NCERT Exemplar for Class 12 Biology Chapter-7 (Book Solutions)

Exercise

Multiple Choice Questions

1. Which of the following is used as an atmospheric pollution indicator?

(a) Lepidoptera

(b) Lichens

(c) Lycopersicon

(d) Lycopodium

Ans: (b) Lichens

2. The theory of spontaneous generation stated that:

(a) life arose from living forms only

(b) life can arise from both living and nonliving

(c) life can arise from non-living things only.

(d) life arises spontaneously, neither from living nor from the non-living.

Ans: (c) life can arise from non-living things only.

3. Animal husbandry and plant breeding programmes are examples of:

(a) reverse evolution

(b) artificial selection

(c) mutation

(d) natural selection

Ans: (b) artificial selection

4. Palaeontological evidences for evolution refer to the:

(a) development of embryo

(b) homologous organs

(c) fossils

(d) analogous organs

Ans: (c) fossils

5. The bones of forelimbs of whale, bat, cheetah, and man are similar in structure, because:

(a) one organism has given rise to another

(b) they share a common ancestor

(c) they perform the same function

(d) they have biochemical similarities

Ans: (b) they share a common ancestor

6. Analogous organs arise due to:

(a) divergent evolution

(b) artificial selection

(c) genetic drift

(d) convergent evolution

Ans: (d) convergent evolution

7. (p+q)2 = p2 + 2pq + q2 = 1 represents an equation used in:

(a) population genetics

(b) mendelian genetics

(c) biometrics

(d) molecular genetics

Ans: (a) population genetics

8. Appearance of antibiotic-resistant bacteria is an example of:

(a) adaptive radiation

(b) transduction

(c) pre-existing variation in the population

(d) divergent evolution

Ans: (c) pre-existing variation in the population

9. Evolution of life shows that life forms had a trend of moving from:

(a) land to water

(b) dryland to wetland

(c) freshwater to seawater

(d) water to land

Ans:  (d) water to land

10. Viviparity is considered to be more evolved because:

(a) the young ones are left on their own

(b) the young ones are protected by a thick shell

(c) the young ones are protected inside the mother's body and are

looked after they are born leading to more chances of survival

(d) the embryo takes a long time to develop

Ans: (c) the young ones are protected inside the mother's body and are looked after they are born leading to more chances of survival

Explanation: In viviparity, the young ones are protected inside the mother's body and are looked at after after they are born leading to more chances of survival.

11. Fossils are generally found in:

(a) Sedimentary rocks

(b) Igneous rocks

(c) Metamorphic rocks

(d) Any type of rock

Ans: (a) Sedimentary rocks

Explanation: Sedimentary rocks are formed over time and have less pressure and heat than metamorphic and igneous rocks enabling the preservation of fossils. 

12. For the MN-blood group system, the frequencies of M and N alleles are 0.7 and 0.3, respectively. The expected frequency of MN-blood group bearing organisms is likely to be

(a) 42%

(b) 49%

(c) 9%

(d) 58%

Ans: (a) 42%

Explanation:  Hardy Weinberg’s Principle states, the allele frequency in a population remains constant and it is shown through a binomial expansion of (p+q)2.

i.e.  (p+q)2 = p2 +q2 +2pq =1

M=0.7 =p ,  N= 0.3 =q

(M+N)2 = (0.7)2 +(0.3)2 +2.0.7 x 0.3 +(0.3)2

= 0.49 +0.09 + 0.42

Frequency of MN = 2pq= 2 MN = 0.42 = 42 %

Therefore, the expected frequency of MN blood group is 42%.

13. Which type of selection explains industrial melanism observed in moth, Biston betularia:

(a) Stabilising

(b) Directional

(c) Disruptive

(d) Artificial

Ans: (b) Directional

Explanation: In directional selection size of the population changes, the population changes towards one specific direction.

