Biodiversity And Conservation Class 12 Important Questions And Answers Biology Chapter 13

Biodiversity And Conservation Important Questions And Answers

Question 1. Name the three important components of biodiversity.

CBSE Class 12 BioIogy Chapter 13 Biodiversity And Conservation Components Of Biodiversity

Question 2. How do ecologists estimate the total number of species present in the world?

There are two methods to estimate the number of species in the world :

  1. By estimating the rate of discovery of new species. ,
  2. By statistical comparison of the temperate-tropical species richness of an exhaustively studied group of insects and extrapolate this ratio to other groups of animals and plants to come up with a gross estimate of the number of species on earth.

Question 3. Give three hypotheses for explaining why tropics show the greatest levels of species richness.

The three hypotheses to explain species richness in the tropics are:

  1. The constant environment in the tropics promotes niche specialization and increased species diversity.
  2. There is longer exposure to solar radiation in tropical regions that contributes directly to higher productivity and indirectly to greater species diversity.
  3. There occurred no glaciation in the tropical region and it remained undisturbed. Thus organisms living in the tropics continued to flourish and evolved more species diversity.

Question 4. What is the significance of the slope of regression in a species-area relationship?

  • The slope of regression in a species-area relationship indicates that species richness decreases with the decrease in area.
  • The regression coefficient (Z) is 0,1 – 0.2 regardless of the taxonomic group or the region example plants in Britain or birds in California.
  • However, when very large areas like the entire continent are analyzed, it was found that the slope of the line is much steeper with Z values in the range of 0.6 to 1.2.

Question 5. What are the major causes of species losses in a geographical region?

There are four major causes (The Evil Quartet):

CBSE Class 12 BioIogy Chapter 13 Biodiversity And Conservation Geographical Region

Question 6. How is biodiversity important for ecosystem functioning?

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Importance of biodiversity for ecosystem functioning –

  1. Stability: Biodiversity is an important aspect of the stability of an ecosystem. Ecologists believe that communities with more species tend to be more stable than those with less species.
  2. Productivity: Ecosystems with higher biodiversity show more productivity than ecosystems with lower biodiversity. David Tilman’s long-term ecosystem experiments using outdoor plots provide confirmation.
  3. Ecosystem health: Rich biodiversity is not only essential for ecosystem health but also imperative for the survival of the human race on Earth. Species are interlinked and so, killing or disappearance of one would affect the others also.
  4. Resilience: Increased biodiversity provides resilience of the ecosystem against natural or man-made disturbances.

Question 7. What are sacred groves? What is their role in conservation?

  • Sacred groves are forest patches for worship in several parts of India All the trees and wildlife in them are venerated and given total protection.
  • They are found in Khasi and Jaintia Hills in Meghalaya, Western Ghat regions of Karnataka Maharashtra, etc.
  • Tribes do not allow anyone to cut even a single branch of a tree in these sacred groves thus sacred groves have been free from all types of exploitations.

Question 8. Among the ecosystem services are control of floods and soil erosion. How is this achieved by the biotic components of the ecosystem?

  1. Control of soil erosion: Plant roots hold the soil particles tightly and do not allow the topsoil to drift away by winds or moving water. Plants increase die porosity and fertility of die soil.
  2. Control of floods: It is earned out by retaining water and preventing runoff of rainwater. Litter and humus of plants function as sponges thus retaining the water which percolates down and gets stored as underground water. Hence, the flood is controlled.

CBSE Class 12 BioIogy Chapter 13 Biodiversity And Conservation Important Questions And Answers

Question 9. The species diversity of plants (22%) is much less than that of animals (72%). What could be the explanations for how animals achieved greater diversification? [IMP.]

Animals have achieved greater diversification than plants due to the following reasons:

  1. They are mobile and thus can move away from their predators or unfavorable environments. On the other hand, plants are fixed and have fewer adaptations to obtain the optimum amount of raw materials and sunlight therefore they show lesser diversity.
  2. Animals have a well-developed nervous system to receive stimuli against external factors and thus can respond to them. On the other hand, plants do not exhibit any such mechanism thus they show lesser diversity than animals.

Question 10. Can you think of a situation where we deliberately want to make a species extinct? How would you justify it?

  • Species that are harmful to human beings can be made extinct example  HIV, poliovirus, etc.
  • Such microorganisms are not part of any food chain and tints, their extinction would not affect die ecosystem.

Ecosystem Class 12 Important Questions and Answers Biology Chapter 12

Ecosystem Question And Answers

Question 1. Difference Between the Grazing food chain and the Detritus food chain

Ecosystem Difference Between Grazing Food Chain And Detritus Food Chain

Question 2. Difference Between Litter And Detritus

Ecosystem Difference Between Litter And Detritus

Question 3. Difference Between  Food chain and Food web

Ecosystem Difference Between Food Chain And Food Wevb

Question 4. Difference Between  Production And Decomposition

Ecosystem Difference Between Production And Decomposition

Question 5. Difference Between  Upright and Inverted Pyramid

Ecosystem Difference Between Upright pyramid And Inverted pyrmaid

Question 6. Difference Between Primary Productivity And Secondary Productivity

Ecosystem Difference Between Primary Productivity And Secondary Productivity

Question 7. Describe the components of an ecosystem.

An ecosystem consists of two types of components, ie., biotic or living and abiotic or non-living. There are three main types of biotic components based on the mode of obtaining their food- producers, consumers, and decomposers,

CBSE Class 12 BioIogy Chapter 12 Ecosystem Components Of An Ecosystem

  1. Producers (autotrophs): are photosynthetic or autotrophic plants that synthesize their organic food from inorganic raw materials with the help of solar radiation. Common producers are algae, plants, and photosynthetic bacteria. Phytoplanktons are the producers of aquatic ecosystems.
  2. Consumers (heterotrophs): They are animals that feed on other organisms or producers to obtain their nourishment. Common consumers are deer, goats, etc.
  3. Decomposers: They are saprotrophs that obtain nourishment from organic remains. They release digestive enzymes to digest the organic matter. Common decomposers are detritivores,
    1. For Example:  Earthworm.

Abiotic components of the ecosystem consist of non-living substances and factors that are as follows:

  1. Temperature
  2. Light
  3. Wind
  4. Humidity
  5. Precipitation
  6. Water

CBSE Class 12 BioIogy Chapter 12 Ecosystem Important Questions And Answers

Question 8. Define ecological pyramids and describe with examples, pyramids of number and biomass.

The relationship between producers and consumers at different trophic levels in an ecosystem can be graphically represented in the form of an ecological pyramid.

Structure: The base always represents tire producers or the first trophic level and the apex represents top-level consumers or the last.

Ecological pyramids are of three types;

  1. Pyramid of number
  2. Pyramid of biomass
  3. Pyramid of Energy

Pyramid of numbers: The relationship between producers and consumers in an ecosystem can be represented in the form of a pyramid in terms of several organisms at different trophic levels called the pyramid of numbers.

Note: It is inverted when you count several insects feeding on a big tree.

