This MCQ module is based on: NCERT Exercises and Solutions: Evolution
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NCERT Exercises and Solutions: Evolution
🎓 Class 12
Biology
CBSE
Theory
Ch 6 – Evolution
⏱ ~8 min
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NCERT Exercises and Solutions: Evolution
Chapter Summary — Evolution
Origin of Life
Earth formed 4.5 bya. Reducing atmosphere of CH₄, NH₃, H₂, H₂O. Oparin–Haldane proposed chemical evolution; Miller–Urey (1953) experimentally produced amino acids from these gases via electric sparks. Spontaneous generation refuted by Pasteur.
Evidence of Evolution
Paleontology (fossils in sedimentary rocks dated by radioactivity), embryology (vestigial gill slits), comparative anatomy (homologous vs analogous organs), molecular biology (gene/protein similarity), biogeography (Darwin's finches), industrial melanism, artificial selection.
Mechanism Theories
Lamarck — use/disuse and inheritance of acquired characters (rejected). Darwin–Wallace — natural selection acting on heritable variation. de Vries — mutation theory (saltation). Modern Synthesis — mutations + recombination + drift + gene flow + selection.
Hardy–Weinberg
p² + 2pq + q² = 1. Equilibrium = no evolution. Five disturbing factors: gene flow, genetic drift (including founder effect), mutation, recombination, natural selection.
Adaptive Radiation
Diversification of one ancestor into multiple species in different niches. Examples: Darwin's finches on Galapagos (beak diversity), Australian marsupials (kangaroo, koala, Tasmanian wolf), placental mammals matching marsupials = convergent evolution.
Human Evolution
Dryopithecus → Ramapithecus → Australopithecus (2 mya) → Homo habilis (650–800 cc) → Homo erectus (900 cc, 1.5 mya) → Neanderthal (1,400 cc) → Homo sapiens (Africa → world, ice age). Cave art at Bhimbetka ~18,000 ya.
Key Terms — Quick Glossary
| Term | Meaning |
|---|---|
| Fossil | Hard-part remains of past life forms preserved in sedimentary rocks. |
| Homologous organs | Same structure, different function (divergent evolution; common ancestry). |
| Analogous organs | Different structure, similar function (convergent evolution; independent origin). |
| Adaptive radiation | Multiple species evolving from one ancestor into different niches in one region. |
| Natural selection | Differential reproduction of heritable variants based on fitness. |
| Fitness | Reproductive success — number of offspring left. |
| Mutation | Sudden heritable change in DNA; raw material for evolution. |
| Genetic drift | Random change in allele frequencies, especially in small populations. |
| Founder effect | Drift caused by a small migrant group establishing a new population. |
| Gene flow | Movement of alleles between populations via migration. |
| Hardy–Weinberg equilibrium | State of constant allele frequencies; no evolution at that locus. |
| Speciation | Formation of new species through reproductive isolation. |
NCERT Exercises — Full Solutions
Q1. Explain antibiotic resistance observed in bacteria in light of Darwinian selection theory.
Step-by-step Darwinian explanation:
- A bacterial population contains heritable variation. By chance, a few cells carry mutations that confer resistance to an antibiotic. These mutations occur randomly, before the antibiotic is applied.
- When the antibiotic is introduced, sensitive bacteria die and resistant ones survive.
- The resistant survivors reproduce. Since bacteria divide every 20–30 minutes, within hours or days the population is dominated by resistant cells.
- The antibiotic acted as a powerful selection pressure; it did not create resistance — it selected for it.
- The frequency of the resistance allele has dramatically increased — a clear-cut case of natural selection in action, observable on a time scale of weeks rather than millennia.
Q2. Find out from newspapers and popular science articles any new fossil discoveries or controversies about evolution.
Sample notable fossil discoveries and current questions:
- Homo naledi (South Africa, 2015) — small-brained hominid (~500 cc) with surprisingly modern hands and feet, dated ~250,000 ya. Raised questions about who first practised burial.
