A Level H1 Biology Evolution Diversity Quiz

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

1. (a)

• Concept: Natural Selection / Differential Survival.
• Explanation:
  1. In industrial areas, soot darkened the tree bark. [1]
  2. The dark carbonaria moths were better camouflaged against predators (birds) than the light typica moths. [1]
  3. Therefore, carbonaria moths had a higher survival rate and reproduced more, passing on the dark allele to the next generation, increasing its frequency. [1]

(b)

• Prediction: The frequency of the typica (light) allele will increase, and the carbonaria (dark) allele will decrease. [1]
• Explanation: As tree bark becomes lighter, light moths are better camouflaged and have higher survival/reproductive success than dark moths. [1]

2. (a)

• Mechanism:
  1. Genetic variation exists in the S. aureus population due to random mutation; some bacteria possess a gene for methicillin resistance. [1]
  2. When methicillin is used, non-resistant bacteria die, while resistant bacteria survive (selection pressure). [1]
  3. Resistant bacteria reproduce and pass the resistance gene to offspring, increasing the frequency of the resistant allele in the population over generations. [1]

(b)

• Explanation: Overuse of antibiotics creates a strong and continuous selection pressure. [1] This kills off susceptible bacteria rapidly, leaving only resistant strains to reproduce and spread, accelerating the evolution of resistance in the population. [1]

3. (a)

• Working:
  • Decrease = $45.2 - 12.1 = 33.1$ mm
  • Percentage decrease = $(33.1 / 45.2) \times 100$
  • Calculation: $73.23\%$
• Answer: 73.2% (accept 73.23%) [2] (1 mark for correct working, 1 mark for correct answer).

(b)

• Analysis:
  1. Seeds from uncontaminated soil grow poorly in high copper (short roots), showing they are not adapted. [1]
  2. Seeds from contaminated soil grow well in high copper (long roots), showing they have evolved tolerance. [1]
  3. This indicates that in the mine environment, copper-tolerant alleles were selected for, leading to a population adapted to high copper levels. [1]

(c)

• Explanation: There may be a metabolic cost to maintaining copper tolerance (e.g., energy used for pumping out copper), which reduces growth slightly even in non-toxic conditions. [1]

4. (a)

• Explanation:
  1. Both sharks and dolphins live in the same aquatic environment and face similar selection pressures (need to move efficiently through water). [1]
  2. Natural selection favoured a streamlined body shape in both lineages independently to reduce drag, leading to convergent evolution. [1]

(b)

• Definition: Analogous structures are structures that have similar functions but different evolutionary origins/anatomical structures. [1]
• Classification: The dorsal fins are analogous. [1]

5. (a)

• Distinction:
  • Pre-zygotic mechanisms prevent the formation of a zygote (fertilization) from occurring. [1]
  • Post-zygotic mechanisms prevent the hybrid zygote from developing into a viable, fertile adult after fertilization has occurred. [1]

(b)

• Example: Geographical isolation. [1]
• Explanation: Physical barriers (mountains, oceans) prevent populations from meeting, so mating cannot occur. [1] (Alternative: Temporal isolation - breed at different times; Behavioural isolation - different courtship).

6. (a)

• Explanation:
  1. The canyon physically separates the population into two groups, preventing gene flow (interbreeding) between them. [1]
  2. Each group experiences different environmental conditions/mutation pressures/genetic drift, leading to different alleles being selected for/against in each area. [1]
  3. Over time, the genetic differences accumulate to the point where the two groups can no longer interbreed successfully even if the barrier is removed. [1]

(b)

• Example: Temporal isolation (breeding at different times) OR Behavioural isolation (different courtship rituals). [1]
• Explanation: If they breed at different times, gametes never meet, preventing fertilization and gene flow. [1] (Or: If courtship rituals differ, mating does not occur).

7. (a)

• Definition: Structures that have the same basic anatomical plan/origin (from a common ancestor) but may have different functions. [1]

(b)

• Explanation:
  1. The presence of the same bone arrangement (humerus, radius, ulna, etc.) in humans, bats, and whales suggests they inherited this structure from a common ancestor. [1]
  2. The modification of these bones for different functions (grasping, flying, swimming) shows adaptive radiation/divergent evolution from that common ancestor. [1]

8. (a)

• Domains: Bacteria, Archaea, Eukarya. [1] (All three must be correct).

(b)

• Differences:
  1. Eukarya have membrane-bound organelles (e.g., nucleus, mitochondria); Bacteria do not. [1]
  2. Eukarya have larger ribosomes (80S); Bacteria have smaller ribosomes (70S). [1] (Alternative: Eukarya have linear DNA associated with histones; Bacteria have circular DNA not associated with histones.)

(c)

• Explanation: Archaea have different cell wall compositions (no peptidoglycan) and different membrane lipid structures compared to Bacteria, and their genetic machinery (e.g., RNA polymerase) is more similar to Eukarya. [1]

9. (a)

• Answer: Human and Chimpanzee. [1]

(b)

• Answer: Nodes represent the most recent common ancestor of the lineages branching from that point. [1]

(c)

• Explanation:
  1. Fewer DNA differences indicate a more recent divergence from a common ancestor. [1]
  2. Since 1.2% < 1.6%, Humans and Chimpanzees shared a common ancestor more recently than Humans and Gorillas did, supporting the tree structure where Human/Chimp branch off after the Gorilla line. [1]

(d)

• Advantage: Molecular evidence is quantitative and objective (can be measured precisely), whereas morphological traits can be subjective or influenced by convergent evolution. [1]

10. (a)

• Working:
  • Frequency of recessive phenotype ($q^2$) = $160 / 1000 = 0.16$
  • Frequency of recessive allele ($q$) = $\sqrt{0.16}$
  • $q = 0.4$
• Answer: 0.4 [3] (1 mark for $q^2$, 1 mark for square root, 1 mark for final answer).

