Maxwell’s cork screw rule (Right-hand screw rule):

Imagine a right-handed screw to be rotated in the direction of current, then the direction of rotation gives the direction of magnetic field lines.

Question 39. What is the nature of the magnetic field produced by a current-carrying circular coil? Explain with the help ofan experiment.
Answer: Bend a copper wire in a circular shape. Pass the coil through a cardboard. Connect the free ends ofthe coil to a battery and a key. Sprinkle some iron filings on the cardboard.

Put on the key, you will find that the iron filings arrange themselves in the form of concentric circles. The magnetic lines of force near each segment of wire are circular and form concentric circles. Whereas the lines of force near the center of the coil are almost straight fines. Note that at the center of the coil, the magnetic field is uniform and perpendicular to the plane of the coil.

Question 40. In a pattern of magnetic field lines due to a bar magnet, how can the regions of relative strength be identified1? Compare the strength of the field near the poles and middle of a bar magnet
Answer:

The relative strength ofthe magnetic field is shown by the degree of closeness ofthe field fines.

The strength of the field near the poles is highest and in the middle of a bar magnetite is the lowest.

Question 41. State one main difference between AC and DC. Why ac is preferred over DC for long-range transmission of electric power? Name one source for each of DC and AC.
Answer: The DC always flows in one direction while AC reverses its direction periodically. This is because in the case of AC electric power can be transmitted over long distances without much loss of energy.

1. Source of AC- AC generator
2. Source of- DC generator/cell

Question 42. Student experiments to study the magnetic effect of current around a current-carrying straight conductor with the help of a magnetic compass. He reports that:

1. The degree of deflection ofthe magnetic compass increases when the compass is moved away from the conductor.
2. the degree of deflection of the magnetic compass increases when the current through the conductor is increased.
3. Which of the above observations ofthe student appears to be wrong and why?

Answer: The first observation is wrong. Because as the distance from the conductor increases, the strength ofthe magnetic field will decrease. So the degree of deflection ofthe compass should decrease instead of increasing.

Question 43. Draw magnetic field lines produced around a current carrying a straight conductor passing through cardboard. How will the strength of the magnetic field change, when the point where the magnetic field is to be determined, is moved away from the straight wire carrying constant current? Justify your answer:
Answer: The diagram is as shown:

We will move a compass needle away from the straight wire. When it is moved away from the straight wire, the deflection of the needle decreases which implies that the strength of the magnetic field decreases.

Question 44. A student while studying the force experienced by a current-carrying conductor in a magnetic field records the following observations.

1. The force experienced by the conductor increases as the current is increased.
2. The force experienced by the conductor decreases as the strength ofthe magnetic field is increased
3. Which of the two observations is correct and why?

Answer: The observation is correct.

Question 45. Magnetic field lines are shown in the given diagram. A student makes a statement that the magnetic field at X is stronger than at Y. Justify this statement. Also, redraw the diagram and mark the direction of magnetic field lines.
Answer: The relative strength ofthe magnetic field is shown by the degree of closeness ofthe field lines. The field lines are closer at X than at Y. Therefore, the field is stronger at X where the field lines are crowded. The diagram is as shown:

Because the force experienced by a current-carrying conductor in a magnetic field is proportional to the strength of the current.

Question 46. How does the strength ofthe magnetic field at the center of a circular coil of a wire depend on:

1. Radius Ofthe Coil
2. Number of Ofturns In The Coil

Answer: 1 As the radius increases, the field decreases.

2. The field produced is directly proportional to the number of turns in the coil.

Question 47. What is a fuse? How does it function?
Answer: An electric fuse is a device that is used to limit the current in an electric circuit. The use of a fuse is to safeguard the circuit and the appliances connected to it from being damaged.

The fuse is a short piece of wire made of a material having a low melting point. When an electric current is passed through it, the fuse gets heated. If the current passing through the fuse exceeds the safe limit, the heat produced melts the fuse and this breaks the circuit.

Question 48. What is meant by the term “magnetic field lines”? List two properties of magnetic field lines.
Answer: A magnetic field line is a path that will be followed by a “hypothetical” north pole in the magnetic field of another magnetite that is allowed to move freely. Two properties of magnetic field lines are:

1. Two magnetic field lines do not intersect each other.
2. They travel from the north to the south pole of a magnet outside the magnet and from the south to the north pole inside the magnet.

Question 49. Draw a rough sketch of the pattern of the field lines due to:

1. Current flowing into a circular coil and
2. Solenoid carrying current

Answer: The sketches are shown below:

Question 50. A magnetic compass shows a deflection when placed near a current-carrying wire. How will the deflection of the compass be affected, if the current in the wire is increased? Support your answer with a reason.
Answer: The deflection increases. The strength of the magnetic field is directly proportional to the magnitude of current passing through the straight conductor.

Question 51. As shown in the figure, a magnetic compass needle is placed on a paper plane near point A. In which plane should a straight current-carrying conductor be positioned so that it passes through A and there is no change in the deflection ofthe compass? Under what condition is the deflection maximum and why?
Answer: In the plane of the paper itself. The axis of the compass is vertical and the field due to the conductor is also vertical. It could result in a dip of the compass needle which is not possible in this case (dips result only if of compass is horizontal). The deflection is maximum when the conductor through Ais perpendicular to the plane paper and the field due to its maximum in the plane of the paper.

Question 52. Under what conditions permanent electromagnet is obtained if a current-carrying solenoid is used? Support your answer with the help of a labeled circuit diagram.
Answer: The current through the solenoid should be a direct current.

The rod inside is made of a magnetic material such as steel.

Question 53. AB is a current-carrying conductor in the plane of the paper as shown in the figure. What are the directions of the magnetic field produced by it at the points P and Q? Given; > r2, where will the strength ofthe magnetic field be larger?
Answer: Into the plane of paper at P and out of at Q. The strength of the magnetic field is larger at the point located closer i.e. at Q

Question 54. A magnetic compass shows a deflection when placed near a current-carrying wire. How will the deflection of the compass be affected if the current in the wire is increased? Support your answer with a reason.
Answer: The deflection increases. The strength magnetic field is directly proportional to the magnitude of current passing through the straight conductor.

Question 55. It is established that an electric current through a metallic conductor produces a magnetic field around it. Is there a similar magnetic field produced around a thin beam of moving alpha particles, and neutrons’? Justify your answer.
Answer:

1. Yes, Alpha particles being positively charged constitute, current to the direction of motion.
2. No, the neutrons being electrically neutral constitute no current.

Question 56. What does the direction of thumb indicate in the right-hand thumb rule? In what way
this rule is different from Fleming’s left-hand rule?
Answer: The thumb indicates the direction of current in the straight conductor held by curled fingers, whereas Fleming’s left-hand rule gives the direction of force experienced by the current-carrying conductor placed in an external magnetic field.

Question 57. Meena draws magnetic field lines of field close to the axis of a current-carrying circular
loop. As she moves away from the center ofthe circular loop she observes that the lines keep
on diverging. How will you explain her observation?
Answer: The strength of the magnetic field falls as distance increases. This is indicated by the decrease in the degree of closeness of the lines of field.

Question 58. What does the divergence of magnetic field lines near the ends of a current carrying a straight solenoid indicate?
Answer: The divergence, that is, the falling degree of closeness of magnetic field lines indicates
the fall in strength of the magnetic field near and beyond the ends of the solenoid.

Question 59. Name four appliances wherein an electric motor, a rotating device that converts electrical energy to mechanical energy, is used as an important component. In what respect motors are different from generators?
Answer: Electric fans, mixers, washing machines, computer drives, etc. Motors convert electrical energy into mechanical energy whereas generators convert mechanical energy into electrical energy.

Question 60. What is the role ofthe two conducting stationary brushes in a simple electric motor?
Answer: The brushes are connected to the battery and touch the outer side of two halves of the split ring whose inner sides are insulated and attached to the axle.

Question 61. What is the difference between a direct current and an alternating current? How many times does AC used in India change direction in one second?
Answer: Direct current always flows in one direction but the alternating current reverses its direction periodically. The frequency of AC in India is 50 Hz and in each cycle it alters direction twice. Therefore AC changes direction 2 x 50 = 100 times in one second.

Question 62. What is the role of the fuse, used in series with an electrical appliance? Why should a fuse
with a defined rating not be replaced by one with a larger rating?
Answer: Fuse is used for protecting appliances due to short-circuiting or overloading. The fuse is rated for a certain maximum current and blows off when a current more than the rated value flows through it. If a fuse is replaced by one with larger ratings, the appliances may get damaged while the protecting fuse does not burn off. This practice of using a fuse of improper rating should always be avoided.

Question 63. Why does a magnetic compass needle pointing North and South in the absence of a nearby magnet get deflected when a bar magnet or a current-carrying loop is brought near it? Describe some salient features of the magnetic lines of field concept.
Answer: Current carrying loops behave like bar magnets and both have their associated lines of field. This modifies the already existing earth’s magnetic field and a deflection results. The magnetic field has both direction and magnitude. Magnetic field lines emerge from the N-pole and enter the S-pole.

The magnetic field strength is represented diagrammatically by the degree of closeness of the field lines. Field lines cannot cross each other as two values of net field at a single point cannot exist. Only one value, a unique net value, can exist. If in a given region, lines of field are shown to be parallel and equispaced, the field is understood to be uniform.

Question 64. With the help of a labelled circuit diagram illustrate the pattern of field lines of the magnetic field around a current carrying a straight long conducting wire. How is the right-hand thumb rule useful to find the direction of the magnetic field associated with a current-carrying conductor?
Answer: The right-hand thumb rule states that if a current-carrying straight conductor is supposedly held in the right hand with the thumb pointing towards the direction of current, then the fingers will wrap around the conductor in the direction ofthe field lines of the magnetic field.

Question 65. Explain with the help of a labeled diagram the distribution of magnetic field due to a current through a circular loop. Why is it that if a current-carrying coil has n turns, the field produced at any point is n times as large as that produced by a single turn?
Answer: The magnetic field (B) produced by current carrying N circular wire depends on:

• Amount of current flowing through wire (I):
  • B∞I
• Number of turns on the circular wire (N)
  • B∞N

If there is a circular coil having N turns, the field Magnetic force (lines) due to produced is N times as large as that produced by a current carrying through a loop single turn.

Magnetic Effects Of Electric Current Multiple-Choice Questions

Question 1. Choose the incorrect statement from the following regarding magnetic lines of the field.

1. The direction of the magnetic field at a point is taken to be the direction in which the north pole of a magnetic compass needle points
2. Magnetic field lines are closed curves
3. Magnetic field lines are parallel and equidistant, they represent zero field strength
4. The relative strength of the magnetic field is shown by the degree of closeness of the field lines.

Answer: 3. If magnetic field lines are parallel and equidistant, they represent zero field strength

Question 2. If the key in the arrangement is taken out (the circuit is made open) and magnetic field lines are drawn over the horizontal plane ABCD, the lines are

1. Concentric Circles
2. Elliptical In Shape
3. Straight Lines Parallel to Each Other
4. Concentric Circles Near The Point O But Of Elliptical Shapes As We Go Away From It

Answer: 3. Straight Lines Parallel to Each Other

Question 3. A circular loop placed in a plane perpendicular to the plane of paper carries a current when the key is ON. The current as seen from points A and B (in the plane of paper and on the axis of the coil) is anticlockwise and clockwise respectively. The magnetic field lines point from B to A. The N-pole of the resultant magnet is on the face close to

1. A
2. B
3. A if the current is small, and B if the current is large
4. B if the current is small and the current is large

Answer: 1. A

Question 4. For a current in a long straight solenoid, N- and S-poles are created at the two ends. Among the following statements, the incorrect statement is

1. The field lines inside the solenoid are in the form of straight lines which indicates that the magnetic field is the same at all the points inside the solenoid
2. The strong magnetic field produced inside the solenoid can be used to magnetize a piece of magnetic material like soft iron when placed inside the coil
3. The pattern of the magnetic field associated with the solenoid is different from the pattern ofthe magnetic field around a bar magnet
4. The N- and S-poles exchange position when the direction of current through the solenoid is reversed

Answer: 3. The pattern of the magnetic field associated with the solenoid is different from the pattern ofthe magnetic field around a bar magnet.

Question 5. A uniform magnetic field exists in the plane of paper pointing from left to right as shown in the given figure. In the field an electron and a proton move as shown. The electron and the proton experience

1. Forces Both Pointing Into The Plane of Paper
2. Forces Both Pointing Out Ofthe Plane Of paper
3. Forces Pointing Into The Plane Ofpaper And Out Of The Plane Ofpaper, Respectively
4. Force Pointing Opposite And Along The Direction Of The Uniform Magnetic Field Respectively

Answer: 1. Forces Both Pointing Into The Plane Ofpaper

Question 6. Commercial electric motors do not use

1. An Electromagnet To Rotate The Armature
2. Effectively Large Number of Turns of Ofconducting Wire In The Current Carrying Coil
3. A Permanent Magnet To Rotate The Armature
4. A Soft Iron Core On Which The Coil Is Wound

Answer: 3. A Permanent Magnet To Rotate The Armature

Question 7. In the arrangement shown in given figure, there are two coils wound on a non-conducting cylindrical rod. Initially, the key is not inserted. Then the key is inserted and later removed. Then

1. The Deflection In Thegalvanometerremains Zero Throughout
2. There Is A Momentary Deflection In The Galvanometer But It Dies Out Shortly And There Is No Effect When The Key Is Removed
3. There Are Momentary Galvanometer Deflections That Die Out Shortly; The Deflections Are In The Same Direction
4. There Are Momentary Galvanometer Deflections That Die Out Shortly; The Deflections Are In Opposite Direction

Answer: 4. There Are Momentary Galvanometer Deflections That Die Out Shortly; The Deflections Are In Opposite Direction

Question 8. Choose the incorrect statement

1. Fleming’s right-hand rule is a simple rule to know the direction of the induced current
2. The right-hand thumb rule is used to find the direction of magnetic fields due to current-carrying conductors
3. The difference between the direct and the alternating current is that the direct current always flows in one direction, whereas the alternating current reverses its direction periodically
4. In India, the AC changes direction after every — second.

Answer: 4. In India, the AC changes direction after every — second.

Question 9. A constant current flows in a horizontal wire in the plane ofthepaper from the east to the west as shown in the figure. The direction of the magnetic field at a point will be North to South

1. Directly Above The Wire
2. Directly Below The Wire
3. At A Point Located In The Plane Of The Paper, On The North Side Of The Wire
4. At A Point Located In The Plane Ofthe Paper, On The South Side Ofthe Wire

Answer: 2. Directly Below The Wire

Question 10. The Strength Magnetic Field Inside A Long Current Carrying a Straight Solenoid Is

1. More At The Ends Than At The Centre
2. Minimum In The Middle
3. Same At All Points
4. Found To Increase From One End To The Other

Answer: 3. Same At All Points

Question 11. To Convert An AC generator Into a DC generator

1. Split-Ring Type Commutator Must Be Used
2. Slip Rings And Brushes Must Be Used
3. A Stronger Magnetic Field Has To Be Used
4. A Rectangular Wire Loop Has To Be Used

Answer: 1. Split-Ring Type Commutator Must Be Used

Question 12. The Most Important Safety Method Used For Protecting Home Appliances From short-circuiting or Overloading Is

1. Earthing
2. Use Ofstabilizers
3. Use Office
4. Use Ofelectric Meter

Answer: 2. Use Of stabilizers

Question 13. Which ofthe following correctly describes the magnetic field near a long straight wire1?
Answer:

1. The field consists of straight lines perpendicular to the wire.
2. The field consists of straight lines parallel to the wire.
3. The field consists of radial lines originating from the wire.
4. The field consists of concentric circles centered on the wire.

Answer: 4. The magnetic field near a long straight wire the field consists of concentric circles centered on the wire.

Question 14. The phenomenon of electromagnetic induction is

1. The Process of Charging A Body.
2. The Process of Generating Magnetic Field Due To A Current Passing Through A Coil.
3. Producing Induced Current In A Coil Due To Relative Motion Between A Magnet And The Coil.
4. The Process Ofrotating A Coil Ofan Electric Motor.

Answer: 3. Electromagnetic induction produces induced current in a coil due to relative motion between a magnet and the coil.

Question 15. The device used for producing electric current is called a

1. Generator
2. Galvanometer
3. Ammeter
4. Motor

Answer: 1. A generator is used for producing electric current.

