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A Level H2 Biology Evolution Diversity Quiz

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A-Level Biology H2 Quiz - Evolution Diversity

Name: _________________________ Class: _________________________ Date: _________________________ Score: ______ / 50

Duration: 45 minutes Total Marks: 50 Instructions: Answer all questions in the spaces provided. The marks for each question are indicated in brackets. Where appropriate, use diagrams and specific examples to support your answers.

Section A: Short Answer and Data Interpretation (Questions 1–8)

Total: 20 marks

1. Distinguish between convergent evolution and divergent evolution, providing one named example of each. (3 marks)

2. Figure 1 shows the forelimb skeletons of four different vertebrate species: a human, a whale, a bat, and a bird.

[Assume Figure 1 shows homologous forelimb structures with similar bone arrangements but different shapes and sizes.]

(a) Identify the type of structure represented by these forelimbs. (1 mark)

(b) Explain how these structures provide evidence for evolution from a common ancestor. (2 marks)

3. The table below shows the percentage similarity of a specific protein (cytochrome c) between humans and four other organisms.

Organism	Percentage similarity of cytochrome c to humans
Chimpanzee	100%
Rhesus monkey	99%
Dog	87%
Tuna fish	64%

(a) State the relationship between percentage similarity and evolutionary relatedness. (1 mark)

(b) Explain why molecular evidence, such as cytochrome c comparisons, is considered more reliable than morphological evidence for determining evolutionary relationships. (2 marks)

4. The Hardy-Weinberg principle states that allele frequencies in a population remain constant from generation to generation in the absence of disturbing factors.

(a) State two conditions that must be met for a population to be in Hardy-Weinberg equilibrium. (2 marks)

(b) In a population of 500 individuals, 20 individuals are homozygous recessive for a particular trait. Calculate the frequency of the heterozygous genotype. Show your working. (3 marks)

5. Explain how stabilising selection differs from directional selection. In your answer, describe the effect of each type of selection on the mean and range of the phenotype in a population. (3 marks)

6. The graph below shows the distribution of beak depths in a population of finches before and after a severe drought on an island.

[Assume the graph shows a shift in the mean beak depth from smaller to larger after the drought, with the range remaining similar.]

(a) Identify the type of natural selection illustrated by the change in beak depth. (1 mark)

(b) Suggest an explanation for the change in beak depth distribution after the drought. (2 marks)

Section B: Structured Questions (Questions 7–14)

Total: 18 marks

7. Describe the process of allopatric speciation. Use a named example to support your answer. (4 marks)

8. Explain how polyploidy can lead to sympatric speciation in plants. (3 marks)

9. The three-domain classification system, based on ribosomal RNA (rRNA) analysis, divides living organisms into Bacteria, Archaea, and Eukarya.

(a) Explain why rRNA is a suitable molecule for constructing phylogenetic trees. (2 marks)

(b) State one key difference between the domains Archaea and Bacteria. (1 mark)

10. Explain how antibiotic resistance in bacteria can evolve through natural selection. Use the terms mutation, selection pressure, and allele frequency in your answer. (3 marks)

11. Figure 2 shows a phylogenetic tree constructed using DNA sequence data from four species (P, Q, R, S) and an outgroup.

[Assume Figure 2 shows a rooted tree: Outgroup branches off first, then P, then Q, then R and S as sister taxa.]

(a) Identify the two most closely related species. (1 mark)

(b) Explain the purpose of including an outgroup in phylogenetic analysis. (2 marks)

12. Distinguish between pre-zygotic and post-zygotic reproductive isolating mechanisms. Provide one example of each. (2 marks)

Section C: Data-Based and Extended Response (Questions 13–20)

Total: 12 marks

13. The table below shows the number of amino acid differences in the haemoglobin beta chain between humans and five other primate species.

Species	Amino acid differences in haemoglobin beta chain (compared to humans)
Chimpanzee	0
Gorilla	1
Rhesus monkey	8
Gibbon	2
Orangutan	3

(a) Based on the data, which species is most closely related to humans? Justify your answer. (1 mark)

(b) Construct a simple branching diagram (cladogram) to show the evolutionary relationships among these primates based on the haemoglobin data. Label each branch with the species name. (2 marks)

14. Explain the concept of a molecular clock and describe one limitation of using molecular clocks to estimate divergence times. (2 marks)

15. Discuss how genetic drift differs from natural selection as a mechanism of evolutionary change. In your answer, explain why genetic drift has a greater effect on small populations. (3 marks)

16. The fossil record provides evidence for evolution. Explain two ways in which the fossil record supports the theory of evolution. (2 marks)

17. Explain what is meant by the term adaptive radiation. Use the example of Darwin's finches or another suitable example to illustrate your answer. (2 marks)

18. In a certain population of plants, flower colour is controlled by a single gene with two alleles: R (red) and r (white). The population consists of 360 red-flowered plants and 40 white-flowered plants. Assume the population is in Hardy-Weinberg equilibrium.

