Class 12 Biology

Sexual Reproduction In Flowering Plants Question And Answers

Question 1. Name the parts of an angiosperm flower in which the development of male and female gametophytes takes place.
Answer:

Development of male and female gametophytes takes place in anther and ovary respectively.

Question 2. Differentiate between microsporogenesis and megasporogenesis. Which type of cell division occurs during these events? Name the structures formed at the end of these two events.
Answer:

Differentiate between microsporogenesis and megasporogenesis:

Meiosis occurs during micro and megasporogenesis. Microspores (pollen grains) are formed at the end of microsporogenesis and female gametophytes (embryo sac) are formed at the end of megasporogenesis.

Question 3. Arrange the following terms in the correct developmental sequence: pollen grain, sporogenous tissue, microspore tetrad, pollen mother cell, and male gametes.
Answer:

Sporogenous tissue – Pollen mother cell – Microspore tetrad – Pollen grain – Male gametes

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Question 4. Describe the parts of a typical angiosperm ovule with a neat, labeled diagram.
Answer:

Structure of megasporangium.

Question 5. What is meant by the monosporic development of a female gametophyte?
Answer:

Out of the four megaspores, three degenerate and only one remains functional, which develops into a female gametophyte or embryo sac. This is called monosporic development, i.e. when an embryo sac develops from one single megaspore it is called a monosporic embryo sac.

Question 6. With a neat diagram and explain the 7-called, 8-nucleate nature of the female gametophyte.
Answer:

A female gametophyte or embryo sac is a small oval structure that contains a 3-celled egg apparatus, 3 antipodal cells, and one binucleate central cell, hence it is a 7 – 7-celled and 8 – -nucleate structure.

1. Egg apparatus: It consists of two synergids and an egg cell towards the micropylar end. The cells of the egg apparatus are uninucleated. Synergids towards their micropylar end have cellular thickening called filiform apparatus that help in guiding the pollen tubes into the synergids
2. Antipodal cells: The chalazal end of the embryo sac contains three cells of various shapes and sizes called antipodal cells. _
3. Central cell: It is the single and largest cell which is bounded by a membrane of an embryo sac. It contains two polar nuclei, which later fuse to form diploid secondary nuclei. After fertilization, the central cell gets converted into a triploid primary endosperm cell (PEC) which forms endosperm.

Question 7. What are chasmogamous flowers? Can cross-pollination occur in cleistogamous flowers? Give
Answer:

Chasmogamous flowers are open flowers with exposed stamens and stigma, which facilitate cross-pollination. No cross-pollination occurs in cleistogamous flowers as these flowers are closed and never open and thus no transfer of pollen from outside to the stigma of the flower is possible.

Question 8. Mention two strategies evolved to prevent self-pollination in flowers.
Answer:

1. The maturation of anthers and stigma at different periods in a bisexual flower prevents self-pollination (dichogamy).
2. Production of unisexual flowers.

Question 9. What is seif-incompatibility? Why does self-pollination not lead to seed formation in self-incompatible species?
Answer:

Self-incompatibility or self-sterility is the inability of an intersexual or bisexual plant to produce viable seeds on self-pollination despite producing functional male and female gametes. Since fertilization does not take place, no seeds are produced. It is a genetic mechanism that prevents self-pollen from fertilizing ovules by inhibiting pollen tube growth in pistils.

Question 10. What is the bagging technique? How Is it useful in a plant breeding program?
Answer:

It is the covering of female plants with butter paper germ to avoid their contamination by foreign pollens during the breeding program.

Question 11. What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.
Answer:

Triple fusion is a fusion of one male gamete and two polar nuclei (or secondary nuclei if the two have already fused) in the central cell of the embryo sac to form the primary endosperm nucleus. It takes place in the central cell of an embryo sac. Three nuclei are involved in triple fusion, i.e. nuclei in the central cell one male nucleus, and two polar nuclei in the central cell.

Question 12. Why do you think the zygote is dormant for some time in a fertilized ovule?
Answer:

The zygote is dormant for some time in a fertilized ovule because the embryo that is developed from the zygote may be obtained from the endosperm.