Question 16. The essential difference between an AC generator and a DC generator is that

1. AC generator has an electromagnet while a DC generator has a permanent magnet.
2. DC generator will generate a higher voltage.
3. AC generator will generate a higher voltage.
4. AC generator has slip rings while the DC generator has a commutator.

Answer: 2. The AC generator has slip rings while the DC generator has a commutator.

Question 17. At the time short circuit, the current in the circuit

1. Reduces Substantially
2. Does Not Change
3. Increase Heavily
4. Vary Continuously

Answer: 3. At The Time Of a Short Circuit The current in the circuit increases greatly

Question 18. State whether the following statements are true or false.

1. An electric motor converts mechanical energy into electrical energy.
2. An electric generator works on the principle of electromagnetic induction.
3. The field at the center of the long circular coil carrying current will be parallel straight
   lines.
4. A wire with green insulation is usually the live wire ofan electric supply.

Answer: 1. False. It converts electrical energy into mechanical energy.

1. True.
2. True. The field is almost uniform at the center of the coil.
3. False. The ware with green insulation is usually the live wire.

Question 19. What happens to the deflection of the compass needle placed at a point near current carrying straight conductor:

1. If the current is increased?
2. If the direction of the current in the conductor is changed (reversed)?
3. If the compass is moved away from the conductor?

Answer:

1. The deflection of the compass needle increases.
2. The direction of deflection in the compass needle changes.
3. The deflection of the compass needle decreases.

Question 20. A coil of insulated wire is connected to a galvanometer. Explain what happens if a bar magnet with its north pole towards one face ofthe coil is:

1. Moved Quickly Towards The Coil,
2. Kept Stationary Inside The Coil, And
3. Moved Quick Away From The Coil?

Answer: The increasing magnetic field induces current in the coil as a result of which the galvanometer shows momentary deflection (say towards the right).

No change in a magnetic field, no induced current, and deflection zero.

The magnetic field decreases, the induced current is produced in the coil and the galvanometer shows momentary deflection in the opposite direction (say towards the left).

Question 21. Which of the following properties of a proton can change while it moves freely in a magnetic field? (There may be more than one correct answer.)

1. Mass
2. Speed
3. Velocity
4. Momentum

Answer: The correct options are (c) and (d). The magnetic force acts perpendicular to the direction of motion of the proton. It does not change its mass and speed but changes its direction of motion. So both velocity and momentum get changed.

Question 22. A positively charged particle (alpha-particle) projected towards the west is deflected towards the north by a magnetic field. The direction of the magnetic field is

1. Towards South
2. Towards East
3. Downward
4. Upward

Answer: The correct option is 4. This is by Fleming’s left-hand rule

Question 23. Choose the correct option.
Answer: A rectangular coil of copper wires is rotated in a magnetic field. The direction of the induced current changes once in each

1. Two Revolutions
2. One Revolution
3. Half revolution
4. One-Fourth Revolution

Answer: The correct option is (b).

Question 24. Name two safety measures commonly used in electric circuits and appliances.

Answer:

1. Earthing
2. Electric fuse

Class 10 Science Chapter Light-Reflection And Refraction

Question 1. Define the principal focus of a concave mirror.
Answer:

It is a point on the principal axis at which a beam of incident light parallel to the principal axis converges after reflection from the concave mirror.

Question 2. The radius of curvature of a spherical mirror is 20 cm. What is its focal length?
Answer:

Focal length = \(\frac{1}{2}\) x Radius of curvature

= \(\frac{1}{2}\) × 20 cm

= 10 cm

Question 3. Name a mirror that can give an erect and enlarged image of an object.
Answer: Concave mirror

Question 5. Find the focal length of a convex mirror whose radius of curvature is 32 cm.
Answer:

As the radius of curvature and focal length of a convex mirror are positive, so

R = +32 cm

and f= \(\frac{R}{2}\)

f = +16 cm

Question 6. A concave mirror produces a times magnified (enlarged) real image of an object placed 10 cm in front of it. Where is the image located?
Answer:

As the image is real, so magnification m must be negative.

∴ \(m=\frac{h^{\prime}}{h}=-\frac{v}{u}=-3\)

Or v = 3u

But u = 10 cm

∴ v = 3 x (-10)

v = -30 cm

Thus, the image is located at a distance of 30 cm from the mirror on the object side of the mirror.

Question 7. A ray of light traveling in air enters obliquely into water. Does the light ray bends towards the normal or away from the normal? Why?
Answer:

Light travels faster in the rarer mediums as air and slower in the denser mediums as water. As a ray of traveling in air enters obliquely into the water, it slows down and bends towards the normal.

Question 8. Light enters from air to glass and has an ing refractive info of dex 1.50. What is the speed of light in the glass? The speed of light in a vacuum is 3 x 10⁸ ms^-1.
Answer:

The refractive index of glass, n_g = 1.50

Speed of light in vacuum, c = 3 × 10⁸ ms^-1

Speed of light in glass = \(\frac{3 \times 10^8 \mathrm{~m} / \mathrm{s}}{1.5}\) = 2 × 10⁸ ms^-1

Question 9. Find out, the medium having the highest optical density. Also, find the medium with the lowest optical density.
Answer:

The diamond has the highest refractive index (2.42), so it has the largest optical density. Air has the lowest refractive index (1.0003), so it has the lowest optical density.

Question 10. You are given kerosene, turpentine, and water. In which of these does the light travel fastest? Use the information given.

Refractive indices of some material media (concerning vacuum):

Answer:

For kerosene, n = 1.44

For turpentine oil, n = 1.47

For water, n = 1.33

As water has the lowest refractive index, so light travels faster in this optically rarer medium than in kerosene and turpentine oil.

Question 11. The refractive index of a diamond is 2.42. What is the meaning of this statement?
Answer:

The refractive index of a diamond is 2.42. It indicates that the ratio of the speed of light in air
to that in diamond is 2.42.

Question 12. Define 1 dioptre of power of a lens.
Answer: One dioptre is the power of a lens whose focal length is 1 meter.

Question 13. A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is the needle placed in front of the convex lens if the image is equal to the size of the object? Also, find the power of the lens.
Answer:

Here, v = +50 cm [v is positive for real image]

As the real image is of the same size as the object, so

⇒ \(m=\frac{h^{\prime}}{h}=\frac{v}{u}=-1\)

Or u = -v=-50 cm

Now,\(\frac{1}{f}=\frac{1}{v}-\frac{1}{u}=\frac{1}{+50}-\frac{1}{-50}=+\frac{2}{50}=+\frac{1}{25}\)

Or f = 25 cm = 0.25 m

P = \(\frac{1}{f}=\frac{1}{+0.25 \mathrm{~m}}\)= + 4 D

Question 14. Find the power of a concave lens of focal length 2 m.
Answer:

As the focal length of a concave lens is negative, so f = − 2 m

Power,

P = \(\frac{1}{f(\text { in } \mathrm{m})}\)

⇒ \(\frac{1}{-2 \mathrm{~m}}=-0.5 \mathrm{D}\)

Question 15. Which one of the following materials cannot be used to make a lens?

1. Water
2. Glass
3. Plastic
4. Clay

Answer: 4. Clay being opaque, does not transmit light.

Question 16. The image formed by a concave mirror is observed to be virtual, erect, and larger than the object. Where should be the position of the object?

1. Between the principal focus and the center of curvature.
2. At the center of curvature.
3. Beyond the center of curvature.
4. Between the pole of the mirror and its principal focus.

Answer: 4. Between the pole of the mirror and its principal focus.

Question 17. Where should an object be placed in front of a convex lens to get a real image of the size of the object?

1. At the principal focus of the lens.
2. At twice the focal length.
3. At infinity.
4. Between the optical center of the lens and its principal focus.

Answer: 2. At twice the focal length.

Question 18. A spherical mirror and a thin spherical lens have each a focal length of -15 cm. The mirror and the lens are likely to be

1. Both concave.
2. Both convex.
3. The mirror is concave and the lens is convex.
4. The mirror is convex, but the lens is concave.

Answer: 1. Both concave (as both concave mirror and concave lens have a negative focal length).

Question 19. No matter how far you stand from a mirror, your image appears erect. The mirror is likely to be

1. Plane.
2. Concave.
3. Convex.
4. Either plane or convex.

Answer: 3. The mirror is convex.

Question 20. Which of the following lenses would you prefer to use while reading small letters found in a dictionary?

1. A convex lens of focal length 50 cm.
2. A concave lens of focal length 50 cm.
3. A convex lens of focal length 5 cm.
4. A concave lens of focal length 5 cm.

Answer: 3. A convex lens of short focal length (5 cm).

Question 21. We wish to obtain an erect image of an object, using a concave mirror of focal length 15 cm. What should be the range of distance of the object from the mirror? What is the nature of the image? Is the image larger or smaller than the object? Draw a ray diagram to show the image formation in this case.
Answer:

The object should be placed between the focus F and the pole P of the concave mirror, i.e., between 0 and 15 cm from the mirror. Then the image will be virtual, erect, and larger than the object.

Question 22. Name the type of mirror used in the following situations:

1. Headlights of a car
2. Side/rear-view mirror of a vehicle
3. Solar furnace
4. Support your answer with reason.

Answer:

1. Concave mirrors are used as reflectors in the headlights of cars. When a bulb is located at the focus of the concave mirror, the light rays after reflection from the mirror travel over a large distance as a parallel beam of high intensity.
2. A convex mirror is used as a side/rear-view mirror of a vehicle because of the following reasons:
   1. A convex mirror always forms an erect, virtual, and diminished image of an object placed anywhere in front of it.
   2. A convex mirror has a wider field of view than a plane mirror of the same size.
3. Large concave mirrors are used to concentrate sunlight to produce heat in solar furnaces.

Question 23. One-half of a convex lens is covered with black paper. Will this lens produce a complete image of the object? Verify your answer experimentally. Explain your observations.
Answer:

As shown in the figure, when the lower half of the convex lens is covered with black paper, it still forms the complete image of the object as that with the uncovered lens. However, the intensity of the image is reduced when one-half of the convex lens is covered with black paper.

Question 24. An object 5 cm in length is held 25 cm away from a converging lens of focal length 10 cm. Draw the ray diagram and find the position, size, and nature of the image formed.
Answer:

A converging lens means a convex lens. As the distances given in the question are large, so we choose a scale of 1:5, i.e., 1 cm represents 5 cm.

Therefore, on this scale, a 5 cm high object, an object distance of 25 cm, and a focal length of 10 cm can be represented by 1 cm high, 5 cm, and 2 cm lines respectively.

Now, we draw the ray diagram as follows:

1. Draw a horizontal line to represent the principal axis of the convex lens.
2. The Centre line is shown by DE.
3. Mark two foci F and F” on two sides of the lens, each at a distance of 2 cm from the lens.
4. Draw an arrow AB of height 1 cm on the left side of the lens at a distance of 5 cm from the lens.
5. Draw a line AD parallel to the principal axis and then, allow it to pass straight through the focus (F) on the right side of the lens.
6. Draw a line from A to C (center of the lens), which goes straight without deviation.
7. Let the two lines starting from A meet at A’.
8. Draw A’B’ perpendicular to the principal axis from A’.
9. Now A’B’ represents the real, but inverted image of the object AB.
10. Then, measure CB’ and A’B’. It is found that CB’ = 3.3 cm and A’B’ = 0.7 cm.
11. Thus, the final position, nature, and size of the image A’ B’are:
    1. Position of image A’B’ = 3.3 cm x 5 = 16.5 cm from the lens of the opposite side.
    2. The nature of image A’ B’ is real and inverted.
    3. Height of image A’B’ = 0.7 cm x 5 = 3.5 cm, i.e., the image is smaller than the object.

Question 25. A concave lens of focal length 15 cm forms an image of 10 cm from the lens. How far is the object placed from the lens? Draw the ray diagram.
Answer:

Focal length, f= -15 cm [If is -ve for a concave lens]

Image distance, v = -10 cm

[Concave lens forms a virtual image on the same side as the object, so v is -ve]

As \(\frac{1}{f}=\frac{1}{v}-\frac{1}{u}\)

∴ \(\frac{1}{u}=\frac{1}{v}-\frac{1}{f}\)

⇒ \(\frac{1}{-10}-\frac{1}{-15}\)

⇒ \(\frac{-3+2}{30}\)

⇒ \(-\frac{1}{30}\)

Object distance, u = −30 cm

Drawing the ray diagram: Using a scale of 1:5, we get u = -2 cm, f= -3 cm. We draw the ray diagram as follows:

1. Draw the principal axis (a horizontal line).
2. Draw a convex lens, keeping the principal center (C) on the principal axis.
3. Mark points F and B on the left side of the lens at a distance of 15 cm and 30 cm. respectively.
4. Join any point D (nearly at the top of the lens) and F by a dotted line.
5. Draw a line AD, parallel to the principal axis.
6. Draw a line A’B’ perpendicular to the principal axis from B’.
7. Draw a line CA’ backward, so that it meets the line from D parallel to the principal axis at A.
8. Draw a line AB, perpendicular (downwards) from A to meet the principal axis at B.
9. The AB is the position of the object. Measure distance BC. It will be found to be equal to 6 cm.

The object is placed at a distance of 6 cm x 5 = 30 cm from the lens.

Question 26. An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm. Find the position and nature of the image.
Answer:

Object distance, u = -10 cm

Focal length, f= +15 cm  [f is +ve for a convex mirror]

Image distance, v =?

As \(\frac{1}{u}+\frac{1}{v}=\frac{1}{f}\)

∴ \(\frac{1}{v}=\frac{1}{f}-\frac{1}{u}\)

⇒ \(\frac{1}{+15}-\frac{1}{-10}\)

⇒ \(\frac{2+3}{30}\)

⇒ \(\frac{1}{6}\)

Image distance, v = +6 cm

As u is +ve, so a virtual, erect image is formed at a distance of 6 cm behind the mirror.

Question 27. The magnification produced by a plane mirror is +1. What does this mean?
Answer:

As m = \(\frac{h^{\prime}}{h}=-\frac{v}{u}\)

Given a plane mirror, m = +1, so

h’ h and v=-u

1. m = 1 indicates that the size of the image is the same as a positive time sign of m indicates that a virtual image is formed behind the mirror.

Question 28. An object 5.0 cm in length is placed at a distance of 20 cm in front of a convex mirror with a radius of curvature of 30 cm. Find the position of the image, its nature, and size.
Answer:

Object size, h = +5 cm

Object distance, u = -20 cm

The radius of curvature, R= +3.0 cm [R is +ve for a convex mirror]

Focal length, \(f=\frac{R}{2}=+15 \mathrm{~cm}\)

From the mirror formula,

∴ \(\frac{1}{v}=\frac{1}{f}-\frac{1}{u}\)

⇒ \(=\frac{1}{+15}-\frac{1}{-20}\)

⇒ \(\frac{4+3}{60}=\frac{7}{60}\)

Image distance, \(v=\frac{60}{7}=8.6 \mathrm{~cm}\)

Magnification, \(m=-\frac{v}{u}=\frac{h^{\prime}}{h}\)

Image size, \(h^{\prime}=-\frac{v h}{u}\)

⇒ \(-\frac{8.6 \times 5}{-20}\)

= 2.15 ≅ 2.2 cm

A virtual, erect image of a height of 2.2 cm is formed behind the mirror at a distance of 8.6 cm from the mirror.

Question 29. An object of size 7.0 cm is placed at 27 cm in front of a concave mirror of a focal length of 18 cm. At what distance from the mirror should a screen be placed, so that a sharp focussed image can be obtained? Find the size and the nature of the image.
Answer:

Object size, h = +7.0 cm

Object distance, u = −27 cm

Focal length, f = -18 cm

Image distance, v =?

Image size, h’ = ?

As \(\frac{1}{u}+\frac{1}{v}=\frac{1}{f}\)

∴ \(\frac{1}{v}=\frac{1}{f}-\frac{1}{u}\)

⇒ \(\frac{1}{-18}-\frac{1}{-27}\)

⇒ \(\frac{-3+2}{54}=\frac{-1}{54}\)

Or V = – 54 cm

The screen should be placed at a distance of 54 cm on the object side of the mirror to obtain a sharp image.

Magnification, \(m=\frac{h^{\prime}}{h}=-\frac{v}{u}\)

Image size, \(h^{\prime}=-\frac{v h}{u}\)

⇒ \(\frac{(-54) \times(+7)}{(-27)}\)

= -14 cm

The image is real, inverted, and enlarged in size.

