Secondary 3 Biology Evolution Diversity Quiz

Secondary 3 Biology Quiz - Evolution Diversity (Answer Key)

Total Marks: 40

Section A: Multiple Choice Questions (10 marks)

1. Answer: A [1]
Explanation: Evolution is defined as the change in the genetic composition (allele frequencies) of a population over successive generations. It occurs at the population level, not the individual level. Option B describes acquired characteristics (Lamarckism), C describes behavioural adaptation, and D describes classification/taxonomy.

2. Answer: B [1]
Explanation: Charles Darwin (along with Alfred Russel Wallace) proposed the theory of natural selection as the mechanism for evolution. Darwin published On the Origin of Species in 1859. Lamarck proposed inheritance of acquired characteristics, Mendel discovered the laws of inheritance, and Wallace independently conceived natural selection.

3. Answer: B [1]
Explanation: Homologous structures are similar structures in different species derived from a common ancestor. The forelimbs of human, bat, whale, and bird have the same basic bone arrangement (humerus, radius, ulna, carpals, metacarpals, phalanges) but different functions (grasping, flying, swimming, flying). Analogous structures have similar functions but different origins (e.g., bird wing vs. insect wing). Vestigial structures are reduced, non-functional remnants. Convergent evolution produces analogous structures.

4. Answer: A [1]
Explanation: The human appendix is a vestigial structure — a reduced, non-functional remnant of a larger caecum that was functional in herbivorous ancestors. The heart, liver, and brain are all vital, fully functional organs.

5. Answer: B [1]
Explanation: Natural selection acts on the phenotype (observable characteristics) because it is the phenotype that interacts with the environment and determines survival and reproduction. Genotype is the genetic makeup; allele frequency changes are the result of natural selection; mutation rate provides the raw material but is not directly acted upon.

6. Answer: B [1]
Explanation: Directional selection occurs when one extreme phenotype is favoured, causing the population's trait distribution to shift in one direction. The dark moths were favoured over light moths due to camouflage on soot-darkened trees, shifting the population toward the dark phenotype. Stabilising selection favours intermediate phenotypes; disruptive selection favours both extremes; genetic drift is random change in allele frequencies.

7. Answer: B [1]
Explanation: Similar DNA (or protein) sequences provide the strongest evidence for common ancestry because they reflect shared genetic inheritance. Similar habitats, body size, or diets can result from convergent evolution or environmental pressures and do not necessarily indicate shared ancestry.

8. Answer: C [1]
Explanation: On a phylogenetic tree, species that share the most recent common ancestor (sister taxa) are most closely related. Species A and B share a node that is more recent than any node shared with other species. The tree shows A and B as sister taxa, C and D as sister taxa, and E as an outgroup.

9. Answer: B [1]
Explanation: Antibiotic resistance arises through random mutation (not caused by the antibiotic) followed by natural selection. Bacteria with random mutations conferring resistance survive and reproduce when antibiotics kill non-resistant bacteria. This is a classic example of natural selection. Options A, C, and D reflect common misconceptions (Lamarckian inheritance, learning, directed mutation).

10. Answer: D [1]
Explanation: Natural selection requires: (1) variation in traits, (2) heritability of traits, and (3) differential survival/reproduction based on traits. A changing environment (not stable) is typically what drives selection pressures. A stable environment would lead to stabilising selection maintaining the status quo, but change is not a requirement — selection can occur in stable environments too. The key is that D is the only statement that is NOT a requirement.

Section B: Structured Questions (20 marks)

11. (a) Any two of the following: [2]

• Increase in body size (from small dog-sized to large horse-sized)
• Reduction in number of toes (from 4 toes → 3 toes → 1 toe)
• Change in tooth structure (from low-crowned/brachydont teeth for browsing to high-crowned/hypsodont teeth for grazing)
• Elongation of limbs and feet
• Fusion of leg bones

Marking: 1 mark per valid observable change, max 2 marks.

(b) Explanation: [2]

• Early horses (Hyracotherium) had low-crowned teeth suited for browsing soft leaves in forests.
• Later horses (Equus) evolved high-crowned (hypsodont) teeth with complex enamel folds suited for grazing tough, abrasive grasses in open grasslands.
• The increase in crown height provides more tooth material to withstand wear from silica phytoliths in grasses and dust/soil ingested while grazing close to the ground.

Marking: 1 mark for linking low-crowned teeth for browsing vs. high-crowned for grazing; 1 mark for explaining the selective pressure (abrasive grasses/soil).

