Niche, allele frequency and conservation — Edexcel International AS Level Biology
Niche and adaptations, the Hardy-Weinberg equation, mutation, selection and speciation, and evaluating zoos and seed banks.
Revision notes
4 short notes, in the order of the specification. Each one in short:
A niche is the role of a species in its habitat, including how it obtains food, the abiotic conditions it tolerates and its interactions with other species. Adaptations that fit organisms to their niche may be behavioural, anatomical or physiological. Two species cannot occupy exactly the same niche in the same place indefinitely, because they would compete.
The Hardy-Weinberg equation, p² + 2pq + q² = 1 with p + q = 1, predicts genotype frequencies in a population in which allele frequencies are not changing. If observed frequencies differ from the predicted ones over generations, allele frequencies are changing. Mutation and natural selection are two causes of change in allele frequency.
When populations of the same species become reproductively isolated, no gene flow occurs between them. Mutation and natural selection, acting in different environments, cause their allele frequencies to diverge. Eventually their members can no longer interbreed to produce fertile offspring, so they are different species.
Zoos conserve endangered animals through captive breeding programmes, reintroduction programmes, scientific research and education. Seed banks store seeds as a low-cost way of conserving plant species and their genetic diversity. Each approach has strengths and limitations, which must be weighed up to evaluate how effective it is.
Exam questions
8 exam-style questions (30 marks), each with its mark scheme.
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14 cards: flip them, mark what you knew, and practise the rest.
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The whole of plant structure and function, biodiversity and conservation on one page, so you can see where this subtopic fits.
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Quick check questions
Define niche.
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The role of a species within its habitat, including how it obtains resources and its interactions with other species.
Name the three types of adaptation.
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Behavioural, anatomical and physiological.
In the Hardy-Weinberg equation, what does 2pq represent?
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The frequency of the heterozygous genotype.
Name two causes of changes in allele frequency.
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Mutation and natural selection.
Why are seeds dried before storage in a seed bank?
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To reduce water content, which slows metabolism and prevents germination and damage from ice crystals.
Frequently asked questions
What is a niche in biology?
A niche is the role of a species within its habitat: how it obtains food and other resources, the abiotic conditions it tolerates and how it interacts with other species. Each species has its own niche, and species with very similar niches compete, so one may be excluded.
What are behavioural, anatomical and physiological adaptations?
Behavioural adaptations are how an organism acts, such as hibernation or migration. Anatomical adaptations are structural features, such as the rolled leaves of marram grass. Physiological adaptations are internal processes, such as a kangaroo rat producing concentrated urine. All of them increase survival and reproduction in the environment.
How do you use the Hardy-Weinberg equation?
Find q² from the frequency of the homozygous recessive phenotype, take the square root to get q, then calculate p = 1 − q. Use p² for homozygous dominant and 2pq for heterozygous. If later generations differ from the predicted frequencies, allele frequencies are changing.
How does reproductive isolation lead to a new species?
When populations are reproductively isolated there is no gene flow. Different mutations arise, and different selection pressures change allele frequencies in each population. Over time their gene pools become so different that members cannot interbreed to produce fertile offspring, so they have become separate species.
What are the pros and cons of zoos and seed banks for conservation?
Zoos protect endangered animals, breed them while maintaining genetic diversity, support research and education and allow reintroduction, but are expensive and hold few individuals. Seed banks cheaply store many seeds and alleles, but some seeds cannot be stored and stored plants do not adapt to change.
Written and checked against the Edexcel International AS Level Biology (XBI11) specification · Updated October 2026