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CBSE · NCERT
BIOLOGY – CHAPTER 6 : EVOLUTION
Chapter-wise Practice Question Paper (Board + Competitive / NEET Level)
General Instructions
- All questions are compulsory. This paper is based on NCERT Class XII Biology, Chapter 6, and includes NEET-style MCQs and Assertion–Reason questions.
- Q.1 to Q.5 are Section A (40 marks): Q.1 has 20 MCQs; Q.2, Q.3, Q.4 and Q.5 have 5 questions each; every question carries 1 mark.
- Q.6 to Q.13 carry 2 marks each; Q.14 to Q.20 carry 3 marks each; Q.21 and Q.22 are case-based questions of 4 marks each; Q.23 to Q.25 carry 5 marks each.
- Internal choice (OR) is given in Q.14 to Q.20 and Q.23 to Q.25. Attempt only one of the alternatives.
- Draw neat, labelled diagrams wherever required. Solutions to all questions are given after the paper.
SECTION – A (Objective Questions · 40 Marks)
Q.1 Choose the correct option.20 × 1 = 20
(i) The theory that the first form of life arose from pre-existing non-living organic molecules (chemical evolution) was proposed by –
(a) Darwin and Wallace(b) Lamarck(c) Oparin and Haldane(d) Louis Pasteur
(ii) In 1953, S. L. Miller created electric discharge in a closed flask containing CH4, H2, NH3 and water vapour at 800 °C. He observed the formation of –
(a) Amino acids(b) Nucleic acids(c) Lipids(d) Polysaccharides
(iii) The theory of spontaneous generation was disproved by –
(a) Oparin(b) Miller(c) Darwin(d) Louis Pasteur
(iv) Which of the following pairs are homologous organs?
(a) Wings of a butterfly and a bird(b) Forelimbs of a whale and a bat(c) Eyes of an octopus and a mammal(d) Flippers of a penguin and a dolphin
(v) Analogous organs are the result of –
(a) Divergent evolution(b) Mutation only(c) Convergent evolution(d) Genetic drift
(vi) The thorn of Bougainvillea and the tendril of Cucurbita are –
(a) Homologous organs(b) Analogous organs(c) Vestigial organs(d) Atavistic organs
(vii) Sweet potato (a root modification) and potato (a stem modification) are an example of –
(a) Homologous organs(b) Vestigial organs(c) Divergent evolution(d) Analogous organs
(viii) The varied beak types of Darwin’s finches on the Galápagos Islands are an example of –
(a) Convergent evolution(b) Adaptive radiation(c) Genetic drift(d) Industrial melanism
(ix) The placental wolf and the Tasmanian wolf (a marsupial) are an example of –
(a) Homology(b) Divergent evolution(c) Convergent evolution(d) Genetic drift
(x) The theory of ‘use and disuse of organs’ and ‘inheritance of acquired characters’ was proposed by –
(a) Lamarck(b) Darwin(c) Hugo de Vries(d) Weismann
(xi) The mutation theory of evolution (saltation) was proposed by –
(a) Darwin(b) Wallace(c) Lamarck(d) Hugo de Vries
(xii) The proportion of dark-winged (melanised) peppered moths increased in industrial areas because –
(a) Smoke caused mutations in the moths(b) On soot-covered trees the dark moths were less visible to predators(c) White moths migrated out of the area(d) Predators preferred the white moths
(xiii) According to the Hardy–Weinberg principle, if the frequency of allele A is 0.6, the frequency of the heterozygote Aa is –
(a) 0.36(b) 0.16(c) 0.48(d) 0.24
(xiv) Which of the following does NOT disturb Hardy–Weinberg equilibrium?
(a) Random mating(b) Genetic drift(c) Mutation(d) Gene flow
(xv) The founder effect is a type of –
(a) Mutation(b) Natural selection(c) Gene flow(d) Genetic drift
(xvi) In disruptive selection –
(a) The peak shifts to one side(b) Individuals at both extremes are favoured, producing two peaks(c) Average individuals are favoured(d) There is no change in the population
(xvii) The first human-like hominid, with a brain capacity of about 650–800 cc, was –
(a) Homo erectus(b) Neanderthal man(c) Homo habilis(d) Australopithecus
(xviii) The brain capacity of Homo erectus was about –
(a) 900 cc(b) 1400 cc(c) 650 cc(d) 1650 cc
(xix) The brain capacity of Neanderthal man was about –
(a) 650 cc(b) 900 cc(c) 1000 cc(d) 1400 cc
(xx) Dryopithecus and Ramapithecus lived about –
(a) 2 million years ago(b) 15 million years ago(c) 65 million years ago(d) 500 million years ago
Q.2 Fill in the blanks.5 × 1 = 5
(i) Miller’s experiment demonstrated the formation of ______ from simple gases.
