Secondary 3 Biology Evolution Diversity Quiz

Answer Key - Secondary 3 Biology Quiz: Evolution Diversity

Marking Note: This content is syllabus-aligned. Where specific keywords are listed, they must be present for full marks.

Section A (2 marks each)

1. Definition of Species: A group of organisms that can interbreed to produce fertile offspring.
2. Evidence for Evolution: Fossils / Comparative anatomy (homologous structures) / DNA sequence comparison / Embryology. (Any one)
3. Selective Pressure: External factors (e.g., predators, climate, disease) that affect an organism's ability to survive and reproduce.
4. Adaptation: An inherited characteristic that increases an organism's chance of survival and reproduction in its environment.
5. Answer: B (The flipper of a whale and the arm of a human share a common ancestral bone structure).
6. Source of Variation: Mutation / Sexual reproduction (meiosis/independent assortment/crossing over).
7. Continuous vs Discontinuous: Continuous variation shows a range of phenotypes (e.g., height); discontinuous variation has distinct categories with no intermediates (e.g., blood group).
8. Discontinuous Example: Blood group / Ability to roll tongue / Earlobe attachment.
9. Fossils Utility: They provide a chronological record of life and show transitional forms between ancestral and modern species.
10. Trait Outcome: The trait becomes more common in the population as those possessing it are more likely to survive and pass the gene to offspring.

Section B (Structured)

11. (a) Natural Selection Process:

    • Variation exists in beetle colour (e.g., green and brown). [1]
    • Environmental change/predation occurs (e.g., birds eat green beetles more easily on brown soil). [1]
    • Brown beetles survive more often, reproduce, and pass the "brown" allele to offspring. [1] (b) Fittest: "Fitness" refers to reproductive success (ability to survive and pass on genes), not physical strength. [2]

12. Analogous vs Homologous:

    • Homologous: Similar structure, different function; suggests common ancestry (e.g., human arm and bat wing). [2]
    • Analogous: Different structure, similar function; suggests convergent evolution due to similar environment (e.g., bird wing and insect wing). [2]

13. (a) Survivors: They possessed a pre-existing genetic mutation that made them resistant to the antibiotic. [2] (b) Prediction: The antibiotic will be ineffective; the population will now be predominantly resistant. [2]

14. Role of Mutations: Mutations create new alleles $\rightarrow$ leads to new phenotypes $\rightarrow$ provides the raw material for natural selection to act upon. [3]

15. DNA Sequences: Compare the base sequences of a specific gene or protein. The fewer the differences in the sequence, the more closely related the two species are (shorter time since common ancestor). [3]

Section C (Extended)

16. Environmental Change & Rate: Rapid environmental changes (e.g., sudden climate shift) increase selective pressure. This accelerates the rate of evolution as non-adapted individuals are quickly eliminated, and only those with advantageous mutations survive. [4]

17. Peppered Moth:

    • Originally, light-coloured moths were camouflaged. [1]
    • Industrial revolution caused soot to blacken trees. [1]
    • Dark moths now had a survival advantage (less predation). [1]
    • Dark moths survived to reproduce, increasing the frequency of the dark phenotype in the population. [1]

18. Lamarckism vs Natural Selection: Lamarckism suggests acquired traits (e.g., stretched neck from effort) are passed on, but these do not change DNA. Natural selection acts on existing genetic variation (mutations) which is heritable. [4]

19. "Perfect" Organism: False. Evolution produces "good enough" adaptations for a specific environment. It is limited by existing genetic variation and often involves trade-offs (e.g., a trait for speed might reduce strength). [4]

20. Common Ancestry: These mammals evolved from a common ancestor that had a basic pentadactyl limb structure. As they diverged into different environments, natural selection modified the existing bone structure for different uses (flying, swimming, grasping), but the underlying blueprint remains. [4]