Question 30. Find the focal length of a lens of power -2.0 D. What type of lens is this?
Answer:

Here, P = -2.0 D

⇒ \(f=\frac{1}{P}\)

⇒ \(=\frac{1}{-2.0 \mathrm{D}}\)

= − 0.5 m

The type of lens is concave.

Question 31. A doctor has prescribed a corrective lens of power +1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging?
Answer:

Here, P = +1.5 D

⇒ \(f=\frac{1}{\mathrm{P}}\)

⇒ \(\frac{1}{+1.5 \mathrm{D}}\)

⇒ \(+\frac{10}{15} \mathrm{~m}\)

= +66.67 cm

As the focal length is positive, the prescribed lens is converging.

Question 32. Define absolute refractive index. Absolute refractive indices of medium ‘A’ and medium ‘B’ are ‘n’ and ‘n’ respectively, what is the refractive index of medium ‘B’ concerning medium ‘A’? How does the velocity of light vary with the change in the optical density of the media?
Answer:

The absolute refractive index of a medium is defined as the ratio of the velocity of light in a vacuum to the velocity of light in the medium. If c is the velocity of light in the vacuum and v in the medium, then n = c/v.

If n_a and n_b are the absolute refractive indices of the medium A and B respectively, then

n_a = \(\frac{c}{v_a} \text { and } n_b=\frac{c}{v_b}\)then

_bn_a = \(\frac{\text { Velocity of light in B }}{\text { Velocity of light in A }}=\frac{v_b}{v_a}=\frac{n_a}{n_b}\)

Question 33. What is the minimum number of rays required for locating the image formed by a concave mirror for an object? Draw a ray diagram to show the formation of a virtual image by a concave mirror.
Answer:

At least two rays are required for locating the image of an object formed by a concave mirror.

A concave mirror forms a virtual image of an object when it is placed between the focus and pole of the mirror as shown:

Question 34.

1. Define the ine power of a lens and write its SI unit.
2. A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is the needle placed in front of the lens, the the if image size is equal to the object size? Also, find the power of the lens.

Answer:

1. It is defined as the reciprocal of focal length lens cans to bend the rays of light falling on it. Its SI unit is dioptre.
2. Given v = 50 cm, since the size of the image and that of the object are the same, therefore, the image is formed at 2f.

Hence, 2f = 50 or f= 25 cm = 0.25 m

Now, P = \(\frac{1}{f}=\frac{1}{0.25}=\frac{100}{25}\)= + 4 D

Question 35. Discuss the position and nature of the image formed by a concave mirror when the object is moved from infinity toward the pole of the mirror.
Answer:

As the object is moved from infinity towards the pole of a concave mirror the image shifts from the focus of the mirror to infinity.

When the object is at infinity, the image is formed at the principal focus or in the focal plane. As the object is shifted, further the image is formed between the principal focus centimeter of curvature, then at the centimeter of curvature, beyond the centimeter of curvature, at infi, city, and finally the image is formed behind the mirror. The size of the increasing.

Question 36. With the help of a ray diagram, show the formation of an image by a convex lens when the object is placed between F and 2F. Write two characteristics of the image so formed.
Answer: The image formed is real, I’ve,  red and diminished.

Question 37.

1. Define the line radius of curvature and focal length of a spherical mirror and show it on a figure.
2. Write the relation between the radius of curvature and the focal length of a spherical mirror.

Answer:

1. The radius of curvature is the radius of the hollow sphere of which the reflecting surface of the spherical mirror forms a part. Focal length is the distance from the pole of the mirror to the focal point F.
2. Relation: \(f=\frac{\mathrm{R}}{2}\)

Question 38. An object of height 5 cm is placed perpendicular to the principal axis of a concave lens of focal length 10 cm. If the distance of the object from the opticenterntre of the lens is 20 cm, determine the position, an true, and size of the image formed using the lens formula.
Answer:

Given h+5 cm, f = – 10 cm, u = -20 cm, v = ?, h’ =?

⇒ \(\frac{1}{f}=\frac{1}{v}-\frac{1}{u}\)

∴ \(\frac{1}{v}=\frac{1}{f}+\frac{1}{u}=\frac{1}{(-10)}+\frac{1}{(-20)}=\frac{-2-1}{20}=\frac{-3}{20}\)

∴ \(v=-\frac{20}{3} \mathrm{~cm}\)

Nature: Virtual, erect.

⇒ \(h^{\prime}=\frac{v}{u} \times h=\left(\frac{-20}{3} \times \frac{1}{-20} \times 5\right) \mathrm{cm}=+\frac{5}{3} \mathrm{~cm}\)

Question 39. If the image formed by a mirror for all positions of the object placed in front of it is always erect and diminished, what type of mirror is it? Draw a ray diagram to justify your answer. Where and why do we generally use this type of mirror?
Answer:

Convex mirror

Use: As rear view mirror in vehicles. Also in malls, hotels, and airports for security reasons.

Reason:

• Forms erect image
• Wider field of view.

Question 40. A convex lens has a focal length of 25 cm. Calculate the distance of the object from the lens if the image is to be formed on the opposite side of the lens at a distance of 75 cm from the lens. What will be the nature of the image?
Answer:

Given, f= + 25 cm, v = 75 cm, u =?

Using \(\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\) We have

⇒ \(\frac{1}{u}=\frac{1}{v}-\frac{1}{f}=\frac{1}{75}-\frac{1}{+25}=\frac{-2}{75}\)

Therefore, u = -37.5cm

The image is real, inverted, and magnified.

Question 41. A 4.5 cm needle is placed 12 cm away from a convex mirror of focal length 15 cm. Give the location of the image and its magnification.
Answer:

Given that O= 4.5 cm, u = − 12 cm, f= + 15 cm

Using the mirror formula \(\frac{1}{u}+\frac{1}{v}=\frac{1}{f}\)

Or \(\frac{1}{v}=\frac{1}{f}-\frac{1}{u}=\frac{1}{15}-\frac{1}{-12}=\frac{9}{60}[/latex

Therefore, v = 6.7 cm

The positive sign indicates that the image formed is on the other side of the mirror.

Also, [latex]m=\frac{1}{\mathrm{O}}=-\frac{v}{u} \Rightarrow \frac{1}{4.5}=-\frac{6.7}{-12}\)

Therefore, I = \(\frac{6.7 \times 4.5}{12}=+2.5 \mathrm{~cm}\)

I = + 2.5 cm

The positive sign indicates that the hat image formed is erect and virtual.

Question 42. How will you decide whether a given piece of glass is a convex lens, concave, lens, or plane glass plate?
Answer:

Hold the given piece of glass over some printed matter.

1. If the letters appear magnified, the given piece is a convex lens.
2. If the letters appear diminished, the given piece is a concave lens.
3. If the letters appear to be of the same size, then it is a plane glass piece.

Question 43. A student wants to project the image of a candle flame on a screen 60 cm in front of a mirror by keeping the flame at a distance of 15 cm from its pole.

1. Write the type of mirror he should use.
2. Find the linear magnification of the image produced.
3. What is the distance between the object and its image?
4. Draw a ray diagram to show the image formation in this case.

Answer:

1. Concave mirror
2. Linear magnification is given by
   1. \(m=\frac{v}{u}=\frac{-60}{-15}=-4\)
3. 60-15 = 45 cm
4. The diagram is as shown:

Question 44. A 4.5 cm needle is placed 12 cm away from a convex mirror of focal length 15 cm. Give the location the the of image and magnification. Describe what happens to the image as the needle is moved farther from the mirror.
Answer:

h1 = 4.5 cm, u = – 12 cm, f = 15 cm, v = ?

Using the equation \(\frac{1}{f}=\frac{1}{v}+\frac{1}{u}\) we have

⇒ \(\frac{1}{15}=\frac{1}{v}+\frac{1}{-12} \text { or } \frac{1}{15}+\frac{1}{12}=\frac{1}{v}\)

Solving for u, we have v = + 6.6 cm

Now, \(m=-\frac{v}{u}=-\frac{6.6}{-12}\) = 0The imagemage will diminish.

Question 45. With the help a  of ray diagram, show that angle of incidence is equal to the angle of reflection when a ray is incident on the concave mirror.
Answer:

In the ray diagram shown below, CB is the normal and ∠i = ∠r, AB is the incident ray and BD is the reflected ray.

Question 46.

1. State Snell’s law of refraction.
2. When a ray of traveling in air enters obliquely into a glass slab, it is observed that the light ray emerges parallel to the incident ray but it is shifted sideways slightly. Draw a ray diagram to illustrate it.

Answer:

1. The ratio the the of sine of the angle of incidence to the signoff the angle of refraction is constant for the light of the color and a given pair of the medium.
2. The diagram is as shown:

Question 47. The power of a lens is 2.5 dioptre. What is the focal length and the type of lens?
Answer:

Power of a lens is P = \(\frac{1}{f}\)

Since power = 2.5 dioptre

2.5 = \(\frac{1}{f}\)

or f= \(\frac{1}{f} \text { or } f=\frac{1}{2.5}\) m = 0.4 m = 40 cm

The focal length of the lens is 40 cm. Since the focal length is positive, therefore, the lens is a convex lens.

Question 48. The refractive index of dense flint glass is 1.65 and for all,ohol it is 1. concerning to air. What is the refractive index of dense flint to alcohol?
Answer:

Given \({ }_a \mu_g=1.65 \text { and }{ }_a \mu_{a l c}=1.36\)

Now, \({ }_{\text {alc }} \mu_g=\frac{{ }_a \mu_g}{{ }_a \mu_{\text {alc }}}=\frac{1.65}{1.36}=1.21\)

Question 49.

1. Water a has a refractive of dex 1.33 and alcohol a has a refractive of dex 1.36. Which of the two mediums is optically denser? Ga’s reason’s your answer. Draw a ray diagram to show the path of a ray of light passing obliquely from water to alcohol.
2. The absolute refractive index of diamond is 2.42 and the absolute refractive index of glass is 1.50. Find the refractive index of a diamond concerning glass.

Answer:

1. Alcohol is optically denser than water. This is because use greater the refractive index more dense the liquid/material.

The diagram is as shown:

2. Given _an_d = 2.42, _an_g = 1.50, _gn_d = ?

Using the expression

⇒ \({ }_g n_d=\frac{{ }_a n_d}{{ }_a n_g}=\frac{2.42}{1.50}=1.61\)

Question 50. Show that the relative refractive index of medium concerning medium 1 can be expressed as the ratio of their absolute refractive indices.
Answer:

If n₁ and n₂ are the absolute refractive indices of media 1 and 2 the and speeds of light in the two media, then

⇒ \(n_1=\frac{c}{v_1} \quad \text { or } \quad v_1=\frac{c}{n_1}\)

and \(n_2=\frac{c}{v_2} \quad \text { or } \quad v_2=\frac{c}{n_2}\)

But the relative refractive index of medium concerning to medium 1 is

⇒ \(n_{21}=\frac{v_1}{v_2}=\frac{c / n_1}{c / n_2}\)

⇒ \(n_{21}=\frac{n_2}{n_1}\)

Question 51. Name the spherical mirror used as:

1. 1. Shaving mirror
   2. Rearview mirror in vehicles
   3. Reflector in searchlights.
2. Write any three differences between a real and virtual image.

Answer:

1. 1. Concave mirror
   2. Convex mirror
   3. Convex mirror

2. Points of difference between a real and virtual image:

Question 52.

1. For the same angle of incidence, 45°, the angle of refraction in two transparent media; 1 and 2 is 20° and 30° respectively. Out of 1 and 2, which medium is optically denser and why?
2. Light enters from the air to the diamond which has a refractive index of 2.42. Calculate the speed of light in a diamond, if the speed of light in air is 3.00 × 10⁸m s^-1. Answer:

1. Medium 1 is optically denser as the angle of refraction is lesser in it, hence light bends more towards normal.
2. n = speed of light in vacuum/speed of light in medium 2.42 = 3 x 10⁸/v or v = 1.24 × 10⁸ ms^-1

Question 53. What is meant by the power of a lens? Give its SI unit. When two or more lenses are placed in contact, what will be their combined power?
Answer:

The power of a lens is defined as the ability of the lens to bend the rays of light incident on it. i.e., P = 1/f

The SI unit of power is called a dioptre. If P₁ and P₂ are the powers, then P of the combination is given by P = P₁ + P₂.

Question 54.

1. What is meant by the refraction of light?
2. If applying the Cartesian sign convention for spherical lenses the image distance obtained is negative. State the significance of the negative sign.

Answer:

1. When light travels obliquely from one medium to another, the direction of propagation of light in the second medium changes. This phenomenon is known as the refraction of light.
2. A negative sign of image distance means the image is virtual and erect and is formed on the same side of the object concerning the lens.

Question 55. A student-focused the image of a candle flame on a white screen by placing the flame at various distances from a convex lens. He noted his observations:

1. From the above table, find the focal length of the lens without using the lens formula.
2. Which set of observations is incorrect and why?
3. In which case the size of the object and image will be the same? Give a reason for your answer.

Answer:

1. From the table of observation, it is clear that for u = 30, v = 30 cm. This means that both u and v must be equal to twice the focal length of the convex lens.
   1. Focal length of the convex lens = \(=\frac{30}{2}\) = 15 cm
2. The observation (v) is incorrect. For this observation, u = 15f, i.e., the object is at
   the focus and the image must be formed at infinity and not 70 cm.
3. Since m = \(\frac{v}{u}\) the size of the image will be equal to the size of the object, if v = u i.e., for the observation (iii).

Question 56.

1. What happens to a ray of light when it travels from one medium to another having equal refractive indices?
2. State the cause of the refraction of light.

Answer:

1. No refraction or bending would take place. The light will travel in a straight line.
2. The refraction occurs due to a change in the speed of light as it enters from one medium to another.

Question 57.

1. What should be the position of the object, when a concave mirror is to be used:
   1. As a shaving mirror, and
   2. In torches producing parallel beams of light?
2. A man standing in front of a mirror finds his image having a very small head and legs of normal size. What type of mirror are used in designing such a mirror?

Answer:

1. 1. The object should be between the pole and the focus.
   2. At the focus.
   1. Small head – convex mirror
   2. Legs of normal size – plane mirror.

Question 58. How can you identify the three types of mirrors without touching them?
Answer:

We will look into the mirror by going close to it:

1. If an image is of the same size and erect – –plane mirror.
2. If an image is bigger and erect – a concave mirror.
3. If an image is of a smaller size and erect – convex mirror.

Question 59.

1. Why does a ray of light pass through the center of curvature of a concave mirror after reflection is reflected along the same path?
2. Why are convex mirrors commonly used as rear-view mirrors in vehicles?
3. A pencil partly immersed in water in a glass tumbler appears to be displaced at the interface of air and water. Name the phenomenon of light responsible for it.

Answer:

1. Because the incident ray falls on the mirror along the normal to the reflecting surface.
2. Because they always give an erect, though diminished image. Thus, convex mirrors enable the driver to view a much larger area.
3. Refraction of light

Question 60. An object is placed at the following distances from a concave mirror of focal length 15 cm

1. 10 cm
2. 20 cm
3. 30 cm
4. 40 cm

Which position of the object will produce:

1. Virtual image
2. A diminished real image
3. An enlarged real image
4. An image of the same size

Answer:

1. 10 cm
2. 40 cm
3. 20 cm
4. 30 cm.

Question 61. A ray of light is incident obliquely on a glass slab. Draw a ray diagram showing the path of the light ray. Mark the angle of incidence, angle of refraction, angle of emergence, and lateral displacement of the ray. Give a formula to find the refractive index of the glass slab in terms of the angle of incidence and angle of refraction.
Answer:

The ray diagram is as shown:

The required formula is \({ }_a n_g=\frac{\sin i}{\sin r}\)

Question 62. Identify the device used as a spherical mirror or lens in the following cases, when the image formed is virtual and erect in each case.

1. The object is placed between the device and its focus, image formed is enlarged and behind it.
2. The object is placed between the focus and the device, image formed is enlarged and on the same side as that of the object.
3. The object is placed between infinity and the device, image formed is diminished and between focus and optical center on the same side as that of the object.
4. The object is placed between infinity and the device, and an image formed is diminished and between the pole and focus, behind it.

Answer:

1. Concave mirror
2. Convex lens
3. Concave lens
4. Convex mirror

Question 63. Why does a light ray incident on a rectangular glass slab immersed in any medium emerge parallel?
Answer:

The extent of bending of the ray of light at the opposite parallel faces of the rectangular glass slab is equal and opposite. This is why the ray emerges parallel to the incident ray on a rectangular glass slab. However, the light ray is shifted sideward slightly.

