🌸Chapter 6
EVOLUTION
( 4 Marks)
1. Describe the Miller and Urey
experiment and its importance in the origin of life.
Answer:
- Stanley Miller and Harold Urey
simulated primitive Earth’s atmosphere using CH₄, NH₃, H₂, and water vapor
in a closed apparatus.
- They provided electric sparks
(for lightning) and maintained high temperature.
- After a week, they found amino
acids, urea, and other organic molecules.
- This experiment proved that
life’s building blocks could form from simple inorganic compounds —
supporting Oparin-Haldane’s theory of chemical evolution.
2. Explain the Oparin-Haldane theory
of chemical evolution of life.
Answer:
- Primitive Earth had a reducing
atmosphere (CH₄, NH₃, H₂, H₂O).
- Under UV light and lightning,
these gases reacted to form organic molecules (amino acids, sugars).
- These accumulated in oceans as
“primordial soup.”
- Over time, molecules aggregated
to form coacervates → protocells → first living cells.
Thus, life originated from non-living matter through gradual chemical evolution.
3. Explain Lamarck’s theory of
evolution. Why was it rejected?
Answer:
- Lamarck proposed the theory
of inheritance of acquired characters.
- He said organisms acquire
traits due to environmental changes and use/disuse of organs (e.g.,
giraffes stretched their necks).
- These traits are inherited by
offspring → gradual evolution.
Rejected because: - No experimental proof.
- Acquired traits don’t alter
genes, so cannot be inherited.
4. Describe Darwin’s theory of
natural selection.
Answer:
1.
Overproduction: Organisms produce more offspring
than can survive.
2.
Variation: Individuals show differences.
3.
Struggle
for existence:
Competition for resources.
4.
Survival
of the fittest:
Those with favorable variations survive.
5.
Inheritance: Advantageous traits are inherited.
Over generations, these lead to formation of new species.
5. Differentiate between Darwinism
and Mutation Theory.
|
Feature |
Darwinism |
Mutation Theory |
|
Proposed by |
Charles Darwin |
Hugo de Vries |
|
Mechanism |
Natural selection acts on variations |
Evolution due to sudden heritable mutations |
|
Rate |
Gradual |
Sudden |
|
Example |
Finches on Galápagos |
Oenothera lamarckiana (Evening primrose) |
6. Explain the concept of adaptive
radiation with suitable examples.
Answer:
- Adaptive radiation = evolution
of several species from a common ancestor in new habitats.
Examples: - Darwin’s finches: On Galápagos Islands, evolved
different beaks adapted to food types.
- Australian marsupials: Evolved into kangaroo, koala,
wolf-like Tasmanian tiger, etc.
Shows how species diversify to occupy different ecological niches.
7. How are homologous and analogous
organs different? Give examples and explain their evolutionary significance.
Answer:
|
Feature |
Homologous |
Analogous |
|
Structure |
Similar |
Different |
|
Function |
Different |
Same |
|
Example |
Forelimbs of human & bat |
Wings of bird & insect |
|
Type of Evolution |
Divergent |
Convergent |
Significance:
- Homologous: evidence of common
ancestry.
- Analogous: evidence of similar
adaptation to environment.
8. Explain fossil evidence of
evolution.
Answer:
- Fossils are preserved remains
or impressions of ancient life forms.
- They show gradual transition
from simple to complex organisms.
Examples: - Archaeopteryx shows link between reptiles
and birds.
- Eusthenopteron connects fish and amphibians.
Importance: Helps trace evolutionary sequence and estimate organism’s age by carbon dating.
9. What are vestigial organs?
Explain their importance in evolution with examples.
Answer:
- Vestigial organs are reduced,
non-functional remnants of structures functional in ancestors.
Examples: Appendix, wisdom teeth, nictitating membrane in humans.
Significance: Evidence of descent with modification — proving common ancestry.
10. What are connecting links? Give
examples.