(ii) The finches of the Galápagos Islands are an example of ______ evolution.
(iii) Industrial melanism was studied in the ______ moth, Biston betularia.
(iv) The sum total of all the alleles of all the genes in a population is called the ______.
(v) The first human-like being (hominid) was ______.
Q.3 Write True or False.5 × 1 = 5
(i) Homologous organs have the same basic structure but may perform different functions.
(ii) Analogous organs show divergent evolution.
(iii) Lamarck’s theory of inheritance of acquired characters is accepted today.
(iv) In Hardy–Weinberg equilibrium the allele frequencies remain constant from generation to generation.
(v) Homo erectus had a larger brain capacity than Homo habilis.
Q.4 Match Column ‘A’ with Column ‘B’.5 × 1 = 5
| Column ‘A’ | Column ‘B’ |
|---|---|
| (i) Biston betularia | (a) Homologous organs |
| (ii) Darwin’s finches | (b) Adaptive radiation |
| (iii) Forelimb of whale and wing of bat | (c) Analogous organs |
| (iv) Wing of butterfly and wing of bird | (d) Industrial melanism |
| (v) Oenothera | (e) Mutation (saltation) |
Q.5 Assertion (A) – Reason (R) type questions. Choose: (a) Both A and R true, R explains A; (b) Both true, R does not explain A; (c) A true, R false; (d) A false, R true.5 × 1 = 5
(i) Assertion (A): Homologous organs show divergent evolution.
Reason (R): Homologous organs have the same basic structure/origin but are modified for different functions.
Reason (R): Homologous organs have the same basic structure/origin but are modified for different functions.
(ii) Assertion (A): Darwin’s finches are an example of adaptive radiation.
Reason (R): Australian marsupials and placental mammals show convergent evolution.
Reason (R): Australian marsupials and placental mammals show convergent evolution.
(iii) Assertion (A): Genetic drift changes allele frequencies by chance.
Reason (R): Genetic drift occurs only in very large populations.
Reason (R): Genetic drift occurs only in very large populations.
(iv) Assertion (A): Homo habilis had a brain capacity of 1400 cc.
Reason (R): Neanderthal man had a brain capacity of 1400 cc.
Reason (R): Neanderthal man had a brain capacity of 1400 cc.
(v) Assertion (A): Disruptive selection can produce two peaks in a population.
Reason (R): In disruptive selection individuals at both extremes of the distribution are favoured.
Reason (R): In disruptive selection individuals at both extremes of the distribution are favoured.
SECTION – B (Very Short Answer · 2 Marks each)
6. Differentiate between homologous and analogous organs with one example each.(2)
7. What did Oparin and Haldane propose about the origin of life?(2)
8. Briefly describe Miller’s experiment. What did it prove?(2)
9. What is adaptive radiation? Give one example.(2)
10. State any two postulates of Darwin’s theory of natural selection.(2)
11. In a population in Hardy–Weinberg equilibrium the frequency of the recessive allele (q) is 0.3. Find the frequency of the homozygous recessive and heterozygous genotypes.(2)
12. What is genetic drift? What is the founder effect?(2)
13. Write the brain capacity and one feature of Homo habilis and Homo erectus.(2)
SECTION – C (Short Answer · 3 Marks each)
14. Explain the Oparin–Haldane theory and Miller’s experiment on the chemical origin of life.(3)
OR
How was the theory of spontaneous generation disproved? What is panspermia?
15. Describe the evidence for evolution from comparative anatomy and morphology.(3)
OR
Describe the evidence for evolution from palaeontology, embryology and biochemistry.
16. Explain adaptive radiation with the examples of Darwin’s finches and Australian marsupials.(3)
OR
Explain convergent evolution with suitable examples.
