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A Level H2 Biology Evolution Diversity Quiz
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Questions
A-Level Biology H2 Quiz - Evolution Diversity
Name: _____________________________
Class: _____________________________
Date: _____________________________
Score: _________ / 60
Duration: 55 minutes
Total Marks: 60
Instructions:
- Answer ALL questions in the spaces provided.
- The number of marks is given in brackets [ ] at the end of each question or part question.
- Where diagrams or figures are referenced, examine them carefully before answering.
- Show all working for calculation questions.
Section A: Short Answer (10 marks)
Answer all questions in this section.
1. Define the term natural selection as proposed by Charles Darwin.
[2 marks]
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2. State the five conditions that must be met for a population to remain in Hardy-Weinberg equilibrium.
[2 marks]
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3. Distinguish between allopatric and sympatric speciation.
[2 marks]
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4. State what is represented by a node on a phylogenetic tree and explain its significance in evolutionary biology.
[2 marks]
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5. Identify two types of evidence, other than fossil records, that scientists use to construct phylogenetic relationships among species.
[2 marks]
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Section B: Structured Questions (30 marks)
Answer all questions in this section.
6. Fig. 6.1 shows the distribution of beak depths in a population of finches on an island before and after a severe drought that reduced the availability of small, soft seeds.
Fig. 6.1
| Beak depth (mm) | Before drought (number of birds) | After drought (number of birds) |
|---|---|---|
| 6.0 – 7.0 | 8 | 2 |
| 7.1 – 8.0 | 28 | 5 |
| 8.1 – 9.0 | 42 | 12 |
| 9.1 – 10.0 | 25 | 18 |
| 10.1 – 11.0 | 10 | 28 |
| 11.1 – 12.0 | 3 | 21 |
(a) With reference to Fig. 6.1, describe the change in the distribution of beak depths after the drought.
[2 marks]
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(b) Explain the change in beak depth distribution in terms of natural selection.
[3 marks]
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7. (a) Describe how a geographical barrier can lead to the formation of two distinct species from an ancestral population.
[3 marks]
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(b) Explain one mechanism, other than geographical isolation, by which reproductive isolation can arise between populations living in the same area.
[2 marks]
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8. In a population of 2500 rabbits, the allele for white fur (W) is dominant over the allele for brown fur (w). 225 rabbits have brown fur.
(a) Assuming the population is in Hardy-Weinberg equilibrium, calculate the frequency of the recessive allele (w). Show your working.
[2 marks]
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(b) Calculate the expected number of heterozygous rabbits (Ww) in this population. Show your working.
[2 marks]
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9. Fig. 9.1 shows a short section of the cytochrome c amino acid sequence aligned across five different species.
Fig. 9.1
| Species | Amino acid sequence (positions 44–55) |
|---|---|
| Human | G-V-E-K-G-K-K-I-F-I-M-K |
| Chimpanzee | G-V-E-K-G-K-K-I-F-I-M-K |
| Rhesus monkey | G-V-E-K-G-K-K-I-F-I-M-K |
| Horse | G-V-E-K-G-K-K-I-F-V-Q-K |
| Tuna | G-V-E-N-G-K-K-I-F-V-Q-K |
(a) With reference to Fig. 9.1, state which species is most distantly related to humans and explain your reasoning.
[2 marks]
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(b) Explain why highly conserved molecules such as cytochrome c are useful for constructing phylogenetic trees across distantly related species.
[2 marks]
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10. The Hawaiian honeycreepers are a group of birds that evolved from a single ancestral finch species that colonised the Hawaiian Islands approximately 5 million years ago. Today, there are over 50 species showing remarkable diversity in beak shape, body size, and feeding habits.
(a) Name the evolutionary process described above.
[1 mark]
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(b) Explain how the availability of diverse ecological niches on the Hawaiian Islands contributed to this evolutionary pattern.
[3 marks]
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11. Define genetic drift and explain why its effects are more pronounced in small populations than in large populations.