(a) Calculate the frequency of the recessive allele r. (1 mark)

(b) Calculate the number of plants that are heterozygous (Rr). (2 marks)

19. Explain how comparative embryology provides evidence for evolution. Provide one specific example. (2 marks)

20. A population of insects shows variation in body colour, ranging from light green to dark brown. The insects live in a habitat with both green vegetation and dark soil. Predatory birds feed on the insects.

(a) Predict the type of natural selection likely to act on body colour in this population. Justify your answer. (2 marks)

(b) Describe the expected distribution of body colour in the population after many generations of selection. (1 mark)

END OF QUIZ

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Answers

A-Level Biology H2 Quiz - Evolution Diversity: Answer Key and Marking Scheme

Total Marks: 50

Section A: Short Answer and Data Interpretation (Questions 1–8)

1. Distinguish between convergent evolution and divergent evolution, providing one named example of each. (3 marks)

Answer:

Convergent evolution: Unrelated species independently evolve similar traits due to similar environmental pressures / analogous structures arise. (1 mark)
Example: Wings of birds and insects / streamlined bodies of dolphins (mammals) and sharks (fish) / any valid example. (0.5 marks)
Divergent evolution: Related species evolve different traits from a common ancestor due to different environmental pressures / homologous structures arise. (1 mark)
Example: Darwin's finches' beak shapes / forelimbs of mammals (human hand, whale flipper, bat wing) / any valid example. (0.5 marks)

2. Figure 1 shows the forelimb skeletons of four different vertebrate species.

(a) Identify the type of structure represented by these forelimbs. (1 mark)

Answer: Homologous structures. (1 mark)

(b) Explain how these structures provide evidence for evolution from a common ancestor. (2 marks)

Answer:

The forelimbs share a similar basic skeletal arrangement / pentadactyl limb structure (same bones: humerus, radius, ulna, carpals, metacarpals, phalanges). (1 mark)
This similarity indicates that these species inherited the basic limb structure from a common ancestor, but the structure has been modified (divergent evolution) for different functions (e.g., grasping, swimming, flying). (1 mark)

3. The table shows the percentage similarity of cytochrome c between humans and four other organisms.

(a) State the relationship between percentage similarity and evolutionary relatedness. (1 mark)

Answer: The higher the percentage similarity, the more closely related the species are / the more recently they shared a common ancestor. (1 mark)

(b) Explain why molecular evidence, such as cytochrome c comparisons, is considered more reliable than morphological evidence for determining evolutionary relationships. (2 marks)

Answer:

Molecular sequences (DNA/protein) change at a relatively constant rate / are less affected by environmental factors compared to morphological traits. (1 mark)
Morphological traits can be influenced by convergent evolution (analogous structures) leading to misleading similarities, whereas molecular similarities directly reflect genetic relatedness. (1 mark)

4. The Hardy-Weinberg principle.

(a) State two conditions that must be met for a population to be in Hardy-Weinberg equilibrium. (2 marks)

Answer: Any two from: (1 mark each)

No mutations
Random mating
No natural selection
Extremely large population size (no genetic drift)
No gene flow / no migration

(b) In a population of 500 individuals, 20 individuals are homozygous recessive for a particular trait. Calculate the frequency of the heterozygous genotype. Show your working. (3 marks)

Answer:

Frequency of homozygous recessive (q²) = 20/500 = 0.04 (1 mark)
Frequency of recessive allele (q) = √0.04 = 0.2 (1 mark)
Frequency of dominant allele (p) = 1 − 0.2 = 0.8
Frequency of heterozygous genotype (2pq) = 2 × 0.8 × 0.2 = 0.32 (1 mark)

Answer:

Stabilising selection: Favours intermediate phenotypes; selects against extreme phenotypes. (0.5 marks) The mean phenotype remains unchanged; the range of phenotypes decreases / variation is reduced. (1 mark)
Directional selection: Favours one extreme phenotype; selects against the other extreme and intermediate phenotypes. (0.5 marks) The mean phenotype shifts towards the favoured extreme; the range may stay similar or shift. (1 mark)

6. The graph shows the distribution of beak depths in a population of finches before and after a severe drought.

(a) Identify the type of natural selection illustrated by the change in beak depth. (1 mark)

Answer: Directional selection. (1 mark)

(b) Suggest an explanation for the change in beak depth distribution after the drought. (2 marks)

Answer:

The drought caused a shortage of small, soft seeds, leaving only large, hard seeds as a food source. (1 mark)
Finches with larger, deeper beaks were better able to crack and eat the hard seeds, so they survived and reproduced more than finches with smaller beaks, shifting the mean beak depth to a larger size. (1 mark)