17. Compare Lamarck’s theory with Darwin’s theory of evolution.(3)
OR
Explain the mutation theory of Hugo de Vries. How do Darwinian variations differ from mutations?
18. Explain industrial melanism as an example of natural selection.(3)
OR
Explain the three types of natural selection.
19. State the Hardy–Weinberg principle. Write the equation and the factors that disturb the equilibrium.(3)
OR
Write short notes on genetic drift, founder effect and gene flow.
20. Describe the features of Dryopithecus, Ramapithecus, Australopithecus and Homo habilis in human evolution.(3)
OR
Describe the features of Homo erectus, Neanderthal man and Homo sapiens.
SECTION – D (Case-Based Questions · 4 Marks each)
21. Read the passage and answer the questions that follow.(4)
Before industrialisation in England (about 1850) white-winged peppered moths were more common than dark-winged moths on the lichen-covered tree trunks. After industrialisation the tree trunks were covered with soot and the proportion of dark-winged moths became greater. In later years, after pollution control, white-winged moths again increased in number.
(i) Name the moth species used in this study.(1)
(ii) Why did the dark-winged moths increase after industrialisation?(1)
(iii) Name the process and its type shown by this example. State its evolutionary significance.(2)
22. Read the passage and answer the questions that follow.(4)
In a population of 1000 individuals in Hardy–Weinberg equilibrium, 90 individuals show a recessive phenotype (aa).
(i) Find the frequency of the recessive allele a.(1)
(ii) Find the frequency of the dominant allele A.(1)
(iii) How many heterozygous (Aa) and homozygous dominant (AA) individuals are expected?(2)
SECTION – E (Long Answer · 5 Marks each)
23. Describe the origin of life on earth: the early earth, the theories of origin, chemical evolution and Miller’s experiment.(5)
OR
Describe the evidences for evolution – comparative anatomy, palaeontology, embryology, biochemistry and adaptive radiation.
24. Explain Darwin’s theory of natural selection with examples. How does it differ from Lamarck’s theory and the mutation theory?(5)
OR
State and explain the Hardy–Weinberg principle. Describe the five factors affecting genetic equilibrium and the types of natural selection.
25. Describe the evolution of human beings, mentioning the characteristic features and the brain capacity of each stage.(5)
OR
Give a brief account of the evolution of life forms on earth from fishes to mammals and the extinction of the dinosaurs.
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CBSE · NCERT
BIOLOGY – CHAPTER 6 : COMPLETE SOLUTIONS
Evolution · Answer Key with Step-by-Step Explanations
Q.1 Quick Answer Key (MCQ)20 × 1 = 20
| i | (c) | ii | (a) | iii | (d) | iv | (b) | v | (c) |
| vi | (a) | vii | (d) | viii | (b) | ix | (c) | x | (a) |
| xi | (d) | xii | (b) | xiii | (c) | xiv | (a) | xv | (d) |
| xvi | (b) | xvii | (c) | xviii | (a) | xix | (d) | xx | (b) |
Q.1 Solutions with Explanation
(i) Ans. (c) Oparin and Haldane
Oparin (Russia) and Haldane (England) proposed that life originated from pre-existing non-living organic molecules (RNA, proteins etc.) and that its formation was preceded by chemical evolution.
(ii) Ans. (a) Amino acids
Miller’s experiment showed that amino acids can form from simple gases under early-earth conditions (support for chemical evolution).
(iii) Ans. (d) Louis Pasteur
Pasteur’s experiments with S-neck flasks showed that life arises only from pre-existing life; killed yeast in a sterilised flask produced no life.
(iv) Ans. (b) Forelimbs of a whale and a bat
Forelimbs of whales, bats, cheetah and humans have the same basic structure but are modified for different functions (divergent evolution). The others are analogous.
(v) Ans. (c) Convergent evolution
Analogous organs have different structure but similar function – similar habitats result in similar adaptive features (convergent evolution).
(vi) Ans. (a) Homologous organs
Both are modified axillary branches (same origin, different functions): homologous structures showing divergent evolution.
(vii) Ans. (d) Analogous organs
Both are tubers with similar function (storage) but different origin – analogous organs showing convergent evolution.