- Tiktaalik (Arctic Canada, 2004) — a "fishapod" with both fish features (scales, fins) and tetrapod features (wrist bones, ribs). A spectacular transitional fossil between fish and amphibians (~375 mya).
- Feathered dinosaurs from China (1996 onwards) — Sinosauropteryx, Anchiornis, etc. provided overwhelming evidence that birds evolved from theropod dinosaurs.
- Denisovans (Siberia, 2010) — a separate human lineage identified initially only from DNA in a finger bone. Modern Tibetans inherited their high-altitude adaptation gene.
- Indian fossil: The Narmada human skull (Madhya Pradesh, 1982) is the only confirmed pre-modern human fossil from India — possibly archaic Homo.
Q3. Attempt giving a clear definition of the term species.
A species is a group of organisms that:
Limitations: The definition does not work for asexual organisms (bacteria), extinct organisms (fossils), or ring species. Alternative concepts:
- share a common gene pool and similar morphological, physiological and behavioural characteristics,
- can interbreed in nature and produce fertile offspring, and
- are reproductively isolated from other such groups.
Limitations: The definition does not work for asexual organisms (bacteria), extinct organisms (fossils), or ring species. Alternative concepts:
- Morphological species: Based on physical resemblance — used for fossils.
- Phylogenetic species: Smallest monophyletic group sharing common ancestry — used in modern systematics.
- Ecological species: Defined by a unique ecological niche.
Q4. Try to trace the various components of human evolution (hint: brain size and function, skeletal structure, dietary preference, etc.)
| Component | Trend over evolution |
|---|---|
| Brain size | Australopithecus ~400 cc → Homo habilis 650–800 cc → Homo erectus ~900 cc → Neanderthal ~1,400 cc → modern human ~1,350 cc |
| Cranium shape | Sloping forehead → high vertical forehead; jaw projecting → flat face; brow ridges large → reduced. |
| Posture & bipedalism | Knuckle-walking apes → Australopithecus (upright but not fully) → Homo erectus (fully bipedal) → modern fully upright with vertical spine. |
| Hands | Grasping hands of apes → precision grip with opposable thumb in Homo; tool use. |
| Teeth | Large canines (apes) → reduced canines in Homo; small molars in modern humans (cooking enables this). |
| Diet | Largely vegetarian Australopithecus → meat-eating Homo erectus → mixed diet of modern humans; cooking from ~500,000 ya. |
| Tools | None in early hominids → simple stone tools (Oldowan, Homo habilis) → hand axes (Acheulean, Homo erectus) → blades and bone tools (Neanderthal, sapiens) → agriculture, metals. |
| Culture | None → fire use → burial of dead (Neanderthal) → cave art (~18,000 ya, sapiens) → language → agriculture → civilisation. |
Q5. Find out through the internet and popular science articles whether animals other than man has self-consciousness.
The mirror self-recognition test (Gallup, 1970) is a standard behavioural test: animals that touch a mark on their own body when shown in a mirror demonstrate some form of self-awareness.
Animals that have passed the test:
Animals that have passed the test:
- Chimpanzees, bonobos, orangutans, gorillas
- Asian elephants
- Bottlenose dolphins, orcas
- European magpies (a bird)
- Cleaner wrasse (a fish — controversial!)
- Tool use: chimps (sticks for termites), New Caledonian crows (hooked tools), sea otters (rocks).
- Numerosity: chimps and crows can count up to small numbers.
- Theory of mind (limited): chimps and ravens appear to anticipate what others know.
- Episodic memory: scrub jays remember what, where, when they cached food.