[2 marks]
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12. Fig. 12.1 shows a phylogenetic tree constructed using DNA sequence data from five related species (A–E).
Fig. 12.1
┌────── Species A
┌───┤
│ └────── Species B
────┤
│ ┌────── Species C
└───┤
│ ┌── Species D
└───┤
└── Species E
(a) Identify the species that is most closely related to Species D.
[1 mark]
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(b) Explain what the branching pattern of this tree reveals about the evolutionary history of these five species.
[2 marks]
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13. Explain how temporal isolation and behavioural isolation can each act as prezygotic reproductive barriers, preventing gene flow between populations.
[3 marks]
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14. The wings of bats (mammals) and the wings of birds are an example of analogous structures, whereas the forelimbs of bats and the forelimbs of whales are homologous structures.
(a) Distinguish between analogous structures and homologous structures.
[2 marks]
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(b) Explain how homologous structures provide evidence for divergent evolution.
[1 mark]
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15. The widespread use of antibiotics has led to the evolution of antibiotic-resistant strains of bacteria such as methicillin-resistant Staphylococcus aureus (MRSA).
Describe how natural selection has contributed to the emergence of antibiotic resistance in bacterial populations.
[3 marks]
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Section C: Data-Based and Extended Response Questions (20 marks)
Answer all questions in this section.
16. Fig. 16.1 shows the frequency of the HbS allele (associated with sickle cell anaemia) in human populations across three regions with differing malaria prevalence.
Fig. 16.1
| Region | Malaria prevalence | HbS allele frequency |
|---|---|---|
| Sub-Saharan Africa | High | 0.10 |
| Mediterranean | Moderate | 0.04 |
| Northern Europe | Absent | 0.001 |
(a) With reference to Fig. 16.1, describe the relationship between malaria prevalence and HbS allele frequency.
[2 marks]
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(b) Explain this relationship in terms of natural selection and heterozygote advantage.
[3 marks]
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17. Fig. 17.1 shows a phylogenetic tree constructed from mitochondrial DNA (mtDNA) sequences for six primate species. The numbers at each branching point represent the estimated time of divergence in millions of years ago (mya).
Fig. 17.1
┌───────── Gibbon (18 mya)
┌───┤
│ │ ┌───── Orangutan (14 mya)
│ └───┤
────┤ │ ┌─ Gorilla (8 mya)
│ └───┤
│ │ ┌── Human (6 mya)
│ └───┤
│ └── Chimpanzee (6 mya)
└────────────── Rhesus macaque (25 mya)
(a) With reference to Fig. 17.1, identify which pair of species shares the most recent common ancestor and state how long ago they diverged.
[2 marks]
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(b) Explain why mitochondrial DNA is particularly useful for studying evolutionary relationships among closely related species.
[2 marks]
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18. The three-spined stickleback (Gasterosteus aculeatus) is a small fish found in both marine and freshwater environments. Marine sticklebacks colonised freshwater lakes formed after the last ice age (approximately 12,000 years ago). Freshwater populations have repeatedly and independently lost their pelvic spines, a bony structure that requires significant energy to produce and is largely unnecessary in freshwater habitats where predatory fish are absent.
(a) Explain how the repeated, independent loss of pelvic spines in different freshwater stickleback populations provides evidence for natural selection, rather than genetic drift.
[3 marks]
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(b) Suggest why the loss of pelvic spines in freshwater environments is an advantageous adaptation.
[2 marks]
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19. Discuss how molecular evidence (DNA and protein sequence comparisons) has transformed our understanding of evolutionary relationships among organisms. In your answer, you should refer to specific examples and explain how molecular data can both support and challenge traditional classification based on morphological characteristics.
[5 marks]
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20. Fig. 20.1 shows the number of nucleotide differences in the cytochrome b gene between pairs of related bird species, plotted against the estimated time since divergence (based on fossil evidence).