(c) Answer: [1]

• Spread of open grasslands / reduction of forests (leading to selection for faster running on hard ground to escape predators).
  OR
• Change from soft forest floor to hard open plains (selecting for single, strong toe/hoof for efficient running).

Marking: 1 mark for a valid environmental change linked to the adaptation.

12. (a) Description of natural selection process: [3]

1. Variation: There is genetic variation in fur thickness within the rabbit population (some have thicker fur, some thinner).
2. Selection pressure: Cold winters act as a selective pressure — rabbits with thicker fur are better insulated, lose less heat, and survive the winter better.
3. Differential survival/reproduction: Rabbits with thicker fur have higher survival rates and produce more offspring.
4. Inheritance: Fur thickness is heritable, so offspring inherit the thicker fur trait from their parents.
5. Result: Over generations, the frequency of alleles for thick fur increases, and the average fur thickness of the population increases.

Marking: 1 mark each for variation, selection pressure/differential survival, inheritance — max 3 marks. Must mention generations/population change.

(b) Any two of the following: [2]

• Genetic drift (random changes in allele frequencies, especially in small populations)
• Gene flow (migration of individuals into/out of the population)
• Mutation (introduces new alleles)
• Non-random mating (sexual selection, inbreeding)

Marking: 1 mark per factor, max 2 marks.

13. (a) Answer: [1]
Humans and chimpanzees share 100% identical cytochrome c amino acid sequences, indicating they share a very recent common ancestor and are the most closely related species in the table.

Marking: 1 mark for conclusion linking 100% similarity to recent common ancestry/close relationship.

(b) Explanation: [2]

• Cytochrome c is a highly conserved protein essential for cellular respiration (electron transport chain) in almost all aerobic organisms.
• Because its function is critical and unchanged across diverse species, mutations in its amino acid sequence are often deleterious and removed by natural selection.
• Therefore, differences in its sequence accumulate slowly and roughly proportionally to evolutionary time, making it a reliable "molecular clock" for comparing distant relationships.

Marking: 1 mark for "highly conserved/essential function in all aerobic organisms"; 1 mark for "slow, steady mutation rate acts as molecular clock" or "differences proportional to divergence time".

(c) Answer: [1]
Chimpanzee (100% similarity).

Marking: 1 mark for correct identification.

14. (a) Answer: [1]
All three vertebrate embryos possess pharyngeal pouches (gill slits/pouches) and a post-anal tail at early developmental stages.

Marking: 1 mark for stating one clear similarity (pharyngeal pouches OR tail).

(b) Explanation: [2]

• The presence of similar embryonic structures (pharyngeal pouches, tail) in fish, birds, and mammals indicates they share a common ancestor that also had these features.
• These structures are homologous at the embryonic level — they develop from the same embryonic tissues and follow similar developmental pathways, even though they may develop into different adult structures (e.g., pharyngeal pouches become gills in fish but parts of the ear/throat in mammals).
• This supports evolution by showing that developmental patterns are conserved from a common ancestor.

Marking: 1 mark for common ancestry/shared developmental pathway; 1 mark for homologous embryonic structures/divergent adult forms.

15. (a) Explanation: [2]

• Adaptive radiation is the rapid diversification of a single ancestral species into multiple descendant species, each adapted to a different ecological niche.
• Darwin's finches evolved from a common ancestor that colonised the Galápagos Islands.
• Different finch species evolved different beak shapes/sizes adapted to different food sources (seeds, insects, nectar, etc.) on different islands, reducing competition and exploiting available niches.

Marking: 1 mark for definition of adaptive radiation (single ancestor → multiple species, different niches); 1 mark for applying to finches (beak adaptations for different diets).

(b) Explanation: [2]

• During the drought, small, soft seeds became scarce, while large, hard seeds remained available.
• Finches with deeper, stronger beaks could crack the hard seeds and survived better.
• Finches with shallower beaks could not access the hard seeds and died at higher rates.
• This is directional selection favouring larger beak depth, causing the population average to increase.

Marking: 1 mark for environmental change (drought → hard seeds); 1 mark for selection mechanism (deep beaks survive/reproduce better → average increases).

16. Answer: [1]
Speciation is the evolutionary process by which one species splits into two or more distinct species that are reproductively isolated from each other (cannot interbreed to produce fertile offspring).

Marking: 1 mark for definition including splitting of species and reproductive isolation.

