Secondary 4 Combined Science Biology Evolution Diversity Quiz

Secondary 4 Combined Science Biology Quiz - Evolution Diversity

Answer Key

Section A: Multiple Choice & Short Answer

1. B — Individuals with advantageous traits are more likely to survive and reproduce
[1 mark]
Common mistake: Choosing A — natural selection is not a conscious choice by organisms.

2. B — Continuous variation
[1 mark]
Shell thickness varies along a continuous range (gradient), not in distinct categories.

3. D — All of the above
[1 mark]
Fossil records, homologous structures, and DNA evidence all support evolution.

4. C — Can interbreed to produce fertile offspring
[1 mark]
This is the biological species concept. Looking similar or living in the same habitat does not define a species.

5. C — Mutation
[1 mark]
Mutation introduces new alleles/variation. Natural selection and genetic drift act on existing variation. Selective breeding is artificial.

6. Evolution is the gradual change in the heritable characteristics of a population over successive generations.
[2 marks]

• 1 mark for "change in characteristics of a population over time/generations"
• 1 mark for mentioning "heritable/inherited" or "over many generations/long period"
  Must refer to population-level change, not individual change.

7.
(i) Variation must exist within the population (in the trait concerned)
(ii) The trait must be heritable / there must be differential survival and reproduction based on the trait
[2 marks — 1 each]
Acceptable alternatives: overproduction of offspring; struggle for existence; competition for resources.

8.
Continuous variation: Characteristics that can take any value within a range (e.g., height, mass, skin colour).
Example: Height in humans

Discontinuous variation: Characteristics that fall into distinct categories with no intermediate values (e.g., blood group, tongue rolling).
Example: Blood group (A, B, AB, O)

[3 marks]

• 1 mark for correct definition of continuous variation
• 1 mark for correct definition of discontinuous variation
• 1 mark for two valid examples (one each)
  Examples must match the type of variation defined.

9.
Before industrialisation, light-coloured moths were camouflaged on lichen-covered tree bark and avoided predation. After industrialisation, soot darkened the tree trunks, making dark-coloured moths better camouflaged. Birds preyed more heavily on the now-visible light-coloured moths. Dark-coloured moths survived and reproduced more successfully, passing on the dark colouration allele. Over generations, the proportion of dark-coloured moths increased.

[3 marks]

• 1 mark for linking pollution/soot to change in camouflage advantage
• 1 mark for differential predation by birds
• 1 mark for increased survival/reproduction of dark moths leading to change in population
  Must explain the mechanism, not just describe the observation.

10.
Definition: An adaptation is a feature (structural, behavioural, or physiological) that increases an organism's chance of survival and reproduction in its environment.

Example: Streamlined body shape of a fish (reduces water resistance for efficient swimming).

[2 marks]

• 1 mark for correct definition (must mention survival/reproduction advantage)
• 1 mark for valid structural adaptation example
  Acceptable examples: thick fur in polar bears, camouflage in chameleons, webbed feet in ducks, etc.

Section B: Structured Response

11.
(a) Anatomical evidence / Homologous structures [1]

(b) The similar bone arrangement (humerus, radius, ulna, carpals, phalanges) in different vertebrates suggests they share a common ancestor. The structures have been modified for different functions (e.g., flying, swimming, grasping) through divergent evolution. [2]

• 1 mark for common ancestry
• 1 mark for divergent evolution / modification for different functions

(c) Any ONE of: Fossil evidence / DNA/molecular evidence / Embryological evidence / Biogeographical evidence [1]

[4 marks]

12.
(a) In a grassy environment, green beetles are better camouflaged than brown beetles. Birds are more likely to spot and eat the brown beetles. Green beetles survive longer and reproduce more, passing the green colour allele to offspring. Over generations, the frequency of the green allele increases, and the proportion of green beetles in the population rises. [4]

• 1 mark for camouflage advantage of green beetles
• 1 mark for differential predation (birds eat more brown beetles)
• 1 mark for survival and reproduction of green beetles
• 1 mark for increase in green allele frequency over generations