Fig. 20.1
| Species pair | Nucleotide differences | Estimated divergence time (mya) |
|---|---|---|
| A – B | 12 | 1.5 |
| C – D | 38 | 5.0 |
| E – F | 64 | 9.0 |
| G – H | 88 | 13.0 |
(a) With reference to Fig. 20.1, describe the relationship between nucleotide differences and estimated divergence time.
[1 mark]
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(b) Explain how this relationship supports the concept of a molecular clock and state one assumption of the molecular clock model.
[2 marks]
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END OF QUIZ
Check your answers carefully before submitting.
Answers
A-Level Biology H2 Quiz - Evolution Diversity — Answer Key
Total Marks: 60
Section A: Short Answer (10 marks)
1. Define the term natural selection as proposed by Charles Darwin.
[2 marks]
Answer:
Natural selection is the process by which organisms with heritable traits that are better suited to their environment are more likely to survive and reproduce [1], leading to an increase in the frequency of those advantageous traits in the population over successive generations [1].
Award [1] for "differential survival and reproduction" and [1] for "heritable traits / increase in allele frequency over generations."
2. State the five conditions that must be met for a population to remain in Hardy-Weinberg equilibrium.
[2 marks]
Answer:
- No mutations [½]
- Random mating [½]
- No natural selection [½]
- Extremely large population size (no genetic drift) [½]
- No gene flow / no migration [½]
Award [2] for all five correct; [1] for three or four correct; [0] for fewer than three. Accept equivalent phrasing.
3. Distinguish between allopatric and sympatric speciation.
[2 marks]
Answer:
Allopatric speciation occurs when a population is divided by a geographical/physical barrier, preventing gene flow between the separated groups [1], whereas sympatric speciation occurs without geographical separation, typically through reproductive isolation mechanisms such as polyploidy or behavioural differences within the same geographical area [1].
Award [1] for each correct distinction. Must clearly contrast the two modes.
4. State what is represented by a node on a phylogenetic tree and explain its significance in evolutionary biology.
[2 marks]
Answer:
A node represents the most recent common ancestor (MRCA) of the lineages that branch from it [1]. It is significant because it indicates the point at which two or more lineages diverged from a shared ancestral population, allowing scientists to infer evolutionary relationships and relative timing of speciation events [1].
5. Identify two types of evidence, other than fossil records, that scientists use to construct phylogenetic relationships among species.
[2 marks]
*Answer (any two of the following, 1 mark each):
- Comparative anatomy / homologous structures
- Molecular evidence (DNA sequence comparisons / protein sequence comparisons)
- Embryological development patterns
- Biogeographical distribution
- Comparative biochemistry
Section B: Structured Questions (30 marks)
6. (a) With reference to Fig. 6.1, describe the change in the distribution of beak depths after the drought.
[2 marks]
Answer:
The distribution shifted towards larger beak depths [1]; the number of birds with smaller beaks (6.0–9.0 mm) decreased substantially, while the number of birds with larger beaks (10.1–12.0 mm) increased markedly after the drought [1].
Accept use of specific data from the table to support description, e.g., "birds with beak depth 6.0–7.0 mm decreased from 8 to 2."
(b) Explain the change in beak depth distribution in terms of natural selection.
[3 marks]
Answer:
The drought reduced the availability of small, soft seeds, creating a selection pressure [1]. Birds with larger, deeper beaks could crack the remaining hard, large seeds and were more likely to survive and reproduce [1]. The trait for larger beak depth is heritable, so offspring inherited larger beaks, increasing the frequency of the large-beak allele in the population over generations [1].
7. (a) Describe how a geographical barrier can lead to the formation of two distinct species from an ancestral population.
[3 marks]
Answer:
A geographical barrier (e.g., mountain range, river, ocean) physically separates a population into two or more isolated groups, preventing gene flow between them [1]. The separated populations experience different selection pressures and/or genetic drift in their respective environments [1]. Over many generations, genetic differences accumulate to the point where individuals from the two populations can no longer interbreed to produce fertile offspring, resulting in reproductive isolation and the formation of two distinct species [1].