(viii) Ans. (b) Adaptive radiation
From a seed-eating ancestral finch, many varieties with different beaks evolved in the island – adaptive radiation (divergent evolution in a geographical area).
(ix) Ans. (c) Convergent evolution
Marsupials of Australia (adaptive radiation) resemble placental mammals of other continents (e.g. placental wolf – Tasmanian wolf) – convergent evolution.
(x) Ans. (a) Lamarck
Lamarck (e.g. giraffe’s neck elongation by stretching) – the idea is not accepted today.
(xi) Ans. (d) Hugo de Vries
Hugo de Vries (work on Oenothera lamarckiana) believed that evolution is a discontinuous, single-step large mutation (saltation).
(xii) Ans. (b) On soot-covered trees the dark moths were less visible to predators
Natural selection: after industrialisation the tree trunks became dark, the dark moths camouflaged better, escaped predation and survived and reproduced more.
(xiii) Ans. (c) 0.48
p = 0.6, q = 0.4; 2pq = 2 × 0.6 × 0.4 = 0.48.
(xiv) Ans. (a) Random mating
Gene flow (migration), genetic drift, mutation, genetic recombination and natural selection change allele frequencies; random mating does not.
(xv) Ans. (d) Genetic drift
The founder effect is a change in allele frequency (genetic drift) when a small sample of a population starts a new population.
(xvi) Ans. (b) Individuals at both extremes are favoured, producing two peaks
Stabilising selection favours the mean; directional favours one extreme; disruptive favours both extremes.
(xvii) Ans. (c) Homo habilis
Homo habilis – brain 650–800 cc, probably did not eat meat.
(xviii) Ans. (a) 900 cc
Homo erectus (about 1.5 mya): brain 900 cc, probably ate meat.
(xix) Ans. (d) 1400 cc
Neanderthal man: brain 1400 cc; lived in East and Central Asia (1,00,000–40,000 years back), used hides and buried the dead.
(xx) Ans. (b) 15 million years ago
Dryopithecus (ape-like) and Ramapithecus (more man-like) existed about 15 mya; Australopithecines about 2 mya.
Q.2 Fill in the blanks5 × 1 = 5
(i) Amino acids
(ii) Adaptive radiation
(iii) Peppered
(iv) Gene pool
(v) Homo habilis
Q.3 True / False5 × 1 = 5
(i) True.
E.g. forelimbs of whale, bat, cheetah and human; they indicate common ancestry (divergent evolution).
(ii) False.
Analogous organs show convergent evolution; homologous organs show divergent evolution.
(iii) False.
Acquired characters are not inherited; Darwin’s natural selection and mutations explain evolution.
(iv) True.
Allele and genotype frequencies are stable if no evolutionary factor acts (p² + 2pq + q² = 1).
(v) True.
H. erectus ≈ 900 cc, H. habilis ≈ 650–800 cc.
Q.4 Matching5 × 1 = 5
(i) – (d) · (ii) – (b) · (iii) – (a) · (iv) – (c) · (v) – (e)
Biston betularia – industrial melanism; Darwin’s finches – adaptive radiation; whale forelimb and bat wing – homologous organs; butterfly and bird wings – analogous organs; Oenothera – mutation theory (de Vries).
Q.5 Assertion – Reason5 × 1 = 5
(i) Ans. (a)
Both true; a common ancestral structure modified for different functions is divergent evolution.
(ii) Ans. (b)
Both true, but R is about another example and does not explain A.
(iii) Ans. (c)
A is true. R is false: drift is significant in small populations.
(iv) Ans. (d)
A is false: H. habilis had 650–800 cc. R is true.
(v) Ans. (a)
Both true; favouring both extremes splits the distribution into two peaks.