Ecosystem Pyramid Of Numbers In A grassland Ecosystem

Pyramid of biomass: The relationship between producers and consumers in an ecosystem can be represented in the form of a pyramid in terms of biomass called a pyramid of biomass. It can be

  1. Upright, Example. in case of grassland ecosystem;
  2. Inverted, Example. in case of pond ecosystem as the biomass of fishes exceeds that of phytoplankton

Ecosystem Pyramid Of Biomass Shows A SharpDecrease In Biomass At Higher Trophic Level

Ecosystem Inverted Pyramids Of Biomass Of Pond ecosystem

Question 9. What is primary productivity? Give a brief description of factors that affect primary productivity.

Primary productivity is the rate of synthesis of biomass by producers, per unit time, per unit area through the process of photosynthesis.

The factors affecting primary productivity are the following

  • Plant species inhabiting a particular area.
  • Environmental factors:
  1. Sunlight: The sunlight directly regulates the primary productivity because the plants perform photosynthesis with the help of sunlight As the tropical region receives maximum sunlight it exhibits higher productivity.
  2. Temperature: Temperature regulates the activity of enzymes. So, the optimum temperature is required for the proper functioning of the enzyme.
  3. Moisture: Rain (humidity) is required for higher primary productivity. Deserts have the lowest primary productivity as dead soil is deficient in moisture.

Question 10. Define decomposition and describe the processes and products of decomposition.

The process of breaking down complex organic matter into inorganic substances like CO, water, and nutrients is called decomposition. The raw materials for decomposition including dead plant remains like leaves, bark, flowers, and animal remains and their fecal matter are called detritus.

Steps of Decomposition

  1. Fragmentation: The process of breaking down detritus into smaller particles is called fragmentation, for example., as done by Earthworm (fanner’s friend).
  2. Leaching: The process by which water-soluble inorganic nutrients go down into the dead soil horizon and get precipitated as unavailable salts is called leaching.
  3. Catabolism: The enzymatic process by which bacterial and fungal enzymes degrade detritus to simpler inorganic substances is called catabolism.
  4. Humification: The process of accumulation of a dark-colored amorphous substance, called humus, that is highly resistant to microbial action and undergoes decomposition at an extremely slow rate is called humification. Humus being colloidal is the reservoir of nutrients.
  5. Mineralization: The process by which humus is further degraded by some microbes to release inorganic nutrients is called mineralization.

Ecosystem Digrammatic representation Of Decomposition Cycle In A Terrestrial Ecosyste

Question 11. Give an account of energy flow in an ecosystem.

The sun is the only source of energy for all ecosystems on earth. Out of the total incident solar radiation, only 50% of it is photosynthetic active radiation (PAR).

  • Plants capture only 2-10 % of the PAR and this small amount of energy sustains the entire living world. So, there is unidirectional flow of energy from the sun to producers and then to consumers
  • The energy is transferred in an ecosystem, in the form of food which is degraded and loses a major part of food energy as heat during metabolic activities and only a very small fraction becomes stored as biomass
  • This is correlated to the second law of thermodynamics, i.e., ecosystems need a constant supply of energy to synthesize molecules they require, to counteract the universal tendency towards increasing disorderliness. –
  • The green plants in the ecosystem that can trap solar energy to convert it into chemical bond energy are called producers.
  • All the animals that depend on food on plants are called consumers or heterotrophs.
  • Consumers are divided into the following categories:
  1. Primary consumers: Animals that feed directly on plants, i.e., herbivores.
  2. Secondary consumers: Consumers that feed on primary consumers, i.e., carnivores.
  3. Tertiary consumers: Consumers that feed on secondary consumers
  • Lindeman’s 10 percent law: At each step of the food chain, when food energy is transferred from one trophic level to the next higher trophic level, only about 10 percent of energy is passed on to the next trophic level. This is known as Lindeman’s 10 percent law given by Lindeman in 1942.

Ecosystem Multiple-Choice Questions

Question 1. Which one of the following has the largest population in a food chain?

  1. Producers
  2. Primary consumers
  3. Secondary consumer
  4. Decomposers

Answer: 1. Producers (decomposers can be maximum but they are excluded from the food chain)

Question 2. The second trophic level in a lake is

  1. Phytoplankton
  2. Zooplankton
  3. Benthos
  4. Fishes

Answer: 2. Zooplankton

Question 3. Secondary producers are

  1. Herbivores
  2. Producers
  3. Carnivores
  4. None of the above

Answer: 1. Herbivores

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Question 4. What is the percentage of photosynthetically active radiation (PAR) in the incident solar radiation?

  1. 100%
  2. 50%
  3. 1-5%
  4. 2-10%

Answer: 2. 50%

Ecosystem Fill In The Blanks

1. Plants are called Producers because they fix carbon dioxide.

2. In an ecosystem dominated by trees, the pyramid (of numbers) is an inverted type.

3. In aquatic ecosystems, the limiting factor for the productivity is Light.

4. Common detritivores in our ecosystem are Earthworms, ants, and mites

5. The major reservoir of carbon on earth is Oceans (71% dissolved carbon)

Organisms and Populations Class 12 Important Questions and Answers Biology Chapter 11

Organisms And Populations Question And Answers

Question 1. List the attributes that populations possess but not individuals.

The attributes that populations but not individuals possess are:

  1. Population density
  2. Mortality or death rate
  3. Population growth
  4. Natality or birth rate
  5. Age distribution
  6. Sex ratio

Question 2. If a population growing exponentially doubles in size in 3 years, what is the intrinsic rate of increase (r) of the population?

t = \(\frac{\log ^2 N}{r}\)

r= \(\frac{\log ^2 N}{t}\)

= \(\frac{0.7931}{3}\)

= 0.2643

The intrinsic rate of increase 0.2643 * 100 = 26.43%

Question 3. Name important defence mechanisms in plants against herbivory.

Leaves modified into thorns, development of spiny margins on the leaves. Many plants produce and store chemicals that make the herbivore sick

Example: Calotripis produces highly poisonous cardiac glycosides. Some other chemical substances like nicotine, quinine, opium, etc are produced by plants and provide defence against grazing animals.

Question 4. An orchid plant is growing on the branch of the mango tree. How do you describe this interaction between the orchid and the mango tree?

The interaction between an orchid and the mango tree is commensalism because the orchid is benefited from getting shelter from the mango tree whereas the mango tree is neither harmed nor benefited.

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CBSE Class 12 BioIogy Chapter 11 Organisms and Populations Questions And Answers

Question 5. What is the ecological principle behind the biological control method of managing pest insects?

The ecological principle operating in the biological control method of managing pest insects is checking their population through predators and parasites.

Question 6. Define population and community,

Population: Groups of individuals of the same species, which can reproduce among themselves and occupy a particular area in a given time.
Community: Groups of organisms of different species that live in common areas, which are interrelated and interdependent. It is a natural aggregation of plants and animals in the same environment.

