A Level H2 Biology Evolution Diversity Quiz

A-Level Biology H2 Quiz - Evolution Diversity (Answer Key)

Total Marks: 40

Section A: Core Concepts & Definitions

1. C

• Reasoning: Natural selection acts on existing variation. Individuals with advantageous traits (phenotypes determined by alleles) have higher fitness (survival/reproduction), passing those alleles to the next generation. A is Lamarckian (incorrect). B implies environment causes specific beneficial mutations (incorrect; mutations are random). D implies intent/need (incorrect).
• [1]

2. Definition of Species:

• A group of organisms [1]
• That can interbreed to produce fertile offspring [1].
• Note: Must mention "fertile".
• [2]

3. Allopatric vs Sympatric Speciation:

• Allopatric: Speciation occurs due to geographical isolation (physical barrier) separating populations [1].
• Sympatric: Speciation occurs within the same geographical area (no physical barrier), often due to reproductive isolation mechanisms like polyploidy or behavioural changes [1].
• [2]

4. Sources of Genetic Variation:

• Any two of the following:
  1. Mutation (gene mutation / chromosomal mutation) [1]
  2. Crossing over (during Prophase I of meiosis) [1]
  3. Independent assortment (of homologous chromosomes during Metaphase I of meiosis) [1]
  4. Random fertilisation [1]
• [2]

5. Percentage Difference Calculation:

• Total bases compared: 10
• Number of differences: 1 (Position 8: G vs A)
• Calculation: $(1 / 10) \times 100 = 10\%$
• Marking: 1 mark for correct calculation/working, 1 mark for correct answer (10%).
• [2]

Section B: Natural Selection in Action

6. B

• Reasoning: Recessive alleles are expressed only in homozygous recessive individuals. Heterozygotes ($Aa$) carry the allele but express the dominant phenotype, so they are not selected against if the selection pressure acts on the phenotype. This "hides" the allele from selection, preventing it from being eliminated completely.
• [1]

7. Explanation of differential survival:

• In industrial areas, tree bark is darkened by soot/lichen death [1].
• Dark moths are camouflaged against the dark bark, while pale moths are conspicuous to predators (birds) [1].
• Therefore, dark moths have a higher survival rate (differential survival) and are more likely to be recaptured [1].
• [3]

8. Prediction and Explanation (Clean Air):

• Prediction: The frequency of the allele for pale colour (typica) will increase, and the dark allele (carbonaria) will decrease [1].
• Explanation: As trees become pale, pale moths are better camouflaged and survive better [1]. They reproduce more, passing on the pale allele to the next generation (natural selection) [1].
• [3]

9. Evolution of resistance:

• Random mutations occur in bacterial DNA, some conferring resistance to the antibiotic [1].
• The use of antibiotics creates a strong selection pressure [1].
• Non-resistant bacteria die, while resistant bacteria survive [1].
• Resistant bacteria reproduce (binary fission), passing the resistance allele to offspring, increasing its frequency in the population [1].
• [4]

10. Horizontal Gene Transfer (Conjugation):

• Conjugation involves the direct transfer of plasmids (containing resistance genes) between bacteria via a pilus [1].
• This can occur between bacteria of the same or different species [1].
• It spreads resistance much faster than waiting for vertical inheritance (cell division) and allows resistance to jump across species boundaries [1].
• [3]

Section C: Phylogenetics & Evidence

11. Difficulty eradicating MRSA:

• MRSA can survive on surfaces/in the environment for extended periods [1].
• Asymptomatic carriers (patients or staff) can harbour the bacteria without showing symptoms, acting as a reservoir for reinfection [1].
• [2]

12. Most closely related:

• Human and Chimpanzee [1].
• [1]

13. Suitability of Cytochrome c:

• Cytochrome c is a protein involved in cellular respiration (electron transport chain), which is essential for all aerobic organisms [1].
• It is highly conserved (changes slowly) but accumulates mutations over long periods, allowing comparison of evolutionary distances between diverse species [1].
• [2]

14. Adaptive Radiation (Part 1):

• Ancestral Population/Isolation: A small population of ancestral finches arrived on the Galapagos. The ocean acts as a barrier, preventing gene flow between island populations (geographical isolation) [1].
• Variation & Selection: Each island had different food sources. Random mutations produced variation in beak shape. Finches with beak shapes best suited to the local food source survived and reproduced more successfully [1].
• Result: This process repeated across islands, leading to many distinct species from a common ancestor [1].
• [3]

15. Niche Partitioning:

• Different beak shapes allow different species to exploit different food resources (niches) such as hard seeds, insects, or cactus flowers [1].
• This reduces interspecific competition for food [1].
• Allows multiple species to coexist on the same island or drives further specialisation [1].
• [3]

Section D: Synthesis & Evaluation

16. Fossil Record Evidence:

• Shows a chronological sequence of organisms, revealing trends in evolution (e.g., horse evolution) [1].
• Demonstrates that modern species are different from ancestral ones [1].
• Example: Archaeopteryx shows features of both reptiles (teeth, tail) and birds (feathers), acting as a transitional form [1].
• [3]

17. Comparative Anatomy Evidence:

• Homologous structures (e.g., pentadactyl limb in mammals) show similar bone structure but different functions [1].
• This indicates descent from a common ancestor [1].
• Despite different uses (flying, swimming, grasping), the underlying anatomical plan is conserved [1].
• [3]

18. Limitations of Fossil Record:

• Incomplete: Fossilisation is a rare event; soft-bodied organisms rarely fossilise [1].
• Gaps: Many transitional forms are missing, making it difficult to trace exact lineage lines [1].
• [2]

19. Reproductive Isolation:

• Over time, populations diverge genetically due to different selection pressures/mutation [1].
• Even if geographical barriers are removed, they can no longer interbreed to produce fertile offspring (behavioural/mechanical/gametic isolation), defining them as separate species [1].
• [2]

20. Genetic Drift vs Natural Selection:

• Natural Selection: Allele frequency changes due to differential survival/reproduction based on advantageous traits (non-random) [1].
• Genetic Drift: Allele frequency changes due to random chance/events (e.g., founder effect, bottleneck), particularly in small populations, regardless of fitness [1].
• [2]

*** End of Answer Key ***