Chapter 6: Evolution Short Questions | biology Class 12 CBSE

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Chapter 6: Evolution Short Questions | biology Class 12 CBSE | ByteNotes.in

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Question 1

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What was the significance of Miller's experiment in understanding the origin of life?

Miller created conditions similar to early earth — electric discharge in a flask containing CH4, H2, NH3 and water vapour at 800°C — and observed the formation of amino acids.
The experiment provided experimental evidence in support of Oparin and Haldane's hypothesis of chemical evolution, showing that organic molecules can form from inorganic precursors.
Analysis of meteorite content also revealed similar organic compounds, suggesting such chemical processes occur elsewhere in the universe, further supporting the chemical origin of life.

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Question 2

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How did Louis Pasteur disprove the theory of spontaneous generation?

Pasteur used pre-sterilised flasks and showed that life did not arise in flasks with killed yeast unless exposed to air, disproving that life emerges spontaneously from non-living matter.
In a control flask open to air, new living organisms arose from killed yeast, demonstrating that life comes only from pre-existing life (biogenesis).
Although Pasteur conclusively disproved spontaneous generation, his experiment did not explain how the very first life form appeared on earth.

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Question 3

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Distinguish between homologous and analogous structures with one example each.

Homologous structures have a similar anatomical plan but perform different functions; they arise due to divergent evolution from a common ancestor. Example: forelimbs of whales, bats, cheetahs, and humans.
Analogous structures perform similar functions but have different anatomical plans; they arise due to convergent evolution in unrelated lineages. Example: wings of a butterfly and a bird.
Homology indicates common ancestry, whereas analogy indicates similar adaptive pressures acting on different groups of organisms without a shared ancestor.

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Question 4

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State the Hardy-Weinberg principle and write the equation it uses.

The Hardy-Weinberg principle states that allele frequencies in a population are stable and remain constant from generation to generation when no evolutionary forces are acting; this is called genetic equilibrium.
If p and q are the frequencies of alleles A and a respectively, the genotype frequencies are p² (AA), 2pq (Aa), and q² (aa), with the equation p² + 2pq + q² = 1.
This equation is a binomial expansion of (p+q)²; when measured frequencies differ from expected values, it indicates evolutionary change has occurred in the population.

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Question 5

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What is panspermia? Why is it still considered by some scientists?

Panspermia is the hypothesis that units of life called spores were transferred to different planets including earth from outer space, explaining the extraterrestrial origin of life.
Early Greek thinkers proposed this idea; it remains a favourite hypothesis for some astronomers because analysis of meteorite content revealed organic compounds similar to those formed in Miller's experiment.
These findings suggest that chemical processes leading to organic molecule formation also occur elsewhere in space, leaving open the possibility that life-related molecules arrived on earth from outside.

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Question 6

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What is adaptive radiation? Name two examples discussed in the chapter.

Adaptive radiation is the process of evolution of different species in a given geographical area starting from a single ancestral stock and radiating into different habitats and ecological niches.
Darwin's finches of the Galapagos Islands are a classic example — from an original seed-eating ancestor, varieties with altered beaks evolved to become insectivorous and vegetarian.
Australian marsupials are another example — many different marsupial species evolved from a single ancestral stock within the isolated Australian continent.

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Question 7

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What is the founder effect? How does it lead to speciation?

The founder effect occurs when a small group from a population migrates to a new area; by chance, the allele frequencies in this small group differ greatly from the original population.
If the change in allele frequency is so pronounced that the new population becomes reproductively distinct from the original, they may eventually become a different species.
The small migrant group that establishes the new population is called the founders; their restricted gene pool drives divergence from the parent population over generations.

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Question 8

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What do fossils tell us about the history of life on earth?

Fossils are remains of hard parts of life-forms found in rock sediments; different-aged rock sediments contain fossils of different life-forms, showing that life changed over time.
Study of fossils in different sedimentary layers indicates the geological period in which various life-forms existed; certain life-forms are restricted to specific geological time-spans.
Fossils also provide evidence of extinct organisms such as dinosaurs, confirming that life forms have evolved, diversified, and sometimes disappeared over earth's geological history.

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Question 9

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What is genetic drift? How does it differ from natural selection?

Genetic drift is a change in allele frequency in a population that occurs by chance events rather than because of selective advantage; it is random and unpredictable.
Natural selection is a directed process: heritable variations that enhance survival and reproduction are favoured, so it is driven by fitness differences among individuals.
Genetic drift is particularly significant in small populations and can lead to loss of alleles or speciation, whereas natural selection consistently favours adaptive traits regardless of population size.

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Question 10

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How did industrial melanism in peppered moths demonstrate natural selection?

Before industrialisation (1850s), white-winged moths were more common because white lichen covered trees and camouflaged them from predators; dark-winged moths were easily spotted and eaten.
After industrialisation (by 1920), tree trunks became dark due to industrial soot; now dark-winged moths were camouflaged and survived, while white-winged moths were picked off by predators.
This reversal in moth population frequencies demonstrates that natural selection favours traits that enable better camouflage (survival) in the current environment, and is called industrial melanism.

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Question 11

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What were the conditions on early earth that Oparin and Haldane proposed for chemical evolution?

Oparin and Haldane proposed that early earth had high temperatures, volcanic storms, and a reducing atmosphere containing methane (CH4) and ammonia (NH3).
Under these conditions, diverse organic molecules — including proteins, RNA, and other biomolecules — could form from inorganic constituents, a process called chemical evolution.
They proposed that formation of diverse organic molecules from inorganic constituents preceded the appearance of the first cellular forms of life, making chemical evolution the precursor to biological evolution.

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Question 12

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What is convergent evolution? Give two examples from the chapter.

Convergent evolution is the independent evolution of similar traits or structures in unrelated lineages due to similar environmental pressures; it results in analogous structures.
The eyes of octopus and mammals are structurally similar despite belonging to entirely different phyla — they evolved independently to perform the same function of vision.
Placental wolf of North America and the Tasmanian wolf (marsupial) of Australia show striking similarity in body plan despite being unrelated, resulting from similar ecological pressures in different continents.

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Question 13

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Name the five factors that can disturb Hardy-Weinberg equilibrium.

The five factors are: gene migration (gene flow), genetic drift, mutation, genetic recombination, and natural selection.
When any of these factors operate, allele frequencies in a population change from their expected values, indicating that evolutionary change is occurring in the population.
When measured allele frequencies differ from expected Hardy-Weinberg values, the direction and magnitude of the difference indicates the extent and direction of evolutionary change.

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Chapter sections

Chapter 6: Evolution | Short Questions

What was the significance of Miller's experiment in understanding the origin of life?

How did Louis Pasteur disprove the theory of spontaneous generation?

Distinguish between homologous and analogous structures with one example each.

State the Hardy-Weinberg principle and write the equation it uses.

What is panspermia? Why is it still considered by some scientists?

What is adaptive radiation? Name two examples discussed in the chapter.

What is the founder effect? How does it lead to speciation?

What do fossils tell us about the history of life on earth?

What is genetic drift? How does it differ from natural selection?

How did industrial melanism in peppered moths demonstrate natural selection?

What were the conditions on early earth that Oparin and Haldane proposed for chemical evolution?

What is convergent evolution? Give two examples from the chapter.

Name the five factors that can disturb Hardy-Weinberg equilibrium.

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