Q6. List 10 modern-day animals and using the internet resources link them to a corresponding ancient fossil. Name both.
| Modern animal | Ancient fossil ancestor |
|---|---|
| Horse (Equus) | Eohippus (Hyracotherium) — small dog-sized 4-toed |
| Elephant (Loxodonta, Elephas) | Moeritherium — pig-sized, no trunk |
| Bird (e.g., pigeon) | Archaeopteryx — feathered dinosaur with teeth and claws |
| Whale (Cetacea) | Pakicetus / Ambulocetus — walking land mammals |
| Frog (Anura) | Ichthyostega — early amphibian |
| Crocodile | Sarcosuchus — giant prehistoric crocodile |
| Human (Homo sapiens) | Australopithecus afarensis ("Lucy") |
| Camel | Protylopus — small primitive camel |
| Snake | Pachyrhachis — fossil snake with hind limbs |
| Bat | Onychonycteris — early bat with claws on all fingers |
Q7. Practise drawing various animals and plants.
Suggested practice set for evolution diagrams:
- Miller–Urey apparatus — label spark electrodes, reaction flask, condenser, trap.
- Geological time scale showing 5 eras and dominant life forms.
- Homologous forelimbs of whale, bat, cheetah, human — show same bone labels (humerus, radius, ulna, carpals, metacarpals, phalanges).
- Darwin's four finches — different beak shapes (large ground, insectivorous, cactus, woodpecker).
- Three patterns of natural selection: stabilising, directional, disruptive (bell curves).
- Skull comparison: adult human, baby chimp, adult chimp.
- Peppered moth on lichen-covered vs sooty tree (light vs dark variant).
- Marsupial vs placental mammal pairs (Tasmanian wolf vs placental wolf).
Q8. Describe one example of adaptive radiation.
Example: Darwin's Finches on the Galapagos Islands
About 2 million years ago, a small flock of seed-eating finches was blown from the South American mainland to the volcanic Galapagos archipelago. Different islands offered different food resources (seeds of different sizes, insects, cactus flowers, tree buds).
From this single ancestor, natural selection produced 13–17 descendant species, each with a beak adapted to its diet:
About 2 million years ago, a small flock of seed-eating finches was blown from the South American mainland to the volcanic Galapagos archipelago. Different islands offered different food resources (seeds of different sizes, insects, cactus flowers, tree buds).
From this single ancestor, natural selection produced 13–17 descendant species, each with a beak adapted to its diet:
- Large ground finch (Geospiza magnirostris) — heavy crushing beak for large hard seeds.
- Small ground finch — small beak for small seeds.
- Cactus finch — long pointed beak for cactus flowers.
- Woodpecker finch — stout beak; uses cactus spines or twigs as tools to extract insects.
- Vegetarian finch — parrot-like beak for leaves and buds.
- Warbler finch — slender beak for tiny insects.
Q9. Can we call human evolution as adaptive radiation?
No, strictly speaking, human evolution is NOT adaptive radiation — at least not in the classic sense.
Adaptive radiation requires:
Adaptive radiation requires:
- A single ancestor diversifying into multiple coexisting species, each in a different niche.
- Driven by access to ecologically empty niches, typically in geographic isolation.
- The various hominid forms (Australopithecus, Homo habilis, Homo erectus, Neanderthal, Homo sapiens) did not all coexist as a diverse radiation; they largely succeeded one another in time, with limited overlap.
- Most lineages went extinct; only Homo sapiens remains today.
- Modern humans occupy many habitats not by speciation but by cultural adaptation — clothes, tools, agriculture — within a single species.
Q10. 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 horse.
Evolution of the Horse (Equus) — One of the most complete fossil records in biology, spanning ~55 million years.
Key trends:
| Genus | Period | Size | Toes | Teeth | Habitat |
|---|---|---|---|---|---|
| Eohippus (Hyracotherium) | ~55 mya (Eocene) | ~30 cm | 4 (front), 3 (back) | Low-crowned, browsing | Forest |
| Mesohippus | ~40 mya (Oligocene) | ~60 cm | 3 per limb | Slightly higher crowned | Open woodland |
| Merychippus | ~25 mya (Miocene) | ~100 cm | 3 (centre weight-bearing) | High-crowned, grazing | Grasslands |
| Pliohippus | ~10 mya (Pliocene) | ~125 cm | 1 (with vestigial 2 splints) | High-crowned, grazing | Open plains |
| Equus (modern horse) | ~1 mya — present | ~150–170 cm | 1 fully developed | High-crowned, grazing | Grasslands worldwide |
- Size: Small (dog-sized) → Large (modern horse).