Question 7. Define the following terms and give one example for each:

  1. Commensalism
  2. Parasitism
  3. Camouflage
  4. Mutualism
  5. Interspecific competition.


  1. Commensalism: It is an interaction between two different species where one is benefited, and the other remains unaffected.
    • Example: Clownfish and sea anemone. Here, the clownfish gets protection from predators which stay away from the stinging tentacles of anemones but sea anemones do not derive any benefit from fish.
  2. Parasitism: It is an interaction between two organisms in which one is benefited, and the other is harmed, i.e. one organism lives at the cost of another organism.
    • Example: Cuscuta, a parasitic plant that is found growing on hedge plants, does not have chlorophyll and thus derives its nutrition from the host.
  3. Camouflage: It is a phenomenon of blending an organism with the surroundings due to similar colour, marking, and shape to avoid predators.
    • Example: Common tree frog, Giant leaf insect.
  4. Mutualism: Positive interspecific interaction in which members of two different species completely depend on each other for growth and survival.
    • Example: Lichen (association between algae and fungi). Here, fungi help in the absorption of nutrients and water, while the algal partner manufactures food.
  5. Interspecific competition: It is the competition among the members of different species for limited natural resources.
    • Example: The Abingdon tortoise in the Galápagos Islands became extinct within a decade after goats were introduced on the Island, apparently due to the greater browsing efficiency of the goats.

Question 8. With the help of a suitable diagram, describe the logistic population growth curve.

Logistic growth :

  • The resources become limited at a certain point in time, so no population can grow exponentially.
  • This growth is more realistic.
  • The maximum number of individuals of a particular species in a habitat that is allowed by nature is called carrying capacity (K).
  • When N is plotted about time t, the logistic growth shows a sigmoid curve also called Verhulst-Pearl logistic growth.

It is given by the following equation:

⇒ \(\frac{\mathrm{dN}}{\mathrm{dt}}=\mathrm{rN}\left[\frac{\mathrm{K}-\mathrm{N}}{\mathrm{N}}\right]\)


N = population density at time

r = intrinsic rate of natural increase

K = carrying capacity

Organisms And Populations Verhulst Pearl Logistic Growth

The graph shows the lag phase, followed by phases of acceleration and deceleration and finally an asymptote when population density reaches the carrying capacity.

Question 9. Select the statement that explains the best parasitism.

  1. One organism is benefited.
  2. Both organisms benefit.
  3. One organism is benefited, the other is not affected.
  4. One organism is benefited, and another is affected.

Answer: 4. One organism is benefited, and another is affected.

One organism is benefited, and another is affected.

Question 10. List any three important characteristics of a population and explain.

The three important characteristics of a population are as follows:

Population density: The population density of a species is the number of individuals of a species per unit area or volume.

PD= N/S Where – PD = Population density

N = Number of individuals in a region

S = Number of unit areas in a region.

Birth rate: It is expressed as the number of births per 1,000 individuals of pollution per year.

Death rate: It is expressed as the number of deaths per 1,000 individuals of pollution per year.

Biotechnology and its Applications Class 12 Important Questions and Answers Biology Chapter 10

Biotechnology And Its Applications Question And Answers

Question 1. Crystals of Bt toxin produced by some bacteria do not kill the bacteria themselves because-

  1. Bacteria are resistant to the toxin
  2. The toxin is immature;
  3. The toxin is inactive ;
  4. Bacteria enclose toxins in a special sac.

Answer: 3. The toxin is inactive.

Question 2. What are transgenic bacteria? Illustrate using any one example.

The bacteria whose DNA is manipulated, carried, and expressed foreign DNA is called transgenic bacteria.

For example, DNA sequences (A and B chains of human insulin) were introduced into the plasmid of bacteria E.coil. The transgenic bacteria start producing an insulin chain,

Question 3. Compare and contrast the advantages and disadvantages of the production of genetically modified crops.

Advantages of genetically modified crops:

CBSE Class 12 Biology Chapter 10 Biotechnology And Its Applications Advantages Of Crop

Disadvantages of genetically modified crops:

CBSE Class 12 BioIogy Chapter 10 Biotechnology And Its Applications Disadvantages Of Crop

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Question 4. What are Cry proteins? Name an organism that produces it. How has man exploited this protein to his benefit?

Cry protein (crystal protein) is a toxin coded by a gene cry and is poisonous to some insects, thus giving resistant characteristics to the plants.

  • Bacillus thuringiensisproduces Cry protein.
  • Cry protein-producing gene is transferred to the plants to provide resistance against insect larvae.
  • Man has developed several transgenic crops by introducing these genes from bacteria to crop plants such as Bt cotton, Bt corn, etc.

Question 5. What is gene therapy? Illustrate using the example of adenosine deaminase (ADA) deficiency.

Gene therapy is a method which corrects or replaces the defective genes. [IMP.J

  • In 1900, the first clinical gene therapy was given to a 4-year-old girl with adenosine deaminase (ADA) deficiency.
  • This enzyme plays an important role in the functioning of the immune system. This disorder is caused due to the deletion of the gene for adenosine deaminase.
  • In gene therapy, lymphocytes from the blood of the patient are grown in a culture outside the body.
  • A functional ADA cDNA (using a retroviral vector) is then introduced into these lymphocytes, which are returned to the patients. However, as these cells are not immortal, hence the patient requires periodic infusion of such genetically engineered lymphocytes.

CBSE Class 12 BioIogy Chapter 10 Biotechnology And Its Applications Questions And Answers

Question 6. Diagrams magically represent the experimental steps in cloning and expressing a human gene (Say the gene for growth hormone) into bacterium-like

It is possible to produce HGH (human growth hormone) by recombinant DNA technology.

This is represented diagrammatically as follows :

CBSE Class 12 BioIogy Chapter 10 Biotechnology And Its Applications Formation Of Growth Hormone By rDNA Technology

Question 7. Can you suggest a method to remove oil (hydrocarbon) from seeds based on your understanding of rDNA technology and the chemistry of oil?

To remove oil from seeds, the genes responsible for the formation of glycerol or fatty acids need to be identified and removed, which is responsible for this synthesis. So, by rDNA technique, one can obtain oil-less seeds by preventing the synthesis of fats.

Question 8. Find out from the internet what is golden rice.

  • Golden rice is a genetically modified rice that contains p-carotene (provitamin A).
  • This rice is modified to enhance the quantity of vitamin – A in it. It is called golden due to the gold-like color it gets from p – p-carotene.

Question 9. Does our blood have proteases and nucleases?

Blood does not contain proteases and nucleases because their function is to break down proteins and nucleic acids.

Question 10. Consult the internet and find out how to make orally active protein pharmaceuticals. What is the major problem to be encountered?

Orally active protein pharmaceuticals can be made by lining it with a substance that will dissolve after it has passed through the stomach. The major problem encountered is that the stomach enzymes and acids may denature the therapeutic protein and render it ineffective.

Biotechnology: Principles and Processes Class 12 Important Questions and Answers Biology Chapter 9

Biotechnology – Principles And Processes Question And Answers

Question 1. Can you list 10 recombinant proteins which are used in medical practice? Find out where they are used as therapeutics (use the internet)

Biotechnology Principles And Processes Recombinat proteins And Therapeutic uses

Question 2. Make a chart (with diagrammatic representation) showing a restriction enzyme, the substrate the DNA on which it acts, the site at which it cuts DNA, and the product it produces. 

CBSE Class 12 BioIogy Chapter 9 Biotechnology - Principles And Processes Step In Formation Of Recombinant DNA

Question 3. From what you have learned, can you tell whether enzymes are bigger or DNA is bigger in molecular size? How did you know? 