When the glass slab is immersed in any medium the interface and glass medium are equal and opposite, so, the emergent ray will always be parallel to the incident ray.

Question 64. When dipped in water in a glass tumbler, a pencil appears to be bent at the interface of air and water. Will the pencil appear to be bent to the same extent, if instead of water we use liquids like kerosene or turpentine? Support your answer with reason.
Answer:

A pencil partly immersed in water in a glass tumbler, appears to be displaced at the interface of air and water. The light reaching out from the portion of the pencil inside the water seems to come from a different direction, compared to the part above the water due to the refraction of light.

The pencil appears to be bent to different extents, if instead of water, liquids like kerosene or turpentine are used as their refractive indices are different which in turn produces deviation from incident ray by different extents.

Question 65. How is the refractive index of a medium related to the speed of light? Obtain an expression for the refractive index of a medium concerning another in terms of speed of light in these two media.
Answer:

Refractive index, μ \(=\frac{\text { Speed of light in vacuum, } c}{\text { Speed of light in medium, } v}\)

For medium 1, refractive index of first medium, μ1 \(=\frac{c}{v_1}\)

For medium 2, refractive index of second medium, μ2 \(\mu_2=\frac{c}{v_2}\)

∴ \(\mu_{21}=\frac{\mu_2}{\mu_1}=\frac{\frac{c}{v_2}}{\frac{c}{v_1}}=\frac{v_1}{v_2}\)

Question 66. The refractive index of diamond concerning glass is 1.6 and the absolute refractive index of glass is 1.5. Find out the absolute refractive index of a diamond.
Answer:

The refractive index of diamond concerning glass, and \(=\frac{v_g}{v}\) = 1.6, absolute refractive

Index of glass, ng= \(\frac{c}{v_g},\) and absolute refractive index of diamond, nd = \(\frac{c}{v_d}\)

Therefore, nd= \(\frac{v_g}{v_d} \times \frac{c}{v_g}\) = 1.6 x 1.5= 2.40

Question 67. A convex lens of focal length 20 cm can produce a magnified virtual as well as real image. Is this a correct statement? If yes, where shall the object be placed in each case for obtaining these images?
Answer:

The statement is correct if the object is placed within 20 cm of the lens in the first case and between 20 cm and 40 cm in the second case.

Question 68. Sudha finds out that the sharp image of the window pane of her science laboratory is formed at a distance of 15 cm from the lens. She now tries to focus on the building visible to her outside the window instead of the window pane without disturbing the lens. In which direction will she move the screen to obtain a sharp image of the building? What is the approximate focal length of this lens?
Answer:

Sudha should move the screen towards the lens to obtain a clear image of the building. The approximate focal length of this lens is 15 cm.

Question 69. How are the power and focal length of a lens related? You are provided with two lenses of focal lengths of 20 cm and 40 cm respectively. Which lens will you use to obtain more convergent light?
Answer:

P= \(\frac{1}{f}\) P∞ \(\frac{1}{f}\) Power of a lens is inversely proportional to its focal length therefore lens has a focal length of 20 cm will provide more convergence.

Question 70. Under what condition in an arrangement of two plane mirrors, incident ray, and reflected ray will always be parallel to each other, whatever may be the angle of incidence? Show the same with the help of a diagram.
Answer:

When two plane mirrors are placed at a right angle to each other then the incident and reflected rays will always be parallel to each other.

Question 71. Draw a ray diagram showing the path of rays of light when they enter with oblique incidence

1. From air into water,
2. From water into air.

Answer:

When a ray of light enters with oblique incidence from air into water, then it goes from an optical rarer medium to an optical denser medium, and the velocity of light decreases which in turn bends the incident light towards the normal. Also i > r.

When a ray of light enters with oblique incidence from water into air, then it goes from an optical denser medium to an optical rarer medium, and the velocity of light increases which in turn bends the incident light away from the normal. Also I < r.

Question 72. At a small town fair, Akshay took his friend and showed him a mirror in which his image showed his upper half very fat and his lower body very thin. Akshay’s friend got upset but Akshay explained to him by showing him a similar image in the mirror.

1. Name two mirrors used in this fair shop.
2. Name the mirror in which the size of the image is small.
3. What values of Akshay are reflected?

Answer:

1. Concave and convex mirror
2. Convex mirror
3. Akshay showed compassion and empathy.

Light-Reflection And Refraction Multiple Choice Question And Answers

Question 1. Which of the following can make a parallel beam of light when light from a point source is incident on it?

1. Concave mirror as well as convex lens
2. Convex mirror as well as concave lens
3. Two plane mirrors placed at 90° to each other
4. Concave mirror as well as concave lens

Answer: 1. Concave mirror as well as convex lens

Question 2. A 10 mm long awl pin is placed vertically in front of a concave mirror. A 5 mm long image of the awl pin is formed at 30 cm in front of the mirror. The focal length of this mirror is

1. -30 cm
2. -20 cm
3. -40 cm
4. -60 cm

Answer: 2. -20 cm

Question 3. Under which of the following conditions a concave mirror can form an image larger than the actual object?

1. When the object is kept at a distance equal to its radius of curvature
2. When an object is kept at a distance less than its focal length
3. When an object is placed between the focus and center of curvature
4. When an object is kept at a distance greater than its radius of curvature

Answer: 3. When an object is placed between the focus and center of curvature

Question 4. The figure shows a ray of light as it travels from medium A to medium B. Refractive index of medium B relative to medium A is

1. √3/√2
2. √2/√3
3. 1/√2
4. √2

Answer: 1. √3/√2

Question 5. A light ray enters from medium A to medium B as shown in the figure. The refractive index of medium B relative to A will be

1. Greater than unity
2. Less than unity
3. Equal to unity
4. Zero

Answer: 2. Less than unity

Question 6. Beams of light are incident through holes A and B and emerge out of box through the holes C and D respectively as shown in the figure. Which of the following could be inside the box?

1. A rectangular glass slab
2. A convex lens
3. A concave lens
4. A prism

Answer: 1. A rectangular glass slab

Question 7. A beam of light is incident through the holes on side A and emerges out of the holes on the other face of the box as shown in the figure. Which of the following could be inside the box?

1. Concave lens
2. Rectangular glass slab
3. Prism
4. Convex lens

Answer: 4. Convex lens

Question 8. Which of the following statements is true?

1. A convex lens has 4 dioptre power having a focal length of 0.25 m
2. A convex lens has -4 dioptre power having a focal length of 0.25 m
3. A concave lens has 4 dioptre power having a focal length of 0.25 m
4. A concave lens has -4 dioptre power having a focal length of 0.25 m

Answer: 1. A convex lens has 4 dioptre power having a focal length of 0.25 m

Question 9. Magnification produced by a rearview mirror fitted in vehicles

1. Is less than one
2. Is there more than one
3. Is equal to one
4. Can be more than or less than one depending upon the position of the object in front of it

Answer: 1. Is less than one

Question 10. Rays from the Sun converge at a point 15 cm in front of a concave mirror. Where should an object be placed so that the size of its image is equal to the size of the object?

1. 15 cm in front of the mirror
2. 30 cm in front of the mirror
3. Between 15 cm and 30 cm in front of the mirror
4. More than 30 cm in front of the mirror

Answer: 2. 30 cm in front of the mirror

Question 11. A full-length image of a distant tall building can be seen by using

1. A concave mirror
2. A convex mirror
3. A plane mirror
4. Both concave as well as plane mirror

Answer: 2. A convex mirror

Question 12. In torches, searchlights, and headlights of vehicles the bulb is placed

1. Between the pole and the focus of the reflector
2. Very near to the focus of the reflector
3. Between the focus and center of curvature of the reflector
4. At the center of the curvature of the reflector

Answer: 2. Very near to the focus of the reflector

Question 13. The laws of reflection hold good for

1. Plane mirror only
2. Concave mirror only
3. Convex mirror only
4. All mirrors irrespective of their shape

Answer: 4. All mirrors irrespective of their shape

Question 14. The path of a ray of light coming from air passing through a rectangular glass slab traced by four students are shown as A, B, C, and D in the figure. Which one of them is correct?

1. 1
2. 2
3. 3
4. 4

Answer: 2. 2

Question 15. You are given water, mustard oil, glycerine, and kerosene. In which of these media a ray of light incident obliquely at the same angle would bend the most?

1. Kerosene
2. Water
3. Mustard oil
4. Glycerine

Answer: 4. Glycerine

Question 16. Which of the following ray diagrams is correct for the ray of light incident on a concave mirror as shown in the figure?

1. 1
2. 2
3. 3
4. 4

Answer: 4. 4

Question 17. Which of the following ray diagrams is correct for the ray of light incident on a lens shown in the figure?

1. 1
2. 2
3. 3
4. 4

Answer: 1. 1

Question 18. A child is standing in front of a magic mirror. She finds the image of her head bigger, the middle portion of her body of the same size, and that of the legs smaller. The following is the order of combinations for the magic mirror from the top.

1. Plane, convex, and concave
2. Convex, concave, and plane
3. Concave, plane, and convex
4. Convex, plane, and concave

Answer: 3. Concave, plane, and convex

Question 19. In which of the following, the image of an object placed at infinity will be highly diminished and point-sized?

1. Concave mirror only
2. Convex mirror only
3. Convex lens only
4. Concave mirror, convex mirror, concave lens, and convex lens

Answer: 4. Concave mirror, convex mirror, concave lens, and convex lens

CBSE Chapter 14 Sources Of Energy Short Question And Answers

Question 1. If you could use any source of energy for heating your food, which one would you use and why?
Answer: We would prefer to use cooking gas like LPG or PNG or electricity. It fulfils many ofthe criteria of a good fuel, most importantly its ignition temperature, good calorific value and non-pollution characteristics.

Question 2. What are the disadvantages of fossil fuels?
Answer: There are the following disadvantages of fossil fuels like coal and petroleum:

1. Burning of coal or petroleum causes air pollution.
2. Acidic oxides like oxides of carbon, nitrogen and sulphur are released on burning fossil fuels. These oxides lead to acid rains, which affect our water and soil resources.
3. Carbon dioxide gas also causes a greenhouse effect in the atmosphere.
4. Fossil fuels are non-renewable sources of energy.

Question 3. Why are we looking at alternate sources of energy?
Answer: Fossil fuels are non-renewable sources of energy and their reserves are limited. Besides, these cause lots of pollution. Hence, we need to conserve them. If we continue consuming these sources at the same rate as presently, we may soon run out of energy. To avoid such a situation we are looking at alternate sources of energy.

Read and Learn More CBSE Class 10 Science Short Answer Questions

Question 4. How has the traditional use of wind and water energy been modified for our convenience?
Answer: To use the kinetic energy of flowing water or the potential energy of water at a height, large dams have been built in hilly regions to store huge amounts of water at a height.

The stored water from the level in the dam is carried through pipes to the turbine at the bottom of the dam and runs the hydropower plant. Similarly, the wind energy is used to generate electricity. For this purpose, the rotatory motion of the windmill is used to turn the turbine ofthe electric generator.

Question 5. What kind of mirror—concave, convex or plain—would be best suited for use in a solar cooker? Why?
Answer: Large-size concave mirrors are best suited for use in a solar cooker because they focus large amounts of solar radiation on a small surface area so the temperature will rise quickly and appreciably.

Question 6. What are the limitations ofthe energy that can be obtained from the oceans?
Answer: Energy from the oceans can be obtained in the form of tidal energy, wave energy and ocean thermal energy.

But these energy sources suffer from the following limitations:

1. There are very few locations where dams to utilise tidal energy can be built.
2. The cost of installation of powerhouses is extremely high and the efficiency of plants is comparatively small.
3. Power plants built in oceans or at seashores will need continuous maintenance as the chances of corrosion are extremely high.

Question 7. What is geothermal energy?
Answer: Geothermal energy is the heat energy present inside the earth in certain regions called ‘hot spots’. Due to geological changes, molten rocks formed in the deeper hot regions of Earth’s crust are pushed upwards and are trapped in hot spots. When underground water comes in contact with the hot spot, steam is generated. This steam is the source of geothermal energy.

Question 8. What are the advantages of nuclear energy?
Answer: The main advantages of nuclear energy are as follows:

1. For a given mass of fuel consumed the amount of energy released is extraordinarily large.
2. Nuclear power plants can be designed and constructed at any convenient place.
3. If proper precautions are taken while running nuclear power plants, a major fraction of energy needed can be obtained from nuclear energy sources which is being done by many developed countries.

Question 9. Can any source of energy be pollution-free? Why or why not?
Answer: We shall call a source of energy to be pollution-free if neither it causes any pollution during its actual operation nor there is any pollution during assembly of devices utilising that source of energy. As an example, the solar cell is a clean and pollution-free source by itself but assembly of solar cell devices may have caused some pollution.

Question 10. Hydrogen has been used as a rocket fuel. Would you consider it a cleaner fuel than CNG? Why or why not?
Answer: Hydrogen can be considered a cleaner fuel because its burning produces only water vapour which is non-polluting. However, due to the explosive nature ofhydrogen, its storage and transportation are difficult.

Question 11. Name two energy sources that you would consider to be renewable. Give reasons for your choices.
Answer: Solar energy, wind energy, ocean energy etc., are renewable sources of energy for the following reasons:

1. These forms of energy are available in plenty of our natural environment in the form of continuous currents of energy.
2. These energy sources will not be depleted so long as the present solar system exists.

Question 12. Give the names of two energy sources that you would consider to be exhaustible. Give reasons for your choices.
Answer: Coal and petroleum are two exhaustible sources of energy. These fuels were formed millions of years ago and there are only limited reserves. If we continue To Use Them As At Present, These Reserves Will Be Exhausted Soon.

Question 13. Compare and contrast fossil fuels and the sun as direct sources of energy.
Answer: The comparison between fossil fuels and the sun as a direct source of energy is as follows:

Question 14. Compare and contrast biomass and hydroelectricity as sources of energy.
Answer: Differences between Biomass and Hydroelectricity:

Question 15. What are the limitations of extracting energy from:

1. The Wind1?
2. Waves?
3. Tides?

Answer:

Limitations of extracting energy from the wind are as given below:

1. Wind energy farms can be established at those places only, where the wind blows for the greater part of a year.
2. For wind energy, the wind speed should be higher than 15 km/h.
3. A wind farm requires a large area and the initial cost of establishment of a farm is high.
4. It requires a high level of maintenance because the tower and blades are exposed to rain, sun, storm, etc.
5. It requires a backup with batteries for periods when there is no wind.
6. Limitations of extracting wave energy are as follows:
7. Wave energy can be harnessed by trapping the sea waves in a dam. Only very few suitable sites exist where dams can be constructed.
8. It is not a continuous and reliable source of energy.
9. It is extremely costly, cumbersome and difficult to maintain a power unit based on wave energy on a sustained basis.
10. The limitations of extracting tidal energy are the same as for wave energy.

Question 16. On what basis would you classify energy sources as

1. Renewable And Non-Renewable?
2. Exhaustible And Inexhaustible?
3. Are the options given in and the same?

Answer: Renewable sources of energy are those sources which can be regenerated again. Nonrenewable sources of energy are those sources which would get depleted someday and cannot be regenerated.

1. Exhaustible sources of energy are those which will get depleted someday and cannot be regenerated. Inexhaustible sources of energy are those which can be regenerated again due to some continuing or repetitive currents of energy.
2. Options are given in and are the same. A non-renewable source is an exhaustible source. A renewable energy source is an inexhaustible source.

Question 17. What are the qualities ofan ideal source of energy?
Answer: The qualities of an ideal source of energy are as given below:

1. It should be an easily accessible, inexhaustible, renewable source of energy and the cost of harnessing energy should be reasonably small.
2. The energy obtained from the source should be easily stored and transferred from one place to another place.
3. The energy source should not cause directly or indirectly any sort of pollution or degradation of the environment.
4. The technology for harnessing energy from a given source should be easily available, cheap and efficient.

Question 18. What are the advantages and disadvantages of using a solar cooker? Are there places where solar cookers would have limited utility?
Answer: Advantages of a solar cooker

1. There is no cost of fuel.
2. It is environment friendly and there is no residue like ash etc.
3. Cooking is hygienic and nutritious.
4. Disadvantages of a solar cooker
5. The cooking is slow. It takes 2-3 hours to attain a temperature of100°C-140°C on a sunny day.
6. It does not work on a cloudy day.