Question 13. Differentiate between:

1. Hypocotyl and epicotyl
2. Coleoptile and coleorrhiza
3. Integument and testa
4. Perisperm and pericarp

Answer:

1. Hypocotyl and epicotyl

2. Coleoptile and coleorrhiza

3. Integument and testa

4. Perisperm and pericarp

Question 14. Why is an apple called a false fruit? Which part (s) of the flower forms the fruit?
Answer:

False fruits are those fruits in which accessory floral parts also contribute to fruit formation. In apples, the thalamus also contributes to fruit formation. Therefore, it is called a false fruit. The fruit develops from the dead ovary of the flower.

Question 15. What is meant by emasculation? When and why does a plant breeder employ this technique?
Answer:

Emasculation is the practice of removal of stamens/anthers before the anther dehiscence from bisexual flowers in female parents. A plant breeder employs this technique in die immature bud condition before die anthers begin to differentiate. It is required to prevent self-pollination.
Uses in plant breeding:

1. Prevention of contamination and pollination of the stigma of female flowers wide foreign undesirable pollens.
2. Prevention of damage by animals.

Question 16.If one can induce parthenocarpy through the application of growth substances, which fruits would you select to induce parthenocarpy and why?
Answer:

Only fleshy fruits like orange watermelon, lemon, etc. should be selected as parthenocarpic fruit. Here seeds of fruits are irritant during consumption of seeds the fruits are even more valuable. It is easy to make fruit juices, jams, etc. with seedless fruits.

Question 17. Explain the role of tapetum In the formation of pollen-grain walls.
Answer:

Tapetum is die innermost wall layer of a microsporangium. It nourishes the developing pollen grains and also helps in the formation of a wall of pollen grains. The cells of tapetum secrete Ubisch granules that provide sporopollenin and other materials for exine formation.

Question 18. What is apomixis and what is its importance?
Answer:

Apomixis is a type of asexual reproduction that mimics sexual reproduction to form seeds without fertilization. In apomictic seeds, parental characters are maintained in the progeny/offspring, as there is no meiosis or segregation of characters. If desired hybrid seeds are made apomictic the farmers can keep on using the hybrid seeds to raise new crops year after year.

Human Reproduction Questions And Answers

Question 1 . Draw a labelled diagram of the male reproductive system.
Answer:

Question 2. Draw a labelled diagram of the female reproductive system.
Answer:

Question 3. Write two major functions each of the testis and ovary.
Answer:

Functions of the Testis :

1. They produce male gametes (sperm) by the process of called spermatogenesis.
2. The ley dig cells of the seminiferous tubules secrete the male sex hormone called testosterone.

Functions of the ovary :

1. They produce female gametes (ovum) by the process of oogenesis.
2. The growing Graafian follicles secrete the female sex hormone called estrogen.

Question 4. Describe the structure of a seminiferous tubule. [IMP.]
Answer:

• A seminiferous tubule is made up of a layer of male germ cells and large Sertoli cells (nurse cells).
• The male germ cells undergo spermatogenesis to produce spermatocytes, spermatids and sperms.
• The regions outside the seminiferous tubules called interstitial spaces have connective tissue, which includes blood vessels and Leydig cells.
• Leydig cells synthesise and secrete the male sex hormones called androgens, of which testosterone is the principal one.

Question 5. What is spermatogenesis? Briefly describe the process of spermatogenesis.
Answer:

It is the process of formation of haploid sperms in seminiferous tubules of testes.

Question 6. Name the hormones involved in the regulation of spermatogenesis,
Answer:

GnRH (Gonadotropin releasing hormone), LH (Luteinising hormone), FSH (Follicle stimulating hormone), androgens.

Question 7. Define spermiogenesis and spermiation.
Answer:

1. Spermiogenesis: The process of transformation of spermatids into spermatozoa in seminiferous tubules, is called spermiogenesis.
2. Spermiation: After spermiogenesis, sperm heads become embedded in the Sertoli cells and are finally released from the seminiferous tubules by the process called spermiation.

