NCERT Exemplar Class 12 Biology Chapter 7 Evolution

In this chapter, we provide NCERT Exemplar Problems Solutions for Class 12 Biology Chapter 7 Evolution for English medium students, Which will very helpful for every student in their exams. Students can download the latest NCERT Exemplar Problems Solutions for Class 12 Biology Chapter 7 Evolution pdf, free NCERT Exemplar Problems Solutions for Class 12 Biology Chapter 7 Evolution book pdf download. Now you will get step by step solution to each question.

TextbookNCERT
ClassClass 12
SubjectBiology
ChapterChapter 7
Chapter NameEvolution
CategoryNCERT Exemplar

NCERT Exemplar Class 12 Biology Chaper 7 Evolution

Multiple Choice Questions
Single Correct Answer Type

1. Which of the following is used as an atmospheric pollution indicator?
(a) Lepidoptera (b) Lichens
(c) Lycopersicon (d) Lycopodium
Answer. (b) Lichens are sensitive to SO2 pollution. Lichens are very good pollution indicators, they do not grow in polluted areas.

2. The theory of spontaneous generation stated that:
(a) Life arose from living forms only
(b) Life can arise from both living and non-living
(c) Life can arise from non-living things only.
(d) Life arises spontaneously, neither from living nor from the non-living.
Answer. (c)

  • For a long time it was also believed that life came out of decaying and rotting matter like straw, mud, etc.
  • According to theory of abiogenesis, life originates from non-living.

3. Animal husbandry and plant breeding programmes are the examples of
(a) Reverse evolution (b) Artificial selection
(c) Mutation (d) Natural selection
Answer. (b) Animal husbandry and plant breeding programmes are the examples of artificial selection.

4. Paleontological evidences for evolution refer to the
(a) Development of embryo (b) Homologous organs
(c) Fossils (d) Analogous organs
Answer. (c) Palaeritological evidences for evolution refer to the fossils. Fossils provide direct and solid evidence in favour of organic evolution through ages. Fossils are studied for knowing about extinct organisms. Birbal Sahni Institute of Palaeobotany is situated at Lucknow. Birbal Sahni is called ‘Father of Indian Palaeobotany’. Age of fossils is determined by Uranium-Lead method (U238) or Potassium-Argon method or Radioactive Carbon dating (C14). ESR (electron-spin-resonance method) is the most accurate method of dating of 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) The have biochemical similarities
Answer. (b) Organs having same origin but different functions are called homologous organs. For example, whales, bats, Cheetah and human (all mammals) share similarities in the pattern of bones of forelimbs. Homology indicates common ancestry.

6. Analogous organs arise due to
(a) Divergent evolution (b) Artificial selection
(c) Genetic drift (d) Convergent evolution
Answer. (d) Organs having different origin but similar function are called analogous. Wings of butterfly and of birds look alike. They are not anatomically similar structures though they perform similar functions. Hence, analogous structures are a result of convergent evolution (different structures evolving for the same function and hence having similarity).

7. (p + q)2= p2 + 2pq + q2 = 1 represents an equation used in
(a) Population genetics (b) Mendelian genetics
(c) Biometrics (d) Molecular genetics
Answer. (a) (p + q)2= p2+ 2pq + q2 = 1 represents an equation used in population genetics.
Above equation is known as Hardy-Weinberg principle in which
p2—Dominant homozygous
2pq — Heterozygous
q2— Recessive homozygous

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
Answer. (c) Appearance of antibiotic-resistant bacteria is an example of 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 wet land
(c) Freshwater to sea water (d) Water to land
Answer. (d) Evolution of life shows that life forms had a trend of moving from 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 bom leading to more chances of survival
(d) The embryo takes a long time to develop
Answer. (c) Viviparity is considered to be more evolved because the young ones are protected inside the mother’s body and are looked after they are bom 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
Answer. (a) Fossils are generally found in sedimentary rocks.

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%
Answer.
ncert-exemplar-problems-class-12-biology-evolution-1

13. 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
Answer. (c) Ramapithecus —> Homo habilis —> Homo erectus —>Homo sapiens

14. Which of the following is an example for link species?
(a) Lobe fish (b) Dodo bird
(c) Seaweed (d) Chimpanzee
Answer. (d) Chimpanzee is an example for link species.