Question 19. What are the environmental consequences of the increasing energy demand? What steps would you suggest to reduce energy consumption?
Answer: Ronment in some way or the other. Either it would cause more pollution or cause environmental damage. Development and consumption of energy would go together. Therefore we should concentrate more on finding better and alternative sources of energy.

When looking for alternative sources, the following points should be kept in mind:

1. Ease and cost of extracting energy from the source,
2. The efficiency of the available technology.
3. Environmental impact of using that source

Answer:

Question 20. Define fuel. List any two characteristics that you would look for in a good fuel.
Answer: Fuel is a source of energy that we choose for doing some work.

1. Amount of ofheat released by it on burning per unit mass
2. Easy storage and transportation
3. Economical
4. Pollution-free.

Question 21. The waste materials collected from a market complex are scrap paper, thermocol, vegetable waste, tin cans and glass bottles. Which ofthese can be used for producing biogas? Mention three advantages of converting these into biogas rather than burning them.
Answer: Scrap paper and vegetables can be used to produce biogas. Converting these into biogas has the following advantages:

1. It produces cheap and valuable fuel for which there is a great demand.
2. It utilises those substances which would, otherwise be wasted and, require space for its safe dumping.
3. If this waste is left as such then it will be decomposed by microorganisms. This
   results in the release of harmful gases which increases environmental pollution.

Question 22. Compare the advantages of generating energy from biomass to getting it from hydropower plants.
Answer:

Question 23. What do you mean by a clean fuel? Is an absolute clean fuel available?
Answer: A clean fuel is that which does not cause environmental damage when used to produce energy.

No fuel is clean. Some environmental damage is caused directly or indirectly by the fuel. We can only call one source less or more cleaner than the others.

Question 24. Mention the advantages and limitations of wind energy.
Answer: Advantages:

1. It IH used to propel sailboats.
2. It is used to drive windmills which further operate water lifting, pumps and flourmills.
3. Aeroplanes use this energy for their upward and downward movements
4. It is used for flying engineless aeroplanes called gliders and for generating electricity.
5. It is free of cost and does not cause any pollution.

Limitations:

1. It is not available at all times.
2. It requires a very large area of land.
3. It is not possible to have a windmill everywhere, as to run it, the minimum wind
   speed of 15 km/h is required.

Question 25. Why is biogas plant considered to a be boon to the farmers? Give reason.
Answer: Biogas plants are considered to be a boon to the farmers because farmers can get clean fuel which does not produce any kind of smoke and pollution as compared to dried dung cakes.

Question 26. List any four reasons why we need to look for alternate sources ofenergy.
Answer: Pollution due to fossil fuels, exhausting fuel reserves, increasing need, replenishment is not easy.

Question 27. Explain why obtaining energy from nuclear fusion reactions is preferable to obtaining energy from nuclear fission reactions. Give two reasons.
Answer: Obtaining energy from nuclear fusion reactions is preferable to obtaining energy from nuclear fission reactions because:

1. For a given mass, the energy released from nuclear fusion is much larger than the energy released from nuclear fission.
2. Nuclear waste in nuclear fission is radioactive. Its disposal is a big challenge. There is no such difficulty in nuclear fusion.

Question 28. Why is tidal energy not likely to be a potential source of energy?
Answer: The harnessing of tidal energy poses many problems. The rise and fall of water during tides is not high enough to generate electricity on a large scale. There are very few sites that are suitable for building dams. It is for these reasons that tidal energy is not likely to be a major source of energy.

Question 29. “Electricity generated by the water stored in a dam can be considered to be another form of solar energy.” Explain describing the series of energy transformations in sequence taking place during the process.
Answer: Given below is the sequence of energy transformations that take place in the generation of electricity from the water stored in a dam.

Solar energy changes into potential energy (PE) of water vapour rising in the atmosphere, during the evaporation of water from rivers, seas, oceans and other water masses. These water vapours form clouds and cover mountains with snow.

1. When clouds burst into rain or the snow melts, their PE changes into kinetic energy of water flowing into streams and rivers.
2. When this flowing water is stored in a dam, its KE changes into PE.
3. When water is released from the dam, its PE once again changes into KE.
4. The KE of water coming out of the dam moves turbines which generate electricity.
5. Thus, it is the solar energy which changes into electricity.

Question 30. What is natural gas? How is it formed?
Answer: Natural gas is a naturally occurring mixture of methane (approx. 85%), ethane (10%), propane (3%), and butane (2%). Other non-combustible gases like CO2, N2 and O2 may also be present in the mixture.

Natural gas is formed by the action of heat, pressure and microorganisms on buried organic matter over millions of years.

Question 31. Give two advantages ofsmokeless chulha over traditional chulha.
Answer:

1. It has more efficiency and produces less smoke
2. It is scientifically designed and consumes less fuel.
3. The complete combustion of fuel takes place in it and it has a tall chimney.

Question 32. Justify the statement ‘Hydrogen is a cleaner and better fuel than CNG’.
Answer: Yes, it is a cleaner fuel because on burning, hydrogen produces only water vapour which is non-polluting. Although it is not used in everyday life due to its explosive nature, storage and transportation problems.

Question 33. What is nuclear waste? What are the hazards of nuclear waste to living beings? How is nuclear waste disposed of?
Answer: The discarded material of the nuclear industry is called nuclear waste such as remains in the containers which are used to handle radioactive substances or radioactive products of nuclear reactions.

1. The waste material more often possesses radioactivity which emits particles capable of damaging man, animal and plant tissues.
2. Nuclear wastes cannot be destroyed by chemical or other methods. These have to be buried deep under the earth.

Question 34. A student constructed a box-type solar cooker. He found that it was not working efficiently. What could this be due to? Give any four possible mistakes in the construction and operation of the solar cooker. What maximum temperature can ordinarily be reached inside a solar cooker?
Answer: He might not have painted the box black from the inside.

1. He might not have placed the blackened sheet in the insulated part of the solar cooker.
2. He might not have attached the reflector at the right angle.
3. He might not have covered his box with a thick glass sheet. He might have used a thin glass sheet.

Question 35. Why is a floating gas holder-type biogas plant considered less advantageous than a fixed dome-type biogas plant? Give reasons.
Answer: Floating gas holder type biogas plant is considered less advantageous because:

1. A floating gas holder type biogas plant is costly as it is made of steel.
2. Gas can leak through it either due to defects in welding or due to corrosion of steel.
3. It has to be repaired and painted frequently which increases its maintenance cost.

Question 36. Why is charcoal considered to be a better fuel than wood? What are the disadvantages of converting wood into charcoal?
Answer: Charcoal is considered as a better fuel than wood because:

1. Charcoal burns easily without producing smoke.
2. It gives twice as much heat as given by the same mass of wood.
3. The disadvantage of converting wood into charcoal is that during destructive distillation of 1 kg of wood only 0.25 kg of charcoal is obtained.
4. In other words, the conversion is expensive; hence charcoal is an expensive fuel.

Question 37. Why can wind energy farms be established only at specific locations? Give reasons to support Your Answer
Answer: Wind energy farms can be set up only in locations:

1. Where the wind blows for the greater part of the year.
2. Where the wind is strong and steady and has a speed of about 16 km h-1.
3. Where large free space is available.
4. Since these conditions cannot be satisfied everywhere, therefore, wind energy farms can be set up only in specific locations.

Question 38. Why is it not possible to make use of solar cells to meet all our energy needs? State at least three reasons to support your answer.
Answer: High cost of installation.

1. Limited availability of special-grade silicon to make solar cells.
2. Unavailability of an efficient system to store electrical energy generated by solar panels.

Question 39. What are thermal power plants? Give a demonstration of how thermal energy can be converted into electrical energy.
Answer: Thermal power plants convert heat energy into electrical energy. In thermal power plants, fuels are burnt to heat water to produce steam which is designed to run the turbine to generate electricity. The class can be demonstrated as follows:

Take a tennis ball and make three silts into it. Fit three small fins of a metal sheet into these slits. Fix the tennis ball on an axle as shown so that the ball has a free rotation.

Now connect this axle to a bulb through a dynamo. Direct a jet of steam from a pressure cooker onto to fins of the ball. Soon the bulb will start glowing. It will glow till the ball is rotating with the help of steam.

Question 40. Biomass has been used as fuel since ancient times, how has it been modified to function as a more efficient fuel in the recent past?
Answer: Coal and petroleum.

Yes, it is a cleaner fuel because on burning only water vapour is produced, which is non-polluting but due to the explosive nature of hydrogen storage and transportation is difficult.

Question 41. State the principle of a reflector-type solar cooker. How is this type of solar cooker different from a box type of solar cooker?
Answer: Reflector-type solar cooker: In this solar cooker, a concave reflector or parabolic reflector is used. It concentrates the solar energy in a small region called focus and therefore quite high temperature can be produced.

This way is different from box-type solar cookers because here food materials requiring strong heating can also be cooked. It can be used for baking and frying also.

Question 42. With the help of a diagram, explain how the design of a box type of solar cooker ensures minimum loss ofheat from its inside.
Answer: The box of the solar cooker is made of-conducting material, for example, plastic or fibreglass with thick inner walls. It is covered with a glass sheet which prevents loss of longer wavelength infrared radiations from inside to outside.

Question 43. Write the composition and source of LPG. Although liquefied gas is present in the cylinder, how does it appear as a gas in the burner?
Answer: LPG contains Butane (main), Propane and Ethane. It occurs over petroleum. Some wells contain only petroleum gas.

It is present in liquid form in the cylinder because it is filled at very high pressure, therefore, it liquefies. But when it comes out of the cylinder, the pressure is released and it appears as a gas in the burner.

Question 44. State four characteristics ofan ideal fuel.
Answer: It should be cheap and easily available.

1. It should have a high calorific value and should burn smoothly.
2. It should have a moderate ignition temperature and should be easy to store, handle
   and transport.
3. It should not leave any residue and should not produce smoke and harmful products.

Question 45. Give the disadvantages of constructing big dams across the river. How does the construction of dams across the river get linked with the production of greenhouse gases?
Answer: Large areas of agricultural land and the human population get submerged.

The problem of rehabilitation of displaced people.

The vegetation which is submerged rots under anaerobic conditions, giving a large amount of methane which is a greenhouse gas.

Question 46. Electricity generated by the water stored in a dam can be considered to be another form of solar energy. Describe the series of energy transformations in sequence during the process.
Answer:

Question 47. How can the pollution caused by fossil fuels be reduced?
Answer: The pollution caused by fossil fuels can somewhat be reduced by:

Increasing the efficiency of the combustion process using various techniques to reduce the escape of harmful gases and ashes into the surroundings.

Question 48. What is a thermal powerplant? Where is preferably situated?
Answer: In thermal power plants, fossil fuel is burnt to convert water into steam which further rotates the turbines to produce electricity.

Such plants are preferably located near coal mines or oil fields and away from habitats. It is easier to transport electricity than to transport coal or petroleum.

Question 49. A student constructed a model of a box-type solar cooker. He used a transparent plastic sheet to cover the open face of the box. He found that this cooker does not function well. What could be the possible drawbacks of his model? List any four drawbacks.
Answer: He may not have used:

1. Black painted aluminium sheet.
2. Black cooking vessel to absorb heat radiation.
3. Glass sheet, which prevents the escape of heat radiation from the box instead of plastic sheet.
4. Mirror plate which reflects the sunlight to fall on the glass sheet.

Question 50. Why is there a need to harness non-conventional sources ofenergy? Give two main reasons.
Answer: Our energy demand is increasing to improve the quality of life and population growth.

• Fossil fuels are limited.

Question 51. Write two different ways of harnessing energy from the ocean.
Answer: The two different ways of harnessing energy from the ocean are as follows:

1. Tidal energy—the energy derived from rising and falling ocean tides is called tidal energy.
2. Ocean thermal energy—solar energy stored in the oceans in heat is known
   as ocean thermal energy.

Question 52. What steps would you suggest to minimise environmental pollution caused by the burning of fossil fuels?
Answer:

1. Use of smokeless appliances
2. Afforestation

Question 53. What is the role of the plane mirror and a glass sheet in a solar cooker?
Answer: A plane mirror acts as a reflector and a glass sheet results in a greenhouse effect.

Question 54. Mention three advantages of solar cells.
Answer: Solar cells have no moving parts.

1. Requires little maintenance.
2. They can be set up in the remote areas.

Question 55. What is biomass? What can be done to obtain bio-energy using biomass?
Answer: The waste material of living things and dead parts of plants and animals is called biomass.

1. It has been a traditional source of energy, e.g. wood, crop residue, and bagasse cow-dung cake are used as fuels for domestic as well as industrial uses.
2. Bio-energy in the form of biogas can be produced from biomass by the decomposition in the absence of air. Biomass such as wood, cow dung etc., is directly used as fuel.

Question 56. What are the limitations of obtaining energy from wind?
Answer: Because wind energy is erratic energy cannot be harnessed continuously.

Large areas are required for wind forms.

Question 57. Suggest any three ways to contribute to saving LPG/CNG at home.
Answer: Soak dais, and rice in water before cooking, so that it takes less time and fuel for cooking.

1. Use a pressure cooker most of the time.
2. Cover the lid of the container while cooking.

Question 58. A student constructed a box-type solar cooker. He found that it was not working efficiently. What could this be due to? Give any four possible mistakes in the construction and operation of the solar cooker. What maximum temperature can ordinarily be reached inside a solar cooker?
Answer: He might not have painted the box black from the inside.

1. He might not have placed the blackened sheet in the insulated part of the solar cooker.
2. He might not have attached the reflector at the right angle.
3. He might not have covered his box with a thick glass sheet. He might have used a thin glass sheet.

Question 59. A student wants to design a car which runs on any alternative source ofenergy. Suggest any two sources ofenergy and give their advantages.
Answer: Solar cell panels can be installed on the top of the roof. It can convert solar energy into electrical energy.

Use water as a fuel which can split into H2 and 02 gas. H2 gas produced is used to run the engine.

Question 60. A person ‘A’ rolled up the glasses of his black car and parked it in the sun for one hour. Another person ‘B’rolled up the glasses of a white car and parked in the sun for one hour. In which car is the temperature higher and why?
Answer: Black car; the black colour is a good absorber ofheat and glass causes the greenhouse effect.

Question 61. The waste materials collected from a market complex are scrap paper, thermocol, vegetable waste, tin cans and glass bottles. Which ofthese can be used for producing biogas? Mention three advantages of converting these into biogas rather than burning them.
Answer: Scrap paper and vegetables can be used to produce biogas. Converting these into biogas has the following advantages:

1. It produces cheap and valuable fuel for which there is a great demand.
2. It utilizes those substances which would, otherwise be wasted and, require space for their safe dumping.
3. If this waste is left as such then it will be decomposed by microorganisms. This results in the release of harmful gases which increases environmental pollution.

Question 62. “A biogas plant solves the fuel as well as environmental problems”. Discuss.
Answer: Biogas is an ideal fuel, as:

1. It has a high calorific value.
2. It does not produce smoke.
3. It has a moderate ignition temperature.
4. It does not form harmful products.
5. It is very cheap and can be made available easily.

Because of the above-mentioned characteristics:

1. Biogas acts as an excellent fuel and hence solves the fuel problem.
2. Biogas does not create air pollution, therefore, it solves environmental problems also.
3. Biogas also prevents water pollution.

Sources Of Energy Multiple Choice Questions

Question 1. Which of the following is a non-renewable source of energy?

1. Wood
2. Sun
3. Fossil fuels
4. Wind

Answer: 3. Fossil fuels

Question 2. Acid, rain happens because.

1. Sun leads to the heating of the upper layer of the atmosphere
2. Burning of fossil fuels releases oxides of carbon, nitrogen and sulphur in the atmosphere
3. Electrical charges are produced due to friction among clouds
4. Earth’s atmosphere contains acids

Answer: 2. Burning of fossil fuels releases oxides of carbon, nitrogen and sulphur in the atmosphere

Question 3. Fuel used in thermal power plants is

1. Water
2. Uranium
3. Biomass
4. Fossil fuels

Answer: 4. Fossil fuels

Question 4. In a hydropower plant

1. Potential energy possessed by stored water is converted into electricity
2. Kinetic energy possessed by stored water is converted into potential energy
3. Electricity is extracted from water
4. Water is converted into steam to produce electricity

Answer: 1. Potential energy possessed by stored water is converted into electricity

Question 5. Which is the ultimate source of energy?

1. Water
2. Sun
3. Uranium
4. Fossil fuels

Answer: 2. Sun

Question 6. Which one of the following forms of energy leads to the least environmental pollution in the process of harnessing and utilisation?