17. Description: [3]

1. Geographic isolation: A physical barrier (e.g., mountain range, river, ocean) separates a population into two or more isolated subpopulations with no gene flow between them.
2. Independent evolution: Each subpopulation experiences different environmental conditions, mutations, and selection pressures. They evolve independently — natural selection, genetic drift, and mutation cause their allele frequencies to diverge.
3. Reproductive isolation: Over time, genetic differences accumulate (in mating behaviours, gamete compatibility, chromosome structure, etc.) such that even if the barrier is removed, the subpopulations can no longer interbreed successfully.
4. Speciation: The subpopulations have become distinct species.

Marking: 1 mark for geographic barrier stopping gene flow; 1 mark for independent evolution/divergence (selection, drift, mutation); 1 mark for evolution of reproductive isolation leading to new species.

Section C: Extended Response Questions (10 marks)

18. (a) Explanation: [2]

• During the Industrial Revolution, soot pollution darkened tree trunks and killed light-coloured lichens.
• The dark (carbonaria) moths were better camouflaged against the dark tree trunks, making them less visible to bird predators.
• The light (typica) moths were more visible on dark bark and were eaten more frequently.
• Therefore, dark moths had higher survival and reproduction rates, increasing their frequency in the population.

Marking: 1 mark for camouflage advantage on dark trees; 1 mark for differential predation/survival leading to frequency increase.

(b) Explanation: [2]

• Clean air legislation reduced soot pollution, allowing lichens to regrow and tree trunks to become lighter again.
• The light (typica) moths were now better camouflaged on the light-coloured bark with lichens.
• The dark (carbonaria) moths became more visible to predators on the light background.
• Light moths had higher survival and reproduction, causing their frequency to increase again (reversal of selection pressure).

Marking: 1 mark for environmental reversal (light trees/lichens return); 1 mark for reversal of selection pressure favouring light moths.

(c) Answer: [1]

• The peppered moth example shows a change in allele frequency within a single species (microevolution), not the origin of a new species (macroevolution/speciation).
  OR
• The genetic basis (single gene, two alleles) is simpler than most traits, which are polygenic.
  OR
• The example relies on bird predation as the selective agent, but other factors (e.g., thermal advantages of dark colour) may also play a role.

Marking: 1 mark for any valid limitation (microevolution not speciation; simple genetic basis; other selective factors).

19. (a) Answer: [1]
Chimpanzee (or bonobo — both are equally close as sister taxa to humans).

Marking: 1 mark for chimpanzee.

(b) Answer: [1]
Approximately 6 million years ago (6 MYA).

Marking: 1 mark for ~6 MYA (accept 5–7 MYA).

(c) Explanation: [3]

• DNA sequences (or protein sequences) are compared across species.
• The number of differences (mutations) in homologous sequences is counted — more differences indicate longer time since divergence from a common ancestor.
• Assuming a roughly constant mutation rate (molecular clock), the genetic distance is used to estimate divergence times.
• Computational algorithms (e.g., maximum likelihood, Bayesian inference) use these distances to construct the most probable branching pattern (tree topology) that reflects evolutionary relationships.
• The resulting phylogenetic tree shows which species share more recent common ancestors based on genetic similarity.

Marking: 1 mark for comparing homologous DNA/protein sequences; 1 mark for molecular clock concept (differences proportional to time); 1 mark for computational tree-building algorithms.

20. (a) Explanation: [3]

1. Variation: Random mutations occur in bacterial populations, some of which confer resistance to a specific antibiotic.
2. Selection pressure: When antibiotics are overused (e.g., for viral infections, incomplete courses, agricultural use), they kill susceptible bacteria but leave resistant mutants alive.
3. Differential survival/reproduction: Resistant bacteria survive and reproduce rapidly (short generation time), passing the resistance allele(s) to offspring.
4. Gene transfer: Resistance genes can spread rapidly between bacteria via horizontal gene transfer (conjugation, transformation, transduction), even across species.
5. Result: The frequency of resistance alleles increases in the bacterial population — evolution by natural selection accelerated by human overuse of antibiotics.

Marking: 1 mark for random mutation providing variation; 1 mark for antibiotic use selecting for resistant bacteria (killing susceptible ones); 1 mark for rapid reproduction and/or horizontal gene transfer spreading resistance.

(b) Any two of the following: [2]

• Use antibiotics only when necessary (not for viral infections).
• Complete the full prescribed course of antibiotics (to kill all bacteria, preventing survival of partially resistant ones).
• Reduce/regulate antibiotic use in agriculture/livestock.
• Develop new antibiotics / alternative treatments (phage therapy, vaccines).
• Infection control measures (hygiene, isolation) to reduce spread of resistant strains.
• Combination therapy (using multiple antibiotics simultaneously).

Marking: 1 mark per valid strategy, max 2 marks.

End of Answer Key