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O Level Biology Evolution Diversity Quiz

Free O Level Biology Evolution Diversity quiz, Qwen3.6 Exam version, with questions, answers, and O Level-style practice for Singapore students.

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O Level Biology From Real Exams Generated by Qwen3.6 Plus Updated 2026-08-17
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O-Level Biology Quiz - Evolution Diversity: Answer Key

Section A: Multiple Choice Questions

  1. B
    Reasoning: Natural selection acts on existing variation; individuals with traits better suited to the environment survive and pass on those traits. A is Lamarckism (incorrect). C is incorrect as evolution varies. D is incorrect; mutations are random, not caused by the environment directly.

  2. B
    Reasoning: Homologous structures (similar bone structure, different function) indicate common ancestry.

  3. A
    Reasoning: Mutation creates variation (2) → Selection pressure applied (3) → Survival of the fittest (1) → Change in population frequency (4).

  4. C
    Reasoning: Mutation is the primary source of new genetic alleles. Mitosis and asexual reproduction produce clones.

  5. C
    Reasoning: Archaeopteryx is a "missing link" or transitional fossil showing traits of both groups.

  6. B
    Reasoning: Dark colouration is dominant (D). In a dark environment, dark moths (DD and Dd) are camouflaged and survive better.

  7. C
    Reasoning: Continuous variation (e.g., height, mass) is usually polygenic and influenced by the environment. A, B, and D describe discontinuous variation.

  8. B
    Reasoning: Adaptive radiation occurs when species diversify rapidly into a multitude of new forms, particularly when a change in the environment makes new resources available.

  9. C
    Reasoning: Sexual reproduction involves meiosis and fertilization, creating unique genetic combinations (variation).

  10. D
    Reasoning: Natural selection requires differential survival. If survival rates are equal, no selection occurs.

Section B: Structured Questions

11. Peppered Moths

(a) Explanation of light moth prevalence:

  • Light-coloured moths were camouflaged against the light-coloured lichens [1].
  • Dark-coloured moths were easily seen and eaten by predators (birds) [1].

(b) Natural selection during industrialisation:

  • Soot darkened the tree trunks, killing lichens [1].
  • Light-coloured moths became visible to predators and were eaten [1].
  • Dark-coloured moths were now camouflaged and survived [1].
  • Surviving dark moths reproduced and passed the dark allele to offspring, increasing its frequency in the population [1].

(c) Prediction after clean air laws:

  • The frequency of the dark-coloured allele will decrease [1].
  • As lichens return, light moths are camouflaged again, so dark moths are selected against (eaten) [1].

12. Variation

(a) Continuous vs. Discontinuous:

  • Continuous: Shows a range of values with no distinct categories; often influenced by environment. Example: Height, weight, skin colour. [2]
  • Discontinuous: Distinct categories with no intermediates; controlled by genes only. Example: Blood group, eye colour, gender. [2]

(b) Causes of variation:

  1. Mutation (changes in DNA sequence) [1]
  2. Sexual reproduction (meiosis/crossing over/random fertilization) [1]
    (Accept: Environmental factors for continuous variation)

(c) Importance for survival:

  • If the environment changes, some individuals may possess traits that allow them to survive the new conditions [1].
  • Without variation, the entire population might be susceptible to the same threat (e.g., disease) and could become extinct [1].

13. Horse Evolution

(a) Trend:

  • Body size has increased over time [1].

(b) Advantage of larger size:

  • Longer legs allow for faster running to escape predators in open grasslands [1].
    (Accept: Larger digestive system to process tough grass)

(c) Incomplete fossil record:

  • Fossilisation is a rare event; many organisms decompose without leaving traces [1].
  • Soft tissues rarely fossilise, and many fossils may have been destroyed by geological activity or remain undiscovered [1].

14. Darwin’s Finches

(a) Type of evolution:

  • Adaptive radiation [1].

(b) Role of isolation in speciation:

  • Geographic isolation (e.g., on different islands) prevents interbreeding between populations [1].
  • Different environments exert different selection pressures (e.g., different food sources) [1].
  • Over time, genetic differences accumulate until the populations can no longer interbreed even if brought together (reproductive isolation) [1].

15. Artificial Selection

(a) Comparison Table:

  • Selective Agent: Natural Selection = Environment/Nature; Artificial Selection = Humans [1]
  • Purpose/Goal: Natural Selection = Survival/Reproduction; Artificial Selection = Human needs/desires [1]
  • Time Scale: Natural Selection = Slow (thousands/millions of years); Artificial Selection = Rapid (few generations) [1]
  • Outcome: Natural Selection = Adaptation to environment; Artificial Selection = Traits beneficial to humans (may reduce survival in wild) [1]

(b) Disadvantage:

  • Reduced genetic diversity makes crops vulnerable to diseases or pests [1].
    (Accept: Undesirable traits may be linked to desirable ones)

16. Phylogenetic Trees

(a) Most closely related:

  • Species A and B [1].
  • They share the most recent common ancestor (node) [1].

(b) Node meaning:

  • It represents a common ancestor from which both species diverged [1].

(c) Is D the ancestor?

  • No [1]. Species D is a modern species that has evolved alongside the others; it is an outgroup, not the direct ancestor.

17. Genetic Drift

(a) Definition:

  • Random changes in allele frequencies in a population due to chance events [1].

(b) Bottleneck effect:

  • A sharp reduction in population size due to a catastrophic event [1].
  • The surviving population has a smaller gene pool, reducing genetic diversity [1].

(c) Significance in small populations:

  • Chance events have a larger impact on allele frequencies when the sample size (population) is small [1].

18. Homologous and Analogous Structures

(a) Analogous structures:

  • Structures with similar functions but different evolutionary origins/structures [1].
  • Example: Wings of a bird and wings of an insect [1].

(b) Why not common ancestry:

  • They evolved independently due to similar environmental pressures (convergent evolution), not from a shared ancestor with that trait [1].

(c) Bird vs. Insect Wing:

  • Analogous [1].
  • Bird wings are modified forelimbs with bones; insect wings are extensions of the exoskeleton with no bones. They have different structural origins [1].

19. Molecular Evidence

(a) DNA comparison:

  • Species with more similar DNA sequences share a more recent common ancestor [1].
  • Fewer differences in base sequences indicate closer relationship [1].

(b) Cytochrome c:

  • It is a universal protein found in many organisms, allowing for broad comparisons across different species [1].

(c) Closer relation:

  • Species X and Species Y [1] (98% similarity is higher than 80%).

20. Reproductive Isolation

(a) Definition:

  • Mechanisms that prevent members of different species from producing fertile offspring [1].

(b) Pre-zygotic barrier:

  • Example: Temporal isolation (breeding at different times), behavioral isolation (different courtship rituals), or habitat isolation [1].

(c) Post-zygotic barrier:

  • Example: Hybrid sterility (offspring are sterile, e.g., mule) or hybrid inviability (offspring die early) [1].

(d) Necessity for speciation:

  • It ensures that the gene pools of the two populations remain separate, allowing them to evolve independently into distinct species [1].