Chapter 7: Evolution – Case-Based Questions with Answers

CBSE Class 12 Biology Case-Based Questions (NCERT): Evolution

Course & Examination Details

Course: CBSE Class 12 Biology
Unit: Unit II – Genetics and Evolution
Chapter: Chapter 7 – Evolution
Prescribed Textbook: NCERT Biology Class XII
Examination: CBSE Class 12 Board Examination
Question Type: Case-Based / Source-Based Questions

Section A: Origin of Life

Case 1

Scientists believe life originated from non-living matter under primitive Earth conditions.
Q. Which theory explains this process?
Answer: The theory of chemical evolution explains that life originated through gradual chemical reactions forming organic molecules from inorganic substances.

Case 2

Early Earth lacked free oxygen but supported formation of organic compounds.
Q. What type of atmosphere existed on primitive Earth?
Answer: A reducing atmosphere containing methane, ammonia, hydrogen, and water vapour existed on primitive Earth.

Case 3

An experiment simulated lightning in a mixture of gases.
Q. Name the experiment and its conclusion.
Answer: The Miller–Urey experiment showed that amino acids could form abiotically under early Earth conditions.

Case 4

Simple organic molecules gradually formed complex macromolecules.
Q. Who proposed this idea?
Answer: A. I. Oparin and J. B. S. Haldane proposed this concept.

Case 5

First life forms survived without oxygen.
Q. Why were early organisms anaerobic?
Answer: Oxygen was absent in the primitive atmosphere, so early organisms relied on anaerobic metabolism.

Section B: Evidences for Evolution

Case 6

Forelimbs of humans, whales, and bats show similar bone structure.
Q. What does this indicate?
Answer: These are homologous organs indicating common ancestry and divergent evolution.

Case 7

Wings of birds and insects perform the same function but differ structurally.
Q. Identify the type of organs.
Answer: These are analogous organs showing convergent evolution.

Case 8

Human appendix has no significant function today.
Q. What type of organ is it?
Answer: It is a vestigial organ indicating evolutionary ancestry.

Case 9

Early embryos of vertebrates resemble each other.
Q. What does this suggest?
Answer: Embryological similarity suggests common evolutionary origin.

Case 10

Fossils show gradual change in organisms over time.
Q. Which type of evidence is this?
Answer: This is palaeontological evidence supporting evolution.

Section C: Adaptive Radiation

Case 11

Finches on different islands developed varied beak shapes.
Q. Name this evolutionary phenomenon.
Answer: This phenomenon is adaptive radiation.

Case 12

A single ancestral species gives rise to many species.
Q. Which type of evolution does this represent?
Answer: It represents divergent evolution.

Case 13

Marsupials diversified in Australia due to isolation.
Q. What evolutionary concept explains this?
Answer: Adaptive radiation explains diversification of Australian marsupials.

Case 14

Different species occupy different ecological niches.
Q. Why is this important?
Answer: It reduces competition and promotes survival through natural selection.

Case 15

Adaptive radiation increases biodiversity.
Q. State one reason.
Answer: It produces multiple species adapted to varied environments from a common ancestor.

Section D: Theories of Evolution

Case 16

Giraffes stretch their necks to reach leaves.
Q. Which theory supports this idea?
Answer: Jean-Baptiste Lamarck proposed inheritance of acquired characters.

Case 17

Acquired traits are not passed to offspring.
Q. Why is Lamarckism rejected?
Answer: Acquired characters do not affect germ cells and are not inherited genetically.

Case 18

Only well-adapted organisms survive environmental challenges.
Q. Which theory explains this?
Answer: Charles Darwin explained this through natural selection.

Case 19

Organisms produce more offspring than can survive.
Q. What does this lead to?
Answer: It leads to struggle for existence and survival of the fittest.

Case 20

Favourable traits increase in a population over time.
Q. What process causes this?
Answer: Natural selection causes increase of advantageous traits.

Section E: Mechanism of Evolution & Hardy–Weinberg Principle

Case 21

Random changes in gene frequency occur in small populations.
Q. Name this mechanism.
Answer: This mechanism is genetic drift.

Case 22

Migration introduces new alleles into a population.
Q. Which evolutionary force is this?
Answer: Gene flow or migration alters allele frequencies.

Case 23

A population shows constant allele frequency over generations.
Q. Which principle explains this?
Answer: The Hardy–Weinberg principle explains genetic equilibrium.

Case 24

Deviation from Hardy–Weinberg equilibrium is observed.
Q. What does this indicate?
Answer: It indicates that evolution is occurring due to evolutionary forces.

Case 25

Fossil and genetic studies trace human origin to one continent.
Q. Which continent is this?
Answer: Africa is considered the cradle of human evolution.