Answer:
Connecting links are organisms showing features of two different groups.
Examples:
- Archaeopteryx → between reptiles and birds.
- Peripatus → between annelids and
arthropods.
Significance: Provide strong evidence for organic evolution.
11. What are the main evidences for
organic evolution?
Answer:
1.
Morphological: Homologous, analogous, vestigial
organs.
2.
Embryological: Similar early embryos of
vertebrates.
3.
Palaeontological: Fossil records.
4.
Molecular: Similarity in DNA, proteins,
enzymes.
These all support the concept of common ancestry.
12. Differentiate between convergent
and divergent evolution with examples.
|
Feature |
Convergent Evolution |
Divergent Evolution |
|
Definition |
Unrelated species develop similar traits |
Related species evolve different traits |
|
Cause |
Similar environment |
Different environment |
|
Example |
Wings of bat & insect |
Forelimbs of mammals |
|
Type |
Analogous |
Homologous |
13. Explain the concept of natural
selection using industrial melanism.
Answer:
- In pre-industrial England,
light-colored moths were camouflaged on lichened trees.
- Post-industrialization, soot
darkened trees → dark moths survived better.
- Natural selection favored
melanic moths (peppered moths).
Conclusion: Environment selects traits best suited for survival.
14. What is Hardy–Weinberg
principle? State its significance and the factors affecting it.
Answer:
- States that allele frequencies
in a population remain constant (genetic equilibrium).
- Formula: p2+2pq+q2=1p^2 + 2pq +
q^2 = 1p2+2pq+q2=1
Significance: Serves as a baseline to study evolutionary change.
Factors affecting: Mutation, gene flow, genetic drift, natural selection, non-random mating.
15. Explain gene flow and genetic
drift.
Answer:
- Gene flow: Movement of alleles between
populations through migration → increases variation.
- Genetic drift: Random change in allele
frequency in small populations due to chance events → may reduce
variation.
Examples: - Founder effect, bottleneck effect.
16. What is the Founder Effect and
Bottleneck Effect?
Answer:
- Founder Effect: A few individuals colonize a
new area → gene pool differs from parent population.
- Bottleneck Effect: Population size drastically
reduces due to natural disaster → random loss of alleles.
Result: Reduced genetic diversity and altered evolution.
17. What is speciation? Explain the
process briefly.
Answer:
Speciation = formation of new species from existing ones.
Process:
1.
Isolation
(geographical/reproductive).
2.
Genetic
divergence due to mutation and selection.
3.
Reproductive
isolation → new species.
Example: Darwin’s finches evolved into different species.
18. Differentiate between allopatric
and sympatric speciation.
|
Type |
Allopatric |
Sympatric |
|
Isolation |
Geographical barrier |
No barrier |
|
Gene flow |
Prevented |
Occurs |
|
Example |
Darwin’s finches |
Polyploidy in plants |
19. Explain the role of variations
in evolution.
Answer:
- Variations are differences in
genetic makeup among individuals.
- They arise by mutations,
recombination, and gene flow.
- Provide raw material for natural
selection → adaptation and evolution.
Without variation, evolution cannot occur.
20. What is meant by microevolution
and macroevolution?
Answer:
- Microevolution: Small genetic changes within a
species (e.g., antibiotic resistance).
- Macroevolution: Formation of new
genera/families due to accumulation of microevolutionary changes (e.g.,
reptiles → birds).
21. Explain stabilizing,
directional, and disruptive selection with examples.
Answer:
- Stabilizing: Favors average traits (e.g.,
human birth weight).
- Directional: Favors one extreme (e.g., dark
moths in pollution).
- Disruptive: Favors both extremes (e.g.,
butterfly coloration).
→ These drive evolution in different directions.
22. Explain the concept of genetic
equilibrium using Hardy–Weinberg principle.
Answer:
If no evolutionary force acts, allele frequency (p and q) remains constant.