SECTION – B (2 Marks each)
6. Ans.
| Homologous organs | Analogous organs |
|---|---|
| Same origin / basic structure, different functions | Different origin, similar function |
| Divergent evolution; e.g. forelimbs of whale, bat, human | Convergent evolution; e.g. wings of butterfly and bird |
7. Ans.
They proposed that the first form of life could have arisen from pre-existing non-living organic molecules (such as RNA and protein). [1] Formation of life was preceded by a period of chemical evolution, i.e. formation of diverse organic molecules from inorganic constituents in the reducing atmosphere of the early earth. [1]
8. Ans.
In 1953 S. L. Miller passed electric discharge through a closed flask containing CH4, H2, NH3 and water vapour at 800 °C. [1] He observed the formation of amino acids, proving that organic molecules could form from inorganic ones under the conditions of the primitive earth (chemical evolution). [1]
9. Ans.
Adaptive radiation is the process of evolution of different species in a given geographical area starting from a point and radiating to other habitats. [1] Example: Darwin’s finches in the Galápagos Islands (different beaks from a seed-eating ancestor) / Australian marsupials. [1]
10. Ans.
(i) Variation exists in a population, some being small, heritable and advantageous. (ii) Struggle for existence due to limited resources and a tendency to produce many offspring. (iii) Individuals with favourable variations are fitter (survival of the fittest) and leave more offspring (reproductive fitness) – natural selection; (iv) it leads to branching descent and speciation. (Any two, 1 mark each)
11. Ans.
p = 1 – q = 0.7. [½] Homozygous recessive (q²) = 0.3 × 0.3 = 0.09. [½] Heterozygous (2pq) = 2 × 0.7 × 0.3 = 0.42. [1] (Homozygous dominant p² = 0.49.)
12. Ans.
Genetic drift: change in the allele frequency of a population by chance (random), prominent in small populations. [1] Founder effect: a type of drift in which a small group of individuals starts a new population, whose allele frequencies differ from the original population. [1]
13. Ans.
Homo habilis: 650–800 cc; the first human-like being; probably did not eat meat. [1] Homo erectus: about 900 cc; lived about 1.5 mya; probably ate meat. [1]
SECTION – C (3 Marks each)
14. Ans.
Early earth: about 4.5 billion years old, hot, volcanic, with a reducing atmosphere (CH4, NH3, H2, water vapour; no free O2). [½] Oparin–Haldane: life originated from pre-existing non-living organic molecules; chemical evolution formed simple organic compounds, then complex ones (RNA, proteins, polysaccharides), then the first cellular forms (in water) – the ‘primitive soup’. [1½] Miller (1953): discharge in CH4, H2, NH3 and water vapour at 800 °C gave amino acids; later similar studies formed sugars, nitrogen bases, pigments and fats. [1]
OR
Spontaneous generation was the belief that life arises from decaying and rotting matter (e.g. straw, mud). [½] Louis Pasteur showed with S-neck flasks that life comes only from pre-existing life: killed yeast in a sterile flask produced no life, but when the neck was broken, life appeared. [1½] Panspermia: the early belief that ‘units of life’ (spores) came from outer space to earth; it is not widely accepted. [1]
15. Ans.
Homologous organs: same structure but different functions – forelimbs of whales, bats, cheetah, humans; thorn of Bougainvillea and tendril of Cucurbita; shows common ancestry and divergent evolution. [1½] Analogous organs: different structure but similar function – wings of butterfly and birds; eyes of octopus and mammals; flippers of penguins and dolphins; sweet potato (root) and potato (stem); shows convergent evolution. [1½]
OR
Palaeontology: fossils found in different strata show that life forms varied over time and some are restricted to certain geological time spans; new forms replaced old ones; fossils are dated by radioactive carbon methods. [1] Embryology: Haeckel’s recapitulation idea (embryos pass through ancestral stages) was disproved by von Baer, but embryos of vertebrates do show similarities (e.g. gill slits). [1] Biochemistry: similarities in proteins, genes and metabolism across organisms (e.g. the universal genetic code) point to a common ancestry. [1]
16. Ans.
Adaptive radiation: evolution of different species in a geographical area starting from a point and radiating to different habitats. [1] Darwin’s finches (Galápagos): from the original seed-eating features many forms evolved with altered beaks suited to insects, buds, fruits and seeds. [1] Australian marsupials: a number of marsupials, all evolved from an ancestral stock within the Australian island continent, each a different species (e.g. kangaroo, koala, Tasmanian wolf). [1]
OR
Convergent evolution: different (unrelated) groups evolve similar adaptive features in similar habitats, so analogous structures arise. [1] Examples: the placental wolf and the Tasmanian wolf (a marsupial); the marsupial and placental ‘mole’, ‘anteater’ and ‘flying squirrel’-like forms; wings of butterfly and bird; eyes of octopus and mammals. [2]