15. Which type of selection is industrial melanism observed in moth, Bistonbitularia?
(a) Stabilising (b) Directional
(c) Disruptive (d) Artificial
Answer. (b) Directional type of selection is industrial melanism observed in moth, Bistonbitularia. (See figure on next page)
ncert-exemplar-problems-class-12-biology-evolution-2

16. Match the scientists listed under column ‘A’ with ideas listed column ‘B’
ncert-exemplar-problems-class-12-biology-evolution-3
(a) i—M; ii—P; iii—N; iv—O (b) i—P; ii—M; iii—N; iv—O
(c) i—N; ii—P; iii—O; iv—M (d) i—p; ii—O; iii—N; iv—M
Answer. (b)
ncert-exemplar-problems-class-12-biology-evolution-4

17. In 1953 S. L. Miller created primitive earth conditions in the laboratory and gave experimental evidence for origin of first form of life from pre-existing non-living organic molecules. The primitive earth conditions created include
(a) Low temperature, volcanic storms, 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 CH, NHetc.
Answer. (d) In 1953 S. L. Miller created primitive earth conditions in the laboratory and gave experimental evidence for origin of first form of life from pre-existing non-living organic molecules. The primitive earth conditions created include high temperature, volcanic storms, reducing atmosphere containing CH, NHetc.

18. Variations during mutations of meiotic recombinations are
(a) Random and direction less (b) Random and directional
(c) Random and small (d) Random, small and directional.
Answer. (a) Variations during mutations of meiotic recombinations are random and direction less.

Very Short Answer Type Questions
1. What were the characteristics of life forms that had been fossilised?
Answer. Fossils are remains of hard parts (like bones, teeth, etc.) of life-forms found in rocks.

2. Did aquatic life forms get fossilised? If, yes where do we come across such fossils?
Answer. Yes, aquatic life forms get fossilised in the sediments of the water bodies. Later, sediments form the part of sedimentary rocks in which fossils, are deposited.

3. What are we referring to? When we say ‘simple organisms’ or ‘complex organisms’.
Answer. When we say simple or complex organisms we are talking in terms of evolutionary history of an Organism. A ‘simple organism’ is considered to be primitive and has simple thallus organisation; The level of complexity of metabolism is also low. On the other hand a ‘complex organism’ refers to a more evolved form forming higher levels of structural and functional complexities. They are believed to have arisen from simple organisms.

4. How do we compute the age of a living tree?
Answer. Age of the living tree is calculated by counting the number of annual rings or by the radioactive carbon dating,

5. Give an example for convergent evolution and identify the features towards which they are converging.
Answer. Presence of wings in birds and butterfly is an example of convergent evolution. They are adapted for flying (volant mode).

6. How do we compute the age of a fossil?
Answer. To compute the age of a fossil, we use radiocarbon dating.

7. What is the most important pre-condition for adaptive radiation?
Answer. Pre-existing variations are the most important pre-condition for adaptive radiation.

8. How do we compute the age of.a rock?
Answer. Age of rock is computed by radiocarbon dating, potassium-argon dating, uranium-lead dating and rubidium-strontium dating method.

9. When we talk of functional macro-molecules (e.g., proteins as enzymes, hormones, receptors, antibodies etc.), towards what are they evolving?
Answer. Similarities in proteins and genes performing a given function among diverse organisms give clues to common ancestry. These biochemical similarities point to the same shared ancestry as structural similarities among diverse organisms. Trypsin (ancient enzyme) is present from protozoa to mammals.

10. In a certain population, the frequency of three genotypes is as follows:
Genotypes: BB, Bbbb
Frequency: 22%, 62%, 16%
What is the likely frequency of B and b alleles?
Answer. Frequency of B allele = all of BB + 1/2 of Bb = 22 + 31 = 53%
Frequency of b allele = all of bb + 1/2 of 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?
Answer. Natural selection and mutation.

12. What is founder effect?
Answer. Sometimes the change in allele frequency is so different in the new sample of population that they become a different species. Small group of population called founders left their habitat and goes into new habitat. In new habitat this population (founders) shows different genotype frequency from that of the original population and leads to variation. The original drifted population becomes founders and the*effect is called founder effect.

