Secondary 4 Pure Biology Evolution Diversity Quiz

Secondary 4 Pure Biology Quiz — Evolution Diversity

Answer Key

Section A: Multiple Choice

1. B
[2 marks]
Natural selection is the process by which individuals with traits that confer a survival or reproductive advantage in a given environment are more likely to pass those traits to the next generation.
Common mistake: Choosing A implies Lamarckian inheritance (organisms "choosing" traits), which is incorrect. Choosing C is wrong because evolution acts on populations over generations, not simultaneously.

2. B
[2 marks]
The graph shows a shift in the mean beak depth toward one extreme (deeper beaks), which is characteristic of directional selection. After the drought, harder seeds were likely more abundant, favouring finches with deeper, stronger beaks.
Common mistake: Students may select stabilising selection if they confuse a shift with a narrowing of the range.

3. C
[2 marks]
Speciation is the process by which populations become reproductively isolated and diverge genetically to the point where they can no longer interbreed to produce fertile offspring.
Common mistake: Choosing B — geographic isolation is one mechanism (allopatric speciation) but not the only route; sympatric speciation can occur without it.

4. B
[2 marks]
Punctuated equilibrium describes long periods of little change (stasis) interrupted by relatively rapid bursts of evolutionary change. This contrasts with gradualism, which predicts slow, continuous change.
Common mistake: Students may choose gradualism if they focus on the "millions of years" without noticing the abrupt replacement.

5. C
[2 marks]
DNA sequence similarity is the most reliable indicator of common ancestry because DNA is inherited directly from ancestors. The more similar the DNA, the more recently two species diverged from a common ancestor.
Common mistake: Choosing A or D — shared habitat or niche may result from convergent evolution, not common ancestry.

Section B: Short Answer and Structured Response

6. The gene pool is the total collection of all the genes (and their alleles) present in a population at a given time. [2]
Marking notes: Award 1 mark for "all the genes/alleles" and 1 mark for specifying "in a population." Answers that only say "all the genes in an organism" are incorrect.

7. Any two of the following: [1 mark each, total 2]
(a) No mutations occur.
(b) The population is very large (no genetic drift).
(c) Mating is random.
(d) There is no natural selection (all individuals have equal reproductive success).
(e) There is no migration (no gene flow into or out of the population).
Marking notes: Students need only state two. Accept equivalent phrasing, e.g., "large population size" or "no emigration or immigration."

8. (a) The number of dark-coloured moths in Town A increased steadily over the 10-year period, from 30 in Year 1 to 125 in Year 10. [2]
Marking notes: Award 1 mark for identifying the increase, 1 mark for referencing specific data (e.g., "from 30 to 125" or quoting figures from the table).

(b) During the Industrial Revolution, soot from factories darkened tree bark. Dark-coloured moths were better camouflaged against predators (birds), so they survived and reproduced more successfully than light-coloured moths. Over time, the frequency of the dark allele increased in the population. [2]
Marking notes: Award 1 mark for linking pollution/darkened surfaces to camouflage, and 1 mark for explaining differential survival/reproduction (natural selection). Answers that only say "pollution killed the light moths" without explaining selection are incomplete.

9. Convergent evolution is the process by which unrelated species independently evolve similar traits as a result of adapting to similar environments or ecological niches. [1]
Example: The streamlined body shape of sharks (fish) and dolphins (mammals), or the wings of insects and birds. [1]

Divergent evolution is the process by which related species evolve different traits, often due to adaptation to different environments, leading to speciation. [1]
Example: Darwin's finches on the Galápagos Islands, which evolved different beak shapes from a common ancestor. [1]

Marking notes: Examples must be named (not just described vaguely). Award 1 mark for each correct definition and 1 mark for each valid example.

10. Genetic drift is the random change in allele frequencies due to chance events. In a small population, chance events (e.g., a few individuals dying before reproducing) can significantly alter the allele frequencies because each individual represents a larger proportion of the gene pool. In a large population, the effect of random events is averaged out and has minimal impact on overall allele frequencies. [2]
Marking notes: Award 1 mark for defining genetic drift or stating it is random, and 1 mark for explaining why small populations are more affected (each individual has a greater proportional impact).

11. (a) Homologous structures. [1]

(b) These structures suggest that the five species share a common ancestor from which the basic pentadactyl limb pattern was inherited. The differences in bone shape and size reflect adaptations to different functions (e.g., flying, swimming, running, grasping) over evolutionary time. [2]
Marking notes: Award 1 mark for stating common ancestry, 1 mark for linking structural differences to functional adaptation. Answers that only say "they look similar" without mentioning common origin are incomplete.

12. (a) In the grassy environment, green beetles are better camouflaged from bird predators than brown beetles. Green beetles therefore have a higher chance of surviving and reproducing, passing the green allele to their offspring. Over several generations, the frequency of the green allele increases in the population, while the frequency of the brown allele decreases. This is natural selection acting on a heritable trait. [3]
Marking notes: Award 1 mark for linking camouflage to reduced predation, 1 mark for differential survival/reproduction, and 1 mark for stating the change in allele frequency over generations.

(b) The frequency of the brown allele would increase over time. In a brown soil environment, brown beetles would be better camouflaged and less likely to be eaten by birds. Brown beetles would survive and reproduce more successfully, passing the brown allele to offspring. Natural selection would favour the brown phenotype. [2]
Marking notes: Award 1 mark for predicting the increase in brown allele frequency, 1 mark for explaining the mechanism (camouflage → differential survival → reproduction).