(b) Mutation [1]

[5 marks]

13.
(a) Species Y and Z are most closely related because their branches meet at the most recent node / they share the most recent common ancestor. [2]

• 1 mark for identifying Y and Z
• 1 mark for correct explanation (most recent common ancestor)

(b) A node represents a common ancestor of the species that branch from it. [1]

(c) Any ONE of: Convergent evolution can make unrelated species appear related; incomplete fossil record; horizontal gene transfer complicates trees; molecular data may give conflicting results. [1]

[4 marks]

14.
(a) Within a bacterial population, genetic variation exists due to random mutations. Some bacteria may carry a mutation that confers resistance to the antibiotic. When the antibiotic is applied, non-resistant bacteria are killed. Resistant bacteria survive and reproduce, passing the resistance allele to offspring. Over time, the proportion of resistant bacteria in the population increases. [4]

• 1 mark for pre-existing variation/mutation in the population
• 1 mark for antibiotic killing non-resistant bacteria
• 1 mark for resistant bacteria surviving and reproducing
• 1 mark for increase in resistance allele over time

(b) Any ONE of: Complete the full course of antibiotics as prescribed; do not overuse/unnecessarily prescribe antibiotics; use antibiotics only for bacterial infections (not viral); develop new antibiotics. [1]

[5 marks]

15.
(a) On different islands, different food sources were available (e.g., large seeds, small seeds, insects). Finches with beak shapes better suited to the available food source on their island were more successful at feeding. These finches survived and reproduced more, passing on their beak shape alleles. Over many generations, natural selection led to different beak shapes becoming common on different islands. [4]

• 1 mark for variation in food sources on different islands
• 1 mark for differential survival based on beak-food match
• 1 mark for reproduction passing on advantageous beak alleles
• 1 mark for accumulation of changes over many generations

(b) The environment determined which beak shape was advantageous (i.e., the environment acted as the selective pressure). [1]

[5 marks]

16.
(a) When an organism dies, its remains may be buried quickly by sediment. Over time, more layers of sediment build up. The hard parts (bones, shells) are gradually replaced by minerals. The surrounding sediment turns to rock, preserving the shape of the organism as a fossil. [2]

• 1 mark for burial by sediment
• 1 mark for mineralisation / replacement of hard parts by minerals

(b) Most organisms decompose completely after death. Fossilisation requires very specific conditions (rapid burial, presence of hard parts, low oxygen). Most environments do not provide these conditions. Erosion and geological activity can also destroy fossils. [2]

• 1 mark for most organisms not being preserved (decomposition)
• 1 mark for specific conditions required / destruction by geological processes

(c) Any TWO of: Fossils show gradual changes in species over time; transitional fossils show intermediate forms between ancestral and modern species; older rock layers contain simpler organisms while younger layers contain more complex organisms; fossils can show how organisms adapted to changing environments. [2 — 1 mark each]

[6 marks]

17.
(a) The percentage of insects resistant to the pesticide increases over the 10 generations. The increase is slow at first (Generations 1–3) and becomes more rapid (Generations 5–7), then slows again as it approaches a high value (Generation 10). [2]

• 1 mark for describing the overall increasing trend
• 1 mark for describing the pattern of increase (slow → rapid → slowing)

(b) Within the insect population, some individuals carry a resistance allele due to random mutation. When the pesticide is applied, non-resistant insects are killed. Resistant insects survive and reproduce, passing the resistance allele to the next generation. Over successive generations, the frequency of the resistance allele increases, so a greater proportion of the population is resistant. [3]

• 1 mark for pre-existing variation (resistance allele from mutation)
• 1 mark for differential survival (pesticide kills non-resistant insects)
• 1 mark for reproduction increasing resistance allele frequency over generations

(c) The frequency of the resistant allele would likely decrease over time. Without the pesticide, there is no selective advantage to being resistant. Resistant insects may have lower fitness (e.g., slower growth, reduced reproduction) in the absence of the pesticide, so non-resistant insects would be favoured by natural selection. [2]