Section B: Structured Questions (Questions 7–14)

7. Describe the process of allopatric speciation. Use a named example to support your answer. (4 marks)

Answer:

A population is divided by a geographical barrier (e.g., mountain range, river, ocean) → gene flow between the subpopulations is prevented. (1 mark)
The two subpopulations experience different environmental conditions / selection pressures → divergent natural selection occurs. (1 mark)
Over many generations, genetic differences accumulate through mutation, natural selection, and genetic drift. (1 mark)
Eventually, the populations become so genetically different that they are reproductively isolated (pre- or post-zygotic barriers) even if the geographical barrier is removed → they are now separate species. (1 mark)
Example: Darwin's finches on the Galápagos Islands (dispersal to different islands led to allopatric speciation) / squirrels on either side of the Grand Canyon / any valid example. (Must be named for full marks; if example is integrated into explanation, award marks accordingly.)

8. Explain how polyploidy can lead to sympatric speciation in plants. (3 marks)

Answer:

Polyploidy is a condition where an organism has more than two complete sets of chromosomes; it can occur through errors in meiosis (e.g., non-disjunction) producing diploid gametes. (1 mark)
If a tetraploid (4n) plant arises from a diploid (2n) population, it can self-fertilise or cross with other tetraploids, but it cannot produce fertile offspring with the original diploid population (triploid offspring are sterile due to chromosome imbalance during meiosis). (1 mark)
This creates instant reproductive isolation between the polyploid and the original population without geographical separation → sympatric speciation. (1 mark)

9. The three-domain classification system.

(a) Explain why rRNA is a suitable molecule for constructing phylogenetic trees. (2 marks)

Answer:

rRNA is present in all organisms (universal) and performs the same essential function (protein synthesis), so it can be compared across all domains of life. (1 mark)
rRNA evolves very slowly / is highly conserved, allowing comparisons between distantly related organisms, and changes accumulate at a relatively constant rate. (1 mark)

(b) State one key difference between the domains Archaea and Bacteria. (1 mark)

Answer: Any one from: (1 mark)

Archaea have histone proteins associated with DNA; Bacteria do not.
Archaea cell walls lack peptidoglycan; Bacteria cell walls contain peptidoglycan.
Archaea membrane lipids have ether linkages; Bacteria have ester linkages.
Archaea have different RNA polymerase structure / more similar to eukaryotes.

10. Explain how antibiotic resistance in bacteria can evolve through natural selection. Use the terms mutation, selection pressure, and allele frequency in your answer. (3 marks)

Answer:

Random mutations in bacterial DNA can produce alleles that confer resistance to a specific antibiotic. (1 mark)
When an antibiotic is applied, it acts as a selection pressure: susceptible bacteria are killed, while resistant bacteria survive and reproduce. (1 mark)
Over generations, the allele frequency of the resistance allele increases in the population, leading to the evolution of an antibiotic-resistant bacterial population. (1 mark)

11. Figure 2 shows a phylogenetic tree.

(a) Identify the two most closely related species. (1 mark)

Answer: R and S. (1 mark)

(b) Explain the purpose of including an outgroup in phylogenetic analysis. (2 marks)

Answer:

The outgroup is a species or group known to have diverged before the lineage containing the species being studied (ingroup). (1 mark)
It serves as a reference point to determine the root of the phylogenetic tree and to infer the direction of character evolution (which traits are ancestral vs derived). (1 mark)

12. Distinguish between pre-zygotic and post-zygotic reproductive isolating mechanisms. Provide one example of each. (2 marks)

Answer:

Pre-zygotic barriers: Prevent mating or fertilisation between species. (0.5 marks) Example: Temporal isolation (different breeding seasons), habitat isolation, behavioural isolation (different mating calls/courtship rituals), mechanical isolation, gametic isolation. (Any one valid example, 0.5 marks)
Post-zygotic barriers: Prevent a hybrid zygote from developing into a viable, fertile adult. (0.5 marks) Example: Hybrid inviability (hybrid embryo dies early), hybrid sterility (e.g., mule), hybrid breakdown (F1 fertile but F2 inviable/sterile). (Any one valid example, 0.5 marks)

Section C: Data-Based and Extended Response (Questions 13–20)

13. The table shows amino acid differences in the haemoglobin beta chain.

(a) Based on the data, which species is most closely related to humans? Justify your answer. (1 mark)

Answer: Chimpanzee, because it has zero amino acid differences (identical haemoglobin beta chain). (1 mark)

(b) Construct a simple branching diagram (cladogram) to show the evolutionary relationships among these primates based on the haemoglobin data. (2 marks)

Answer: Cladogram should show:

Branching order reflecting number of differences: (Human, Chimp) as sister group, then Gorilla, then Gibbon, then Orangutan, then Rhesus monkey (or similar topology where fewer differences = more recent common ancestor). (1 mark for correct branching order, 1 mark for correct labels)
Example: (Human, Chimp) → Gorilla → Gibbon → Orangutan → Rhesus monkey (from most to least related).