13. Who among the Dryopithecus and Ramapithecus was more man-like?
Answer. Ramopithecus was more man-like wille Dryopithecus was more a ape-like

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

15. Among Ramapithecus, Australopithecus and Homo habilis, who probably did not eat meat?
Answer. 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.
Answer. We can correct the statement of Louis Pasteur’s because Oparin of Russia and Haldane of England proposed that the first form of life could have come
from pre-existing non-living organic molecules (e.g., RNA, protein, etc.) and that formation of life was preceded by chemical evolution, i.e., formation of diverse organic molecules from inorganic constituents.

2. The scientists believe that evolution is gradual. But extinction, part of evolutionary story, are ‘sudden’ and ‘abrupt’ and also group-specific. Comment whether a natural disaster can be the cause for extinction of species.
Answer. Natural disaster like earth quake can be the cause for extinction of species. During the long period since the origin and diversification of life on earth there were five episodes of mass extinction of species.

3. Why is nascent oxygen supported to be toxic to aerobic life forms?
Answer. Nascent oxygen is highly reactive. It can react readily with different kinds of molecules, including DNA, proteins present in the cells of aerobic life forms. This may lead to mutations and undesirable metabolic changes.

4. While creation and presence of variation is direction less, natural selection is directional as it is in the context of adaptation. Comment.
Answer. Creation and variation occur in a sexually reproducing population as a result of crossing over during meiosis and random fusion of gametes. It is however the organisms that are selected over a period of time which are determined by the environmental conditions. In other words, the environment provides the direction with respect to adaptations so that the organisms are more and more fit in terms of survival.

5. The evolutionary story of moths in England during industrialisation reveals, that ‘evolution is apparently reversible’. Clarify this statement.
Answer. In a collection of moths made in 1850s, i.e., before industrialisation set in, it was observed that there were more white-winged peppered moths (Biston betularia) on trees than dark-winged or melanised moths (Biston carbonaria). However, in the collection carried out from the same area, but after industrialisation, i.e., in 1920, there were more dark-winged moths in the same area, i.e., the proportion was reversed.

  • Before industrialisation set in, thick growth of almost white-coloured lichen covered the trees—in that background the white winged moth survived but the dark-coloured moth were picked out by predators. Lichens can be used as industrial pollution indicators. They will not grow in areas that are polluted. During post-industrialisation period, the tree trunks became dark due to industrial smoke and soots.
  • Under this condition the white-winged moth did not survive due to predators, dark-winged or melanised moth survived. Hence, moths that were able to camouflage themselves, i.e., hide in the background, survived. This understanding is supported by the fact that in areas where industrialisation did not occur, e.g., in rural areas, the count of melanic moths was low. This showed that in a mixed population, those that can better-adapt, survive and increase in population size.

6. Comment on the statement that “evolution and natural selection are end result or consequence of some other processes but themselves are not processes”.
Answer. The world we see, inanimate .and animate, is only the success stories of evolution. When we describe the story of this world we describe evolution as a process. On the other hand when we describe the story of life on earth, we treat evolution as a consequence of a process called natural selection. We are still not very clear whether to regard evolution and natural selection as processes or end result of unknown processes.

7. State and explain any three factors affecting allele frequency in populations.
Answer. (i) Gene migration or gene flow: When migration of a section of population to another place and population occurs, gene frequencies change in the original as well as in the new population. New genes/alleles are added to the new population and these are lost from the old population. There would be a gene flow if this gene migrationhappens multiple times.
(ii) Genetic drift: If the same change occurs by chance, it is called genetic drift. Sometimes the change in allele frequency is so different in the new sample of population that they become a different species. The original drifted population becomes founders and the effect is called founder effect.
(iii) Mutation: Microbial experiments show that pre-existing advantageous mutations when selected will result in observation of new phenotypes. Over few generations, this would result in speciation. Natural selection is a process in which heritable variations enabling better survival are enabled to reproduce and leave greater number of progeny.

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 population of the world, can we not predict human migratory patterns in pre-history and history? Do you agree or disagree? Provide explanation to your answer.
Answer. Yes, I agree. Gene flow occurs through generations. By studying specific allele frequencies, we can predict the human migratory patterns in prehistory and history. Studies have used specific genes/chromosomes/mitochondrial DNA to trace the evolutionary history and migratory patterns of humans. (The project is known as the Human Genographics Project).