DNA is bigger in molecular size. DNA is made up of sugar, phosphate, and nitrogenous bases. An enzyme is m|de up of only one or few polypeptides. The enzyme is synthesized from a portion of DNA.

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Question 4. What would be the molar concentration of human DNA in a human cell? Consult your teacher.

The molar concentration of human DNA in a human diploid ceil as follows:

  • Total number of chromosomes x 6.023 x 10”
  • 46 x 6.023× 1023
  • 277.06 × 1023 Moles.

Hence, the molar concentration of DNA in each diploid cell in humans is 277.06 × 1023 moles.

CBSE Class 12 Biology Chapter 9 Biotechnology - Principles And Processes Question And Answers

Question 5. Do eukaryotic cells have restriction endonucleases? Justify your answer. 

Eukaryotic cells have no restriction enzymes as the DNA molecules of eukaryotes are heavily methylated. It is present in prokaryotic cells (like bacteria) where these act as defense mechanisms to restrict the growth of bacteriophages.

Question 6. Besides better aeration and mixing properties, what other advantages do stirred-tank bioreactors have over shake flasks?

Shake flask is used for small-scale production but the stirred-tank bioreactors are used for large-scale production of biotechnological products.

The advantages of stirred tank bioreactors over shake flasks are that these facilitate:
  • Temperature control system,
  • pH control system,
  • Foam control system and

Sampling ports from where small, volumes of the cultures can be obtained and tested from time to time.

Question 7. Collect 5 examples of palindromic DNA sequences by consulting your teacher, better try to create a palindromic sequence by following base pair rules.

  1. 5’ GAATTC 3’
    3’ CTTAAG 5’
  2. 5′ GGATCC 3′
    3′ CCTAGG 5‘
  3. 5’ ACTAGT 3′
    3’ TGATCA 5′
  4. 5′ AAGCTT 3′
    3’ TTCGAA 5′
  5. 5’AGGCCT3′
    3’ TCCGGA 5′

Question 8. Can you recall meiosis and indicate at what stage a recombinant DNA is made?

Meiosis is the cell division process of gamete formation. It occurs in two steps – Meiosis-I and Meiosis-II D during the pachytene stage of prophase -I of meiosis-I, crossing over takes place between non-sister chromatids of homologous chromosomes and a recombinant DNA is made.

Question 9. Can you think and answer how a reporter enzyme can be used to monitor the transformation of host cells by foreign DNA in addition to a selectable marker? 

A reporter gene is used to monitor die transformation of host cells by foreign DNA, They act as a selectable marker to determine whether the host cell has taken up the foreign DNA or the foreign gene gets expressed in the cell.

  • Here, the reporter gene is used as a selectable marker to find out the successful uptake of the gene of interest.
  • An example of a reporter gene includes the lac Z gene which encodes 0- galactosidase enzyme.

Question 10. Describe briefly the following:

  1. Origin of replication
  2. Bioreactors
  3. Downstream processing


1. Origin of replication:- It is a DNA sequence that initiates any piece of linked DNA to replicate and is also called on-site. It controls the copy numbers of the linked DNA.

2. Bioreactors:- Bioreactors are vessels of large volumes (100-1000 liters) in which raw materials are biologically converted into specific products.

It provides all die optimal conditions for achieving the desired product by providing optimal growth conditions like temperature, pH, substrates, vitamins and oxygen.
Stirred tank bioreactors are commonly used bioreactors.

A bioreactor has die following components:

CBSE Class 12 BioIogy Chapter 9 Biotechnology - Principles And Processes A bioreactor

3. Downstream processing -All the processes to which a product is subjected to before being marketed as a finished product are called downstream processing.

  • It includes the separation of the product from the reactor.
  • Purification of the product
  • Formulation of the product with suitable preservatives
  • Quality control testing and trials in the case of drugs.

Question 11. Explain briefly.

  1. PCR
  2. Restriction enzymes and DNA
  3. Chitinase


  1. PCR – PCR stands for polymerase chain reaction, which is a method for amplification of small segments of DNA.
  2. Restriction enzymes and DNA– Restriction enzymes are called ‘molecular scissors’ because they cut the helix of DNA at a specific site. DNA is the genetic material, which carries and passes the genetic characteristics or information from one generation to another.
  3. Chitinase – Chitinase is an enzyme that is used to degrade the cell wall of fungi to release its cellular components.

Question 12. Discuss with your teacher and find out how to distinguish between

  1. Plasmid DNA and chromosomal DNA
  2. DNA and RNA
  3. Exonuclease and endonuclease


1. Plasmid DNA and chromosomal DNA

Biotechnology Principles And Processes Plasmid DNA And Chromosomal DNA

2. DNA and RNA

Biotechnology Principles And Processes DNA And RNA

3. Exonuclease and endonuclease

Biotechnology Principles And Processes Exonuclease And Endonuclease

Molecular Basis of Inheritance Class 12 Important Questions and Answers Biology Chapter 5

Molecular Basis Of Inheritance Questions And Answers

Question 1. Group the following as nitrogenous bases and nucleosides: Adenine, Cytidine, Thymine, Guanosine, Uracil, and Cytosine.

Nitrogenous bases-Adenine, Thymine, Uracil, and Cytosine Nucleosides-Cytidine and Guanosine.

Question 2. If a double-stranded DNA has 20 percent cytosine, calculate the percent of adenine in the DNA.

Cytosine 20%, therefore Guanine = 20%

According to Chargaff’s rule,

A+T =100 – (G + C) ‘

A+T =100-40. Since both adenine and thymine are in equal amounts

Thymine = Adenine=60/2=30%

Question 3. If the sequence of one strand of DNA is written as follows:


Write down the sequence of the complementary strand in the 5′ → 3’ direction.



Question 4. If the sequence of the coding strand in a transcription unit is written as follows:


Write down the sequence of niRNA.


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Question 5. Which property of the DNA double helix led Watson and Crick to hypothesize a semi-conservative mode of DNA replication? Explain.

Watson and Crick observed that the two DNA strands are antiparallel, and have opposite polarity. This means that the 5′ phosphate of one strand faces the 3′ hydroxyl group of the other strand and that the 5′ phosphate group of two strands are present in opposite positions. The antiparallel arrangement of two helices allows hydrogen bonding between amino and carbonyl groups of complementary base pairs; This led them to the hypothesis of die semiconservative mode of DNA replication where two strands of DNA first separate from each other followed by copying of each template strand to form DNA molecules each carrying one parental strand and newly synthesized strands.

CBSE Class 12 BioIogy Chapter 5 Molecular Basis Of Inheritance Questions And Answers

Question 6. Depending upon the chemical nature of the template (DNA or RNA) and the nature of nucleic acids synthesized from It (DNA or RNA), list the types of nucleic acid polymerases.

DNA template

  1. DNA polymerase for DNA replication.
  2. RNA polymerase for RNA synthesis or transcription.

RNA template

  1. RNA-dependent RNA polymerase for synthesis of RNA in some RNA viruses.
  2. Reverse transcriptase to synthesize cDNA (complementary DNA) over RNA template.