17. Ans.
| Lamarck | Darwin |
|---|---|
| Use and disuse of organs | Natural selection of heritable variations |
| Inheritance of acquired characters | Only heritable variations are passed on |
| Organisms change by internal effort (e.g. giraffe neck) | Struggle for existence and survival of the fittest decide who survives |
| Not supported by evidence | Widely accepted (modified as modern synthetic theory) |
OR
Mutation theory (Hugo de Vries, on Oenothera lamarckiana): evolution is a discontinuous process – large, sudden, single-step, heritable changes called mutations (saltation) lead to new species. [1½] Difference: Darwinian variations are small and directionless and accumulate gradually; mutations are random, large and appear suddenly. [1½]
18. Ans.
In England before industrialisation (about 1850) there were more white-winged peppered moths (Biston betularia) on lichen-covered trees than dark-winged ones. [1] After industrialisation tree trunks became covered with soot, so dark-winged (melanised) moths camouflaged better and escaped predators, while the white ones were picked out – the proportion of dark moths increased. [1] The adaptive trait that was more fit increased in the population: an example of natural selection (similarly herbicide, pesticide and antibiotic resistance). [1]
OR
Stabilising selection: more individuals acquire the mean character value, reducing the extremes. [1] Directional selection: individuals of one extreme are favoured, so the peak shifts in one direction. [1] Disruptive selection: individuals at both extremes are favoured, giving two peaks (the middle type reduced). [1]
19. Ans.
Principle: allele frequencies in a population are stable and constant from generation to generation (the gene pool remains constant) – genetic equilibrium. [1] Equation: p² + 2pq + q² = 1 (or (p + q)² = 1) where p and q are frequencies of alleles A and a. [1] Disturbing factors: gene migration/gene flow, genetic drift, mutation, genetic recombination and natural selection. [1]
OR
Genetic drift: random change in allele frequencies by chance, important in small populations; it may eliminate some alleles. [1] Founder effect: allele frequencies in a new population started by a few founders differ from those of the original population. [1] Gene flow: movement of alleles between populations by migration; it may add alleles to or remove them from a gene pool. [1]
20. Ans.
Dryopithecus and Ramapithecus: about 15 mya; hairy; walked like gorillas and chimpanzees; Dryopithecus was more ape-like, Ramapithecus more man-like. [1] Australopithecus: about 2 mya, East African grasslands; hunted with stone weapons but probably ate fruit. [1] Homo habilis: the first human-like being; brain capacity 650–800 cc; probably did not eat meat. [1]
OR
Homo erectus: about 1.5 mya; brain about 900 cc; probably ate meat. [1] Neanderthal man: brain about 1400 cc; lived in East and Central Asia between 1,00,000 and 40,000 years back; used hides to protect their bodies and buried their dead. [1] Homo sapiens: arose in Africa about 75,000–1,00,000 years ago, moved across continents and developed into distinct races; cave art about 18,000 years ago; agriculture about 10,000 years back. [1]
SECTION – D (Case-Based · 4 Marks each)
21. Ans.
(i) Biston betularia (peppered moth). [1]
(ii) On the soot-covered dark tree trunks the dark moths were camouflaged and escaped predators, whereas the white moths were easily seen and eaten; so dark moths survived and reproduced more. [1]
(iii) Natural selection (directional selection, as the population shifted towards the dark form). [1] It shows that the individuals better adapted to the changed environment survive and leave more offspring, so allele frequencies change, leading to evolution. [1] [2]
22. Ans.
(i) q² = 90/1000 = 0.09; q = √0.09 = 0.3. [1]
(ii) p = 1 – q = 1 – 0.3 = 0.7. [1]
(iii) Aa = 2pq = 2 × 0.7 × 0.3 = 0.42 → 420 individuals. [1] AA = p² = 0.49 → 490 individuals. (Check: 490 + 420 + 90 = 1000.) [1] [2]
SECTION – E (Long Answer · 5 Marks each)