13. Any two of the following: [1 mark each]
(a) Mutation
(b) Sexual reproduction / random fertilisation / crossing over during meiosis / independent assortment
(c) Gene flow (migration of individuals between populations)
Marking notes: Accept equivalent phrasing. "Genetic recombination" is acceptable for (b).

14. Geographic isolation occurs when a physical barrier (e.g., a mountain range, river, or ocean) separates a population into two or more groups. The separated populations experience different environmental conditions and selection pressures. Over time, genetic differences accumulate through natural selection, mutation, and genetic drift. Eventually, the populations become so genetically different that they can no longer interbreed to produce fertile offspring — they have become separate species. [2 for mechanism + 1 for example]

Example: The Galápagos finches — ancestral finches colonised different islands, became geographically isolated, and adapted to different food sources on each island, leading to the evolution of multiple species with distinct beak shapes. [1]

Marking notes: Award up to 2 marks for a clear explanation of the mechanism (barrier → different selection → genetic divergence → reproductive isolation) and 1 mark for a named example. Answers without an example lose 1 mark.

15. (a) Adaptive radiation is the rapid evolution of many species from a single common ancestor, each adapted to a different ecological niche. [2]
Marking notes: Award 1 mark for "many species from one ancestor" and 1 mark for "different niches/environments."

(b) The Galápagos Islands provided a variety of unoccupied ecological niches (different food sources, habitats) with few competing species. This allowed the ancestral finch population to diversify and adapt to different niches on different islands, driven by natural selection and geographic isolation. [2]
Marking notes: Award 1 mark for mentioning available/vacant niches, and 1 mark for linking this to diversification (natural selection or isolation).

Section C: Extended Response

16. [5 marks]
Step-by-step explanation:

1. Variation exists: Within a bacterial population, genetic variation arises through random mutations. Some bacteria may carry a mutation that confers resistance to a particular antibiotic (e.g., a change in the target protein or an enzyme that breaks down the antibiotic). [1]

2. Selection pressure: When the antibiotic is introduced, it acts as a selection pressure. Non-resistant bacteria are killed or inhibited from reproducing. [1]

3. Differential survival and reproduction: Resistant bacteria survive the antibiotic treatment and reproduce, passing the resistance gene to their offspring. [1]

4. Change in allele frequency: Over successive generations, the frequency of the resistance allele increases in the population because resistant individuals contribute more offspring to the next generation. [1]

5. Result: Eventually, the majority (or all) of the bacterial population carries the resistance allele, and the antibiotic becomes ineffective. This is evolution by natural selection. [1]

Marking notes: Award 1 mark for each of the five key points above. Answers that omit variation or allele frequency change lose the corresponding mark. Award a maximum of 4 marks if the answer is well-structured but misses one key concept.

17. (a) Species A and B are most closely related. [1] This is determined by identifying the most recent common ancestor — A and B share Node 1, which is the most recent branching point compared to the nodes connecting the other species. [1]

(b) Species D (or E) is the outgroup to the A–B–C clade. [1]
Marking notes: Accept either D or E, as both are equally distant from the A–B–C clade. The outgroup is the species that branches off earliest from the clade in question.

(c) The fossil with intermediate traits suggests that species C evolved gradually from the ancestor at Node 2 through a series of small, incremental changes. This supports the gradualism model of evolution, as it shows a transitional form linking the ancestor to the modern species. [2]
Marking notes: Award 1 mark for identifying gradual change/transitional form, and 1 mark for linking it to gradualism or the evolutionary pathway.

18. [3 marks — 1 mark per line of evidence]

Fossil evidence: The fossil record shows a chronological sequence of life forms, with simpler organisms in older rock layers and more complex organisms in younger layers. For example, transitional fossils such as Archaeopteryx (which has both reptilian and avian features) provide evidence of evolutionary links between major groups. [1]

Comparative anatomy: Homologous structures, such as the pentadactyl limb in vertebrates, indicate common ancestry despite differences in function. The similar bone arrangement in the forelimbs of humans, bats, whales, and horses suggests descent from a shared ancestor. [1]

Molecular biology: Comparing DNA or protein sequences between species reveals degrees of similarity that reflect evolutionary relationships. For example, humans and chimpanzees share approximately 98–99% of their DNA, indicating a recent common ancestor. [1]

Marking notes: Award 1 mark for each line of evidence that includes both a specific example and a clear explanation of how it supports evolution. Vague answers (e.g., "fossils show change over time" without an example) receive 0.5 marks.

19. (a) (i) Gradualism [1]
(ii) Punctuated equilibrium [1]

(b) The fossil record showing long periods with no morphological change (stasis) in a species, followed by the sudden appearance of a distinctly different form without intermediate transitional fossils, would support punctuated equilibrium. [1]
Marking notes: Award 1 mark for describing stasis and sudden change in the fossil record. Answers that only say "the fossil record" without elaboration receive 0 marks.

20. [2 marks]
The student's statement is inaccurate for the following reasons:

1. Evolution does not necessarily lead to greater complexity. Some organisms have evolved to become simpler over time (e.g., parasites losing complex organ systems). Evolution favours traits that improve reproductive success in a given environment, not complexity. [1]

2. Evolution does not have a direction toward "better." Natural selection favours traits that are advantageous in a specific environment, not traits that are universally "better." What is advantageous in one environment may be disadvantageous in another. Evolution is not goal-oriented or progressive. [1]

Marking notes: Award 1 mark for each valid reason (maximum 2). Answers that only say "the student is wrong" without explanation receive 0 marks. Accept other valid points, such as: evolution acts on populations, not individuals; "better" is subjective and environment-dependent.

End of Answer Key