Question 7. How did Hershey and Chase differentiate between DNA and protein in their experiment while proving that DNA is the genetic material?

Hershey and Chase (1952) conducted experiments in bacteriophages to prove that DNA is the genetic material.


  • Some bacteriophage viruses were grown on a medium that contained radioactive phosphorus (32P) and some in another medium with radioactive sulfur (35S),
  • Viruses grown in the presence of radioactive phosphorus (32P) contained radioactive DNA.
  • Similar viruses grown in the presence of radioactive sulphur (35S) contained radioactive problems.
  • Both the radioactive virus types were allowed to infect Exoli separately.
  • Soon after infection, dead bacterial cells were gently agitated in a blender to remove viral coats from the bacteria.
  • The culture was also centrifuged to separate the viral particle from the dead bacteria cell.

Observation and Conclusions:-

  • Only radioactive (32P) was found to be associated with a bacterial cell, whereas radioactive (35S) was only found in the surrounding medium and not in the bacterial cell.
  • This indicates that only DNA and not the protein coat entered the bacterial cell.
  • This proves that DNA is the genetic material that is passed from vims to bacteria and not protein.

Molecular Basis Of Inheritance The Hershey Chase Experiment

Question 8. Differentiate between the following; 

  1. Repetitive DNA and satellite DNA
  2. mRNA and tRNA
  3. Template strand and coding strand


1. Repetitive DNA and satellite DNA

Molecular Basis Of Inheritance Repetitive DNA And Satellite DNA

2. mRNA and tRNA

Molecular Basis Of Inheritance Repetitive mRNA And tRNA

3. Template strand and coding strand

Molecular Basis Of Inheritance Repetitive Template Strand And Coding Strand

Question 9. List two essential roles of the ribosome during translation.

Two essential roles of the ribosome during translation are:

  1. One of the rRNA (23S in prokaryotes) acts as a peptidyl transferase ribozyme for the formation of peptide bonds
  2. Ribosome provides sites for attachment of mRNA and charged (RNAs for polypeptide synthesis)

Question 10. In the medium where E.coliwas growing, lactose was added, which induced the Sac operon. Then, why does the lac operon shut down sometime after adding lactose to the medium?

This is because the repressor protein binds to the operator region of the operon and prevents RNA polymerase from transcribing the operon.

Question 11. Explain (in one or two lines) the function of the following:

  1. Promoter
  2. tRNA
  3. Exons


  1. Promoter: It is the segment of DNA that lies adjacent to the operator and functions as the binding site for RNA polymerase to carry transcription if allowed by an operator.
  2. RNA: It acts as an adaptor molecule that picks up a particular amino acid from cellular poll and takes the same over to site A of mRNA for incorporation into a polypeptide chain.
  3. Exons: These are die-coding segments present in the primary transcript, which after splicing join to form functional mRNA.

Question 12. Why is the Human Genome Project called a mega project?

The Human Genome Project is called a mega project for the following reasons:

  • Sequencing of more than 3 x 109 bp.
  • Identification of all the approximately 20,000-25000 genes in human DNA.
  • High expenditure of more than 9 billion US dollars
  • Identification of all die alleles of genes and their functions.
  • Storage of data for sequencing would require space equal to 3300 books of 1000 pages each if each page contains 1000 letters. ‘

Question 13. What is DNA fingerprinting? Mention its application.

DNA fingerprinting is a die technique to determine die relationship by studying the similarity and dissimilarity of VNTR (variable number of tandem repeats), its applications are:

  • It is used as a tool in forensic tests to identify criminals.
  • To settle paternity disputes.
  • To identify racial groups to study biological evolution.

Question 14. Briefly describe the following:

  1. Transcription
  2. Polymorphism
  3. Translation
  4. Bioinformatics


1. Transcription: It is the formation of RNA over the template of DNA. It forms single-stranded RNA which has coded information similar to the sense or coding strand of DNA, except that thymine is replaced by uracil.

2. Polymorphism: Genetic polymorphism means the occurrence of genetic material in more than one form. It is of two major types, i.e. allelic polymorphism and SNP.

    • Allelic polymorphism: Allelic polymorphism occurs due to multiple alleles of a gene Alleles possess different mutations that alter the structure and function of a protein formed by, as a result, a change in phenotype may occur.
    • SNP or single nucleotide polymorphism: Over 1.4 million single-base DNA differences have been observed in human beings. According to SNP, every human being is unique. SNP is very useful for locating alleles, identifying disease-associated sequences, and tracing human history.

3. Translation: It is a dying process during which the genetic information stored in the sequence of nucleotides in mRNA molecules is converted following the direction of the genetic code into a die sequence of amino acids in the polypeptide. It takes place in the cytoplasm in both eukaryotes and prokaryotes.

4. Bioinformatics: The science that deals with handling, and storing huge information of genomics as databases, analysing, modelling, and providing various aspects of biological information especially the molecules connected with genomics and proteomics is called bioinformatics.

Microbes in Human Welfare Class 12 Important Questions and Answers Biology Chapter 8

Microbes In Human Welfare Question And Answers

Question 1. Bacteria cannot be seen with the naked eye, but these can be seen with the help of a microscope. If you have to carry a sample from your home to your biology laboratory to demonstrate the presence of microbes with the help of a microscope, which sample would you Carry and why?

The most common household product that we would like to carry is curd which is common in Lactic acid bacteria (Lactobacillus sp.).

Question 2. Give examples to prove that microbes release gases during metabolism.

The puffed-up appearance of dough is used for making dosa, idli, and bread due to gas production.

  • Methanogens (bacteria) in the biogas plant produce methane and carbon dioxide.
  • Also large holes in the ‘Swiss cheese’ are due to the production of a large amount of CO2 during its production.

Question 3. In which food would you find lactic acid bacteria? Mention some of their useful applications.

The lactic acid bacteria (LAB) are found in curd.

  • LAB converts the lactose sugar of milk into lactic acid.
  • Lactic acid coagulates the milk protein called casein.
  • It also increases the nutritional quality of curd as the curd contains vitamin B12 along with other vitamins. They also check the growth of other harmful microbes.

Question 4. Name some traditional Indian foods made of wheat, rice, and Bengal gram (or their products) that involve the use of microbes.

‘Dosa’ and ‘idli’ (from rice), bread (from wheat), and ‘dhokla’ (from Bengal gram) are traditional Indian foods that involve the use of microbes.

Read and Learn More Class 12 Biology Chapter Wise

CBSE Class 12 BioIogy Chapter 8 Microbes In Human Welfare Questions And Answers

Question 5. In which way have microbes played a major role in controlling diseases caused by harmful bacteria?

The major role of microbes in controlling diseases is ‘antibiotic production, Antibiotics have been used against pathogenic bacteria, for example, penicillin from streptomycin from Streptomyces griseus, etc.

Question 6. Name any two species of fungus, which are used in the production of antibiotics.

  1. Penicillium notatum (for penicillin production).
  2. Aspergilus fumigatus(for fumagillin production).

Question 7. What is sewage? In which way can sewage be harmful to us?

Sewage is the municipal waste water containing large quantities of human excreta and other organic wastes.