- Toes: Multiple toes (4–3) → Single hoof (1) — adapted for fast running on hard ground.
- Teeth: Low-crowned browsing teeth → High-crowned grazing teeth — as habitat shifted from forest leaves to tough grasses.
- Legs: Short and flexible → Long and stiff for endurance running.
- Habitat: Forest browser → Open plains grazer.
Interactive: Hominid Timeline Explorer
Pick a hominid to see its key features:
Brain size: —
Diet: —
Notable features: —
Activity 7.5 — Apply Hardy–Weinberg in Real Data
Setup: A school of 600 students is screened for a recessive blood disorder. 24 students are found to be homozygous recessive (affected).
Predict and calculate: Find q, p and the number of carriers (heterozygotes).
Step 1: q² = 24/600 = 0.04
Step 2: q = √0.04 = 0.2
Step 3: p = 1 − 0.2 = 0.8
Step 4: 2pq = 2(0.8)(0.2) = 0.32
Step 5: Number of carriers = 0.32 × 600 = 192 carriers
Reflection: 192 silent carriers vs 24 affected — 8× more carriers than affected individuals. This is why genetic counselling matters: most disease alleles "hide" in heterozygous carriers.
Competency-Based Questions
Q1. Who proposed the principle of natural selection along with Darwin? L1 Remember
Answer: (c) Alfred Russel Wallace. Wallace independently arrived at the same idea while working in the Malay Archipelago. Their joint paper was read at the Linnean Society in 1858.
Q2. The Bhimbetka rock shelter is famous for: L1 Remember
Answer: (b). Bhimbetka in Raisen district, Madhya Pradesh — cave paintings by pre-historic humans dating ~18,000 years. UNESCO World Heritage Site since 2003.
Q3. Calculation: 1% of a population shows a recessive trait. Find the frequency of carriers. L3 Apply
q² = 0.01, q = 0.1, p = 0.9. Carriers = 2pq = 2(0.9)(0.1) = 0.18 = 18%. Eighteen times more carriers than affected.
Q4. Analyse: Why did Homo sapiens migrate from Africa during the ice age? L4 Analyse
Answer: During the ice age (75,000–10,000 ya), sea levels dropped (water locked up in glaciers), exposing land bridges between continents. Humans expanded across these into the Middle East, Asia, Australia and the Americas. Migration was driven by:
- Search for new food sources as climates changed.
- Population pressure in Africa.
- Following migrating prey animals.
- Land bridges (Bering Strait connecting Asia–Americas) became available.
Q5. HOT (Create): Design a thought experiment that could distinguish Lamarckian inheritance from Darwinian natural selection. L6 Create
Thought Experiment (Lamarck vs Darwin in a single test):
- Setup: Take a colony of bacteria and split it into two flasks (A and B). Both flasks have identical starting bacteria, no antibiotic.
- Treatment A: Expose flask A to a low dose of antibiotic for 24 hours, then test for resistance.
- Treatment B: Take many replica plates of flask B (using velvet — Lederberg's method) before any antibiotic exposure. Then expose the replicas to antibiotic.
- Lamarckian prediction: Resistance arises only in cells exposed to antibiotic (induced by the environment). The replicas, never having "seen" antibiotic, should show no resistance.
- Darwinian prediction: Resistance is pre-existing (random mutations). Both flask A survivors AND the replica colonies should show resistant cells in identical positions on the plate.
- Actual result (Joshua & Esther Lederberg, 1952): Replicas showed resistant colonies in exactly the same positions as the original — proving resistance existed before antibiotic exposure. Lamarck wrong, Darwin right.