1. Nuclear energy
2. Thermal energy
3. Solar energy
4. Geothermal energy

Answer: 3. Solar energy

Question 7. Ocean thermal energy is due to

1. Energy Stored By Waves In The Ocean
2. Temperature Difference At Different Levels In The Ocean
3. Pressure Difference At Different Levels In The Ocean
4. Tides Arising Out In The Ocean

Answer: 2. Temperature Difference At Different Levels In The Ocean

Question 8. The major problem in harnessing nuclear energy is how to

1. Split Nuclei?
2. Sustain The Reaction?
3. Dispose Of Spent Fuel Safely?
4. Convert Nuclear Energy Into Electrical Energy?

Answer: 3. Convert Nuclear Energy Into Electrical Energy?

Question 9. Which part of the solar cooker is responsible for the greenhouse effect?

1. Coating with black colour inside the box
2. Mirror
3. Glass sheet
4. The outer cover of the solar cooker

Answer: 3. Outer cover of the solar cooker

Question 10. The main constituent of biogas is

1. Methane
2. Carbon Dioxide
3. Hydrogen
4. Hydrogen Sulphide

Answer: 1. Methane

Question 11. The power generated in a windmill is greater in the rainy season since damp air would mean more air mass hitting the blades

1. Depends On The Height Of The Tower
2. Depends On Wind Velocity
3. Can Be Increased By Planting Tall Trees Close To The Tower

Answer: 3. Can Be Increased By Planting Tall Trees Close To The Tower

Question 12. Choose the correct statement

1. Sun can be taken as an inexhaustible source of energy
2. There is infinite storage of fossil fuel inside the earth
3. Hydro and wind energy plants are non-polluting sources of energy
4. Waste from a nuclear power plant can be easily disposed off

Answer: 1. The Sun can be taken as an inexhaustible source of energy

Question 13. In a hydroelectric power plant, more electrical power can be generated if water falls from a greater height because

1. Its Temperature Increases
2. Larger Amount Of Potential Energy Is Converted Into Kinetic Energy
3. The Electricity Content Of Water Increases With Height
4. More Water Molecules Dissociate Into Ions

Answer: 2. Larger Amount Of Potential Energy Is Converted Into Kinetic Energy

Question 14. Choose the incorrect statement regarding wind power

1. It is expected to harness wind power to a minimum in open space
2. The potential energy content of wind blowing at high altitudes is the source of wind power
3. Wind hitting the blades of a windmill causes them to rotate. The rotation thus achieved can be utilised further
4. One possible method of utilising the energy of the rotational motion of the blades of a windmill is to run the turbine of an electric generator.

Answer: 2. The potential energy content of wind blowing at high altitudes is the source of wind power

Question 15. Choose the incorrect statement

1. We are encouraged to plant more trees to ensure a clean environment and also provide biomass fuel
2. Gobar gas is produced when crops, vegetable wastes etc., decompose in the absence of oxygen
3. The main ingredient of biogas is ethane and it gives a lot of smoke and also produces a lot of residual ash
4. Biomass is a renewable source of energy

Answer: 3. The main ingredient of biogas is ethane and it gives a lot of smoke and also produces a lot of residual ash.

Question 16. A solar water heater cannot be used to get hot water on

1. A Sunny Day.
2. A Hot Day.
3. A Cloudy Day.
4. A Windy Day.

Answer: 2. A cloudy day (because on a cloudy day, no radiations from the sun are incidentÿn the solar water heater. Hence, it cannot be used to get hot water).

Question 17. Which of the following is not an example of a biomass energy source?

1. Wood
2. Gobar-Gas
3. Nuclear Energy
4. Coal.

Answer: 3. Nuclear energy.

Question 18. Most ofthe sources of energy we use represent stored solar energy. Which ofthe following is not ultimately derived from the Sun’s energy?

1. Geothermal energy
2. Nuclear energy
3. Wind energy
4. Biomass

Answer: 1. Geothermal energy.

Human Eye And Colourful World Very Short Answer Questions

Question 1. A person with a myopic eye cannot distinctly see objects beyond 1.2 m. What should be the type of corrective lens used to restore proper vision?
Answer: Diverging or concave lens.

Question 2. What are the far and near points of the human eye with normal vision?
Answer: For a human eye with normal vision, the far point is at infinity and the near is at 25 cm from the eye.

Question 3. A student has difficulty reading the blackboard while sitting in the last row. What could be the defect the child is suffering from? How can it be corrected?
Answer: The child is suffering from myopia. He should use concave lenses of suitable focal length.

Question 4. What is astigmatism?
Answer: It is a defect in which a person cannot see in all directions equally well.

Question 5. Where does the greatest degree of refraction oflight occur in the eye?
Answer: At the cornea.

Question 6. A man wearingglassesatfocal length of +1 cannot see objects beyond 1 what is the defect in his eye?
Answer: Myopia.

Read and Learn More CBSE Class 10 Science Very Short Answer Questions

Question 7. What is the function of the choroid?
Answer: It, contains black pigments which avoid internal reflections within the eye.

Question 8. What happens to the lens and the ciliary muscles when you are looking at
Answer: The ciliary muscles contract and the lens becomes thick, i.e. its radius of curvature decreases.

Question 9. Define dispersion of white light.
Answer: The splitting of white light into seven colours on passing through a transparent medium, i.e. glass prism, is called dispersion of light.

Question 10. What is presbyopia?
Answer: It is a defect of vision due to which an old person cannot see nearby objects clearly due to loss of power of accommodation of the eye.

Question 11. Name a natural phenomenon which is caused by the dispersion of sunlight in the sky.
Answer: Formation of the rainbow.

Question 12. Give one cause of sightedness.
Answer: Increase the focal length of the eye lens.

Question 13. What would have been the colour ofthe earth’s sky if there were no atmosphere?
Answer: It would have been dark.

Question 14. State one function ofthe crystalline lens in the human eye.
Answer: It produces a real and inverted image of the object on the retina.

Question 15. Name the type of particles which act as a prism in the formation of the rainbow in the sky.
Answer: Water droplets are present in the atmosphere.

Question 16. Name two types of cells in the retina of the eye which respond to light.
Answer: Rods and cones.

Question 17. What is the Tyndall effect?
Answer: The scattering oflight by particles in its path is called the Tyndall effect.

Question 18. On what factor does the colour ofthe scattered light depend?
Answer: It depends on the size of the scattering particles.

Question 19. How is the sense of vision carried from the eye to the brain?
Answer: Through the optic nerve.

Question 20. What is an iris?
Answer: The coloured diaphragm between the cornea and lens.

Question 21. Why does the sky appear dark to astronauts?
Answer: For scattering oflight, particles are required since there are no particles in space the sky appears dark to an astronaut.

Question 22. Give one example of a phenomenon where the Tyndall effect can be observed.
Answer: When a beam of sunlight enters a dusty room through a window, its path becomes visible to us.

Question 23. Give an example of an optical phenomenon which occurs in nature due to atmospheric refraction.
Answer: Advanced sunrise and delayed sunset.

Question 24. A person suffering from an eye defect uses lenses of power -10. Name the defect he is suffering from and the nature of the lens used.
Answer: Myopia, concave lens.

Question 25. Name the condition resulting due to the eye lens becoming cloudy.
Answer: Cataract.

Question 26. Name the two phenomena involved in the formation of a rainbow.
Answer: 1. Dispersion

Question 27. A person is advised to wear spectacles with concave lenses. What types of defect of the vision is he suffering from?
Answer: Myopia or short-sightedness.

Question 28. What is a blind spot?
Answer: A point at which the optic nerve leaves the eye.

Question 29. Why is blind spot so-called?
Answer: An image formed at this point is not sent to the brain.

Question 30. What is the role of the pupil in the human eye?
Answer: The pupil regulates and controls the amount oflight entering the eye.

Question 31. Which colour of white light suffers the least deviation and maximum deviation when a beam of white light passes through a glass prism?

1. Red
2. Violet

Answer: 2. Total internal reflection

Question 32. What is the range of vision for a normal human eye?
Answer: It is 25 cm to infinity.

Question 33. Name the part of the human eye that helps in changing the focal length of the eye lens.
Answer: Ciliary muscles.

Question 34. Does a beam of white light give a spectrum on passing through a hollow prism?
Answer: No, because dispersion oflight cannot occur through a hollow prism containing prism.

Question 35. Can an observer see a rainbow on the moon1?
Answer: No, there is no atmosphere on the moon.

Question 36. Is the position of a star as seen by us in its true position? Justify your answer.
Answer: No, light from stars undergoes atmospheric refraction which occurs in the medium of gradually changing refractive index.

Question 37. Is the position of a star as seen by us its true position? Justify your answer.
Answer: No. Light from stars undergoes atmospheric refraction which occurs in the medium of gradually changing refractive index.

Question 38. How are we able to see nearby and also the distant objects?
Answer: By use of bifocal length. It enables us to see both distant and nearby objects.

Question 39. Explain why the planets do not twinkle.
Answer: Planets being of larger size can be taken as a collection of large numbers of sized objects/sources oflight, which nullify the twinkling effect of each other.

Question 40. We see advertisements for eye donations on television or in newspapers. Write the importance of such advertisements.
Answer: Such advertisements motivate people to pledge their eyes for donation after death. They also spread awareness about eye donation amongst the people. They dispel myths and misconceptions associated with eye donation.

Question 41. No rainbow could be observed from the surface of the moon by the astronaut. Give reason.
Answer: The moon does not have any atmosphere and no water droplets are present. Hence, no dispersion oflight is possible. Therefore, astronauts cannot see a rainbow from the moon.

Question 42. What are rods and cones?
Answer: These are light-sensitive cells present in the retina. Rods control the intensity of light, while cones control the colour perceptions.

CBSE Class 10 Science Chapter 4 Carbon And Its Compounds Very Short Question And Answers

Question 1. Name the element, other than carbon, which exhibits the property of catenation up to seven or eight atoms. Are these compounds stable?
Answer: Silicon. No, they are very reactive.

Question 2. What are oxidizing agents?
Answer: An oxidizing agent oxidizes other substances by providing oxygen or removing hydrogen

Question 3. What change will you observe if you test soap with litmus paper (red and blue)?
Answer: When we test soap with red and blue litmus paper: red will turn blue but blue will remain as blue.

Question 4. Would you be able to check if water is hard by using a detergent?
Answer: No, detergent cannot be used to check if water is hard.

Question 5. The formula of a hydrocarbon is CnH2n. Name the family to which it belongs and also predict its nature.
Answer: The hydrocarbon belongs to the alkene family. It is unsaturated.

Question 6. An unknown compound has the smell of vinegar. Identify it.
Answer: The compound is ethanoic acid also called acetic acid.

Read and Learn More CBSE Class 10 Science Very Short Answer Questions

Question 7. What do we get when ethanoic acid reacts with ethanol in the presence of concentrated sulphuric acid?
Answer:  Ethyl ethanoate (CH₃ COOC₂H₅) is formed by esterification reaction. It has a fruity smell.

Question 8. How is scum formed? 
Answer:  When soap reacts with hard water, the minerals present in water react with soap and form a white curdy substance known as scum. It reduces the cleaning ability of soap.

Question 9. Draw the electron dot structure of ethane
Answer:

Electron dot structure of ethane:

Question 10. Why do carbon compounds not conduct electricity?
Answer: Since carbon, compounds do not give rise to any ions or charged particles in a molten state or aqueous solutions.

Question 11. Which two of the following compounds belong to the same homologous series
Answer: C₂H₆O, CH₄O.

Question 12. Why are organic compounds present in such a large number?
Answer: Due to catenation.

Question 13. Write the number of covalent bonds in CHr
Answer: Four

Question 14. Why unsaturated hydrocarbon gives a yellow flame with lots of black smoke when burnt in oxygen?
Answer: Due to incomplete combustion.

Question  15. What are the essential constituents of all organic compounds?
Answer: Carbon and hydrogen are the essential constituents of all organic compounds. However, carbon tetrachloride (CCl₄) is an exception

Question 16. What is the valency of carbon in its compounds?.
Answer: Carbon is tetravalent in its compounds.

Question 17. Draw the structural formula of methanoic acid. 
Answer:

Methanoic acid. 

Or HCOOH

Question 18. Carbon has four electrons in its valence shell. How does carbon attain stable electronic configuration?
Answer: Carbon is tetravalent because it has four valence electrons. To achieve noble gas configuration, it shares these electrons with four electrons of other atoms

The formula of citric acid is as follows: C₆H₈O₇

Question 19. State the name of-COOH functional group in citric acid.
Answer: Carboxylic acid

Question 20. Which of the following belongs to the same homologous series?
Answer: C₃H₆ and C₄H₈ belong to the same homologous series, which is alkenes with the general formula C_nH_2n

Question 21. Which has a triple bond; C₂H₄, C₃H_4, and C₃H₆?
Answer: C₃H₄ has a triple bond with the formula CH₃C ≡ CH.

Question 22. The molecular formula of butane is C₄H₁₀. What is the formula of butene?
Answer: The formula of butene is C₄H₈.

Question 23. A compound with the molecular formula C₃H₆O is used as a fuel. Identify the compound.
Answer: The compound is ethanol with formula C₂H₅OH.

Question 24. Write the names of the next homologous of CH₃CH₂OH and HCOOH.
Answer: Propanol and ethanoic acid, respectively.

Question 25. Give a test to identify the presence of ethanoic acid.
Answer: Dip a strip of blue litmus paper in the solution of ethanoic acid. Its colour will change to red.

Question 26. Out of butter and groundnut oil, which is unsaturated?
Answer: Groundnut oil is unsaturated.

Question 27. Write the molecular formula of alcohol, which can be derived from butane.
Answer: CH₃—CH₂—CH₂—CH₂—OH (Butanol)

Question 28. Name the second member of the alkyne family. Give its structure.
Answer: The second member of the alkyne family is propyne. Its structural formula is

Question 29. List two characteristic features of carbon which when put together rise to several carbon compounds.
Answer:

1. Catenation
2. Tetravalent

Question 30. The molecular formula of’A’ is C₁₀H₁₈ and B’ is C₁₈H₃₆ Name the homologous series to which they belong.
Answer: ‘A’ belongs to alkyne and ‘B’ belongs to alkene.

Question 31. How did ethanoic acid get its name as glacial acetic acid?
Answer: The melting point of ethanoic acid is 290K, and hence it often freezes during winter and forms ice-like flakes.

Question 32. Why are carbon and its compounds used as fuel for most applications
Answer: Carbon and its compounds are used as a fuel because when they are burnt, they give a large amount of energy in the form of heat

Question 33. Intake of small quantities of methanol can be lethal. Comment.
Answer:

Methanol is oxidized to methanal in the liver. Methanal reacts rapidly with the components of cells. It causes the protoplasm to coagulate. It also affects the optic nerve, causing blindness.

Question 34. Catenation is the ability of an atom to form bonds with other atoms of the same element. It is exhibited by both carbon and silicon. Compare the ability concatenation of the two elements. Give reasons.
Answer:

Carbon exhibits catenation much more than silicon or any other element due to its smaller size, which makes the C-C bonds strong while the Si-Si bonds are comparatively weaker due to their large size.

Question 35. Unsaturated hydrocarbons contain multiple bonds between the two C-atoms and show addition reactions. Give the test to distinguish ethane from ethene.
Answer: The two can be distinguished by subjecting them to the flame. Saturated hydrocarbons generally give a clear flame, while unsaturated hydrocarbons give a yellow flame with lots of black smoke.

Question 36. Which of the following hydrocarbons undergo additional reactions: C₂H₆, C₃H₈, C₃H₆, C₂H_2, and CH₄.
Answer: Unsaturated hydrocarbons undergo additional reactions. The following are the Unsaturated hydrocarbons among the given examples: C₃H₆ and C₂H₂.

Question 37. Which organic compound is added to make ethanol unfit for drinking purposes?  What is the name of the mixture formed?
Answer:  Methanol which is highly poisonous methanol is added in small amounts to ethanol to make it unfit for drinking purposes. The mixture is called methylated spirit or denatured alcohol.

Question 38. List two characteristics of covalent compounds.
Answer: Covalent compounds have low melting and boiling points. Covalent compounds do not conduct electricity.

Question 39. How will you convert ethene into ethanol? Give the chemical reaction involved.
Answer: Ethene is converted into ethanol by passing its vapours through water in the presence of sulphuric acid. This reaction is called the hydration of ethene.