  1. Sewage could be harmful to us as it contains many pathogenic microbes and produces a foul smell. It is the cause of many water-borne diseases.
  2. It is also the cause of the eutrophication of water bodies thereby killing many aquatic organisms.

Question 8. What is the key difference between primary and secondary sewage treatment?

The key difference between primary and secondary treatment of sewage is that primary treatment
is the physical process of removing grit and floating debris while secondary treatment is a biological process that involves digestion of organic matter by microbes.

Question 9. Do you think microbes can also be used as a source of energy? If yes, how?

Yes, microbes can be used to produce energy indirectly.

Methanogens (bacteria) like Methanobacterium are involved in the production of biogas which is used as a source of energy.

Question 10. Microbes can be used to decrease the use of chemical fertilizers and pesticides. Explain how this can be accomplished.

Microbes can be used both as fertilizers and pesticides called biofertilizers and biopesticides respectively.

  • Microbes are used as biofertilizers to enrich the soil nutrients, eg Rhizobium, Azotobacter, Azospirillum, etc. which can fix atmospheric nitrogen in the soil.
  • Bacillus thuringiensis bacteria act as biopesticides to control the growth of insect pests.
  • Trichoderma, a fungal species, is an effective biocontrol agent for several plant pathogens.
  • Baculoviruses used as control agents in the genus are excellent for species-specific, narrow-spectrum insecticidal applications.

Question 11. Three water samples namely river water, untreated sewage water, and secondary effluent discharged from a sewage treatment plant were subjected to the BOD test The samples were labeled A, B, and C; but the laboratory attendant did not note which was which. The BOD values of the three samples A, B, and C were recorded as 20 mg/L, 8 mg/1., and 400 mg/L, respectively. Which sample of the water is most polluted? Can you assign the correct label to each assuming the river water is relatively clean?

Sample C is the most polluted (Highest BOD).

Sample A-River water

Sample B- Secondary effluent (Least BOD)

Sample C- Untreated sewage (Highest BOD)

Question 12. Find out the name of the microbes from which cyclosporin A (an immunosuppressive drug) and statins (blood cholesterol lowering agents) are obtained.

  1. Cyclosporin A is obtained from Trichoderma polysporum.
  2. Statins are obtained from the yeast Monascus purpureus.

Question 13. Find out the role of microbes in the following and discuss it with your teacher.

  1. Single-cell protein (SCP)
  2. Soil


1. Single-cell protein (SCP): It is a protein-rich microbial biomass that can be used as food. Microbes are being grown on an industrial scale as a source of good protein. For example, Blue-green algae like Spirulina

  • Methylophilus methylotrophic bacteria
  • Mushrooms

2. Soil: Soil is the habitat of numerous microbes. Microbes in the soil increase the fertility of soil by decomposing organic matter. Some microbes convert nitrates into free nitrogen that escapes into the atmosphere for replenishment.

Question 14. Arrange the following in the decreasing order (most important first) of their importance, for the welfare of human society. Give reasons for your answer.

  1. Penicillin
  2. Biogas
  3. Curd
  4. Citric acid.
    1. Penicillin:- It is an antibiotic used in curing numerous bacterial diseases.
    2. Biogas:- It is a source of energy in rural areas, produced by anaerobic degradation of organic matter
    3. Curd:- It is a vitamin-rich milk preparation that is easily digested.
    4. Citric acid:- It is an organic acid used as a preservative in juices, jams jellies, etc.

Question 15. How do biofertilizers enrich the fertility of the soil?

Biofertilizers are microorganisms that bring about nutrient enrichment of soil by enhancing the availability of nutrients to crops. They are of the following types:

  1. Nitrogen-fixing bacteria and cyanobacteria- They form symbiotic associations with plants. They get food and shelter from plants and on the other hand, plants get nitrogen fixed by these bacteria. For example Rhizobium and A nabena.
  2. Mycorrhiza: It is an association between a fungus and the roots of higher plants. It takes pan in the solubilization and absorption of nutrients from organic matter. Many members of the genus Glomus form mycorrhiza.
  3. Manures: They are semi-decayed organic remains of various types-manure, green manure compost, and vermicompost.

Human Health and Disease Class 12 Important Questions and Answers Biology Chapter 7

Human Health And Disease Question And Answers

Question 1. What are the various public health measures, which you would suggest as safeguards against infectious diseases?

A few of the public health measures as a safeguard against infectious diseases are :

  • Proper disposal of waste and excreta
  • Periodic cleaning and disinfection of water reservoirs, pools, cesspools, and tanks
  • Observing standard practices of hygiene in public catering

Question 2. In which way has the study of biology helped us to control infectious diseases?

The advancements made in biological science have armed us to effectively deal with many infectious diseases.

  • The use of vaccines and immunization programs has enabled us to completely eradicate a deadly disease like smallpox and to control other infectious diseases like polio, diphtheria, pneumonia, and tetanus to a large extent.
  • Biotechnology is on the verge of making available newer and safer vaccines.
  • The discovery of antibiotics and various other drugs has also enabled us to effectively treat infectious diseases.

Question 3. How does the transmission of each of the following diseases take place?

  1. Amoebiasis
  2. Malaria
  3. Ascariasis
  4. Pneumonia


  1. Amoebiasis:- Houseflies act as mechanical carriers and serve to transmit the pathogen (Entamoeba histolytica) from the feces of infected persons to food and food products, thereby contaminating them. Drinking water and food contaminated by fecal matter are the main sources of infection.
  2. Malaria:- Malaria is transmitted to a healthy person with the bite of an infected female Anopheles mosquito. The female mosquito is the vector (transmitting agent) for
    the pathogen (Plasmodium).
  3. Ascariasis:- The eggs of the pathogen are excreted along with the feces of infected persons which contaminate soil, water, plants, etc. A healthy person acquires this
  4. Pneumonia:- A healthy person acquires the infection by inhaling the droplets/aerosol released by an infected person or even by sharing glasses and utensils with an infected person.

CBSE Class 12 BioIogy Chapter 7 Human Health And Disease Questions And Answers

Read and Learn More Class 12 Biology Chapter Wise

Question 4. What measures would you take to prevent water-borne diseases?

Measures particularly essential to prevent water-borne diseases are:

  • Maintenance of personal hygiene by :
  • Keeping the body clean
  • Consumption of clean drinking water, food, vegetables, fruits, etc

Maintenance of public hygiene by :

  • Proper disposal of waste and excreta
  • Periodic cleaning and disinfection of water reservoirs, pools, cesspools and tanks
  • Observing standard practices of hygiene in public catering

Question 5. Discuss with your teacher what ‘a suitable gene’ means, in the context of DNA vaccines.

‘A suitable gene’ means that a disease-resistant gene present in the genome of lower organisms. By the technique of genetic engineering, this ‘suitable gene’ is transferred into a vaccine to inject into human beings to induce the development of immunity.

Question 6. Name the primary and secondary lymphoid organs.

Primary lymphoid organs – Bone Marrow, Thymus gland.

Secondary lymphoid organs – Spleen, Lymph nodes, Tonsils, Peyer’s patches of small intestine, Appendix.

