A species of finch lives on an isolated island. The finches feed on seeds found on the ground. Over many generations, a drought reduces the availability of small, soft seeds, leaving mainly large, hard seeds. Explain how the finch population may change as a result of natural selection over many generations.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A species of finch lives on an isolated island. The finches feed on seeds found on the ground. Over many generations, a drought reduces the availability of small, soft seeds, leaving mainly large, hard seeds.
Model answer (5 marks)
1. There is variation in beak size within the finch population.
2. Finches with larger or stronger beaks can crack open large, hard seeds and are more likely to survive.
3. Finches with smaller beaks are less able to obtain food and are more likely to die or be selected against.
4. Surviving finches with larger beaks are more likely to reproduce and pass on the alleles for larger beaks to their offspring.
5. Over many generations the proportion of finches with larger beaks increases in the population.
2. Finches with larger or stronger beaks can crack open large, hard seeds and are more likely to survive.
3. Finches with smaller beaks are less able to obtain food and are more likely to die or be selected against.
4. Surviving finches with larger beaks are more likely to reproduce and pass on the alleles for larger beaks to their offspring.
5. Over many generations the proportion of finches with larger beaks increases in the population.
Examiner tips
- Use the word ‘explain’ to link cause and effect; include all five points in order.
- Show how natural selection acts on variation, survival, reproduction and allele frequency change.
- Use precise terms: variation, survival advantage, reproductive success, allele frequency.
Mark scheme (5 marks)
- There is variation in beak size within the finch population
- Finches with larger or stronger beaks are better able to crack open large, hard seeds and so are more likely to survive
- Finches with smaller beaks are less able to obtain food and are more likely to die / be selected against
- Surviving finches with larger beaks are more likely to reproduce and pass on the alleles for larger beaks to offspring
- Over many generations the proportion of finches with larger beaks increases in the population
Key terms in this question
natural selection · population
Related
- All Pearson Edexcel A-Level Biology A (9BI0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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