Question 8. Draw a labelled diagram of sperm.
Answer:

Question 9. What are the major components of seminal plasma?
Answer:

The major components of seminal plasma are :

• Secretions of the accessory sex glands of males – prostate gland, seminal vesicles, bulbourethral glands.
• Mainly composed of – calcium, fructose, and other enzymes

Question 10. What are the major functions of male accessory ducts and glands?
Answer:

The major functions of the male accessory ducts and glands are as follows:

Male accessory ducts

1. Vasa efferentia: Conducts sperms from the rete testis to the epididymis.
2. Rete testis: Stores sperms that are produced by seminiferous tubules.
3. Epididymis: Physiological maturation of sperms, storage and nouri shipment.
4. Vas deferens: Conducts sperms from epididymis to the urethra.

Male accessory glands

1. Seminal vesicles: Activates and provides energy to facilitate sperm motility after ejaculation.
2. Prostate gland: Nourishes and activates sperm, and enhances sperm motility.
3. Cowper’s gland: It enhances the mobility & survival potentiality of sperms in the genital tract of the female reproductive system and neutralizes the activity of acidic female vaginal secretions.

Question 11. What is oogenesis? Give a brief account of oogenesis.
Answer:

Oogenesis is the phenomenon of the formation of haploid female gametes known as ova from diploid oogonia in the ovary is called as oogenesis. Oogenesis can be explained through the following flow chart.

Question 12. Draw a labelled diagram of a section through the ovary.
Answer:

The diagram of a section of an ovary is as follows-

Question 13. Draw a labelled diagram of a Graafian follicle.
Answer:

The diagram of a Graafi follicle is as follows:

Question 14. Name the functions of the following :

1. Corpus luteum
2. Endometrium
3. Acrosome
4. Sperm tail
5. Fimbria

Answer:

The functions of each are as follows :

1. Corpus luteum – The corpus luteum secretes the hormone progesterone during the luteal phase of the menstrual cycle.
2. Endometrium -The endometrium is the innermost layer of the uterus comprising glands that undergo cyclic changes during different stages of the menstrual cycle to prepare themselves for the embryo-implantation process.
3. Acrosonie -It consists of the sperm lysin enzyme that helps in penetration of the outer membrane of the egg by sperm which facilitates the sperm to perforate through the egg during fertilization.
4. Sperm tail – The sperm tail makes up for the longest part of the sperm, enabling the movement of the sperm, once it has entered the female reproductive tract.
5. Fimbriae – Towards the ovarian end of the fallopian tube, finger-like projections emerge, these are the fimbriae which assist in the collection of the ovum after the ovulation.

Question 15. What is the menstrual cycle? Which hormones regulate the menstrual cycle?
Answer:

It is a reproductive cycle in female primates (e.g. monkeys, apes and human beings), in females menstruation is repeated at an average interval of about 28/29 days, the cycle of events starting from one menstruation till the next one is called the menstrual cycle.
The different hormones that regulate the menstrual cycle are LH – Luteinising hormone, FSH – follicle stimulating hormone, progesterone, and estrogen.

Question 16. What is parturition? Which hormones are involved in the induction of parturition?
Answer:

Parturition is the process wherein a fully developed foetus from the mother’s womb is expelled after the completion of the gestation period. The two critical hormones are involved in the induction of parturition are:

Oxytocin – It directs the full-term foetus towards the birth canal, as it causes the contraction of the smooth muscles of the myometrium of the uterus leading the baby to be expelled.

Relaxin – It relaxes the pelvic ligaments, widening the pelvis to assist in an easier childbirth.

Question 17. In our society, women are often blamed for giving birth to daughters. Can you explain why this is not correct?
Answer:

This is not correct to blame women for giving birth to daughters.

• The male sperm contain either X or Y chromosomes whereas the female egg contains only the X chromosome.
• At the time of fertilization, sperm with a Y chromosome combine with an egg-containing X chromosome which would be male.
• Thus scientifically sex of the baby is determined by the father and not by the mother as blamed in our society.

