🌸Chapter 6
EVOLUTION
( 3 Marks)
1. Describe the conditions on
primitive Earth that favored chemical evolution.
Answer:
- The primitive Earth had a hot,
reducing atmosphere containing gases like methane (CH₄), ammonia (NH₃),
hydrogen (H₂), and water vapor (H₂O).
- Oxygen and ozone were absent.
- Lightning and UV radiation
provided energy for chemical reactions.
- These conditions favored the
formation of simple organic molecules like amino acids and sugars, leading
to life.
2. What was the contribution of Oparin
and Haldane to the origin of life theory?
Answer:
- They proposed the chemical
evolution theory of life.
- According to them, life
originated from non-living inorganic molecules through a series of
chemical reactions.
- Organic molecules accumulated
in oceans forming a “primordial soup,” which eventually led to the
formation of primitive cells.
3. Describe Miller and Urey’s
experiment and its significance.
Answer:
- They simulated early Earth’s
atmosphere using CH₄, NH₃, H₂, and H₂O vapor in a closed system.
- Electric sparks (to mimic
lightning) were passed for a week.
- They observed the formation of
organic molecules like amino acids.
- This experiment supported Oparin–Haldane’s
theory of chemical evolution.
4. How did Pasteur’s experiment
disprove the theory of spontaneous generation?
Answer:
- Pasteur boiled nutrient broth
in an S-shaped flask; no life appeared as microorganisms were trapped in
the flask neck.
- When the neck was broken,
microbes grew, showing life arises from pre-existing life only —
disproving spontaneous generation.
5. Explain the evidences of
evolution from comparative anatomy.
Answer:
- Homologous organs: Similar structure but
different function (e.g., forelimbs of human and whale) → common ancestry.
- Analogous organs: Different structure but same
function (e.g., wings of bat and insect) → convergent evolution.
- Vestigial organs: Reduced and non-functional
organs (e.g., appendix) → evidence of evolution from ancestors.
6. What is adaptive radiation? Give
examples.
Answer:
Adaptive radiation is the evolution of several species from a common ancestor
in different environmental conditions.
Examples:
- Darwin’s finches evolved on
Galápagos Islands with different beak shapes suited to food types.
- Australian marsupials evolved
into kangaroo, koala, etc., from a common ancestor.
7. Differentiate between homologous
and analogous organs with examples.
Answer:
|
Feature |
Homologous Organs |
Analogous Organs |
|
Structure |
Same structure |
Different structure |
|
Function |
Different function |
Same function |
|
Example |
Forelimbs of human, whale |
Wings of bat, insect |
|
Evolution |
Divergent |
Convergent |
8. What is convergent and divergent
evolution? Give examples.
Answer:
- Convergent evolution: Unrelated species evolve
similar traits (e.g., wings of bat and bird).
- Divergent evolution: Species from a common ancestor
evolve different traits (e.g., forelimbs of mammals).
9. Explain fossil evidence in
support of evolution.
Answer:
- Fossils show gradual changes
from simple to complex life forms.
- Transitional forms like Archaeopteryx
show evolution from reptiles to birds.
- Fossil dating techniques help
determine the age and sequence of life on Earth.
10. How do vestigial organs support
the theory of evolution?
Answer:
Vestigial organs are remnants of functional structures present in ancestors,
e.g.:
- Appendix (in herbivorous
ancestors for cellulose digestion).
- Nictitating membrane in humans.
These indicate descent from ancestors with functional versions of these organs.
11. Describe Lamarck’s theory of
evolution.
Answer:
- Proposed by Jean Baptiste
Lamarck.
- He believed evolution occurred
through inheritance of acquired characters.
Example: Giraffes stretched necks to reach leaves, and longer necks were inherited.
Rejected: No genetic proof; acquired traits are not inherited.
12. State Darwin’s theory of natural
selection.
Answer:
- Population shows variations.
- Struggle for existence occurs
due to limited resources.
- Only the fittest survive
(natural selection).
- Favored variations are
inherited, leading to evolution of new species.
13. Explain the significance of
Darwin’s finches.
Answer:
- Darwin observed 14 species of
finches on Galápagos Islands.
- They evolved from a common
ancestor but developed different beak shapes based on food habits (seeds,
insects, etc.).