Question 40. What is a homologous series? Which two of the following organic compounds belong to the homologous series? ,C₂H₆,C₂H₆O,C₂H₆O₂,CH₆O
Answer: For the definition of homologous series, consult the text part. The compounds CH₄O and C₂H₆O belong to the same homologous series known as alkanols.

NCERT Solutions For Class 10 Science Chapter 4 Carbon And Its Compounds Definitions

1. Carbon:

Carbon is tetravalent and easily forms a large variety of compounds on combination with carbon and other atoms by sharing ofelectrons. It exhibits the phenomenon of allotropy, i.e., exists in two or more forms in the same state

For example: Graphite and diamond.

2. Covalent bond:

When two atoms achieve stability by sharing an electron pair, each contributes one electron to the electron pair. In this way, the atoms can be regarded as having acquired a noble gas configuration.

3. Covalent compounds:

Some atoms share electrons among themselves or with other atoms to attain a stable octet configuration. Bonds formed are covalent bonds and the compounds so formed are covalent compounds. Depending on the number of shared pair ofelectrons, there is a single covalent bond, a double covalent bond, or a triple covalent bond.

These compounds have low melting points and boiling points. They do not dissolve in water, do not conduct electricity, and are directional.

4. Catenation: Catenation is the property of carbon to get attached to other carbon atoms. Up to 60 carbon atoms are found to get attached in the shape of a ball (Fullerenes).

5. Allotropy:

When an element possesses two or more different forms in the same state, they are called allotropes and the phenomenon is known as allotropy. For example, diamond and graphite are the two allotropes of carbon.

6. Fullerenes: Fullerenes are allotropes of carbon.

For example: Buckminsterfullerene is an allotrope of carbon with 60 carbon atoms arranged in the shape of a football.

7. Hydrocarbons: Hydrocarbon Compounds containing only carbon and hydrogen are called hydrocarbons.

8. Saturated hydrocarbons: Compounds of carbon and hydrogen attached in chains, branches, or rings, by single covalent bonds

For example: Alkanes (CnH_2n+2): methane (CH₄), ethane (C₂H₅), propane (C₃H₈), and butane (C₄H₁₀).

9. Unsaturated hydrocarbons:

Unsaturated hydrocarbons are compounds of carbon and hydrogen with either a carbon-carbon double bond (C ≡ C) or a carbon-carbon triple bond (C = C) in their molecules.

For example: Alkenes (C_nH₂), ethene (C₂H₄), propene (C₃H₆), butene (C4Hg). Alkynes (C_nH_32n-2): ethyne (C₂H₂), propyne (C₃H₄) and butyne (C₄H₆).

10. Functional groups:

Groups that determine the chemical nature of an organic compound. In a hydrocarbon, one or more hydrogen atoms are replaced by another element or group. These confer specific properties to the compound regardless of the length and nature chain and hence are called functional groups.

11. Alkyl radical: The group formed by removing the hydrogen atom from an alkane molecule is called an alkyl radical or group.

12. Functional group: A group that determines the chemical nature of a compound is called a functional group.

13. A homologous: A homologous series is a group or family of compounds that contain the same functional group but have different chain lengths. In their molecular formulae, two successive homologs differ by one carbon and two hydrogen atoms.

14. Isomerism: In carbon compounds, different compounds are formed with different structures but with the same molecular formula.

These compounds are called isomers and the phenomenon is called isomerism.

For example: Butane(C₄H₁₀)can be written as:

15. Nomenclature of carbon compounds:

1. Identify the number of carbon atoms in the main chain. For example, methane, ethane, propane, and butane for one, two, three, four carbon atoms, etc.
2. The name of the functional group can be given either a prefix or a suffix (see table below).
3. If the functional group is used as a suffix, the e- of hydrocarbon is substituted by a suffix.
4. The carbon atoms are numbered from the side of the functional group.

16. Fatty acid:

Carboxylic acids containing long chains of carbon atoms are fatty acids. They are used as mild acids in foods, cold drinks, drugs, and perfumes and are chief constituents of washing soap.

17. Chemical properties of carbon compounds:

Carbon and its compounds burn in oxygen with liberation of heat and light. Saturated hydrocarbons burn with a blue flame and unsaturated with a yellow flame.

18. Addition reactions: Unsaturated hydrocarbons add up hydrogen or halogens

⇒ \(\underset{\text { Ethene }}{\mathrm{CH}_2}=\mathrm{CH}_2+\mathrm{Br}_2 \longrightarrow \underset{\text { 1, 2-Dibromoethane }}{\mathrm{CH}_2 \mathrm{Br}-\mathrm{CH}_2 \mathrm{Br}}\)

19.  Substitution reactions: In the presence of light, halogens are substituted with hydrogen in saturated hydrocarbons

20. Ethanol: Ethanol is produced on a large scale by the fermentation of sugar or starch with enzymes (invertase and zymase) present in the yeast.

1. It reacts vigorously with sodium with the evolution of H₂
2. It can be dehydrated at 443 K with excess concentrated sulphuric acid.

21. Esterification: Reaction in which alcohol combines with carboxylic acid in the presence of concentrated sulphuric acid.

It gives ethanal (acetaldehyde) in the presence of mild oxidizing agents like cupric oxide (Cu₂O) and acetic acid in the presence of acidified potassium dichromate.

21. Enzymes: Enzymes are catalysts, which bring about biochemical changes.

For example:  Lactose enzyme turns milk-sugar, lactose into lactic acid.

22. Denatured alcohol: To make alcohol unfit for drinking, it is mixed with poisonous substances like methanol, pyridine, and blue dyes.

23. Ethanoic acid gets neutralized by bases like sodium hydroxide, and sodium carbonate to give sodium acetate salt.

24. Soaps:

Soaps are sodium or potassium salts of chain carboxylic acid molecules, in which two ends have different properties, one is hydrophilic (dissolves in water), while the other end is hydrophobic (dissolves in hydrocarbons). When cleansing clothes, the hydrophobic part attaches to dirt (oily) and the hydrophilic part attaches to water which on washing pulls away the hydrophobic part along with dirt.

25. Detergents:  Detergents are similar to soaps buthydrocarbonpart here is obtained from p

NCERT Solutions For Class 10 Science Chapter 4 Carbon And Its Compounds Short Question And Answers

Question 1. What would be the electron dot structure of carbon dioxide which has the formula CO₂ The electron-dot formula of CO₂ is given as:
Answer:

Question 2. What would be the electron dot structure ofa molecule of sulfur which is made up of eight atoms of sulfur?
Answer:

The electron-dot structure of sulfur is made of eight atoms of sulfur in a ring as shown.

Question 3. How many structural isomers can you draw for pentane?
Answer:

Three structural isomers can be drawn for pentane:

Question 4. What are the properties of carbon which lead to the huge number of carbon compounds we see around us?
Answer:

Two properties of carbon which lead to the huge number of carbon compounds are:

1. Tetravalency
2. Catenation

Question 5. What will be the formula and electron dot structure of cyclopentane?
Answer:

The formula of cyclopentane will be C₅H₁₀ Its electron-dot structure is written as

Question 6. Draw the structure for the following compounds

1. Ethanoic acid
2. Bromopentane
3. Butanone
4. Hexanal

Answer:

Question 7. How can ethanol and ethanoic acid be differentiated based on their physical and chemical properties?

Question 8.  Explain the formation of sum when hard water is treated with soap.
Answer:

Hard water contains soluble salts of sulfates and chlorides of calcium and magnesium. When soap is used to clean using hard water, calcium and magnesium present in hard water produce an insoluble substance called scum that remains after washing the cloth with water.

Question 9. What is hydrogenation? What is its industrial application?
Answer:

The addition of hydrogen to an unsaturated hydrocarbon in the presence of catalysts such as palladium or nickel to give saturated hydrocarbons is called hydrogenation. The process is used to make healthy vegetable oils in industry.

Question 10. What is the difference between two consecutive members in a homologous series of alkanes in terms of:

1. Molecular mass.
2. Number of atoms of elements.

Answer:

Difference in: Molecular mass = 14u Number of atoms = CH₂

Question 11. State the valency ofeach carbon atom in

1. An alkane and
2. An alkyne.

Answer:

1. The valency of a carbon atom in an alkane is four.
2. The valency of carbon atoms in an alkyne is four

Question 12. Write the molecular formula of benzene and state the number of double bonds in its structure.
Answer:

1. The molecular formula of benzene is C₆H₆.
2. It contains three double bonds in its structure.

Question 13. Which of these has the minimum number of carbon atoms? Answer:

1. Unsaturated hydrocarbons with double bonds.
2. Compound ‘C’ has a minimum number of carbon atoms.

Question 14. Why are alkanes regarded as saturated hydrocarbons while alkenes and alkynes as unsaturated hydrocarbons?
Answer:

Alkanes contain C—C bonds in the molecules and a normal tetrahedral bond angle of 109°. 28′ is not disturbed. On the other hand, both alkenes and alkynes have multiple bonds (>C = C< or – C ≡ C – bond). The tetrahedral bond angle is no longer present. These are under strain and therefore, unsaturated.

Question 15. A compound ‘X has the molecular formula C₃H₆O with the structural formula CH₃CH₂CHO. Give its IUPAC name. Can another compound have the same molecular formula? Give the structure and IUPAC name of that compound also.
Answer:

The IUPAC name of X’ is: Propanal. Another compound Y can also have the same molecular formula but a different structural formula. It is propanone.

The compounds X and Y are related to each other as functional isomers.

Question 16. What happens when- (Give equations also).

1. Methane reacts with excess chlorine in the presence of diffused sunlight.
2. Ethanol undergoes combustion.

Answer:

Question 17. List four characteristics of homologous series.
Answer:

1. Same functional group.
2. Similar chemical properties.
3. Successive member differ by- CH₂unit/14u./
4. Gradation in physical properties.

Question 18.

1. Draw the structures of the following compounds

1. Ethanoic acid
2. Butanone

2. Why is the conversion of ethanol to ethanoic acid considered an oxidation reaction?
Answer:

1.

2. When ethanol (C₂H₅OH) changes to ethanoic acid (CH₃COOH):

• There is a decrease in the number of hydrogen atoms by two.
• There is an increase in the number of oxygen atoms by one.

2. Therefore, the conversion represents an oxidation reaction.

Question 19.

1. What are esters? How are they formed? 
2. Write two uses of esters.

Answer:

1. Esters are the group of organic compounds that contain the functional group(—COOR) called the ester group.  The value of R may change as -CH₃, -C₂H₅, -C₃H₇, etc.

A few examples of esters are:

Esters are formed as a result of a chemical reaction called esterification.

2. Uses of esters

• Esters have a pleasant smell. These are used as flavoring agents and also in perfumes.
• Esters of glycerol known as triglycerides, are used in the manufacture of soaps.
• This reaction is called the saponification reaction.

Question 20. State the meaning of the functional group in a carbon compound. Write the functional group present in Ethanol and Ethanoic acid and also draw their structures.
Answer:

An atom or group of atoms that determine the chemical properties of organic compounds is called a functional group. They confer specific properties to the compound, regardless of the  length and nature of the carbon chain

Question 21.

1. Distinguish between saturated hydrocarbon and unsaturated hydrocarbon with the help of the combustion process.
2. Write the chemical names of C₄H₁₀ and C₂H₂ and draw their structures.

Answer:

Question 22. Why vegetable oils are considered healthy as compared to vegetable ghee? How are vegetable oils converted into vegetable ghee? Name and define the process involved. Answer:

• Vegetable oils contain unsaturated fatty acids while vegetable ghee contains saturated fatty acids which are said to be harmful to health.
• Vegetable oils are converted into vegetable ghee by adding hydrogen in the presence of catalysts palladium (Pd) or nickel (Ni).
• The process involved in this is an addition reaction (hydrogenation).It is defined as the addition of hydrogen atoms in carbon atoms of an organic compound.

Question 23. Give the electron dot structure and structural formula of the first member of the alkene and alkyne families Answer:

Question 24. How will you convert ethene into ethanol? Give the chemical reaction involved.
Answer:

Ethene is converted into ethanol by passing its vapors through water in the presence of sulphuric acid. This reaction is called the hydration of ethane

Question 25. What happens when:

1. Ethanol is burnt in the air and
2. It is oxidized? Write the corresponding reactions involved.

Answer: 1. Ethanol produces carbon dioxide, water, and energy when it is burnt in the air CH₃CH₂OH + 3O₂ → 2CO₂ + 3H₂O + Energy 2. Ethanol is oxidized into ethanoic acid

Question 26. Why are detergents preferred over soaps for washing clothes in hard water? Explain
Answer:

Detergents are preferred over soaps for washing clothes in hard water because:

1. They do not form insoluble precipitates with calcium and magnesium ions in hard water.
2. They give more lather in hard water.
3. They have strong cleansing action.

Question 27. What happens when ethyl alcohol and acetic acid react with each other in the presence of cone H₂SO₄
Answer:

When C₂H₅OH reacts with CH₃COOH, i.e., ethanol with ethanoic acid, a sweet-smelling ester is formed.

Question 28. State two characteristic features of carbon which when put together give rise to a large number of carbon compounds.
Answer:

The size of the carbon atom is very small (Atomic radius bonds = 77 pm) The strength of the C-C bond is quite high (355 kJ mol^-1) Therefore, any number of carbon atoms can be linked by covalent bonds. This self-linking property is called catenation.

Question 29. Why are some compounds saturated while others are unsaturated? 
Answer:

The compounds in which all the four valences of carbon are satisfied by hydrogen atoms are saturated in nature while the compounds in which the required number of hydrogen atoms are not available are unsaturated.

For example:

Question 30. Write the name and molecular formula ofan organic compound having its name suffixed with ‘-ol’ and having two carbon atoms in the molecule. With the help of a balanced chemical equation indicate what happens when it is heated with an excess of one. H₂SO₄
Answer:

The compound is ethanol and its molecular formula is C₂H₅OH. Upon heating with an excess of the cone. H₂SO₄ loses a molecule of H₂O and forms ethene. The reaction is known as the dehydration reaction.

Question 31. Explain with the help of chemical equations, the following properties of carbon.

1. Combustion
2. Oxidation

Answer:

1. Combustion:

C₂H₅OH + 3O₂→ 2CO₂ + 3H₂O

2. Oxidation

Question 32. Name an element, other than carbon which exhibits the property of catenation upto seven or eight atoms’? Are these compounds stable?
Answer:

The element is silicon (Si). It also belongs to group 14. It also shows catenation but its size is more than that of carbon, and the Si-Si bond is comparatively weak. Though upto seven to eight atoms can be linked to form different compounds, the stability of these compounds decreases gradually.

Question 33. Write the structure of

1. Hexanal
2. But-2-ene

Answer:

Question 34. How will you name the following compounds?

Answer:

1. Ethanal
2. Ethanol
3. Methanal
4. Chloroethane

Question 35. The molecular formula C₂H₆O can represent an aldehyde as well as a ketone. Write their structures and name them. How are they related to each other? 
Answer:

The aldehyde and ketone with formula C₂H₆O are propanal and propanone. Having the same molecular formula, these are isomers. As the functional groups are different, these are regarded as functional isomers.

For example:

Question 36. Write the name and general formula of a chain of hydrocarbons in which an addition reaction with hydrogen can take place. Stating the essential conditions required for an addition reaction to occur write the chemical equation giving the name of the reactants and the product of such a reaction.

Answer:

1. Alkanes. General formula: C_nH_2n+2

2. Conditions: Presence of catalysts such as Palladium or Nickel.

3. Equations:

Question 37. Draw the electron-dot structure for ethyne. A mixture ofethyne and oxygen is burnt for welding. In your opinion, why cannot we use a mixture of ethyne and air for this purpose?

Answer: In pure oxygen, ethyne undergoes complete combustion, and a high temperature suitable for welding is attained.

Whereas air contains less percentage/amount of oxygen which results in incomplete combustion of ethyne and the temperature required for welding is not attained.

Question 38. What is meant by a homologous series of carbon compounds? Classify the following carbon compounds into two homologous series and name them. 

1. C₃H₄
2. C₃H₆
3. C₄H₆
4. C₄H₈
5. C₅H₈
6. C₅H₁₀

Answer: A group of organic compounds having the same functional group and similar structures in which the successive members differ by CH₂ group. C₃H₄, C₄H₆, C₅H₈ : Alkyne C₃H₆,C₄H₈, C₅H₁₀ , Alkenes

Question 39. Why does micelle formation take place when soap is added to water? Will a micelle be formed in all types of solvents? Justify your answer.
Answer:

When soap is added to water, micelle formation takes place. This is because the hydrocarbon chains of soap molecules are hydrophobic while the ionic ends are hydrophilic and hence soluble in water. Micelle will not form in all types of solvents. It will form in such type of solvent where soap is insoluble in that particular solvent.