14. The most accepted line of descent in human evolution is:

(a) Australopithecus - Ramapithecus - Homo sapiens - Homo habilis

(b) Homo erectus - Homo habilis - Homo sapiens

(c) Ramapithecus - Homo habilis - Homo erectus - Homo sapiens

(d) Australopithecus - Ramapithecus - Homo erectus - Homo habilis - Homo sapiens.

Ans: (c) Ramapithecus - Homo habilis - Homo erectus - Homo sapiens

Explanation: Human evolution started from Ramapithecus about 14-15 million years ago. Then about 2 million years ago Homo habilis appeared. Then the Homo erectus and around 10,000 years ago modern man appeared.

15. Which of the following is an example for link species?

(a) Lobe fish

(b) Dodo bird

(c) Seaweed

(d) Chimpanzee

Ans: (a) Lobe fish

Explanation: Lobe fish belongs to bony fishes, and show characters from other two groups of animals, therefore they are considered link species.

16. Match the scientists listed under column ‘I’ with ideas listed in column ‘II’.

(a) A-i; B-iv; C-ii; D-iii

(b) A-iv; B-i; C-ii; D-iii

(c) A-ii; B-iv; C-iii; D-i

(d) A-iv; B-iii; C-ii; D-i

Ans: (b) A-iv; B-i; C-ii; D-iii

17. In 1953 S. L. Miller created primitive earth conditions in the laboratory and gave experimental evidence for the origin of the first form of life from preexisting non-living organic molecules. The primitive earth conditions created include:

(a) low temperature, volcanic storms, an atmosphere rich in oxygen

(b) low temperature, volcanic storms, reducing atmosphere

(c) high temperature, volcanic storms, non-reducing atmosphere

(d) high temperature, volcanic storms, reducing atmosphere

containing CH4, NH3 et(c)

Ans: (d) high temperature, volcanic storms, reducing atmosphere

containing CH4, NH3 et(c)

18. Variations during mutations of meiotic recombination are:

(a) random and directionless

(b) random and directional

(c) small and directional

(d) random, small, and directional

Ans: (a) random and directionless

Explanation: Mutation is a sudden inheritable change in the DNA. It appears in all directions.

Very Short Answer Type Questions

1. What were the characteristics of life forms that had been fossilized?

Ans: Life forms had some hard parts such as Bones, teeth, etc. which could be fossilized.

2. Did aquatic life forms get fossilized? If, yes where do we come across such fossils?

Ans: Yes, aquatic life forms get fossilized. Many of these fossils have been discovered in oil wells. Many more have been discovered in sedimentary rocks as a result of sedimentation filling up many water bodies.

3. What are we referring to? When we say 'simple organisms' or 'complex organisms'.

Ans: When we say ‘simple organisms’ or ‘complex organisms’ we refer to the complexity of the division of labor, metabolism, and the level of organization in the organisms.  

4. How do we compute the age of a living tree?

Ans: We can compute the age of a tree by counting the number of annual rings or with the help of carbon dating.

5. Give an example for convergent evolution and identify the features towards which they are converging.

Ans:  Flippers of dolphins and penguins are examples of convergent evolution. In both of the organisms, flippers have different origins but perform similar functions.

6. How do we compute the age of a fossil?

Ans: Age of fossil is computed by using carbon dating. The presence of radioactive carbon is calculated to compute the age of a rock.

7. What is the most important precondition for adaptive radiation?

Ans: The most important precondition for radiation is common ancestry.

8. How do we compute the age of a rock?

Ans: The age of the rock is computed by using radiocarbon dating. The presence of radioactive carbon is calculated to compute the age of a rock.

9. When we talk of functional macromolecules (e.g. proteins as enzymes, hormones, receptors, antibodies, etc), what are they evolving?

Ans: Functional macromolecules are evolving towards living forms.

10. In a certain population, the frequency of three genotypes is as follows:

What is the likely frequency of B and b alleles?