Question 18. How many eggs are released by a human ovary in a month? How many eggs do you think would have been released if the mother gave birth to identical twins? Would your answer change if the twins born were fraternal?
Answer:

Typically in a month, human ovaries release only one egg, rarely two. In the case of identical twins or monozygotic twins, one egg is released by the ovary which splits into two post fertilization. This is why identical twins exhibit the same genetic features.

On the other hand in fraternal twins or dizygotic twins, two eggs are released which are fertilized by two different sperms causing the fraternal twins to exhibit different genetic characteristics.

Question 19. How many eggs do you think were released by the ovary of a female dog which gave birth to 6 puppies?
Answer:

To have given birth to six puppies, the ovary of the female dog released six eggs. Hence, six zygotes were formed for each to develop into a puppy.

Human Reproduction Fill In The Blanks

Question 1. Humans reproduce______________(asexually/sexually)
Answer: Sexually

Question 2. Human are______________(oviparous, viviparous, ovoviviparous)
Answer: Viviparous

Question 3. Fertilization is human, (external/internal)______________
Answer: Internal

Question 4. Male and female gametes are (diploid/haploid)’______________
Answer: Haploid

Question 5. Zygote is______________(diploid/haploid).
Answer: Diploid

Question 6. The process of release of ovum from a mature follicle is called______________
Answer: Ovulation

Question 7. Ovulation is induced by a hormone called ______________
Answer: Luteinising hormone

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Question 8. The fusion of male and female gametes is called______________
Answer: Fertilization

Question 9. Fertilization takes place in______________
Answer: Ampulla of the oviduct

Question 10. The zygote divides to form______________which is implanted in the uterus.
Answer: Blastocyst

Question 11. The structure which provides a vascular connection between the foetus and the uterus is called______________
Answer: Placenta

Human Reproduction Identify True/False Statements

Identify True/False statements. Correct each false statement to make it true.

Question 1.  Androgens are produced by Sertoli cells
Answer: False

Correct statement: Androgens are produced by the Ley dig cells.

Question 2.  Spermatozoa get nutrition from Sertoli cells.
Answer: True

Question 3.  Leydig cells are found in the ovary.
Answer: False

Correct statement: Leydig cells are found in the testis.

Question 4. Ley dig cells synthesise androgens.
Answer: True

Question 5. Oogenesis takes place in the corpus luteum.
Answer: False

Correct statement: Oogenesis takes place in the ovary.

Question 6. The menstrual cycle ceases during pregnancy.
Answer: True

Question 7. The presence or absence of hymen is not a reliable indicator of virginity or sexual experience.
Answer: True

Reproductive Health Questions And Answers

Question 1. What do you think is the significance of reproductive health in a society?
Answer:

In a society, if people are aware of birth control methods to avoid sexually transmitted diseases and the importance of breastfeeding and post-natal care of the mother and baby, then that society can have healthy children who are the future citizens of a nation.

Question 2. Suggest the aspects of reproductive health which need to be given special attention in the present scenario.
Answer:

Important aspects:

• Counselling and creating awareness among people especially the youth about various aspects of reproductive health such as sexually transmitted diseases, available contraceptive methods, cases of pregnant mothers and adolescents, etc.
• Providing support and facilities such as medical assistance to people during pregnancy, STIs, abortions, contraceptives, infertility, etc. for building a reproductively healthy society.

Question 3. Is sex education necessary in schools? Why? 
Answer:

Yes, sex education is necessary for schools because

• It will provide proper information about reproductive organs, adolescence, safe, hygienic sexual practices, and sexually transmitted infections (STIs).
• It will provide the right information to avoid myths and misconceptions about sex-related queries.