(b)

• Working:
  • $p + q = 1 \Rightarrow p = 1 - 0.4 = 0.6$
  • Frequency of heterozygotes ($2pq$) = $2 \times 0.6 \times 0.4 = 0.48$
  • Number of heterozygotes = $0.48 \times 1000 = 480$
• Answer: 480 mice [3] (1 mark for $p$, 1 mark for $2pq$, 1 mark for final number).

(c)

• Conditions:
  1. No mutation. [1]
  2. No migration (gene flow). [1] (Alternatives: Large population size, Random mating, No natural selection).

11. (a)

• Answer: Directional selection. [1]

(b)

• Graph:
  • X-axis: Shell Colour (Light to Dark). Y-axis: Frequency/Number of Beetles. [1]
  • Curve shifts to the right (towards darker colour) in the "After" distribution compared to "Before". [1]

(c)

• Explanation:
  1. Genetic diversity decreases as alleles for light shell colour are eliminated from the population. [1]
  2. The population becomes more uniform for the dark shell colour trait. [1]

12. (a)

• Distinction:
  • Artificial selection is driven by human choice for desired traits. [1]
  • Natural selection is driven by environmental pressures and survival/reproductive success. [1]

(b)

• Risk: Reduced genetic diversity. [1]
• Explanation: This makes the crop population more vulnerable to diseases or environmental changes, as there may be no resistant alleles present. [1]

13. (a)

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

(b)

• Explanation:
  1. A small group breaks away from the main population to establish a new colony. [1]
  2. The allele frequencies in this small group may not represent the original population (by chance, some alleles may be over/under-represented). [1]
  3. If a rare allele for a disorder is present in the founders, it may become common in the descendant population. [1]

(c)

• Explanation: In small populations, chance events have a larger proportional impact on allele frequencies. [1]

14. (a)

• Explanation:
  1. Fossilization requires specific conditions (e.g., rapid burial, lack of oxygen) which are rare. [1]
  2. Many organisms have soft bodies that do not fossilize well. [1]

(b)

• Explanation:
  1. Transitional fossils show characteristics intermediate between ancestral and descendant groups. [1]
  2. Archaeopteryx has features of both reptiles (teeth, tail) and birds (feathers, wings), linking the two groups. [1]

15. (a)

• Similarity: Presence of pharyngeal pouches/slits or a post-anal tail. [1]

(b)

• Explanation:
  1. These similarities suggest that vertebrates share a common ancestor that had these features. [1]
  2. The genes controlling early development are conserved across these species. [1]

16. (a)

• Explanation:
  1. Birds with larger/deeper beaks were better able to crack the large, hard seeds that remained. [1]
  2. Therefore, they had higher survival rates during the drought. [1]

(b)

• Explanation:
  1. Beak depth is a heritable trait. [1]
  2. Survivors passed the alleles for larger beaks to their offspring. [1]

(c)

• Answer: Microevolution. [1]
• Justification: It involves a change in allele frequencies within a population, not the formation of a new species. [1] (Note: Mark awarded for correct classification and brief justification).

17. (a)

• Answer: Species A and Species B. [1]

(b)

• Tree:
  • A and B branch from a recent common node. [1]
  • C branches off earlier, and D branches off earliest (or C and D form a clade separate from A/B, but D is most distant). Correct topology: ((A,B),C),D). [1]

(c)

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

18. (a)

• Working:
  • $q^2$ (white) = $45 / 500 = 0.09$
  • $q$ (recessive allele r) = $\sqrt{0.09} = 0.3$
  • $p$ (dominant allele R) = $1 - 0.3 = 0.7$
• Answer: 0.7 [3] (1 mark for $q^2$, 1 mark for $q$, 1 mark for $p$).

(b)

• Working:
  • Frequency of homozygous dominant ($p^2$) = $0.7^2 = 0.49$
  • Number of plants = $0.49 \times 500 = 245$
• Answer: 245 plants [2] (1 mark for $p^2$, 1 mark for final number).

19. (a)

• Explanation:
  1. Gene flow occurs between adjacent populations in the ring. [1]
  2. Alleles can spread around the ring through this chain of interbreeding. [1]

(b)

• Explanation:
  1. Reproductive isolation has evolved between the two end populations. [1]
  2. They can no longer exchange genes directly, fulfilling the biological species concept criteria for separate species. [1]

20. (a)

• Definition: In science, a theory is a well-substantiated explanation of some aspect of the natural world that is acquired through the scientific method and repeatedly tested and confirmed through observation and experimentation. [2]

(b)

• Explanation:
  1. Evolution is a fact because we observe changes in allele frequencies and species over time (e.g., antibiotic resistance). [1]
  2. Evolution is a theory because it provides the comprehensive framework (natural selection, genetic drift, etc.) that explains how and why these changes occur, supported by vast evidence from multiple fields. [2]