Equation: p2+2pq+q2=1p^2 + 2pq + q^2 = 1p2+2pq+q2=1
Deviation from equilibrium indicates that evolution is occurring.
23. What are transitional fossils?
Explain with examples.
Answer:
Fossils showing traits of two groups, linking them evolutionarily.
Examples:
- Archaeopteryx: reptile + bird features.
- Eusthenopteron: fish + amphibian.
These fossils confirm gradual evolution.
24. Write short notes on the
evidence from embryology supporting evolution.
Answer:
- Early embryos of vertebrates
(fish, frog, bird, human) resemble each other.
- Presence of gill slits and
notochord in all embryos shows common ancestry.
This concept is called recapitulation theory (Ontogeny repeats Phylogeny).
25. Explain molecular evidence
supporting evolution.
Answer:
- Similarities in DNA, RNA, and
proteins (like cytochrome-c, hemoglobin) across species.
- Humans and chimpanzees have
~98% DNA similarity.
- Proves common ancestry among
organisms.
26. Explain the process of human
evolution in brief.
Answer:
1.
Australopithecus – bipedal, 4 mya.
2.
Homo
habilis – tool
user, 2 mya.
3.
Homo
erectus – used
fire, 1.5 mya.
4.
Neanderthal
man – culture, 1,00,000 years ago.
5.
Homo
sapiens – modern
humans, 75,000 years ago.
27. What are the main
characteristics of Homo erectus?
Answer:
- Upright posture, used fire.
- Brain size ~900 cc.
- Made stone tools.
- Lived in caves; first to leave
Africa.
→ Intermediate between H. habilis and H. sapiens.
28. Describe the Out-of-Africa
theory of human evolution.
Answer:
- Homo sapiens evolved in Africa ~200,000
years ago.
- Migrated to Asia & Europe,
replacing earlier Homo species.
- Supported by fossil and DNA
studies → African origin of modern humans.
29. What evidences support the
theory of human evolution?
Answer:
1.
Fossil
records (Australopithecus to Homo sapiens).
2.
Anatomical
similarities (skull, limb structure).
3.
DNA
similarity with chimpanzees.
4.
Archaeological
remains (tools, art, dwellings).
30. Explain the difference between
natural selection and genetic drift.
|
Feature |
Natural Selection |
Genetic Drift |
|
Cause |
Environmental pressure |
Chance events |
|
Acts on |
Variations |
Small populations |
|
Direction |
Adaptive |
Random |
|
Result |
Favors fit traits |
Reduces diversity |
31. What is coevolution? Give
examples.
Answer:
Mutual evolutionary influence between interacting species.
Examples:
- Flowers and pollinators evolve
together.
- Predator-prey relationships
(e.g., cheetah and gazelle).
→ Ensures survival and mutual adaptation.
32. What is the role of isolation in
evolution?
Answer:
- Prevents gene flow between
populations.
- Leads to genetic divergence and
speciation.
Types: - Geographical (mountains,
rivers).
- Reproductive (mating barriers).
Isolation is the first step in formation of new species.
33. Explain continental drift and
its effect on evolution.
Answer:
- Continents once formed Pangaea
→ drifted apart.
- Isolation led to independent
evolution of species.
Example: Unique Australian marsupials evolved separately.
Supports the idea of geographical isolation in speciation.
34. Explain the role of mutation in
evolution.
Answer:
- Mutation = sudden change in
DNA.
- Source of new alleles → genetic
variation.
- Some beneficial mutations are
preserved by natural selection, leading to adaptation and speciation.
35. Describe how fossils are formed
and their importance.
Answer:
Formation: Burial of organisms → sedimentation → mineralization →
preservation.
Importance:
- Reveal structure of past
organisms.
- Indicate age and evolutionary
relationships.
- Show transitional forms.
36. Describe the main steps in the
origin of life.
Answer:
1.
Formation
of simple inorganic molecules.
2.
Chemical
reactions → simple organic molecules.