Question 40. Carbon does not from ionic compounds. Why?
Answer:

To form ionic bonds carbon either should lose 4^e+ or gain 4^e- to form C⁴⁺ or C^-4-ion. Losing 4^e+ needs a large amount of energy and by gaining 4^e-, it will have 10^e-. It is difficult for 6 protons to hold 10e^–. So C⁴⁺ and C^4- is not possible.

Question 41. What are soaps? Why do they form scum with hard water?
Answer:

1. Soaps are sodium or potassium salts of higher fatty acids.
2. The soluble Ca and Mg salts present in hard water react with soap to give insoluble salts to produce scum.

Question 42. Write the names ofthe following compounds

Answer:

1. Pentanoic acid
2. Butyne
3. Heptanal
4. Pentanol

Question 43. Identify and name the functional groups present in the following compounds

.

Answer:

Question 44. A compound X is formed by the reaction ofa carboxylic acid and alcohol in the presence ofa few drops of H₂SO₄. The alcohol on oxidation with alkaline KMnO4 followed by acidification gives the same carboxylic acid as used in this reaction. Give the names and structures of

1. Carboxylic acid
2. Alcohol and 
3. The compound X.

Also, write the reaction.

Answer:

1. Carboxylic acid is ethanoic acid
2. Alcohol is ethanol
3. X is ethyl ethanoate

Question 45. A gas is evolved when ethanol reacts with sodium. Name the gas that evolved and also write the balanced chemical equation ofthe reaction involved.
Answer:

The gas that evolved is hydrogen.

The reaction is as follows:

2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂↑

Question 46. Carbon, a Group (14) element in the Periodic Table, is known to form compounds with many elements. Write an example of a compound formed with

1. Chlorine (Group 17 of Periodic Table)
2. Oxygen (Group 16 of the periodic Table)

Answer: Carbon tetrachloride (CCl₄) Carbon dioxide (CO₂)

Question 47. In electron dot structure, the valence shell electrons are represented by crosses or dots.

1. The atomic number of chlorine is 17. Write its electronic configuration.
2. Draw the electron dot structure of the chlorine molecule.

Answer:

1. K =2 ,L = 8 , M = 7

2.  Chlorine

Question 48. Match the reactions given in Column (A) with the names given in column (B)

Answer: 1- D,2- A,3- B,4-C

Question 49. A compound having molecular formula C₂H₆O is a saturated hydrocarbon and is a very good solvent. How can you convert it into unsaturated hydrocarbon?IdentifyXand shows its conversion with the help of the equation.
Answer:

‘X’is CH₃—CH₂OH (ethanol). It can be made unsaturated by heating it with a cone. H₂SO₄ which is a dehydrating agent that removes water from it, thereby forming ethene.

Question 50. Ethene is formed when ethanol at 443 K is heated with excess ofconcentrated sulphuric acid. What is the role of sulphuric acid in this reaction? Write the balanced chemical equation of this reaction.
Answer:

Sulphuric acid acts as a dehydrating agent.

NCERT Solutions For Class 10 Science Chapter 4 Carbon And Its Compounds Multiple Choice Questions

Question 1. Carbon exists in the atmosphere in the form of

1. Carbon monoxide only
2. Carbon monoxide in traces and carbon dioxide
3. Carbon dioxide only
4. Coal

Answer: 3. Carbon dioxide only

Question 2. Which of the following statements is usually correct for carbon compounds?

1. These are good conductors of electricity

2. These are poor conductors of electricity

3. These have strong forces of attraction between their molecules

4. These do not have strong forces of attraction between their molecules

1. 1 and 3
2. 2 and 3
3. 1 and 4
4. 2 and 4

Answer: 4.  2 and 4

Question 3. A molecule of ammonia (NH₃) has

1. Only single bonds
2. only double bonds
3. Only triple bonds
4. Two double bonds and one single bond

Answer: 1. Only single bonds

Question 4. Buckminsterfullerene is an allotropic form of

1. Phosphorus
2. Sulfur
3. Carbon
4. Tin

Answer: 3.  Carbon

Question 5. Which of the following are the correct structural isomers of butane?

Answer: 1

Question 6.

In the above-given reaction, alkaline KmnO₄ acts as

1. Reducing agent
2. Oxidizing agent
3. Catalyst
4. Dehydrating agent

Answer: 2. Oxidizing agent

Question 7. Oils treated with hydrogen in the presence of palladium or nickel catalyst form fats. This is an example of

1. Addition reaction
2. Substitution reaction
3. Displacement reaction
4. Oxidation reaction

Answer: 1. Addition reaction

Question 8. In which ofthe following compounds, —OH is the functional group?

1. Butanone
2. Butanol
3. Butanoic acid
4. Butanal

Answer: 2. Butanol

Question 9. The soap molecule has a

1. A hydrophilic head and a hydrophobic tail
2. A hydrophobic head and a hydrophilic tail
3. A hydrophobic head and a hydrophobic tail
4. A hydrophilic head and a hydrophilic tail

Answer: 1. A hydrophilic head and a hydrophobic tail

Question 10. Which ofthe following is the correct representation of the electron dot structure of nitrogen?

Answer: 4

Question 11. The structural formula of ethyne is

Answer: 1

Question 12. Identify the unsaturated compounds from the following

1. Propane

2. Propene

3. Propyne

4. Chloropropane

1. 1 and 2
2. 2 and 4
3. 3 and 4
4. 2 and 3

Answer: 4. 2 and 3

Question 13. Chlorine reacts with saturated hydrocarbons at room temperature in the

1. Absence of sunlight
2. Presence of sunlight
3. Presence of water
4. Presence of hydrochloric acid

Answer: 2.  Presence of sunlight

Question 14. In the soap micelles

1. The ionic end of soap is on the surface ofthe cluster while the carbon chain is in the interior ofthe cluster
2. The ionic end of soap is in the interior of the cluster and the carbon chain is out of the cluster
3. Both the ionic end and carbon chain are in the interior ofthe cluster
4. Both the ionic end and carbon chain are on the exterior ofthe cluster

Answer: 1. The ionic end of soap is on the surface ofthe cluster while the carbon chain is in the interior ofthe cluster

Question 15. Pentane has the molecular formula C₅H₁₂. It has

1. 5 covalent bonds
2. 12 covalent bonds
3. 16 covalent bonds
4. 17 covalent bonds

Answer: 3. 16 covalent bonds

Question 16. The structural formula of benzene is

Answer: 3

Question 17. Ethanol reacts with sodium and forms two products. These are

1. Sodium ethanoate and hydrogen
2. Sodium ethanoate and oxygen
3. Sodium ethoxide and hydrogen
4. Sodium ethoxide and oxygen

Answer: 3. Sodium ethoxide and hydrogen

Question 18.  The correct structural formula of butanoic acid is

Answer: 4

Question 19. Vinegar is a solution of

1. 50%- 60% acetic acid in alcohol
2. 5%- 8% acetic acid in alcohol
3. 5%- 8% acetic acid in water
4. 50%- 60% acetic acid in water

Answer: 3.  5%- 8% acetic acid in water

Question 20. Mineral acids are stronger acids than carboxylic acids because

1. Mineral acids are completely ionised

2. Carboxylic acids are completely ionised

3. Mineral acids are partially ionised

4. Carboxylic acids are partially ionised

1. 1 and 4
2. 2 and 3
3. 1 and 2
4. 3 and 4

Answer: 1.  1 and 4

Question 21. Carbon forms four covalent bonds by sharing its four valence electrons with four univalent atoms,

Example: Hydrogen. After the formation of four bonds, carbon attains the electronic configuration of

1. Helium
2. Neon
3. Argon
4. Krypton

Answer: 2. Neon

Question 22. The correct electron dot structure ofa water molecule is

Answer: 3

Question 23. Which of the following is not a straight-chain hydrocarbon?

Answer: 4

Question 24. Which among the following are unsaturated hydrocarbons?

1. 1 and 3
2. 2 and 3
3. 2 and 4
4. 3 and 4

Answer: 3. 2 and 4

Question 25. Which ofthe following does not belong to the same homologous series?

1. CH
2. C₂H₆
3. C₂H₆
4. C₄H₈

Answer: 4. C₄H₈

Question 26. The name ofthe compound CH₃—CH₂—CHO is

1. Propanal
2. Propane
3. Ethanol
4. Ethanal

Answer: 1.  Propanal

Question 27. The heteroatoms present in CH₃—CH₃—O—CH₂—CH₂ Cl are

1. Oxygen

2. Carbon

3. Hydrogen

4. Chlorine

1. 1 and 2
2. 2 and 3
3. 3 and 4
4. 1 and 4

Answer: 1. 1 and 2

Question 28. Which of the following represents the saponification reaction?

Answer: 4

Question 29. The first member of the alkyne homologous series is

1. Ethyne
2. Ethene
3. Propyne
4. Methane

Answer: 1.  Ethyne

Question 30. Ethane, with the molecular formula C₂H₆ has

1. 6 covalent bonds
2. 7 covalent bonds
3. 8 covalent bonds
4. 9 covalent bonds

Answer: 2. 7 covalent bonds

Question 31. Butanone is, a four-carbon the functional compound

1. Carboxylic acid.
2. Aldehyde
3. Ketone
4. Alcohol.

Answer: 3. Ketone

Question 32. While cooking, if the bottom of the vessel is getting blackened on the outside, it means that

1. The food is not cooked completely.
2. The fuel is not burning completely.
3. The fuel is wet.
4. The fuel is burning completely.

Answer:  2. The fuel is not burning completely.

CBSE Class 10 Science Chapter 1 Chemical Reactions And Equations Very Short Question And Answers

Question 1. Out of rusting of iron or melting of iron, which one is a physical change?
Answer: Melting of iron

Question 2. In the electrolysis of water, why is the volume of gas collected over one electrode double that of gas collected over the other electrode?
Answer:

Because during electrolysis, water splits into two molecules of hydrogen and one molecule of oxygen.

2HO  → (Electrolysis )  → 2 H₂O

Question 3. Which one is a chemical change, electrolysis of water or Sodium chloride exposed to sunlight?
Answer: Electrolysis of water

Question 4. All decomposition reactions are endothermic reactions. Explain why?
Answer: Because energy in the form of heat, light or electricity is required for decomposition.

Question 5. What change in colour is observed when white silver chloride is left exposed to sunlight? State the type of chemical reaction in this change.
Answer:  Silver chloride becomes grey. It is a photochemical decomposition reaction.

Question 6. Balance the given chemical equation:

⇒ \(\mathrm{Fe}(\mathrm{s})+\mathrm{H}_2 \mathrm{O}(\mathrm{g}) \longrightarrow \mathrm{Fe}_3 \mathrm{O}_4(\mathrm{~s})+\mathrm{H}_2(\mathrm{~g})\)

Read and Learn More CBSE Class 10 Science Very Short Answer Questions

Answer:

⇒ \(3 \mathrm{Fe}(\mathrm{s})+4 \mathrm{H}_2 \mathrm{O}(\mathrm{g}) \longrightarrow \mathrm{Fe}_3 \mathrm{O}_4(\mathrm{~s})+4 \mathrm{H}_2(\mathrm{~g})\)

Question 7. Balance the given chemical equation:
Answer: FeSO₄(s)   → (Heat) → Fe₂O₃(s) + SO₂(g) + SO₃(g)

Question 8. Balance the following chemical equation:

⇒ \(\mathrm{Fe}(s)+\mathrm{H}_2 \mathrm{O}(g) \longrightarrow \mathrm{Fe}_3 \mathrm{O}_4(s)+\mathrm{H}_2(g)\)

Answer:

⇒  \(3 \mathrm{Fe}(s)+4 \mathrm{H}_2 \mathrm{O}(\mathrm{g}) \longrightarrow \mathrm{Fe}_3 \mathrm{O}_4(\mathrm{~s})+4 \mathrm{H}_2(g)\)

Question 9. What type of coating is formed on silver articles when they get corroded?
Answer: The silver articles form a black coating of silver sulphide (Ag₂S).

Question 10. On what basis is a chemical equation balanced?
Answer: It is based on the law of conservation of mass.

Question 11. Balance the given chemical equation:

Al(s) + CuCl₂(aq)→  AlCl₃(aq) + Cu(s)

Answer: 2Al(s) + 3CuCl₂(aq)→ 2AlCl₃(aq) + 3Cu(s)

Question 12. What type of coating is formed on copper articles when they get corroded?
Answer: The copper articles form a green coating of basic copper carbonate

Question 13. State one basic difference between a physical change and a chemical change.
Answer:

In a physical change, no new substance is formed whereas in a chemical change, a new substance is formed.

Question 14. On adding dilute hydrochloric acid to copper oxide powder, the solution formed is blue-green. Predict the new compound formed which imparts a blue-green colour to the solution.
Answer:

The new compound formed is copper (II) chloride (CuCl2) which imparts a blue-green colour to the solution.

Question 15. Name the oxidising and reducing agent in the following reaction: Cu + H₂O→Cu + H₂O
Answer:

The oxidising agent is CuO.

The reducing agent is H₂.

Question 16. What is meant by the skeletal equation?
Answer: An unbalanced chemical equation is called a skeletal equation.

Question 17. If copper metal is heated over a flame, it develops a coating. What is the colour and composition of this coating?
Answer: The colour of the coating is black and it is composed of CuO or copper oxide.

Question 18. Which one is a chemical change – Electrolysis of water or sodium chloride exposed to sunlight?
Answer: Electrolysis of water

Question 19. A magnesium ribbon should be cleaned before burning it in the air. Why?
Answer: It should be cleaned to remove the dust particles and the oxide that may be present on its upper surface so that it comes directly in contact with air.

Question 20. Which of the following is a chemical change?

1. Burning of wax
2. Melting of wax

Answer: 1. Burning of wax

Question 21. Why do gold and platinum not corrode in moist air?
Answer: They are least reactive and do not react with substances present in moist air.

Question 22. Why do potato chip manufacturers fill the packet of chips with nitrogen gas?
Answer: To provide an inert atmosphere to prevent chips from getting oxidised. N₂ does not allow chips to get spoiled by oxidation.

Question 23. How will you define a reducing agent?
Answer: A reducing agent is a substance which can lose electrons or which can add hydrogen or remove oxygen.

Question 25. Name the process in which the gain of electrons takes place.
Answer: Reduction is a process which involves the gain of electrons

Question 24. A white salt on heating decomposes to give brown fumes, and a residue is left behind. Name the salt.
Answer: Lead nitrate is white salt.

Question 25. Hydrogen is a highly inflammable gas and oxygen is a supporter of combustion, yet water which is a compound made up of hydrogen and oxygen is used to extinguish fire. Why?
Answer:

This is because the properties of the compound (H₂O) are different from the properties of its constituting elements, i.e., H₂ and O₂.

Question 26.

• AgNO₃(aq) + NaCl(aq)→ AgCl(s) ↓ + NaNO₃(aq)
• FeS + H₂SO₄ →FeSO₄ + H₂S ↑

Consider the above-mentioned two chemical equations with two different kinds of arrows(↑ and ↓) along with products. What do these two different arrows indicate?
Answer:

↑ shows the gas evolved, whereas shows an insoluble substance (precipitate) formed.

Question 27. What is the colour of FeSO₄.7H₂O crystals? How does the colour change upon heating? Give a balanced chemical equation for the change. 
Answer:

FeSO₄. 7H₂O is green and loses water of crystallisation when it is heated. It is then decomposed to Fe₂O₃ (brown-coloured), SO₂ and SO₃

2FeSO₄(s) → Fe₂O₃(s)+  SO₂(g) + SO₃(g)

Question 28. Oil and fat-containing food items are flushed with nitrogen. Why?
Answer: To keep food items fresh and to save from the oxidising effect of oxygen, food items are flushed with nitrogen gas.

Question 29. Why do we store silver chloride in dark-coloured bottles?
Answer: Because silver chloride on exposure to sunlight undergoes dissociation.

Question 30. A boy has been collecting silver coins and copper coins. One day he observed a black coating on silver coins and a green coating on copper coins. Which chemical phenomenon is responsible for these coatings?
Answer: The phenomenon responsible for these coatings is corrosion.

Question 31. FeSO₄. 7H₂O, green colour crystals on heating changes colour. Why?
Answer:  The green colour of ferrous sulphate crystals is due to the presence of 7 water molecules (water of crystallisation).