Chapter 24 Evolution Class 12 Biology Short Questions | Theory of Special Creation, Hydrothermal Vents, Endosymbiont Hypothesis, Lamarckism, Neo-Darwinism & Biogeography Evidence

Chapter 24: Evolution

Short Answers (2–3 Marks) – Punjab Board / RTS / HED Exams (Point-wise + examples + tables = full marks)

1) Define theory of special creation

Theory of Special Creation (also called Divine Creation):

Life was created by a supernatural power (God) in its present form.
Species are fixed and immutable (no change or evolution).
All organisms were created in 6 days (as per Bible).
Supported by religious beliefs; no scientific evidence.
Oldest theory of origin of life.

2) Define hydrothermal vents

Hydrothermal Vents: Deep-sea hot springs (black smokers) on ocean floor where superheated water (up to 400°C) rich in minerals and H₂S comes out from cracks in Earth’s crust.

Proposed by J.B.S. Haldane and others as possible site for origin of life.
Provide energy (chemosynthesis) and reducing environment for formation of organic molecules.
First life (chemoautotrophs) may have originated here.

3) What is endosymbiont hypothesis?

Endosymbiont Hypothesis (Lynn Margulis, 1967): Mitochondria and chloroplasts originated from free-living prokaryotes (aerobic bacteria and cyanobacteria) that were engulfed by primitive eukaryotic cells and lived in symbiosis.

Evidence:

Both have their own circular DNA and 70S ribosomes (like bacteria).
Divide by binary fission independently.
Double membrane (outer from host, inner from symbiont).

This explains origin of eukaryotic cell organelles.

4) Explain membrane invagination hypothesis

Membrane Invagination Hypothesis (also called Infolding Hypothesis): Eukaryotic cell organelles (nucleus, ER, Golgi, mitochondria-like structures) originated by invagination (folding inward) of the plasma membrane of a primitive prokaryotic cell.

Steps:

Plasma membrane folded inward → formed nuclear membrane and ER.
Further invaginations → formed other membrane-bound organelles.

Evidence:

Nuclear membrane and ER are continuous.
Explains origin of endomembrane system without symbiosis.

5) Describe Lamarckism briefly

Lamarckism (Jean-Baptiste Lamarck, 1809): First theory of evolution based on inheritance of acquired characters.

Two main principles:

Use and Disuse – Organs used frequently become stronger; unused organs become weak.
Inheritance of Acquired Characters – Changes acquired during lifetime are passed to offspring.

Example: Giraffe’s long neck (ancestors stretched neck to eat leaves → neck became longer and passed to next generations).

Criticism: Acquired characters (e.g., cut tail of mice) are not inherited.

6) Define neo-Darwinism

Neo-Darwinism (Modern Synthetic Theory): Modern version of Darwinism that combines Darwin’s natural selection with Mendelian genetics, mutation, gene flow, genetic drift and reproductive isolation.

Key Contributors:

Julian Huxley, Ernst Mayr, Theodosius Dobzhansky.

Main Points:

Variations arise due to mutation and recombination.
Natural selection acts on these variations.
Leads to speciation through reproductive isolation.

This is the accepted theory of evolution today.

7) How biogeography provides evidence for evolution?

Biogeography (distribution of organisms on Earth) provides strong evidence for evolution because:

Endemic species on islands show similarity with mainland but modifications (e.g., Galapagos finches – different beak shapes according to food).
Marsupials only in Australia (evolved in isolation after continental drift).
Discontinuous distribution (e.g., placental mammals in rest of world vs marsupials in Australia).
Fossil distribution matches continental positions (e.g., Glossopteris flora in all southern continents).

Density-Dependent and Density-Independent Factors: Mechanisms Influencing Population Dynamics
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