What you need to know
- 4.15–4.16Variety of life, biodiversityThe variety of life in an area, including species richness and genetic diversity. and endemicDescribes a species found naturally in only one geographical area..
- 4.17–4.18Richness, heterozygosityA measure of genetic diversity: H = number of heterozygotes ÷ number of individuals, for one gene locus. index and D.
- 4.19nicheThe role of a species in its habitat: how it uses biotic and abiotic resources and interacts with other organisms. and three types of adaptationA feature that increases an organism’s chance of survival and reproduction in its niche..
- 4.20Hardy–WeinbergEquations p + q = 1 and p² + 2pq + q² = 1 that predict allele and genotype frequencies in a large population that is not evolving., mutationA change in the sequence of bases in DNA., selection and isolation.
- 4.21Evaluate zoos and seed bankA store of seeds kept dry and cold so that they stay viable for many years..
Numerical sets are illustrative. Photosynthesis and ecosystems are covered in Topic 5.
By the end, you should be able to…
- Choose richness, H or D to match the question.
- Carry a speciationThe formation of a new species, when populations become reproductively isolated and their gene pools change. argument from isolation to fertile offspring.
- Evaluate conservationProtecting and managing species and habitats to maintain biodiversity. without ignoring genetic diversityThe variety of alleles in a population or species..
Build your understanding
Pick the right tool
If the question counts speciesA group of organisms that can interbreed to produce fertile offspring., that is richness. If it gives heterozygousHaving two different alleles of a gene. and N, calculate H. If it gives abundances across species, calculate D with the −1 terms. If it gives a recessiveAn allele that is expressed in the phenotype only when no dominant allele is present (when homozygous). phenotypeThe observable characteristics of an organism, produced by its genotype interacting with the environment. count, start from q².
If it asks about zoos, name research, breeding, reintroduction and education, then limit each. endemicDescribes a species found naturally in only one geographical area. belongs in any “why this place matters” argument.
Keep processes distinct
mutationA change in the sequence of bases in DNA. supplies alleleA different version of the same gene, found at the same locus.. Selection changes their frequencies. Isolation stops them mixing. speciationThe formation of a new species, when populations become reproductively isolated and their gene pools change. is the possible outcome. habitatThe place where an organism lives. loss is a human threat, not a type of adaptationA feature that increases an organism’s chance of survival and reproduction in its niche.. All questions below are original.
Make your reasoning visible
Show D working
N, N(N−1), each n(n−1), the sum, then D. A bald decimal is easy to mark wrong.
Evaluate means both sides
A strength without a limitation is incomplete for 4.21.
Avoid this misconception
The claim: D, H and richness are interchangeable biodiversityThe variety of life in an area, including species richness and genetic diversity. scores.
The correction: They measure different levels. Using the wrong one is a content error, not a rounding error.
Check your understanding
Try each question before opening the suggested answer.
Check your understanding (continued)
Check your understanding (continued)
Practice question
Retrieval and explanation · suggested answer
Distinguish biodiversity from endemism.
Show suggested answer
Biodiversity is the variety of life at genetic, species and habitat levels. Endemism is natural occurrence only in one defined place.
Practice question
Retrieval and explanation · suggested answer
A fictional quadrat contains 8 species. Why is that not enough to say the habitat is more diverse than another quadrat with 8 species?
Show suggested answer
Richness is equal. D could differ if abundances are uneven, and genetic diversity is unmeasured.
Practice question
Retrieval and explanation · suggested answer
Calculate H if 9 of 30 animals are heterozygotes at a marker.
Show suggested answer
H = 9/30 = 0.30.
Practice question
Retrieval and explanation · suggested answer
A fictional sample has n = 7, 5 and 3. Calculate D.
Show suggested answer
N = 15, N(N−1) = 210, Σn(n−1) = 42 + 20 + 6 = 68, D = 210/68 ≈ 3.09.
Practice question
Retrieval and explanation · suggested answer
Why is “niche = habitat” incomplete?