3.
Polymerization
→ complex molecules (proteins, nucleic acids).
4.
Aggregation
→ protocells → first living cell.
Life thus originated from non-living matter (abiogenesis).
37. Explain how biochemical
similarities among organisms provide evidence for evolution.
Answer:
- DNA, RNA, and enzymes are
similar in all organisms.
- Similar genetic code indicates
common origin.
- Example: Cytochrome-c structure
conserved from yeast to humans.
38. Describe the role of natural
selection in speciation.
Answer:
- Acts on variations → survival
of best-adapted individuals.
- Over time, populations
accumulate differences.
- Reproductive isolation occurs →
formation of new species.
39. What are the major types of
evidence for biological evolution?
Answer:
1.
Morphological
(homology, analogy).
2.
Palaeontological
(fossils).
3.
Embryological
(common development stages).
4.
Molecular
(DNA/protein similarities).
All indicate descent from a common ancestor.
40. Describe the role of environment
in evolution.
Answer:
- Environment determines which
variations are beneficial.
- Climate, food, and habitat
influence natural selection.
- Example: Industrial melanism,
polar bear’s white fur, camel’s hump.
41. Explain the importance of
variations and mutations in evolution.
Answer:
- Variations increase
adaptability.
- Mutations introduce new genes.
- Provide raw material for
natural selection.
Without them, evolution would stop.
42. What is artificial selection?
How has it helped humans?
Answer:
- Human-controlled breeding for
desired traits.
- Used in crops (wheat, cabbage)
and animals (dogs, cattle).
- Demonstrates how selective
breeding can modify species quickly — supporting Darwin’s ideas.
43. How does molecular biology
support Darwin’s theory?
Answer:
- Similar DNA and protein
sequences across species.
- Universal genetic code.
- Molecular clocks estimate
evolutionary time.
Supports that all life descended from common ancestors.
44. Explain the role of natural
disasters in evolution.
Answer:
- Events like volcanic eruptions
or asteroid impacts cause mass extinctions.
- Eliminate unfit species → new
ecological niches.
- Surviving species adapt and
radiate — promoting evolution.
45. What is the significance of
Hardy-Weinberg principle in studying evolution?
Answer:
- Predicts allele distribution
under ideal conditions.
- Deviation from expected values
indicates evolutionary forces acting.
- Useful in genetic counseling
and population studies.
46. Describe the major events in
human evolution.
Answer:
|
Species |
Key Features |
Time |
|
Australopithecus |
Bipedal, ape-like |
4 mya |
|
Homo habilis |
Tool user |
2 mya |
|
Homo erectus |
Used fire |
1.5 mya |
|
Neanderthal |
Culture, burial |
100,000 yrs |
|
Homo sapiens |
Modern humans |
75,000 yrs |
47. Explain how Darwin’s finches
illustrate adaptive radiation.
Answer:
- Common ancestor reached
Galápagos Islands.
- Evolved into many species with
different beak shapes adapted to specific diets (seeds, insects).
→ Example of evolution by natural selection in different ecological niches.
48. What is the biochemical origin
of life according to Oparin?
Answer:
- Early Earth had CH₄, NH₃, H₂O,
H₂ under reducing atmosphere.
- Lightning + UV energy produced
organic molecules.
- Molecules aggregated into
coacervates → protocells → living cells.
Hence, life originated chemically, not spontaneously.
49. Explain the concept of
"descent with modification."
Answer:
Proposed by Darwin — all organisms share a common ancestor, but with
accumulated modifications suited to different environments.
Example: Finches with different beaks from one ancestral species.
50. Describe the evidence of evolution
from comparative embryology and molecular biology.
Answer:
- Embryology: Vertebrate embryos show
similar stages (pharyngeal gill slits, notochord).
- Molecular biology: Similar DNA and proteins
(cytochrome-c, hemoglobin).
→ Both confirm a common ancestry of life forms.