(b) Explain one mechanism, other than geographical isolation, by which reproductive isolation can arise between populations living in the same area.
[2 marks]
*Answer (any one of the following):
- Temporal isolation: Populations breed at different times of day, seasons, or years, preventing interbreeding [1]. This reduces gene flow and can lead to speciation if differences in breeding time are reinforced over generations [1].
- Behavioural isolation: Differences in courtship rituals, mating calls, or other behaviours prevent individuals from recognising each other as potential mates [1], reducing gene flow between populations [1].
- Mechanical isolation: Differences in reproductive structures prevent successful mating between individuals from different populations [1], acting as a prezygotic barrier to gene flow [1].
8. (a) Calculate the frequency of the recessive allele (w). Show your working.
[2 marks]
Answer:
Brown fur rabbits = homozygous recessive (ww) = 225 / 2500 = 0.09 = q²
q = √0.09 = 0.3 [1 for correct calculation]
Frequency of recessive allele (w) = 0.3 [1 for correct answer with working]
(b) Calculate the expected number of heterozygous rabbits (Ww). Show your working.
[2 marks]
Answer:
p = 1 − q = 1 − 0.3 = 0.7 [½]
Frequency of heterozygotes (2pq) = 2 × 0.7 × 0.3 = 0.42 [1]
Expected number of heterozygous rabbits = 0.42 × 2500 = 1050 [½]
Award full marks for correct answer with clear working. Accept equivalent methods.
9. (a) With reference to Fig. 9.1, state which species is most distantly related to humans and explain your reasoning.
[2 marks]
Answer:
Tuna is most distantly related to humans [1] because it has the greatest number of amino acid differences from the human sequence (3 differences: E vs K at position 5, V vs I at position 10, and K vs M at position 12), indicating a more distant common ancestor / longer time since divergence [1].
(b) Explain why highly conserved molecules such as cytochrome c are useful for constructing phylogenetic trees across distantly related species.
[2 marks]
Answer:
Highly conserved molecules evolve slowly because most changes to their amino acid sequence are deleterious and eliminated by natural selection [1]. Because they change slowly, their sequences retain enough similarity across distantly related species to allow meaningful comparison and alignment, enabling construction of phylogenetic trees spanning deep evolutionary time [1].
10. (a) Name the evolutionary process described above.
[1 mark]
Answer:
Adaptive radiation [1].
(b) Explain how the availability of diverse ecological niches on the Hawaiian Islands contributed to this evolutionary pattern.
[3 marks]
Answer:
The Hawaiian Islands offered a variety of unoccupied ecological niches with different food sources, habitats, and environmental conditions [1]. Different subpopulations of the ancestral finch adapted to exploit different niches through natural selection, with variations in beak shape, body size, and feeding behaviour being favoured in different environments [1]. Over time, this led to the divergence of the ancestral species into multiple descendant species, each specialised to a particular niche, reducing competition between them [1].
11. Define genetic drift and explain why its effects are more pronounced in small populations than in large populations.
[2 marks]
Answer:
Genetic drift is the random change in allele frequencies in a population from one generation to the next, due to chance events rather than natural selection [1]. Its effects are more pronounced in small populations because random fluctuations have a proportionally larger impact on the gene pool; in large populations, chance events are diluted by the larger number of individuals, so allele frequencies remain more stable [1].
12. (a) Identify the species that is most closely related to Species D.
[1 mark]
Answer:
Species E [1].
(b) Explain what the branching pattern of this tree reveals about the evolutionary history of these five species.
[2 marks]
Answer:
The branching pattern indicates that all five species share a common ancestor [1]. Species A and B share a more recent common ancestor with each other than either does with Species C, D, or E. Similarly, Species C, D, and E form a clade, with D and E being more closely related to each other than either is to C. This reflects the relative order and timing of speciation events [1].