Show suggested answer
Habitat is the place; niche is the organism’s role, including resources and interactions.
Practice question
Retrieval and explanation · suggested answer
A fictional population has 9 recessive phenotypes in 100 individuals. Estimate q and the expected heterozygote frequency, stating the assumption.
Show suggested answer
Assuming a recessive allele in Hardy–Weinberg, q² = 0.09, q = 0.30, p = 0.70, 2pq = 0.42.
Practice question
Retrieval and explanation · suggested answer
Outline how reproductive isolation can lead to new species.
Show suggested answer
Gene flow stops; mutation and selection accumulate different alleles; the groups may no longer produce fertile offspring.
Practice question
Retrieval and explanation · suggested answer
Evaluate seed banks as a method for conserving plant genetic diversity.
Show suggested answer
They can store many genotypes cheaply for decades, but not all species seed well, collections need many parents, and restoration still requires habitat and living partners such as pollinators.
Take the idea further
Apply the same specification knowledge to an unfamiliar problem. Any extra assumptions are supplied in the question.
Stretch question
Habitat X: n = 20, 1, 1. Habitat Y: n = 8, 7, 7. Both N = 22. Without full calculation, which has higher D, and how would a seed bank plus a zoo each fail to recreate Y’s community?
Show a hint
Evenness, then ex situ limits.
Explore the reasoning
Y is more even, so Σn(n−1) is smaller and D is higher (X is almost a monoculture). A seed bank stores plant genotypes, not the animal community or their interactions. A zoo might hold a few animals but not the habitat’s abundances, niches or gene flow. Neither recreates Y without in situ habitat.
Recall this lesson
Lesson recall questions
Question 1 of 5: How can a botanic garden support an endemic plant?
Biodiversity and endemism
Practice question
Retrieval and explanation · suggested answer
How can a botanic garden support an endemic plant?
Lesson: 4C 1: Biodiversity and Endemism
Try this from memory first.
Put your biology to work
Explore where these ideas appear in the world. Enrichment, not extra required recall.
Conservation as a coordinated claim
4C · Exam PracticeThe World Association of Zoos and Aquariums describes conservation as a priority for member collections, including work beyond the exhibit. Treat that as an institutional aim to evaluate…Specification 4.21Read & use the scienceClose article
Why this matters
The World Association of Zoos and Aquariums describes conservation as a priority for member collections, including work beyond the exhibit. Treat that as an institutional aim to evaluate with 4.21, not as proof that every zoo succeeds. Ask what was measured: births, surviving wild releases, genetic diversity, or visitor numbers. A zoo can contribute through research, breeding, reintroduction and education, but evidence for each differs. Coordinating pedigree records may reduce inbreeding; releasing animals requires habitat and survival monitoring; education claims need measured behaviour change. An association statement establishes an aim, not the outcome. The specification asks students to evaluate methods, so a strong response gives a potential benefit and a limitation linked to an endangered species rather than describing only attractive exhibits.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 2, pp. 21–24. The application extends beyond required recall.
- 4.21 be able to evaluate the methods used by zoos and seed banks in the conservation of endangered species and their genetic diversity, including scientific research, captive breeding programmes, reintroduction programmes and education
Use the science
Why are visitor numbers a weak measure of whether captive breeding conserved genetic diversity?
Explore a possible response
Attendance does not record relatedness, inbreeding or whether released animals survived. Diversity needs genetic or pedigree evidence.
Explore the source
- WAZA: conservationWorld Association of Zoos and Aquariums
A global catalogue is not D
4C · Measuring BiodiversityThe IUCN Red List assesses extinction risk for named species using criteria such as decline and range. It is a conservation tool, not a substitute for calculating D…Specification 4.17 · 4.18Read & use the scienceClose article
Why this matters
The IUCN Red List assesses extinction risk for named species using criteria such as decline and range. It is a conservation tool, not a substitute for calculating D in a school quadrat. A habitat can have a high D of common invertebrates and still hold few threatened endemics, or the reverse. A conservation assessor asks whether a species may disappear. A field ecologist calculating D asks how individuals are distributed among species in a sampled habitat. A geneticist calculating the heterozygosity index asks a third question within one species. These measures can disagree without any of them being wrong because their denominators and purposes differ. Students should identify what was sampled, define N and n correctly, and avoid reading a global extinction-risk label as a substitute for local abundance data.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 2, pp. 21–24. The application extends beyond required recall.