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

  •  Race is a group of people who share similar and distinct physical characteristics.
  • A group of animals related by descent and similar in most characters like general appearance, features, size, configuration, etc., are said to belong to a breed.
  • A cultivar is a plant or grouping of plants selected for desirable characteristics that can be maintained by propagation.
  • A taxonomic category that ranks below species, its members differing from others of the same species in minor but heritable characteristics is called variety.

10. When we say “survival of the fittest”, does it mean that
a. those which are fit only survive, or
b. those that survive are called fit? Comment.
Answer. Those individuals which survive and reproduce in their respective environment are called fit.

11. Enumerate three most characteristic criteria for designating a Mendelian population.
Answer. Population must be sufficiently large with potentialities for free flow of genetic material among individuals (through sexual reproduction). Migration should either be nil or negligible.

12. “Migration may enhance or blur the effects of selection”. Comment.
Answer. Migration may cause enrichment of the gene pool of such alleles that are being selected for, or blur the effects of selection through replenishment of alleles that were selected against by nature.

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?
Answer. Hardy-Weinberg principle states that the sum of allelic frequencies in a population remains constant. Five factors are known to affect Hardy-Weinberg equilibrium. These are gene migration or gene flow, genetic drift, mutation, genetic recombination and natural selection.

2. Explain divergent evolution in detail. What is the driving force behind it?
Answer. Whales, bats, Cheetah and human (all mammals) share similarities in the
pattern of bones of forelimbs. Though these forelimbs perform different functions in these animals, they have similar anatomical structure. All of them have humerus, radius, ulna, carpals, metacarpals and phalanges in their forelimbs.
Hence, in these animals, the same structure developed along different directions due to adaptations to different needs. This is divergent evolution and these structures are homologous. Homology indicates common ancestry. Driving force behind the divergent evolution is adaptation in different environments.

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.
Answer. In the population of Peppermoth, two variants were already existing in the population, the black and the grey. In the absence of industrialisation the grey moths were prevalent because they blended very well with the lichen and moss covered trees camouflage and the predators cannot spot them. The black ones were easily spotted and killed by predators and therefore were fewer in numbers. With industrialisation the stems got covered with black
soot. This provided better camouflage tb the black variant and their number increased. If the industries had been removed the population of black moths would have declined because as stated earlier they would have been spotted better by predators and therefore be eaten more frequently.

4. What are the key concepts in the evolution theory of Darwin?
Answer. Branching descent and natural selection are the two key concepts of Darwinian Theory of Evolution.

  • The novelty and brilliant insight of Darwin was this: He asserted that variations, which are heritable and which make resource utilisation better for few (adapted to habitat better) will enable only those to reproduce and leave more progeny. Hence for a period of time, over many generations, survivors will leave more progeny and there would be a change in population characteristic and hence new forms appear to arise.
  • The fitness, according to Darwin, refers ultimately and only to reproductive fitness. Hence, those who are better fit in an environment, leave more progeny than others. These, therefore, will survive more and hence are selected by nature. He called it natural selection and implied it as a mechanism of evolution.

5. Two organisms occupying a particular geographical area (say desert) show similar adaptive strategies. Taking examples, describe the phenomenon.
Answer. One can say that it is the similar habitat that has resulted in selection of similar adaptive features in different groups of organisms but toward the same function. Spins of Opuntia and cactus are modifications of leaves to prevent the loss of water in desert.

6. We are told that evolution is a continuing phenomenon for all living things. Are humans also evolving? Justify your answer.
Answer. Yes, human is also evolving. Fossils give the evidences that evolution is a continuous phenomenon. Our ancestors like Ramapithecus, Australopithecus, Homo habilis, Homo erectus, Neanderthal man and Cro-magnon man continuously evolving and modem man (Homo sapiens sapiens) arises from certain modifications.

7. Had Darwin been aware of Mendel’s work, would he been able to explain the origin of variations. Discuss.
Answer. Yes, Darwin has been aware of Mendel’s work. Even though Mendel had talked of inheritable ‘factors’ influencing phenotype, Darwin either ignored these observations or kept silence.
Darwin would have been able to explain the origin of variations. He asserted that variations, which are heritable and which make resource utilisation better for few (adapted to habitat better) will enable only those to reproduce and leave more progeny. Hence for a period of time, over many generations, survivors will leave more progeny and there would be a change in population characteristic and hence new forms appear to arise.

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