13. Explain how temporal isolation and behavioural isolation can each act as prezygotic reproductive barriers, preventing gene flow between populations.
[3 marks]
Answer:
Temporal isolation: Populations breed at different times (different seasons, different times of day, or different years), so they do not encounter each other during reproductive periods [1]. This prevents mating between individuals of the different populations, blocking gene flow [½].
Behavioural isolation: Populations have distinct courtship behaviours, mating calls, or rituals that are not recognised by individuals of other populations [1]. Individuals will only respond to and mate with those displaying the correct species-specific signals, preventing interbreeding and gene flow [½].
Award up to [3]; must explain both types with clear link to preventing gene flow.
14. (a) Distinguish between analogous structures and homologous structures.
[2 marks]
Answer:
Analogous structures are features that have similar functions but different evolutionary origins (e.g., bat wing and bird wing — both used for flight but evolved independently) [1]. Homologous structures are features that share a common evolutionary origin but may have different functions (e.g., bat forelimb and whale flipper — same ancestral forelimb structure adapted for different purposes) [1].
(b) Explain how homologous structures provide evidence for divergent evolution.
[1 mark]
Answer:
Homologous structures indicate that different species inherited the same basic body plan from a common ancestor, and the structures subsequently diverged in form and function as populations adapted to different environments / selection pressures, demonstrating divergent evolution [1].
15. Describe how natural selection has contributed to the emergence of antibiotic resistance in bacterial populations.
[3 marks]
Answer:
Within a bacterial population, there is genetic variation, and some individuals may possess mutations or resistance genes that confer resistance to a particular antibiotic [1]. When the antibiotic is applied, it acts as a selection pressure, killing susceptible bacteria while resistant bacteria survive and reproduce [1]. The resistance alleles are passed to offspring, and over generations, the frequency of resistance alleles increases in the population, resulting in a predominantly resistant bacterial strain [1].
Section C: Data-Based and Extended Response Questions (20 marks)
16. (a) With reference to Fig. 16.1, describe the relationship between malaria prevalence and HbS allele frequency.
[2 marks]
Answer:
There is a positive correlation / direct relationship between malaria prevalence and HbS allele frequency [1]; regions with higher malaria prevalence have higher frequencies of the HbS allele, while regions with absent malaria have very low HbS frequencies [1].
(b) Explain this relationship in terms of natural selection and heterozygote advantage.
[3 marks]
Answer:
In regions with high malaria prevalence, individuals heterozygous for the HbS allele (HbA/HbS) have a selective advantage because they are more resistant to malaria than homozygous normal individuals (HbA/HbA), while not suffering from sickle cell disease like homozygous recessive individuals (HbS/HbS) [1]. This heterozygote advantage means that the HbS allele is maintained in the population by natural selection despite its harmful effect in the homozygous state [1]. In regions without malaria, the HbS allele confers no advantage, and is selected against because homozygotes develop sickle cell disease, resulting in very low allele frequencies [1].
17. (a) With reference to Fig. 17.1, identify which pair of species shares the most recent common ancestor and state how long ago they diverged.
[2 marks]
Answer:
Human and chimpanzee share the most recent common ancestor [1], diverging approximately 6 million years ago [1].
(b) Explain why mitochondrial DNA is particularly useful for studying evolutionary relationships among closely related species.
[2 marks]
Answer:
Mitochondrial DNA (mtDNA) has a relatively high mutation rate compared to nuclear DNA because it lacks efficient DNA repair mechanisms and is exposed to reactive oxygen species from oxidative phosphorylation [1]. This higher mutation rate generates more sequence differences over shorter evolutionary timescales, providing greater resolution for distinguishing between closely related species that diverged relatively recently [1].
18. (a) Explain how the repeated, independent loss of pelvic spines in different freshwater stickleback populations provides evidence for natural selection, rather than genetic drift.