Question 7. The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its full form:

  1. MALT
  2. CMI
  3. AIDS
  4. NACO
  5. HIV


  1. MALT = Mucosa Associated Lymphoid Tissue
  2. CMI = Cell-Mediated Immunity
  3. AIDS = Acquired Immuno Deficiency Syndrome
  4. NACO = National AIDS Control Organisation
  5. HIV = Human Immunodeficiency Virus

Question 8. Differentiate the following and give examples of each:

  1. Innate and acquired immunity
  2. Active and passive immunity


Difference Between Innate Immunity and Acquired Immunity

Human Health And Disease Difference Between Innate Immunity And Acquired Immunity


Difference Between Active Immunity And Passive Immunity

Human Health And Disease Differene Between Active Immunity And Passive Immunity

Question 9. Draw a well-labeled diagram of an antibody molecule.

Human Health And Disease Structure Of Antibody Molecule

Question 10. What are the various routes by which transmission of the human immune deficiency virus takes place?

Transmission of HIV infection generally occurs :

  • Sexual contact with an infected person
  • By transfusion of contaminated blood and blood products
  • By sharing infected needles as in the case of intravenous drug abusers From an infected mother to her child through the placenta

Question 11. What is the mechanism by which the AIDS virus causes a deficiency of the immune system of the infected person?

HIV enters into helper T-lymphocytes and produces progeny viruses. The progeny viruses released in the blood attack other helper T-lymphocytes. This is repeated, leading to a progressive decrease in the number of helper T-lymphocytes in the body of the infected person. Due to a progressive decrease in the number of helper T-lymphocytes, the person becomes immunodeficient.

Question 12. How is a cancerous cell different from a normal cell?

CBSE Class 12 BioIogy Chapter 7 Human Health And Disease Normal Cell

Question 13. Explain what is meant by metastasis.

Cells sloughed from such tumors reach distant sites through blood and wherever they get lodged in the body & they start a new tumor there. This property called metastasis is the most feared property of malignant tumors.

Question 14. List the harmful effects caused by alcohol/drug abuse.

A few of the harmful effects caused by alcohol/drug abuse are :

  • Immediate adverse effects of drug and alcohol abuse are reckless behavior, vandalism, violence, etc.
  • Excessive doses of drugs may lead to coma, death due to respiratory failure, heart failure, or cerebral hemorrhage.
  • A combination of drugs or their intake along with alcohol generally results in overdosing and even death.
  • The chronic use of drugs and alcohol damages the nervous system and liver (cirrhosis). of The use of drugs and alcohol during pregnancy is also known to adversely affect the fetus.

Question 15. Do you think that friends can influence one to take alcohol/drugs? If yes, how may one protect himself/herself from such an influence?

One of the reasons for alcohol drinking or dating abuse is peer pressure, so one can be easily influenced by one’s friends to take alcohol /drugs. One must avoid undue peer pressure with one’s willpower or may seek the help of one’s parents and teachers.

Question 16. Why is it that once a person starts taking alcohol or drugs, it is difficult to get rid of this habit? Discuss it with your teacher.

Use of alcohol or drugs even once can be a forerunner to addiction. Thus, the addictive potential of drugs and alcohol pulls the user into a vicious circle leading to their regular use (abuse) from which the person may not be able to get out. In the absence of any guidance or counseling, the person gets addicted and becomes dependent on their use. Dependence is the tendency of the body to manifest a characteristic and unpleasant withdrawal syndrome if the regular dose of drugs/alcohol is abruptly discontinued. This is characterized by anxiety, shakiness, nausea, and sweating, which may be relieved when use is resumed again.
In some cases, withdrawal symptoms can be severe and even life-threatening and the person may need medical supervision.

Question 17.In your view what motivates youngsters to take to alcohol or drugs and how can this be avoided? 

Causes for motivation among youngsters towards alcohol or drug use include:

  • Natural curiosity
  • Need for adventure and excitement Experimentation
  • The perception that it is ‘cool’ or progressive to smoke use drugs or alcohol
  • To escape facing problems (like stress, from pressures to excel in academics or examinations)
  • unstable or unsupportive family structures, and peer pressure

And Measures particularly useful to avoid alcohol or drug abuse among youngsters include:

  • Avoid undue peer pressure
  • Education and counseling
  • Seeking help from parents and peers
  • Looking for danger signs
  • Seeking professional and medical help

Evolution Class 12 Important Questions and Answers Biology Chapter 6

Evolution Question And Answers

Question 1. Explain antibiotic resistance observed in bacteria in light of Darwinian selection theory.

Darwinian selection theory states that individuals with favorable variations are better adapted than individuals with a less favorable variation.

  • It means that nature selects the individuals with useful variation as these individuals are better evolved to survive in the existing environment. An example of such selection is antibiotic resistance in bacteria. When the bacterial population was grown on an agar plate containing antibiotic penicillin, the colonies that were sensitive to penicillin died, whereas one or a few bacterial colonies that were resistant to penicillin survived.
  • This is because these bacteria had undergone chance mutation, which resulted in the evolution of a gene that made them resistant to the penicillin drug. Hence, the resistant bacteria multiplied quickly as compared to nonresistant (sensitive) bacteria, thereby increasing their number. Hence, the advantage of an individual over another helps in the struggle for existence.

Question 2. Find out from newspapers and popular science articles any new fossil discoveries or controversies about evolution.

A recent study of fossils revealed a small terrestrial dinosaur with feathers covering the limb and body. This finding established that feathers evolved earlier than wings and may be functioning as thermoregulators to face adverse conditions. This newly developed feather earlier helped in gliding and then flying

Read and Learn More Class 12 Biology Chapter Wise

Question 3. Attempt to give a clear definition of the term species.

Species can be defined as a group of organisms that have the capability to that can interbreed to produce fertile offspring.

Question 4. Try to trace the various components of human evolution.

Evolution Various Components Of human Evolution

Question 5. Find out through the internet and popular science articles whether animals other than man have self-consciousness.

There are many animals other than humans, which have self-consciousness. An example of an animal being self-conscious is a dolphin. They are highly intelligent They have a sense of self and they also recognize others among themselves and others. They communicate with each other by whistles, tail-slapping, and other body movements. Not only dolphins there are certain other animals such as crow, parrot, chimpanzee, gorilla, orangutan, etc., which exhibit self-consciousness.

Question 6. List 10 modern-day animals and using the internet resources link it to a corresponding ancient fossil. Name both.

Evolution Modern Animals


Question 7. Describe one example of adaptive radiation.

Darwin’s finches on Galapagos Island once had a common ancestor but with evolution, they modified into different types according to their food habitat.

CBSE Class 12 BioIogy Chapter 12 Evolution Questions And Answers

Question 8. Can we call human evolution adaptive radiation?

No, human evolution cannot be called adaptive radiation because parent species of sapiens have evolved by progressive evolution from Homo habilis to Homo sapiens lineage.

Question 9. Using various resources such as your school library or the internet and discussions with your teacher, trace the evolutionary stages of any one animal, say a horse. 