Ans:  Frequency of B alleles = BB +\[\frac{1}{2}\] Bb 

= 22%+31%

=53%

Frequency of b alleles =bb+\[\frac{1}{2}\] Bb  

=16%+31%

=47%

11. Among the five factors that are known to affect Hardy-Weinberg equilibrium, three factors are gene flow, genetic drift, and genetic recombination. What are the other two factors?

Ans:  The two factors are: Natural selection and Mutation 

12. What is founder effect?

Ans: There is the loss of genetic variation when a small group of individuals becomes isolated from a larger population.

13. Who among the Dryopithecus and Ramapithecus was more man-like?

Ans: Ramapithecus

14. By what Latin name the first hominid was known?

Ans: Homo habilis 

15. Among Ramapithecus, Australopithecines and Homo habilis - who

probably did not eat meat?

Ans: Homo habilis

Short Answer Type Questions

1. Louis Pasteur’s experiments, if you recall, proved that life can arise from only pre-existing life. Can we correct this as life evolves from pre-existent life or otherwise we will never answer the question as to how the first forms of life arose? Comment.

Ans: Louis Pasteur used a sterile flask and another one that was open to the air. New yeast organisms were developed in a flask that was open to air, but in the sterilized flask yeast did not produce new organisms. This experiment contributed to the rejection of the spontaneous generation theory. Miller’s later experiment, on the other hand, demonstrated that organic molecules may evolve from inorganic molecules, leading to the origin of life. Therefore, we can correct the statement that the first form of life could have arisen from pre-existing non-living organic molecules. 

2. Scientists believe that evolution is gradual. But extinction, part of the evolutionary story, is 'sudden' and 'abrupt' and also group-specific. Comment whether a natural disaster can be the cause for extinction of species.

Ans: Natural disasters such as earthquakes can result in the extinction of species. A majority of scientists believe that a meteor struck the earth, causing widespread destruction and the extinction of dinosaurs.

3. Why is nascent oxygen supported to be toxic to aerobic life forms?

Ans: Nascent oxygen is highly reactive. It can react easily and cause a reaction with a variety of compounds, including DNA and proteins found in cells of aerobic life forms. This may result in Mutations and unfavorable metabolic changes.

4. While the creation and presence of variation is directionless, natural selection is directional as it is in the context of adaptation. Comment.

Ans: Variation continues to appear in each generation. However, because nature may not support such variations, most of them are not retained by the organism. When a new recombinant passes the test of natural selection, then only it is inherited in species through generation to generation. As a result, creation and the presence of variation can be considered to be directionless, but natural selection and adaptation are directional.

5. The evolutionary story of moths in England during industrialization reveals, that 'evolution is apparently reversible'. Clarify this statement.

Ans: In England before industrialization, the white-winged moths were able to thrive because whitish lichens and moss flourished on tree trunks. White-winged moths blended very well and therefore had better chances of survival against the whitish background. But when the industrial revolution started the tree trunks turned dark, Lichens and mosses did not survive. As a result, the population of white-winged moths decreased and the population of white-winged moths increased. Thus, the evolution of white-winged moth reversed due to industrialization. 

6. Comment on the statement that "evolution and natural selections are end result or consequence of some other processes but themselves are not processed".

Ans: It is controversial whether evolution and natural selection are processes in and of themselves, or if they are the end result or consequence of other processes. When we talk about the success of life on Earth, we consider evolution and natural selection to be processed. However, when discussing how life arose from primitive beginnings, evolution and natural selection appear to be the outcomes of other processes. This is still a debatable topic in the scientific community. 

7. State and explain any three factors affecting allele frequency in populations.

Ans: The allele frequency in population can be affected by the following factors:

1. Mutation: Mutation is a sudden inheritable change in the DNA, it leads to the formation of new species and therefore changes in allelic frequency.

2. Natural Selection: Natural selection theory that states, Nature only selects the fittest organisms which survive in changed environmental conditions.

