Edexcel A Level Biology B
Edexcel A Level Biology B Topic 3: Classification and Biodiversity Exam Questions
Free Edexcel A Level Biology B exam questions for Topic 3: Classification and Biodiversity, with a mark scheme for every pack. Covers taxonomic hierarchy, three domains, molecular classification, natural selection, adaptation, measuring biodiversity and conservation.
Topic 3: Classification and Biodiversity exam questions
3 question packs of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About Edexcel A Level Biology B Topic 3: Classification and Biodiversity
Topic 3 of Edexcel A Level Biology B looks at how organisms are classified, how species change by natural selection and how biodiversity is measured. You learn the taxonomic hierarchy, binomial naming and the three domain system, and how molecular evidence from DNA and protein sequences has changed classification. Natural selection explains how adaptations arise and allele frequencies change. Biodiversity is studied at the level of habitats, species and genes, using species richness and an index of diversity. The topic links to Topic 8 on the origins of genetic variation and Topic 10 on ecosystems. Questions often involve interpreting phylogenetic trees or calculating diversity indices.
What you need to know
- Classification Organisms are classified into domain, kingdom, phylum, class, order, family, genus and species. Binomial names use genus and species.
- Three domains The three domains are Bacteria, Archaea and Eukarya, based on differences in rRNA, cell membranes and cell walls.
- Molecular evidence Comparing DNA base sequences and amino acid sequences shows how closely related organisms are. Scientific claims are validated by peer review.
- Natural selection Random mutations create variation; individuals with advantageous alleles survive and reproduce more; these alleles become more frequent in the next generation.
- Measuring biodiversity Species richness is the number of species. Index of diversity D = N(N - 1) / sum of n(n - 1). Genetic diversity can be measured by the number of alleles in a population.
- Conservation Biodiversity can be conserved in situ (protected areas) and ex situ (zoos, seed banks), each with advantages and limitations.
Common mistakes in Topic 3: Classification and Biodiversity
- Thinking species richness is the same as biodiversity; evenness and genetic diversity also matter.
- Saying individuals evolve; populations evolve as allele frequencies change.
- Writing that mutations happen because they are needed; mutations are random.
- Confusing genus and species when writing binomial names; the genus has a capital letter, the species does not.
- Assuming organisms that look similar are always closely related; molecular evidence can show otherwise.
Try three Topic 3: Classification and Biodiversity exam-style questions
1. A habitat contains three species with 12, 5 and 3 individuals. Calculate the index of diversity using D = N(N - 1) / sum of n(n - 1). (3 marks)
Show the mark scheme answer
N = 20 so N(N - 1) = 380; sum of n(n - 1) = 132 + 20 + 6 = 158; D = 380 / 158 = 2.41.
2. Explain how comparing DNA sequences can show how closely related two species are. (3 marks)
Show the mark scheme answer
DNA from both species is sequenced; the more similar the base sequences the more recently they shared a common ancestor; fewer differences means fewer mutations have accumulated since they diverged.
3. Describe how natural selection can lead to an adaptation becoming common in a population. (4 marks)
Show the mark scheme answer
Variation exists due to mutation; a selection pressure acts on the population; individuals with the advantageous allele survive and reproduce; they pass on the allele so its frequency increases over generations.
Topic 3: Classification and Biodiversity FAQs
What does Edexcel A Level Biology B Topic 3: Classification and Biodiversity cover?
It covers the taxonomic hierarchy, the three domains, molecular evidence for classification, natural selection, measuring biodiversity and conservation.
Which paper is Topic 3 examined in?
At A Level, Topics 1 to 4 can be assessed in both Paper 1 and Paper 2, and every topic can also appear in Paper 3, which focuses on general and practical principles.
Which calculations do I need for Topic 3?
You need to calculate the index of diversity and compare values between habitats, and be able to interpret data on DNA or amino acid sequence differences.