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Question 4. Do you think that reproductive health in our country has improved in the past 50 years? If yes, mention some such areas of improvement
Answer:

• Yes, reproductive health has tremendously improved in India in the last 50 years. The areas of improvement are as follows.
• Batter awareness about sex-related matters.
• Increase the number of medically assisted deliveries and better post-natal care of child and mother, leading to decreased maternal and infant mortality rates.
• Increase the number of couples with small families.
• Better detection and cure of STIs and overall increased medical facilities for all sex-related problems

Question 5. What are the suggested reasons for the population explosion?
Answer:

The suggested reasons for the population explosion are :

• rapid decline in the death rate.
• decline in maternal mortality rate (MMR)
• decline in infant mortality rate (IMR) and
• increase in number of people in reproducible age

Question 6. Is the use of contraceptives justified? Give reasons.
Answer:

Yes, the use of contraceptives is justified. The human population is increasing tremendously. Therefore, regulating the population growth by regulating reproduction has become a necessary demand in the present times. Various contraceptive devices have been devised to reduce unwanted pregnancies which help in bringing down the increased birth rate and hence, in checking population explosion.

Question 7. Removal of gonads cannot be considered as a contraceptive option. Why?
Answer:

The removal of gonads not only stops the production of gametes but also stops the secretion of various important hormones required for body functions. This method is irreversible and thus, cannot be considered as a contraceptive method.

Question 8. Amniocentesis for sex determination is banned in our country. Is this ban necessary? Comment.
Answer:

Yes, the ban is necessary because amniocentesis is misused for determining the sex of the fetus and then aborting the child if it is a female.

Question 9. Suggest some methods to assist infertile couples to have children.
Answer:

The reasons for infertility could be physical, congenital diseases, drugs, immunological, and even psychological. Specialized healthcare units called infertility clinics could help in the diagnosis and corrective treatment of some of these disorders. Through special techniques called assisted reproductive technologies (ART), infertile couples could be assisted to have children.

ART includes:

1. In vitro fertilisation,
2. Gamete intra fallopian transfer (GIFT),
3. Intra cytoplasmic sperm injection (ICSI), and
4. Artificial insemination (AI).

Question 10. What are the measures one has to take to prevent contracting STDs?
Answer:

Sexually transmitted Infections (STIs) get transferred from one individual to the other through sexual contact. Adolescents and young adults are at the greatest risk of acquiring these sexually transmitted diseases. Hence,

• Creating awareness among adolescents regarding its after-effects can prevent them from contracting STIs.
• The use of contraceptives such as condoms etc. while intercourse can prevent the transfer of these diseases.
• Sex with unknown partners or multiple partners should be avoided as they may have such diseases.
• Specialists should be consulted immediately in case of doubt to ensure early detection and cure of die disease.

Reproductive Health Identify The True Or False Statements

1. State True / False with an explanation.

Question 1. Abortions could happen spontaneously, too.
Answer: True

Due to internal factors like incompatibility, abortion could happen spontaneously.

Question 2. Infertility is defined as die inability to produce a viable offspring and is always due to abnormalities/ defects in the female partner.
Answer: False 

Infertility may also be caused due to a male partner when the sperm count is low or their mobility is less.

Question 3. Complete lactation could help as a natural method of contraception.
Answer: True

Lactational amenorrhea is a method of contraception, as ovulation does not occur during the period of intense lactation following parturition.

Question 4. Creating awareness about sex-related aspects is an effective method to improve the reproductive health of dying, people.
Answer: True

Creating awareness about sex-related aspects removes myths and misconceptions about these problems.

Reproductive Health Correct The Following Statements

Question 1. Correct The Following Statements:

1. Surgical methods of contraception prevent gamete formation.
2. All sexually transmitted diseases are completely curable.
3. Oral pills are very popular contraceptives among rural women.
4. In E.T. techniques, embryos are always transferred into the uterus.

Answer:

1. The surgical method of contraception prevents gamete motility.
2. All sexually transmitted diseases are curable if they are detected early and treated properly. AIDS is still an incurable disease.
3. Oral pills are very popular contraceptives among urban women.
4. In the embryo transfer technique, 8-celled embryos are transferred into die fallopian tube while more than 8-celled embryos are transferred into the uterus.

• Sexual Reproduction in Flowering Plants Important Questions
• Human Reproduction Important Questions
• Reproductive Health  Important Questions
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