3. Genetic Recombination: The new organism or traits produced that differ from parents is called genetic recombination.

8. Gene flow occurs through generations. Gene flow can occur across language barriers in humans If we have a technique of measuring specific allele frequencies in different populations of the world, can we not predict human migratory patterns in pre-history and history? Do you agree or disagree? Provide an explanation of your answer.

Ans:  Yes, I agree. Gene flow occurs across generations. The project known as  Human Genome Project has used specific genes/chromosomes and mitochondrial DNA to trace the evolutionary history and migratory patterns of humans. Therefore with the help of HGP by studying specific allele frequencies, we can predict the human migratory patterns in prehistory and history. 

9. How do you express the meaning of words like race, breed, cultivars, or variety?

Ans: Race: Race is a group of people that share similar and distinct physical characteristics. Members of different races of the same species can interbreed.

Breed: Breed is a group of animals that are similar in physical appearance.

Cultivars: Cultivar is a selected group of plants that can be propagated through vegetative parts.

Variety: Variety is a taxonomic category that ranks below species level in the plant kingdom.

10. When we say "survival of the fittest", does it mean that (a) those who are fit only survive, or (b) those that survive are called fit? Comment.

Ans: The “survival of the fittest” means the organisms with suitable and useful adaptations survive and reproduce in the varied environmental conditions that are known to be fit.

11. Enumerate the three most characteristic criteria for designating a Mendelian population.

Ans: The three most important criteria for the mendelian population :

1. The population must be sufficiently large

2. The population must have potentialities for the free flow of genetic material among individuals.

3. Migration should be nil or negligible in the population.

12. "Migration may enhance or blur the effects of selection”. Comment.

Ans: Migration can enhance the natural selection process by bringing in alleles and traits within the population. And it can blur the effect of selection by removing the useful traits and genes from the population.

Long Answer Type Questions

1. Name the law that states that the sum of allelic frequencies in a population remains constant. What are the five factors that influence these values?

Ans: Hardy Weinberg Principle, also known as Hardy Weinberg Law.

The law states that the sum of allelic frequencies in a population remains constant from generation to generation in the absence of disturbing factors. 

Hardy Weinberg Equation: (p+q)2 = p2+2pq+q2=1

Where p is the frequency of dominant allele

q is the frequency of recessive allele

p2 is the frequency of  homozygous dominant allele

2pq is the frequency of individuals with heterozygous genotype

q2 is the frequency of individuals with the homozygous recessive allele

The extent of evolutionary change can be evaluated by measuring the difference between the values.

The factors that influence these values are as follows : 

(a) Gene migration or gene flow 

(b) Genetic drift 

(c) Genetic recombination 

(d) Mutation 

(e) Natural selection 

2. Explain divergent evolution in detail. What is the driving force behind it?

Ans: Divergent evolution is when there are two organisms or species having common ancestors but different characteristics due to adaptation. These organisms are in different habitats and share similar anatomical structures but perform different functions. This is known as Divergent evolution. For example, the forelimbs of Whales, bats, Human and Cheetah are similar in structure but they perform different functions. 

Divergent evolution occurs due to the changed environmental conditions. The driving force behind this evolution is an adaptation to a new habitat and altering environmental conditions.

3. You have studied the story of Pepper moths in England Had the industries been removed, what impact could it have on the moth population? Discuss.

Ans:  In England, Two varieties of Pepper moths were present in the population. But before industrialization, the number of White-winged Pepper moths was much higher than the black-winged moths. Colored wings help in camouflage. Therefore they were not spotted by the predators due to their camouflage they blended very well in the moss and lichens-covered tress. 

After the industrial revolution, tree trunks became dark, lichens did not survive. As a result, the black-winged moth population started increasing because the dark tree trunk helped them to camouflage. And the now the white ones were easily spotted and killed by the predators. Again if the industries are removed the population of Black-winged moths will decrease and the population of white-winged moths will increase.

4. What are the key concepts in the evolution theory of Darwin?

Ans: Darwin’s theory of evolution was based on two key concepts:

Branching descent and natural selection.