[3 marks]
Answer:
The repeated, independent occurrence of the same trait (pelvic spine loss) in multiple isolated freshwater populations is highly unlikely to be due to chance alone, as genetic drift would produce random and different changes in each population [1]. The pattern suggests a common selective pressure — the absence of predatory fish and the energetic cost of producing pelvic spines — favoured spine loss in each freshwater environment [1]. This convergent evolutionary outcome across independent lineages is a hallmark of natural selection acting on similar selection pressures, rather than the random effects of drift [1].
(b) Suggest why the loss of pelvic spines in freshwater environments is an advantageous adaptation.
[2 marks]
Answer:
Pelvic spines require significant energy and resources to produce and maintain [1]. In freshwater habitats where predatory fish are absent, the spines provide no survival benefit, so individuals that do not produce spines can allocate more energy to growth and reproduction, increasing their fitness [1].
19. Discuss how molecular evidence (DNA and protein sequence comparisons) has transformed our understanding of evolutionary relationships among organisms. In your answer, you should refer to specific examples and explain how molecular data can both support and challenge traditional classification based on morphological characteristics.
[5 marks]
Answer — Marking guidelines:
| Mark | Descriptor |
|---|---|
| 5 | Comprehensive discussion with specific examples; clear explanation of how molecular data supports AND challenges morphological classification; well-structured, coherent argument. |
| 4 | Clear discussion with at least one specific example; explains both support and challenge aspects; mostly well-structured. |
| 3 | Adequate discussion; may lack a specific named example or focus more on one aspect (support or challenge); some structure evident. |
| 2 | Basic discussion; limited examples or explanation; may describe without fully discussing transformation of understanding. |
| 1 | Minimal relevant points; largely descriptive; lacks examples or coherent argument. |
| 0 | No relevant content. |
Expected content elements:
How molecular evidence supports morphological classification:
- DNA/protein sequences often confirm relationships inferred from morphology (e.g., humans and chimpanzees share ~98–99% DNA sequence identity, supporting their close relationship based on anatomical similarities).
- Cytochrome c comparisons confirm vertebrate relationships previously established by comparative anatomy.
- Molecular phylogenies broadly align with the traditional tree of life.
How molecular evidence challenges morphological classification:
- Molecular data has led to major reclassifications, e.g., the reclassification of fungi as more closely related to animals than plants, despite plant-like morphology.
- Whales (cetaceans) were traditionally classified with other aquatic mammals; molecular evidence revealed their closest living relatives are hippopotamuses (artiodactyls), leading to the clade Cetartiodactyla.
- Giant pandas were historically debated as bears or raccoons; molecular evidence confirmed they are true bears (Ursidae).
Transformation of understanding:
- Molecular clocks allow estimation of divergence times independent of fossil records.
- Horizontal gene transfer in prokaryotes challenges the concept of a simple branching tree of life.
- Molecular data provides a more objective and quantifiable basis for phylogenetic inference, reducing reliance on subjective morphological character assessment.
Award marks for: clear examples, balanced discussion, coherent explanation of transformation.
20. (a) With reference to Fig. 20.1, describe the relationship between nucleotide differences and estimated divergence time.
[1 mark]
Answer:
There is a positive linear correlation — as the estimated divergence time increases, the number of nucleotide differences also increases [1].
(b) Explain how this relationship supports the concept of a molecular clock and state one assumption of the molecular clock model.
[2 marks]
Answer:
The roughly constant rate of nucleotide difference accumulation over time (as shown by the approximately linear relationship) supports the molecular clock hypothesis, which proposes that genetic changes accumulate at a relatively constant rate over evolutionary time [1].
One assumption (any one):
- The rate of mutation is constant over time and across lineages [1].
- The gene/protein being studied is not under strong selection (i.e., most changes are neutral) [1].
- Generation times are similar across the lineages being compared [1].
END OF ANSWER KEY