A Level H2 Biology Evolution Diversity Quiz

A-Level Biology H2 Quiz - Evolution Diversity (Answer Key)

Total Marks: 40

Section A: Natural Selection and Adaptation

1. (a)

1. Variation exists in the population (light and dark forms) due to genetic mutation.
2. In industrial areas, tree trunks became darkened by soot; dark moths were better camouflaged from predators (birds).
3. Dark moths survived and reproduced more successfully, passing the allele for dark colour to offspring, increasing its frequency. [3] (1 mark for variation/mutation, 1 mark for selection pressure/camouflage, 1 mark for differential survival/reproduction)

(b)

1. Air quality improvement reduced soot, allowing lichens to grow and lightening tree trunks.
2. Light moths became better camouflaged and had higher survival rates, increasing their frequency. [2]

2. (a)

1. Random mutation in some bacteria produces a gene for resistance (e.g., altered target site or enzyme production).
2. Use of methicillin kills non-resistant bacteria (selection pressure).
3. Resistant bacteria survive and reproduce (binary fission), passing the resistance allele to offspring, increasing its frequency in the population. [3]

(b)

1. Natural selection acts on existing genetic variation (mutations) in the population; the antibiotic does not cause the mutation.
2. Lamarckism suggests acquired characteristics (exposure to antibiotic) are inherited, which is incorrect; resistance is genetic. [2]

3. (a) Directional selection. [1]

(b)

1. Drought caused small, soft seeds to become scarce, leaving mostly large, hard seeds.
2. Finches with larger/deeper beaks could crack these hard seeds and survive.
3. Finches with smaller beaks starved/died; survivors reproduced, passing alleles for larger beaks. [3]

4. (a)

1. Random mutation (change in DNA base sequence).
2. Horizontal gene transfer (conjugation, transformation, or transduction). [2] (Accept any two valid sources of bacterial variation)

(b) Bacteria reproduce asexually (binary fission), so there is no meiosis or fusion of gametes to mix genetic material. [1]

5. (a) An increase in the frequency of dark-coloured (melanic) forms of a species in industrial/polluted areas. [1]

(b)

1. Green leaves provide a background where dark moths are highly visible to predators.
2. There is no selective advantage for melanism; light/green camouflage would be favoured instead. [2]

Section B: Speciation and Isolation

6. (a) Speciation that occurs when biological populations of the same species become isolated due to geographical changes. [1]

(b)

1. Geographical barrier prevents gene flow between populations.
2. Different environmental conditions exert different selection pressures / genetic drift occurs.
3. Accumulation of different mutations/alleles leads to genetic divergence.
4. Eventually, reproductive isolation occurs (they can no longer interbreed to produce fertile offspring). [3] (Max 3 marks: 1 for no gene flow, 1 for different selection/mutations, 1 for reproductive isolation)

7. (a) Geographical isolation. [1]

(b)

1. Changes in chromosome number or structure (chromosomal mutation).
2. Accumulation of genetic differences preventing gamete fusion or zygote development (genetic incompatibility). [2]

8. (a) Speciation that occurs without geographical isolation (within the same habitat). [1]

(b)

1. Failure of meiosis leads to gametes with double the chromosome number (polyploidy).
2. Fusion of these gametes produces a polyploid offspring.
3. The polyploid offspring is reproductively isolated from the parent population (diploid) because hybrid offspring would be triploid and infertile (odd number of chromosomes cannot pair in meiosis). [3]

9. (a)

1. Specific courtship rituals ensure mating only occurs between members of the same species.
2. If rituals diverge (due to mutation/selection), individuals no longer recognise each other as mates, preventing gene flow. [2]

(b)

1. Pre-zygotic barriers prevent the waste of energy/gametes on producing inviable or infertile offspring.
2. Post-zygotic barriers involve the production of a zygote that fails to develop or is infertile, which is energetically costly. [2]

10. (a)

1. Gene flow occurs between adjacent populations along the ring.
2. However, genetic differences accumulate gradually around the ring.
3. At the ends, the accumulated genetic differences are sufficient to cause reproductive isolation. [2]

(b) Species boundaries can be gradual/clinal rather than distinct/discrete. [1]

Section C: Classification and Phylogeny

11. (a) The evolutionary history and relationships of a species or group of species. [1]

(b)

1. Phylogenetic classification is based on evolutionary ancestry/common descent.
2. Linnaean classification is based primarily on observable morphological/structural similarities. [2]

12. (a)

1. DNA code is degenerate (multiple triplets code for the same amino acid).
2. Therefore, DNA sequences can vary (silent mutations) without changing the amino acid sequence, providing more data points for comparison. [2]

(b)

1. Cytochrome c is essential for aerobic respiration, so it is found in all aerobic organisms.
2. It evolves slowly (conserved protein), allowing comparison between distantly related species where fast-evolving proteins would be too different to align. [2]

13. (a) A and B. [1]

(b) A common ancestor. [1]

(c) Fossil record / Embryological development / Anatomical structures. [1]

14. (a)

1. Cell wall composition: Bacteria have peptidoglycan; Archaea do not (or have pseudopeptidoglycan/other polymers).
2. Membrane lipids: Bacteria have ester-linked lipids; Archaea have ether-linked lipids. [2]

(b)

1. Archaea and Eukarya share similar mechanisms for DNA replication and transcription (e.g., RNA polymerase structure).
2. Archaea and Eukarya both have histones associated with DNA (Bacteria generally do not). [2]

15. (a) Structures that have the same basic anatomical structure/origin but different functions. [1]

(b)

1. The pentadactyl limb is found in diverse groups (mammals, birds, reptiles) with different functions (flying, swimming, running).
2. This suggests they all inherited the structure from a common ancestor, supporting descent with modification. [2]

Section D: Application and Evaluation

16. (a)

1. Low genetic diversity means the population is genetically uniform.
2. If the environment changes (e.g., new disease), it is less likely that some individuals possess alleles for resistance, leading to potential total extinction. [2]

(b) Introduce individuals from other wild populations (outbreeding) to introduce new alleles. [1]

17. (a)

1. HIV is a retrovirus with a high mutation rate (reverse transcriptase lacks proofreading).
2. HIV reproduces rapidly, generating many variants in a short time. [2]

(b)

1. The virus antigens change rapidly (antigenic variation).
2. A vaccine targeting one strain may not be effective against new mutant strains. [2]

18. (a)

1. In artificial selection, humans choose the traits; in natural selection, the environment chooses.
2. Artificial selection is often much faster than natural selection. [2]

(b) Reduced genetic diversity makes crops vulnerable to diseases/pests. [1]

19. (a) Structures that have similar functions but different evolutionary origins/structures. [1]

(b)

1. Organisms with analogous structures may look similar due to convergent evolution (similar selection pressures).
2. This can lead to them being classified together incorrectly if evolutionary history is not considered. [2]

20. (a)

1. Not all organisms fossilise (soft-bodied organisms decay).
2. Geological processes (erosion, subduction) destroy fossils. [2]

(b) It shows a sequence of forms changing gradually over time (transitional fossils). [1]