• Branching descent: This is usually referred to as the “Tree of life”. Every organism originated from a single common ancestor. Every new species is developed by adaptation to new environmental conditions. Ex. Darwin’s finches arose from grain eaters, Australian marsupials evolved from common marsupials.

• As the following diagram shows that the various life forms we see today have evolved from one common ancestor. One branch evolved into fishes, another one evolved into amphibians. The third branch has given rise to various terrestrial animals: reptiles, aves, and mammals. 

• Natural Selection: According to Darwin's theory, only the fittest organisms can survive the changing environmental conditions. Every living trying to cope with the changed environmental conditions by developing certain adaptations. Only those organisms with suitable adaptation are capable of surviving. Therefore, natural selection is an important phenomenon in evolution.

5. Two organisms occupying a particular geographical area (say desert) show similar adaptive strategies. Take examples, describe the phenomenon.

Ans: Two organisms occupying a particular geographical area may show similar adaptive strategies, this phenomenon is known as convergent evolution. This is because both organisms are reacting to the same environmental conditions. 

For Example, Cereus peruvianus and euphorbia virosa, are desert plants and not related to one another.  Both of the species show similar adaptations:

• Stem modification: Fleshy stem, green succulent parts store water and perform the function of photosynthesis.

• Leaf modification: Leaves are modified into spines to reduce water loss.

• Root modification: Roots penetrate deep into the ground to access groundwater.

Analogous organs that are indications of convergent evolution are depicted in these examples.

6. We are told that evolution is a continuing phenomenon for all living things. Are humans also evolving? Justify your answer.

Ans:  Evolution is a continuous process. Microevolution goes on continuously and there are inheritable gradual changes in the organism and its population. 

The evolution process is continuous in human beings also as it takes place in all living beings. All the modern-day organisms are descended from their ancestors.  Modern man Homo sapiens arose from the ancestors that are Ramapithecus, Australopithecus, Homo habilis, Homo erectus, Neanderthal man, Cro-Magnon man, etc.  

• The average human life expectancy has increased, it is almost double the of primitive times. 

• All the other animals develop lactose intolerance in adulthood. Other mammals do not have the facility to consume other mammals’ milk. But human beings can consume milk throughout life and rarely develop lactose intolerance.

• Humans have developed resistance to many infectious diseases.

These are the signs of evolution.  Although evolution can take place through geographical isolation and genetic drift.

7. Had Darwin been aware of Mendel’s work, would he have been able to explain the origin of variations. Discuss.

Ans: Gregor Mendel and Charles Darwin were born in the same era. Darwin was apparently aware of Mendel’s work but could not explain the origins of Variation. Mendel proposed his theories and principles of genetics.  His work was extensively limited to particular species and he put forward laws about the inheritance and variations among the organisms. The parent’s genotype is responsible for offspring’s character has been proved by Mendal through his Pigeon Pea plant experiments. And at the time Darwin seems to ignore the fact that the variation among the population of the organism is due to their genes or alleles. There are many other factors that may change the allele frequency, for example, Mutation, Genetic recombination, genetic drift, etc. So, after many generations, there would be a change in the gene pool, organism’s characteristics, and therefore new forms appear to arise in the population. 

Important Concepts In Evolution

There are many important concepts in the chapter, but the most important ones are mentioned below. You can find notes on these topics in the Vedantu app and can also look up LIVE classes in which professors teach these with brilliance.  

• Origin of Life

• Evolution of Life Forms – A Theory

• What is the Evidence for Evolution?

• What is Adaptive Radiation?

• Biological Evolution

• Mechanism of Evolution

• Hardy – Weinberg Principle

• A Brief Account of Evolution

• Origin and Evolution of Man 

Free PDF download of NCERT Exemplar for Class 12 Biology Chapter 7 - Evolution solved by expert Biology teachers on Vedantu.com as per NCERT (CBSE) Book guidelines is available. All Chapter 7 - Evolution exercise questions with solutions are designed to help you revise the complete syllabus and score more marks in your examinations.