Secondary 3 Biology Evolution Diversity Quiz

Secondary 3 Biology Quiz - Evolution Diversity

Answer Key

Section A: Multiple Choice

1. B [2]
Explanation: Natural selection is the process by which individuals with traits better suited to their environment have higher survival and reproductive success, passing those advantageous traits to offspring. Option A is incorrect because organisms do not "choose" traits. Option C is incorrect because evolution occurs across generations, not simultaneously. Option D is incorrect because mutations are random, not directed.

2. B [2]
Explanation: After a drought that leaves only large, hard seeds, finches with deeper (larger) beaks are better able to crack and eat these seeds. They survive and reproduce more successfully, shifting the population's average beak depth to the right over generations. This is directional selection.

3. D [2]
Explanation: All three options — embryological similarities, transitional fossils, and homologous structures — are categories of evidence that directly support the theory of evolution. Transitional fossils are particularly direct because they show intermediate forms between ancestral and descendant species.

4. B [2]
Explanation: Resistance arises from random mutations that occur before antibiotic exposure. Antibiotics act as a selective pressure, killing non-resistant bacteria while resistant individuals survive and reproduce. The key misconception to avoid (Options A, C, D) is that antibiotics cause the resistance or that bacteria adapt during their lifetime — evolution by natural selection acts on pre-existing genetic variation.

5. C [2]
Explanation: Allopatric speciation occurs when a physical barrier (such as a canyon) separates a population, preventing gene flow. Over time, genetic differences accumulate through mutation, natural selection, and genetic drift until the populations can no longer interbreed — they have become separate species. Sympatric speciation occurs without geographic separation. Convergent evolution involves unrelated species evolving similar traits. Artificial selection involves human intervention.

Section B: Short Answer

6. [2]
Answer: Variation refers to the differences in characteristics (phenotypes) among individuals within a population.
Marking notes: Award 1 mark for "differences in characteristics/traits" and 1 mark for specifying "within a population" or "among individuals." Accept "differences in features/appearance" as equivalent to characteristics.

7. [2]
Answer:
(a) Mutation (random changes in DNA/genetic material)
(b) Sexual reproduction / random fertilisation / crossing over / independent assortment during meiosis
Marking notes: Award 1 mark each for any two valid sources. Accept "genetic recombination" for (b). Do not accept "environment" alone as a source of genetic variation (environmental variation is not heritable).

8. [2]
Answer: A transitional fossil is a fossil that shows intermediate characteristics between an ancestral species and its descendants. It is important because it provides direct evidence of evolutionary change over time, showing how one species or group gradually changed into another.
Marking notes: Award 1 mark for defining transitional fossil correctly and 1 mark for explaining its significance as evidence for evolution.

9. [2]
Answer:

• Continuous variation shows a range of values with no distinct categories (e.g., height, body mass, skin colour). It is usually controlled by multiple genes (polygenic) and influenced by the environment.
• Discontinuous variation falls into distinct categories with no intermediate values (e.g., blood group, ability to roll tongue). It is usually controlled by a single gene and is not significantly affected by the environment.
  Marking notes: Award 1 mark for each correct distinction with a valid example. Students must show the key difference (range vs. categories) for full marks.

10. [2]
Answer: The presence of the pentadactyl limb in all these groups suggests that mammals, reptiles, amphibians, and birds share a common ancestor that had a five-digit limb. The basic limb structure has been modified (divergent evolution) for different functions — walking, flying, swimming, grasping — but the underlying bone plan remains similar, indicating homology.
Marking notes: Award 1 mark for identifying common ancestry and 1 mark for explaining divergent modification / homology. Accept "homologous structures" as part of the answer.

Section C: Structured Response

11.
(a) Homologous structures [1]

(b) The presence of homologous structures suggests that the four organisms share a common ancestor from which the basic limb plan was inherited. Over time, the limb was modified by natural selection for different functions in different environments — this is an example of divergent evolution. [2]
Marking notes: Award 1 mark for "common ancestor" and 1 mark for "divergent evolution" or equivalent explanation of modification for different functions.

(c) Any one of the following: molecular/biochemical evidence (DNA/protein comparisons), embryological evidence, fossil evidence, biogeographical evidence. [1]
Marking notes: Accept any valid category of evolutionary evidence.

12.
(a) Charles Darwin [1]

(b) [4]

1. Within the moth population, there is genetic variation — some moths are light-coloured and some are dark-coloured due to random mutations/genetic differences.
2. Before industrialisation, light-coloured moths were better camouflaged against the pale, lichen-covered tree trunks, so they were less likely to be eaten by predators. Dark moths were more visible and more likely to be preyed upon.
3. After industrialisation, pollution killed the lichen and the tree trunks became darkened with soot. Now dark-coloured moths were better camouflaged and light-coloured moths were more visible to predators.
4. The dark moths had a selective advantage — they survived and reproduced more successfully, passing the dark colour allele to their offspring. Over generations, the frequency of the dark form increased in the population.
   Marking notes: Award 1 mark each for the four key points: variation, pre-industrial selection pressure, change in environment/reversal of selection, and change in allele frequency over generations. This is the classic peppered moth example.