• 1 mark for stating the frequency would decrease
• 1 mark for correct explanation (no selective advantage / fitness cost of resistance)

[7 marks]

Section C: Extended Response

18.
(a) Evidence includes:

• A layer of iridium-rich sediment found globally at the Cretaceous-Paleogene (K-Pg) boundary — iridium is rare on Earth but common in asteroids.
• The Chicxulub crater in Mexico, dated to approximately 66 million years ago, matching the timing of the extinction.
• Shocked quartz and tektites (glass beads) found in sediment layers from that period, indicating a massive impact event. [3 — 1 mark each for any three valid pieces of evidence]

(b) The impact would have ejected massive amounts of dust and debris into the atmosphere, blocking sunlight. This would have caused a dramatic drop in temperature ("impact winter") and reduced photosynthesis. Plants would have died, leading to the collapse of food chains. Herbivorous dinosaurs would have starved, followed by carnivorous dinosaurs. Acid rain from the impact may have further damaged ecosystems. [3]

• 1 mark for dust/debris blocking sunlight
• 1 mark for reduced photosynthesis and plant death
• 1 mark for collapse of food chains leading to dinosaur extinction

(c) Any TWO of: Volcanic activity (e.g., Deccan Traps eruptions); climate change (global cooling or warming); changes in sea levels; competition from other species; disease. [2 — 1 mark each]

[8 marks]

19.
(a) Artificial classification groups organisms based on a few selected, often superficial characteristics (e.g., habitat, colour, usefulness to humans) that may not reflect evolutionary relationships. Natural classification groups organisms based on their evolutionary relationships and shared characteristics inherited from a common ancestor, using multiple lines of evidence (anatomy, embryology, DNA). [4]

• 1 mark for defining artificial classification
• 1 mark for defining natural classification
• 1 mark for stating artificial classification does not reflect evolutionary relationships
• 1 mark for stating natural classification reflects evolutionary relationships / common ancestry

(b) Any THREE of: Morphological features (body structure); DNA/RNA sequences; Embryological development; Biochemistry (e.g., protein structure); Cell structure (prokaryotic vs eukaryotic, cell wall composition); Reproductive features; Fossil evidence. [3 — 1 mark each]

(c) Classification systems change as new evidence becomes available (e.g., DNA sequencing may reveal that organisms previously thought to be closely related are not). Improved technology and new fossil discoveries can also lead to revisions. Our understanding of evolutionary relationships improves over time. [2]

• 1 mark for new evidence (e.g., DNA data)
• 1 mark for improved understanding / technology leading to revision

[9 marks]

20.
(a) Any TWO of:
(i) Increase in body size (from small, dog-sized Hyracotherium to larger Equus).
(ii) Reduction in the number of toes (from four toes on front feet to a single hoof).
(iii) Increase in the length and height of the teeth (development of high-crowned teeth for grazing).
(iv) Lengthening of the limbs (for faster running in open grasslands). [2 — 1 mark each]

(b) The environment changed from forested areas to open grasslands over time. Horses with mutations for larger body size, longer limbs, and high-crowned teeth were better adapted to running on open ground and grazing on tough grasses. These individuals survived and reproduced more successfully. Over many generations, natural selection favoured these traits, leading to the evolution of Equus from Hyracotherium. [4]

• 1 mark for environmental change (forest → grassland)
• 1 mark for variation in traits (from mutation)
• 1 mark for differential survival of better-adapted individuals
• 1 mark for accumulation of advantageous traits over generations

(c) Hyracotherium and Equus are considered different species because they would not be able to interbreed to produce fertile offspring (if they coexisted). They have accumulated sufficient genetic and morphological differences over time that they are reproductively isolated. [2]

• 1 mark for inability to interbreed / reproductive isolation
• 1 mark for accumulation of differences over time

[8 marks]

END OF ANSWER KEY