23. Ans.
Early earth: formed about 4.5 billion years ago; hot, with volcanic storms and a reducing atmosphere (CH4, NH3, H2, water vapour); no free oxygen. Water vapour condensed to form oceans. Later UV rays split water, giving oxygen. [1]
Theories: special creation; spontaneous generation (disproved by Louis Pasteur); panspermia (units of life came from outer space). [1]
Chemical evolution (Oparin–Haldane): life arose from pre-existing non-living organic molecules; simple organic molecules formed in the primitive atmosphere, then complex molecules (RNA, protein, polysaccharides); then the first cellular forms (non-cellular → cellular, heterotrophic). [1½]
Miller (1953): in a closed flask with CH4, H2, NH3 and water vapour at 800 °C with electric discharge, amino acids formed; similar later experiments formed sugars, nitrogen bases, pigments and fats. [1½]
Theories: special creation; spontaneous generation (disproved by Louis Pasteur); panspermia (units of life came from outer space). [1]
Chemical evolution (Oparin–Haldane): life arose from pre-existing non-living organic molecules; simple organic molecules formed in the primitive atmosphere, then complex molecules (RNA, protein, polysaccharides); then the first cellular forms (non-cellular → cellular, heterotrophic). [1½]
Miller (1953): in a closed flask with CH4, H2, NH3 and water vapour at 800 °C with electric discharge, amino acids formed; similar later experiments formed sugars, nitrogen bases, pigments and fats. [1½]
OR
Comparative anatomy: homologous organs (forelimbs of whale, bat, cheetah, human; Bougainvillea thorn and Cucurbita tendril) – divergent evolution; analogous organs (wings of butterfly and bird; potato and sweet potato) – convergent evolution. [1½]
Palaeontology: fossils in different sedimentary strata show a progressive change of life forms; some forms are restricted to specific time spans. [1]
Embryology: Haeckel’s idea of recapitulation (rejected by von Baer) – but embryonic similarities exist. [½] Biochemistry: similarity in proteins and genes, universal genetic code. [½]
Adaptive radiation: Darwin’s finches and Australian marsupials. [1½]
Palaeontology: fossils in different sedimentary strata show a progressive change of life forms; some forms are restricted to specific time spans. [1]
Embryology: Haeckel’s idea of recapitulation (rejected by von Baer) – but embryonic similarities exist. [½] Biochemistry: similarity in proteins and genes, universal genetic code. [½]
Adaptive radiation: Darwin’s finches and Australian marsupials. [1½]
24. Ans.
Darwin (HMS Beagle voyage; Wallace independently): populations have variations; resources are limited so there is a struggle for existence (Malthus); those with favourable variations are the fittest (survival of the fittest) and leave more offspring; over generations new forms (species) arise by branching descent. Variations are small and directionless. [2]
Examples: industrial melanism in Biston betularia; resistance to herbicides, pesticides and antibiotics. [1]
Lamarck: use and disuse of organs and inheritance of acquired characters (giraffe’s neck) – not supported. Hugo de Vries: mutation (saltation) – large single-step changes (Oenothera). [2]
Examples: industrial melanism in Biston betularia; resistance to herbicides, pesticides and antibiotics. [1]
Lamarck: use and disuse of organs and inheritance of acquired characters (giraffe’s neck) – not supported. Hugo de Vries: mutation (saltation) – large single-step changes (Oenothera). [2]
OR
HW principle: allele frequencies in a population are stable and remain constant over generations, if no evolutionary factors act: p² + 2pq + q² = 1. [1½]
Factors: gene migration (flow), genetic drift (and founder effect), mutation, genetic recombination, natural selection – change in allele frequency means evolution. [2]
Natural selection: stabilising (mean favoured), directional (one extreme; peak shifts), disruptive (both extremes; two peaks). [1½]
Factors: gene migration (flow), genetic drift (and founder effect), mutation, genetic recombination, natural selection – change in allele frequency means evolution. [2]
Natural selection: stabilising (mean favoured), directional (one extreme; peak shifts), disruptive (both extremes; two peaks). [1½]