13.
(a) Chimpanzee is most closely related to humans because it has zero amino acid differences in cytochrome c compared to humans, indicating the highest degree of molecular similarity and the most recent common ancestor. [2]
Marking notes: Award 1 mark for identifying chimpanzee and 1 mark for explaining that fewer differences = closer relationship.

(b) Molecular / biochemical evidence (or "DNA/protein evidence") [1]

(c) Molecular evidence is strong because it provides a quantitative and objective measure of relatedness. DNA and proteins are inherited directly from ancestors, so similarities reflect shared evolutionary history. The more similar the molecular sequences, the more closely related the species are and the more recently they diverged from a common ancestor. [1]
Marking notes: Award 1 mark for any valid reason — accept "quantitative/objective," "directly inherited," or "reflects common ancestry."

14. [4]

1. A population is split into two or more groups by a geographic barrier (e.g., mountain range, river, canyon), preventing gene flow between the groups.
2. Random mutations occur independently in each isolated population, introducing new genetic variations.
3. The two environments may have different selection pressures (e.g., different food sources, predators, climates). Natural selection favours different advantageous traits in each population, causing them to diverge genetically over many generations.
4. Over time, the genetic differences accumulate to the point where the populations can no longer interbreed even if they come into contact again — they have become reproductively isolated and are now separate species.
   Marking notes: Award 1 mark each for: geographic barrier / no gene flow, mutation introducing variation, natural selection in different environments, and reproductive isolation / speciation.

15. [4]

1. Within a bacterial population, random mutations occur during DNA replication. Some mutations may confer resistance to a particular antibiotic. These mutations arise before exposure to the antibiotic — the antibiotic does not cause the mutation.
2. When the antibiotic is applied, it acts as a selective pressure. Non-resistant bacteria are killed, while resistant bacteria survive.
3. The resistant bacteria reproduce, passing the resistance gene to their offspring (vertical gene transfer). Bacteria can also share resistance genes through horizontal gene transfer (e.g., via plasmids), speeding up the spread.
4. Over successive generations, the proportion of resistant bacteria increases in the population. The population has evolved — the allele frequency for resistance has changed — which is the definition of evolution by natural selection.
   Marking notes: Award 1 mark each for: random pre-existing mutation, antibiotic as selective pressure, reproduction/passing on resistance, and change in population allele frequency / evolution. Accept mention of horizontal gene transfer as a bonus point but do not require it.

Section D: Data Interpretation

16. [2]
Answer: The fossil record shows that ammonite shells became increasingly complex over time. The oldest (bottom) layer has simple, loosely coiled shells. The middle layer shows moderately coiled shells with simple ribbing. The most recent (top) layer has tightly coiled shells with complex ribbing and spines. There is a clear trend of increasing coiling tightness and surface ornamentation through geological time.
Marking notes: Award 1 mark for identifying the trend (increasing complexity) and 1 mark for describing at least two specific changes across the layers.

17. [2]
Answer: This trend suggests that ammonites evolved from simpler ancestral forms with loosely coiled shells to more derived forms with tightly coiled, ornamented shells. The gradual change in shell morphology over time supports the idea of gradual evolution through natural selection, where successive generations accumulated small modifications.
Marking notes: Award 1 mark for stating that ammonites evolved from simpler to more complex forms and 1 mark for linking this to gradual evolution / natural selection.

18. [1]
Answer: Any one of the following:

• The fossil record is incomplete — many organisms do not fossilise (especially soft-bodied organisms).
• Fossilisation requires very specific conditions (rapid burial, hard body parts).
• Many fossils have been destroyed by geological processes (erosion, metamorphism).
• It is difficult to find and date all transitional forms.
  Marking notes: Award 1 mark for any valid limitation.

19. [3]
Answer:

1. The two islands have different habitats — Island X is sandy desert while Island Y is rocky with dense vegetation. These environments exert different selection pressures on limb length.
2. On Island X (sandy desert), longer limbs may be advantageous for running quickly across open sand, escaping predators, or regulating body temperature. Lizards with longer limbs survive and reproduce more successfully.
3. On Island Y (rocky, vegetated), shorter limbs may be advantageous for climbing rocks, manoeuvring through dense vegetation, or maintaining a low centre of gravity. Lizards with shorter limbs survive and reproduce more successfully.
4. Over many generations, natural selection has caused the two populations to diverge in limb length as each population adapts to its local environment.
   Marking notes: Award 1 mark for identifying different selection pressures in different environments, 1 mark for explaining the advantage of long limbs in desert, and 1 mark for explaining the advantage of short limbs in rocky/vegetated habitat. Award a maximum of 2 marks if the student only addresses one island.

20. [2]
Answer: If lizards from Island X (long-limbed) were introduced to Island Y, they would be at a selective disadvantage in the rocky, vegetated habitat because long limbs are less suited to climbing and manoeuvring through dense vegetation. Over many generations, natural selection would favour shorter-limbed individuals on Island Y. The limb length distribution on Island Y would likely remain centred around short limbs (or shift even further toward shorter limbs), as the introduced long-limbed lizards would have lower survival and reproductive success.
Marking notes: Award 1 mark for predicting that long-limbed lizards would be at a disadvantage on Island Y, and 1 mark for explaining that natural selection would maintain or favour short limbs. Accept alternative reasonable predictions with valid reasoning (e.g., if the student argues the introduced lizards could introduce variation but selection would still favour short limbs).

Total: 40 marks