CBSE Class 12 BioIogy Chapter 12 Evolution Horse Evolution

The evolution of the horse is represented as follows:

  1. Eohippus:- This stage is characterized by a short head and neck. It had four functional toes, a splint of 1 to 5 on each hind limb and a splint of 1 to 3 in each forelimb. The molars were short crowned that was adapted for grinding the plant dies.
  2. Mesohippus:- It was slightly taller than Eoliippus. It had three toes in each foot
  3. Merychippus:- it had a size of approximately 100 cm. Although it still has three toes in each foot, it could run on one toe. The side toe did not touch the ground. The molars were adapted for chewing the grass.
  4. Pliohippus:- It resembled the modem horse and was around 120 cm tall. It had a single functional toe with splints of second and fourth in each limb,
  5. Equus:- Pliohippus gave rise to Equus or the modem horse with one toe in each foot. They have incisors for cutting grass and molars for grinding food.

Principles of Inheritance and Variation Class 12 Important Questions and Answers Biology Chapter 4

Principles Of Inheritance And Variation Questions And Answers

Question 1. Mention the advantages of selecting a pea plant for the experiment by Mendel.

  • Annual plant with short life cycle of 2–3 months.
  • It has many contrasting traits.
  • Pea seeds are large.
  • Easy to cultivate.
  • Pea plants are naturally self-pollinating.
  • Artificial cross-pollination can be easily performed.

Question 2. Differentiate between the following.

  1. Dominance and Recessive.
  2. Homozygous and Heterozygous.
  3. Monohybrid and Dihybrid.


1. Dominance and Recessive:

Read and Learn More Class 12 Biology Chapter Wise

Principles Of Inheritance And Variation Difference Between Dominance And Recessive

2. Homozygous and Heterozygous:

Principles Of Inheritance And Variation Diffrence Between Homozygous And Heterozygous

3. Monohybrid and Dihybrid:

Principles Of Inheritance And Variation Diffrence Between Monohybrid And Dihybrid

Question 3. A diploid organism is heterozygous for 4 loci, how many types of gametes can be produced?

A diploid organism heterozygous for 4 loci, will have four different contrasting characters at four different loci.

For example, if an organism is heterozygous at four loci with four characters, say AaBbCcDd then during meiosis it will segregate to form 16 separate gametes.

Type of gamete = 2“ where n is no of heterozygous pair

Son = 4 so24 so 16 gametes.

CBSE Class 12 BioIogy Chapter 4 Principles Of Inheritance And Variation Questions And Answers

Question 4. Explain the Law of Dominance using a monohybrid cross.

When two different factors (genes) or a pair of contrasting forms of a character are present in an organism, only one expresses itself in the Fi generation and is termed dominant while the other remains unexpressed and is called a recessive factor (gene).

Question 5. Define a test-cross.

When an individual is crossed with the homozygous recessive parent. It is called test cross

6. Using a Punnett Square, work the distribution of phenotypic features in the first filial generation after a cross between a homozygous female and a heterozygous male for a single

Principles Of Inheritance And Variation Phenotypic Features

Question 7. When a cross is made between a tall plant with yellow seeds (TtYy) and a tall plant with green seeds (Ttyy), what proportions of phenotype in the offspring could be expected to be Tall and green Dwarf and green.

Tall & Yellow Seeds Tall & Green Seeds:

Principles Of Inheritance And Variation Proportions Of Phenotype

  1. Tall and green : 3
  2. Dwarf and green: 1

Question 8. Two heterozygous parents are crossed. If the two loci are linked, what would be the distribution of phenotypic features in Fi generation for a dihybrid cross?

The co-existence of two or more genes in the same chromosome is termed as linkage. If the genes are located close to each other and on the same chromosome, they are inherited together and are referred to as linked genes. If two heterozygous parents exhibit linkage, then the outcome is as follows:

BbLl x BbLl

Blue long Blue long

So in the F1 generation, the parental combination will comparatively be more than the newer combinations, which are less in number.

Question 9. Briefly mention the contribution of T.H. Morgan in genetics.

Thomas Hunt Morgan is called the father of experimental genetics.

  • Experimental verification of the chromosomal theory of inheritance was given by Thomas Hunt Morgan and his colleagues, which led to the discovery of the basis for the variation that sexual reproduction produced.
  • Morgan worked with the tiny fruit files, Dr were found very Drosophila melanogaster which were found very suitable for such studies.
  • Morgan carried out several dihybrid crosses in Drosophila to study genes that were sex-linked.
  • He stated and established that genes are located on the chromosome.
  • He established the principle of linkage, crossing over, and sex-linked inheritance and discovered the relationship between genes and chromosomes.
  • He established the technique of chromosome mapping.

Question 10. What is pedigree analysis? Suggest how such an analysis, can be useful.

A pedigree is a record of inheritance of a specific genetic trait for two or more generations which is presented in the form of a diagram or family tree. Pedigree analysis is an analysis of several generations of a family which is used on human beings.

The usefulness of pedigree analysis:

  • Serves as a powerful tool which can be used to trace the inheritance of a particular trait, disease or abnormality
  • It is helpful for genetic counsellors to suggest to couple the possibility of having children with genetic abnormalities such as colour blindness, Haemophilia, thalassemia, sickle-cell anaemia etc
  • Helpful in reasoning why marriage between close relatives is harmful.

Question 11. How is sex determined in human beings?

Sex determination in humans is done by the XX-XY type method. In humans, females have XX chromosomes and males have two different types of sex chromosomes (XY).

Principles Of Inheritance And Variation Sex Determined In Human Being

Male progeny 50% female progeny – 50%

Question 12. A child has blood group O. If the father has blood group A and the mother’s blood group B, work out the genotypes of the parents and the possible genotypes of the other offspring.

Principles Of Inheritance And Variation Genotype Of The parents

The possible genotype of other offspring – IAIB, IAI°, IB1°, I°I°

Question 13. Explain the following terms with examples.

  1. Co-dominance
  2. Incomplete dominance


  1. Co-dominance: In this phenomenon, both the alleles can express themselves independently when found together in a heterozygote. They are termed as co-dominant alleles. E.g., – ABO blood group
  2. Incomplete dominance: Incomplete dominance may be defined as the partial /expression of both alleles in a heterozygote so that the phenotype is intermediate between those of two homozygotes.


  1. Flower colours of Mirabilis jalapa (4 o’clock plant)
  2. Snapdragon

Question 14. What b point mutation? Give one example.

Mutations arising due to changes in a single base pair of DNA are called point mutations.

Example: sickle cell anaemia.

Question 15. Who proposed the chromosomal theory of inheritance?

In 1902 the chromosomal theory of inheritance was proposed by Theodore Boveri and Walter Sutton.

Question 16. Mention any two autosomal genetic disorders with their symptoms.

Sickle cell anaemia


  • The shape of RBCs changes from biconcave to sickle-shaped(curved) under the influence of low oxygen tension.
  • These sickle-shaped RBCs are more rapidly destructed than the normal ones, causing anaemia Phenylketonuria:-
  • This inborn error of metabolism is also inherited as the autosomal recessive trait. The affected individual lacks an enzyme that converts the amino acid phenylalanine into tyrosine. As a result of this phenylalanine is accumulated and converted into phenyl pyruvic acid and other derivatives.


  • Accumulation of these in the brain results in mental retardation. These are also excreted through urine because of their poor absorption by the kidneys.