25. Ans.
Dryopithecus and Ramapithecus (about 15 mya): hairy, walked like gorillas/chimpanzees; Dryopithecus ape-like, Ramapithecus man-like. [1]
Australopithecus (about 2 mya): East Africa; hunted with stone weapons; probably ate fruit. [1]
Homo habilis: first human-like being; 650–800 cc; did not eat meat. Homo erectus (1.5 mya): 900 cc; ate meat. [1½]
Neanderthal man: 1400 cc; East and Central Asia, 1,00,000–40,000 years back; used hides, buried the dead. Homo sapiens: arose in Africa, 75,000–1,00,000 years ago; cave art about 18,000 years ago; agriculture about 10,000 years ago; civilisations followed. [1½]
Australopithecus (about 2 mya): East Africa; hunted with stone weapons; probably ate fruit. [1]
Homo habilis: first human-like being; 650–800 cc; did not eat meat. Homo erectus (1.5 mya): 900 cc; ate meat. [1½]
Neanderthal man: 1400 cc; East and Central Asia, 1,00,000–40,000 years back; used hides, buried the dead. Homo sapiens: arose in Africa, 75,000–1,00,000 years ago; cave art about 18,000 years ago; agriculture about 10,000 years ago; civilisations followed. [1½]
OR
Fishes: about 500 mya jawless fishes evolved; about 350 mya jawed, bony fishes. [1]
Amphibians: some lobefins with stout, strong fins could move on land (the coelacanth, thought extinct, was caught in South Africa in 1938); they became the first amphibians that lived on both land and water (e.g. Ichthyostega). [1]
Reptiles: amphibians evolved into reptiles, which lay thick-shelled eggs; reptiles of different shapes and sizes dominated (e.g. Tyrannosaurus rex, about 20 feet high with huge dagger-like teeth). [1]
Mammals: small, shrew-like mammals existed with the reptiles; after the reptiles’ decline mammals diversified. [1]
Dinosaurs disappeared about 65 mya; reasons are uncertain (climate change, water-living forms, evolution into birds). [1]
Amphibians: some lobefins with stout, strong fins could move on land (the coelacanth, thought extinct, was caught in South Africa in 1938); they became the first amphibians that lived on both land and water (e.g. Ichthyostega). [1]
Reptiles: amphibians evolved into reptiles, which lay thick-shelled eggs; reptiles of different shapes and sizes dominated (e.g. Tyrannosaurus rex, about 20 feet high with huge dagger-like teeth). [1]
Mammals: small, shrew-like mammals existed with the reptiles; after the reptiles’ decline mammals diversified. [1]
Dinosaurs disappeared about 65 mya; reasons are uncertain (climate change, water-living forms, evolution into birds). [1]
QUICK REVISION · HIGH-YIELD POINTS (NEET / CBSE)
- Origin of life: Oparin–Haldane (chemical evolution); Miller 1953 (CH4, H2, NH3, water vapour, 800 °C, spark → amino acids); Pasteur disproved spontaneous generation (S-neck flask); panspermia = life from space.
- Homologous (same origin, different function) → divergent evolution; analogous (different origin, same function) → convergent evolution. Examples: whale/bat forelimb; Bougainvillea thorn–Cucurbita tendril; butterfly–bird wing; potato–sweet potato.
- Adaptive radiation: Darwin’s finches (Galápagos), Australian marsupials; convergent: placental wolf – Tasmanian wolf. Haeckel’s recapitulation was rejected by von Baer.
- Lamarck: use and disuse, inheritance of acquired characters. Darwin: natural selection, struggle for existence, survival of the fittest, branching descent. De Vries: mutation (saltation) in Oenothera.
- Industrial melanism (Biston betularia): dark moths increased after industrialisation by natural selection. Also herbicide, pesticide and antibiotic resistance.
- Selection types: stabilising (mean), directional (one extreme, peak shifts), disruptive (both extremes, two peaks).
- Hardy–Weinberg: p² + 2pq + q² = 1; p + q = 1. Factors: gene flow, genetic drift (founder effect), mutation, recombination, natural selection. Example: q = 0.3 → aa 0.09, Aa 0.42, AA 0.49.
- Timeline: jawless fish ~500 mya; jawed fish ~350 mya; amphibians; reptiles (dinosaurs disappeared ~65 mya); mammals.
- Human evolution: Dryopithecus and Ramapithecus (~15 mya); Australopithecus (~2 mya); Homo habilis 650–800 cc; Homo erectus ~900 cc (1.5 mya); Neanderthal ~1400 cc; Homo sapiens (75,000–1,00,000 years ago in Africa).
- Cave art ~18,000 years ago; agriculture ~10,000 years ago; earth ~4.5 billion years old.
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