A Level H1 Biology Evolution Diversity Quiz

A-Level Biology H1 Quiz - Evolution Diversity (Answer Key)

Total Marks: 40

Section A: Multiple Choice & Short Concepts

1. C
[1 mark]
Reasoning: Natural selection acts on existing variation; individuals with advantageous traits survive/reproduce more, passing on alleles. A is Lamarckian; B implies environment causes specific helpful mutations (incorrect); D is too vague/incorrect (strength isn't the only factor).

2. B
[1 mark]
Reasoning: Analogous structures have similar functions but different evolutionary origins (convergent evolution). Homologous structures share ancestry.

3. B
[1 mark]
Reasoning: DNA base sequence comparison is the most direct and precise measure of genetic relatedness.

4. 0.6
[2 marks]
Working:

1. Frequency of recessive phenotype ($q^2$) = 0.16.
2. Frequency of recessive allele ($q$) = $\sqrt{0.16} = 0.4$.
3. Frequency of dominant allele ($p$) = $1 - q = 1 - 0.4 = 0.6$.
   [1 mark for correct working/logic, 1 mark for final answer]

5. Speciation is the evolutionary process by which populations evolve to become distinct species.
[2 marks]
Key points:

• Formation of new species [1]
• From an existing population [1]
• Usually involves reproductive isolation.

6. Any two of the following:
[2 marks, 1 each]

• No mutation
• No migration (gene flow)
• Large population size (no genetic drift)
• Random mating
• No natural selection

7. In small populations, chance events (such as the death of a few individuals) can significantly alter allele frequencies.
[2 marks]
Key points:

• Allele frequencies change due to chance/random sampling error [1]
• Effect is magnified because the sample size is small / loss of alleles is more impactful [1]

8.

1. Variation exists in the bacterial population due to random mutation [1].
2. Some bacteria possess an allele for resistance to methicillin [1].
3. When exposed to methicillin, non-resistant bacteria die, while resistant bacteria survive (selection pressure) [1].
4. Resistant bacteria reproduce and pass the resistance allele to offspring, increasing its frequency in the population [1].

9.

1. Different antibiotics target different bacterial mechanisms/pathways [1].
2. It reduces the probability that a bacterium will have simultaneous mutations conferring resistance to all drugs used [1].

10. Homologous structures
[1 mark]

Section B: Structured Response & Data Interpretation

11.

1. The whale flipper contains the same bone structure (humerus, radius, ulna, etc.) as terrestrial mammals [1].
2. This suggests they share a common ancestor that had limbs for walking on land [1].
3. Over time, natural selection modified the limb shape for swimming, but the underlying skeletal pattern remained [1].

12.

1. Whale flipper: Divergent evolution from a common tetrapod ancestor (homologous) [1].
2. Shark body: Convergent evolution; sharks and whales do not share a recent common ancestor with this trait, but evolved similar shapes due to similar aquatic environments [1].

13.

1. Cytochrome c is essential for aerobic respiration, so it is found in almost all eukaryotes [1].
2. It evolves slowly, allowing comparisons between distantly related species [1].

14.

1. Chimpanzee [1].
2. It has zero amino acid differences, indicating the most recent common ancestor and highest genetic similarity [1].

15.

1. The statement is incorrect regarding "recent" [1].
2. While they share a common ancestor (evidenced by the presence of the protein), the large number of differences (45) indicates the ancestor lived a very long time ago [1].

16. Allopatric Speciation (6 marks)
Marking Guide:

1. Geographical Barrier: A physical barrier (e.g., ocean, mountain range) separates a single population into two or more isolated populations [1].
2. No Gene Flow: The separated populations cannot interbreed, preventing the exchange of alleles [1].
3. Different Selection Pressures: The environments in the separated areas differ (e.g., climate, food sources, predators) [1].
4. Natural Selection: Individuals with alleles advantageous in their specific environment survive and reproduce more successfully [1].
5. Genetic Drift/Mutation: Random mutations occur independently in each population; genetic drift may alter allele frequencies, especially if populations are small [1].
6. Accumulation of Differences: Over time, genetic and phenotypic differences accumulate to the point where the populations are distinct [1].

Section C: Extended Response & Synthesis

17. Pre-zygotic Barriers (3 marks)
Marking Guide:

1. Definition: Mechanisms that prevent fertilization from occurring [1].
2. Example 1: Temporal isolation (breeding at different times/seasons) OR Behavioral isolation (different courtship rituals) [1].
3. Example 2: Mechanical isolation (physical incompatibility) OR Ecological isolation (different habitats) [1].

18. Post-zygotic Barriers (3 marks)
Marking Guide:

1. Definition: Mechanisms that operate after fertilization has occurred [1].
2. Example 1: Hybrid inviability (hybrid zygote fails to develop or dies early) [1].
3. Example 2: Hybrid sterility (hybrid survives but is sterile, e.g., mule), preventing gene flow back into parent populations [1].

19.

1. Divergent Evolution: Related species evolve different traits due to different environments. Example: Darwin's finches or whale flipper vs. human hand [2].
2. Convergent Evolution: Unrelated species evolve similar traits due to similar environments. Example: Shark body shape vs. Dolphin/Whale body shape or Bat wing vs. Butterfly wing [2].

20.

1. Mutations are random changes in DNA sequence that create new alleles/genetic variation [1].
2. Without this variation, natural selection would have no raw material to act upon, preventing adaptation and evolution [1].