14. Explain the concept of a molecular clock and describe one limitation of using molecular clocks to estimate divergence times. (2 marks)

Answer:

The molecular clock hypothesis states that DNA and protein sequences evolve at a relatively constant rate over time, so the number of genetic differences between two species can be used to estimate the time since they diverged from a common ancestor. (1 mark)
Limitation: Different genes/proteins evolve at different rates / the rate of molecular change is not always constant across lineages or over time / calibration requires reliable fossil evidence which may be incomplete. (Any one valid limitation, 1 mark)

Answer:

Genetic drift is a random change in allele frequencies due to chance events (e.g., which individuals survive and reproduce), not based on fitness. Natural selection is a non-random process where individuals with advantageous traits are more likely to survive and reproduce, increasing the frequency of beneficial alleles. (1 mark)
Genetic drift can lead to the loss or fixation of alleles regardless of their adaptive value; natural selection specifically increases beneficial alleles and decreases harmful ones. (1 mark)
Genetic drift has a greater effect on small populations because chance events have a proportionally larger impact on allele frequencies when the gene pool is small (e.g., the death of a few individuals can significantly alter allele frequencies). In large populations, random fluctuations average out. (1 mark)

16. The fossil record provides evidence for evolution. Explain two ways in which the fossil record supports the theory of evolution. (2 marks)

Answer: Any two from: (1 mark each)

Fossils show a progression of life forms from simpler to more complex over geological time, consistent with descent with modification.
Transitional fossils (e.g., Archaeopteryx – reptile to bird; Tiktaalik – fish to amphibian) show intermediate characteristics between ancestral and descendant groups.
Fossils of extinct species show that life on Earth has changed over time; many past species no longer exist, and modern species are different.
Fossils found in younger rock layers are more similar to modern species than fossils in older layers, showing gradual change.

17. Explain what is meant by the term adaptive radiation. Use the example of Darwin's finches or another suitable example to illustrate your answer. (2 marks)

Answer:

Adaptive radiation is the rapid diversification of a single ancestral lineage into many species, each adapted to exploit a different ecological niche / different environmental conditions. (1 mark)
Example: Darwin's finches on the Galápagos Islands evolved from a common ancestral finch species into multiple species with different beak shapes and sizes adapted to different food sources (e.g., seeds, insects, cactus flowers). / Hawaiian honeycreepers / cichlid fishes in African lakes. (1 mark for valid example with brief explanation)

(a) Calculate the frequency of the recessive allele r. (1 mark)

Answer:

Total plants = 360 + 40 = 400
Frequency of homozygous recessive (white, rr) = q² = 40/400 = 0.1
Frequency of recessive allele (q) = √0.1 = 0.316 (accept 0.32 or √0.1) (1 mark)

(b) Calculate the number of plants that are heterozygous (Rr). (2 marks)

Answer:

p = 1 − q = 1 − 0.316 = 0.684 (1 mark for correct p)
Frequency of heterozygotes (2pq) = 2 × 0.684 × 0.316 = 0.432
Number of heterozygous plants = 0.432 × 400 = 172.8 ≈ 173 plants (1 mark for correct number; accept 173 or 172–173)

19. Explain how comparative embryology provides evidence for evolution. Provide one specific example. (2 marks)

Answer:

Embryos of different vertebrate species show striking similarities in early developmental stages (e.g., presence of pharyngeal pouches, post-anal tail, similar body segmentation), suggesting they share a common ancestor. (1 mark)
These shared embryonic features may develop into different structures in adults (e.g., pharyngeal pouches become gills in fish but parts of the ear and throat in humans), indicating divergence from a common developmental plan. (0.5 marks)
Example: Vertebrate embryos (fish, amphibian, reptile, bird, mammal) all show pharyngeal arches/pouches and a tail at early stages. (0.5 marks)

(a) Predict the type of natural selection likely to act on body colour in this population. Justify your answer. (2 marks)

Answer:

Disruptive selection / diversifying selection. (1 mark)
Light green insects are camouflaged on green vegetation, and dark brown insects are camouflaged on dark soil; intermediate-coloured insects are not well camouflaged in either habitat and are more likely to be preyed upon. This favours both extreme phenotypes and selects against the intermediate phenotype. (1 mark)

(b) Describe the expected distribution of body colour in the population after many generations of selection. (1 mark)

Answer: A bimodal distribution with two peaks at the extremes (light green and dark brown) and few intermediate-coloured individuals. (1 mark)

END OF ANSWER KEY