Assertion–Reason Questions
Choose: (A) Both true, R explains A. (B) Both true, R doesn't explain A. (C) A true, R false. (D) A false, R true.
A: Modern Homo sapiens shows much less genetic diversity than chimpanzees.
R: Our species passed through a small population bottleneck during the late Pleistocene.
Answer: (A). Both true; R explains A. Genetic studies show human populations have remarkably low genetic diversity — explained by ancestry through a small founding population in Africa (~10,000 individuals during the last ice age).
A: A Darwin finch population with q² = 0.04 has 32% carriers.
R: Carrier frequency = 2pq where p + q = 1.
Answer: (A). Both true; R explains A. q² = 0.04 → q = 0.2, p = 0.8. 2pq = 2(0.8)(0.2) = 0.32 = 32%.
A: Australopithecus could walk upright.
R: Fossil footprints (Laetoli, Tanzania) and pelvic bone structure both support bipedalism in Australopithecus.
Answer: (A). Both true; R explains A. The Laetoli footprints (3.6 mya) preserved in volcanic ash show two upright walkers — likely Australopithecus afarensis. Combined with skeletal evidence (broad pelvis, angled femur), bipedalism in early hominids is well established.
Frequently Asked Questions - NCERT Exercises and Solutions: Evolution
What are the most-asked NCERT exercise questions in Chapter Evolution?
NCERT Class 12 Biology Chapter on Evolution exercises cover definitions, mechanisms, labelled diagrams, comparison tables, and application-based questions. The MyAiSchool solution set provides full step-by-step solutions for every NCERT question, aligned with the CBSE board exam pattern. Students should master scientific terminology, mechanism flowcharts, and concept comparison to score full marks.
How should students approach diagram-based questions in Evolution?
For diagram-based questions in NCERT Class 12 Biology Chapter on Evolution: (1) draw clean, proportional, large diagrams with sharp pencil lines, (2) label all parts horizontally on the right side using a ruler, (3) use scientific terminology (Latin/Greek names where applicable), (4) write a 1-2 line description if asked. The MyAiSchool solutions provide editable reference diagrams aligned with NCERT textbook figures.
What types of CBSE board questions come from Evolution?
CBSE Class 12 Biology board questions from Evolution typically include: (1) 1-mark MCQs on definitions and processes, (2) 2-mark short-answer mechanism/comparison questions, (3) 3-mark labelled-diagram questions, (4) 5-mark long-answer essays combining mechanism + diagram + significance. The MyAiSchool exercise set tags each question by mark weight and Bloom level (L1-L6).
How do I compare two biological processes in 5-mark questions?
For 5-mark comparison questions in NCERT Class 12 Biology on Evolution: (1) use a two-column table with feature headings down the left side, (2) compare on at least 5-6 features (definition, location, mechanism, control, outcome, significance), (3) include one labelled diagram if relevant, (4) end with biological significance. The MyAiSchool solutions follow this CBSE-aligned tabular format consistently for full marks.
What are common mistakes in Evolution exercises?
Common mistakes in NCERT Class 12 Biology Evolution include: (1) confusing similar terms (mitosis vs meiosis, syngamy vs triple fusion, etc.), (2) skipping intermediate steps in mechanisms, (3) missing examples or species names, (4) writing essays when tables are expected, (5) forgetting biological significance. The MyAiSchool solutions highlight these traps with red flags so students avoid losing marks.
How does the MyAiSchool solution differ from other NCERT solution sets?
MyAiSchool Class 12 Biology Evolution solutions use NEP 2024-aligned pedagogy with Bloom Taxonomy tagged questions (L1 Remember to L6 Create), step-by-step working with biological reasoning, fully labelled SVG diagrams, comparison tables, interactive simulations, and Competency-Based Questions (CBQs) for board exam practice. Each solution is verified against NCERT and CBSE marking schemes.
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