- 4.17 know how biodiversity can be measured within a habitat using species richness, and within a species using genetic diversity by calculating the heterozygosity index: number of heterozygotes / number of individuals in the population
- 4.18 understand how biodiversity can be compared in different habitats using the formula to calculate an index of diversity (D): N(N−1) / Σn(n−1)
Use the science
Why might a woodland with a high D still be a poor site for an endemic plant?
Explore a possible response
D summarises the sampled community’s richness and evenness. It does not tell you whether a particular endemic is present or whether its habitat requirements are met.
Explore the source
- IUCN: the Red List of Threatened SpeciesInternational Union for Conservation of Nature
Why a “no change” equation is still biology
4C · Gene Pool and Genetic DiversityNature Education’s Scitable account treats Hardy–Weinberg as the genotype frequencies expected in a diploid population that is not evolving. If observed frequencies differ, at least one assumption has…Specification 4.20(i)Read & use the scienceClose article
Why this matters
Nature Education’s Scitable account treats Hardy–Weinberg as the genotype frequencies expected in a diploid population that is not evolving. If observed frequencies differ, at least one assumption has failed. That is exactly how 4.20(i) uses the equation: as a test for change, not as a promise that wild populations are ideal. Hardy–Weinberg predicts genotype frequencies from allele frequencies under specified assumptions, including random mating and no selection, migration or mutation. If measured data do not fit, a biologist investigates which assumption or sampling issue matters. One count cannot establish the cause of change. Researchers often repeat sampling across generations and compare loci. In an exam calculation, define p and q, apply p² + 2pq + q² = 1, and then interpret what the comparison actually permits you to conclude.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 2, pp. 21–24. The application extends beyond required recall.
- 4.20(i) understand how the Hardy-Weinberg equation can be used to see whether a change in allele frequency is occurring in a population over time
Use the science
Why does one generation of classroom data not “prove Hardy–Weinberg forever”?
Explore a possible response
It tests those students, that locus, that time. Selection or mutation can still act in later generations or at other loci.
Explore the source
- Scitable: the Hardy–Weinberg principleNature Education
A backup of backups
4C · Conservation: Why and How?The Crop Trust describes the Svalbard Global Seed Vault as a backup of seed collections from genebanks around the world, held in permafrost as insurance against loss of…Specification 4.21Read & use the scienceClose article
Why this matters
The Crop Trust describes the Svalbard Global Seed Vault as a backup of seed collections from genebanks around the world, held in permafrost as insurance against loss of those collections. It is not a zoo, and it is not a wild habitat. It is one designed answer to the genetic-diversity half of 4.21, with the usual limit that frozen seed does not replace living ecosystems. Seed banks protect samples of genetic diversity, while zoos can coordinate breeding of living animals. Neither method is a substitute for protecting the conditions in which a species survives. The Svalbard backup illustrates why copies of seed collections are useful after accident or conflict, but viability, regeneration and access still require active management. In an evaluation, compare a method with the actual conservation goal: keeping alleles, restoring a wild population, or educating people. Each demands different evidence of success.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 2, pp. 21–24. The application extends beyond required recall.
- 4.21 be able to evaluate the methods used by zoos and seed banks in the conservation of endangered species and their genetic diversity, including scientific research, captive breeding programmes, reintroduction programmes and education
Use the science
Why does duplicating samples in Svalbard not by itself restore a vanished farmland variety to farmers?
Explore a possible response
Someone must still grow, select and share the seed under suitable conditions. The vault reduces the chance the last samples are lost.
Explore the source
- Crop Trust: Svalbard Global Seed VaultCrop Trust