- This showed adaptive
radiation and natural selection.
14. Differentiate between Darwinism
and Mutation theory.
Answer:
|
Basis |
Darwinism |
Mutation Theory |
|
Proposed by |
Charles Darwin |
Hugo de Vries |
|
Mechanism |
Natural selection |
Sudden mutations |
|
Nature of change |
Gradual |
Sudden |
|
Example |
Finches |
Oenothera plant |
15. What is mutation? How does it
help in evolution?
Answer:
Mutation is a sudden, heritable change in DNA.
It introduces new traits into a population, creating genetic variation which,
if favorable, is preserved by natural selection—leading to evolution.
16. What is genetic drift? Explain
with an example.
Answer:
Random change in allele frequencies in small populations due to chance.
Example: Founder effect—when a few individuals form a new colony, their
gene pool may differ from the parent population.
17. Write the Hardy-Weinberg
principle and its importance.
Answer:
Equation: p2+2pq+q2=1p^2 + 2pq + q^2 = 1p2+2pq+q2=1
- p = frequency of dominant
allele; q = recessive allele.
- Allele frequencies remain
constant in absence of evolutionary forces.
Importance: Serves as a baseline to detect evolutionary changes.
18. List any five factors affecting
Hardy-Weinberg equilibrium.
Answer:
1.
Mutation
2.
Gene
flow
3.
Genetic
drift
4.
Natural
selection
5.
Non-random
mating
Each causes change in gene frequencies, leading to
evolution.
19. Explain gene flow with an
example.
Answer:
Gene flow is movement of genes between populations by migration or
interbreeding.
Example: Migration of individuals between neighboring populations introduces
new alleles, increasing variation.
20. What is reproductive isolation
and how does it lead to speciation?
Answer:
When populations cannot interbreed and produce fertile offspring, they become
reproductively isolated.
Over time, genetic differences accumulate, leading to formation of new species.
21. Differentiate between
microevolution and macroevolution.
Answer:
|
Aspect |
Microevolution |
Macroevolution |
|
Scale |
Small changes |
Large changes |
|
Time |
Short-term |
Long-term |
|
Example |
Color variation in moths |
Evolution of birds from reptiles |
22. Explain the concept of
speciation.
Answer:
Speciation is the formation of new species from an existing population due to:
- Geographic isolation (allopatric
speciation),
- Reproductive isolation,
- Accumulation of genetic
variations over time.
23. What is the founder effect?
Answer:
When a few individuals colonize a new area, their small gene pool may cause
large differences in allele frequencies compared to the parent population —
leading to genetic drift and evolution.
24. Define natural selection and its
types.
Answer:
Natural selection is the process where better-adapted individuals survive and
reproduce.
Types:
- Stabilizing selection
- Directional selection
- Disruptive selection
25. Explain industrial melanism as
an example of natural selection.
Answer:
Before industrialization, light-colored moths were common.
After soot deposition on trees, dark (melanic) moths were camouflaged better
and survived.
Natural selection favored dark-colored moths in polluted areas.
26. What is the difference between
allopatric and sympatric speciation?
Answer:
|
Type |
Allopatric |
Sympatric |
|
Isolation |
Geographic barrier |
No physical barrier |
|
Example |
Darwin’s finches |
Polyploidy in plants |
27. How is evolution related to
genetic variation?
Answer:
Genetic variation arises from mutation, recombination, and gene flow.
It provides raw material for natural selection to act upon, driving evolution.
28. What are transitional fossils? Give
examples.
Answer:
Fossils showing features of two groups, linking them evolutionarily.
Examples: Archaeopteryx (reptile + bird), Eusthenopteron
(fish + amphibian).
29. What evidences are provided by
embryology for evolution?
Answer:
- Early embryos of vertebrates
show similarities (gill slits, notochord).
- These resemblances indicate
common ancestry among vertebrates.
30. Explain molecular evidence of
evolution.
Answer:
- Similarities in DNA, RNA, and
protein sequences among species show common ancestry.
- Example: Cytochrome-c and
hemoglobin structures are highly conserved.
31. What are the major events in
human evolution?
Answer:
- Australopithecus → bipedal, used tools.
- Homo habilis → first tool maker.
- Homo erectus → used fire.
- Neanderthal man → culture and burial
practices.
- Homo sapiens → modern humans.
32. Name and describe any three
species of genus Homo.
Answer:
1.
Homo
habilis – tool
user, 2.0 mya.
2.
Homo
erectus –
upright, used fire, 1.5 mya.
3.
Homo
sapiens – modern
man, developed speech and culture.
33. Mention any three important
fossil hominids and their characteristics.
Answer:
- Australopithecus: Bipedal, small brain.
- Homo erectus: Upright posture, used fire.
- Neanderthal man: Cultural development, lived
in caves.
34. Describe the Out-of-Africa theory.
Answer:
- Modern humans (Homo sapiens)
originated in Africa around 200,000 years ago.
- They migrated to Asia and
Europe, replacing earlier Homo species.
- Supported by fossil and DNA
evidence.
35. Explain Darwin’s idea of
struggle for existence.
Answer:
Population increases geometrically while resources are limited, leading to
competition for food, space, and mates.
This struggle allows only the fittest to survive — key to natural selection.
36. Explain the role of mutation and
recombination in evolution.
Answer:
- Mutation: introduces new alleles.
- Recombination: shuffles existing alleles
during meiosis.
Together, they create variation essential for evolution by natural selection.
37. Why are homologous structures
considered evidence of common ancestry?
Answer:
Because organisms with similar structural designs (e.g., limb bones) have
evolved from a shared ancestor but adapted to different functions.
38. What is the role of natural
selection in evolution?
Answer:
Natural selection favors beneficial traits, increasing their frequency.
Over generations, this leads to adaptation and formation of new species.
39. What are the evidences from
biogeography that support evolution?
Answer:
- Related species found in
geographically close regions (Darwin’s finches).
- Isolated continents show
distinct fauna (Australia’s marsupials).
→ Supports common descent and adaptation to environment.
40. Explain the role of continental
drift in evolution.
Answer:
Movement of land masses separated populations, causing isolation and
independent evolution (e.g., unique species in Australia).
41. What is co-evolution? Give an
example.
Answer:
Mutual evolutionary influence between two species.
Example: Flowering plants and pollinators like bees evolve together for
mutual benefit.
42. Mention any three evidences
supporting human evolution.
Answer:
- Fossil records
(Australopithecus → Homo sapiens).
- Comparative anatomy (similar
skeletal features).
- Molecular evidence (DNA
similarity with chimpanzees).
43. Define atavism and give
examples.
Answer:
Reappearance of ancestral traits in modern organisms.
Examples: Tail in human newborns, thick body hair.
44. What is the importance of
variation in evolution?
Answer:
Variations help species adapt to changing environments, ensuring survival and
the possibility of new species formation.
45. Describe the timeline of life
formation on Earth.
Answer:
- 4.6 bya: Earth formed.
- 3.5 bya: First prokaryotes.
- 2.0 bya: Eukaryotes.
- 0.5 bya: Multicellular
organisms.
- 0.002 bya: Humans evolved.
46. What are the differences between
Lamarck’s and Darwin’s theories?
Answer:
|
Aspect |
Lamarck |
Darwin |
|
Mechanism |
Use and disuse, inheritance of acquired traits |
Natural selection |
|
Evidence |
None |
Fossil & variation |
|
Example |
Giraffe neck |
Finches |
47. Explain stabilizing,
directional, and disruptive selection with examples.
Answer:
- Stabilizing: Favors average (human birth
weight).
- Directional: Favors one extreme (industrial
melanism).
- Disruptive: Favors both extremes
(butterfly color forms).
48. What is the biochemical evidence
for evolution?
Answer:
Similarity in DNA, RNA, and protein sequences among organisms suggests common
ancestry — e.g., cytochrome-c similarity in humans and chimpanzees.
49. Explain how fossils are dated.
Answer:
- Relative dating: Using rock strata sequence.
- Absolute dating: Using radioactive isotopes
(C-14, K-Ar).
Helps determine the age of fossils and evolutionary timeline.
50. What are the main evidences
supporting Darwin’s theory of evolution?
Answer:
1.
Fossil
records
2.
Homologous
structures
3.
Vestigial
organs
4.
Biogeographical
distribution
5.
Natural
selection examples like industrial melanism
