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3.4.6 Biodiversity within a community

AQA A-level Biology 3.4.6 practice on Biodiversity within a community, with free MCQs, clues and worked explanations drawn from the Genetic information, variation and relationships between organisms section of specification 7402.

Specification route
3.4.6
Question bank
16 questions
Course stage
AS / Year 12

Sample questions

QUESTION 1 · 3.4.6 · LEVEL 3

What is the difference between 'species richness' and an 'index of diversity'?

  • Species richness measures only the number of different species, while an index of diversity also accounts for the number of individuals in each species.
  • Species richness accounts for the number of individuals, while an index of diversity only counts the number of different species.
  • Species richness is used for animals, while an index of diversity is used exclusively for plants.
  • They are identical terms that both measure the total number of organisms in a habitat.
Show clue

A forest with 99 oak trees and 1 pine tree has the same richness as a forest with 50 oak trees and 50 pine trees, but a very different index of diversity.

Show answer and explanation

Answer: Species richness measures only the number of different species, while an index of diversity also accounts for the number of individuals in each species.

Species richness is a measure of the number of different species in a community. An index of diversity describes the relationship between the number of species in a community and the number of individuals in each species.

QUESTION 2 · 3.4.6 · LEVEL 1

What is the general effect of standard agricultural farming techniques on biodiversity?

  • Farming techniques reduce biodiversity.
  • Farming techniques increase biodiversity by introducing new crop species.
  • Farming techniques have no measurable impact on local biodiversity.
  • Farming techniques increase species richness but decrease genetic diversity.
Show clue

Monocultures (growing a single crop over a large area) eliminate natural habitats.

Show answer and explanation

Answer: Farming techniques reduce biodiversity.

Farming techniques reduce biodiversity. The balance between conservation and farming is an important ecological issue.

QUESTION 3 · 3.4.6 · LEVEL 4

A student surveys two different fields. Both fields contain exactly $10$ different species of insects. However, Field A has a high index of diversity, while Field B has a very low index of diversity. How is this possible?

  • Field A has an even distribution of individuals across all species, while Field B is heavily dominated by one species with very few individuals in the others.
  • Field B contains a significantly larger total number of individual insects than Field A.
  • Field A contains species that are more genetically diverse within their own populations.
  • The student miscalculated species richness, as equal richness always means equal diversity.
Show clue

Index of diversity accounts for species richness AND the relative abundance of each species.

Show answer and explanation

Answer: Field A has an even distribution of individuals across all species, while Field B is heavily dominated by one species with very few individuals in the others.

An index of diversity describes the relationship between the number of species... and the number of individuals in each species. A community dominated by one species has a lower index of diversity than one where individuals are evenly spread, even if species richness is identical.

QUESTION 4 · 3.4.6 · LEVEL 2

Which agricultural practice most directly reduces the species richness of an area by physically removing natural habitats?

  • The destruction of hedgerows to create larger fields.
  • The use of artificial fertilisers to increase crop yields.
  • The implementation of crop rotation cycles over multiple years.
  • The selective breeding of dairy cows for higher milk production.
Show clue

These structures provide shelter, food, and breeding grounds for many wild species.

Show answer and explanation

Answer: The destruction of hedgerows to create larger fields.

Farming techniques reduce biodiversity. The removal of hedgerows destroys a complex habitat, directly reducing the number of plant and animal species that can live in the area.

QUESTION 5 · 3.4.6 · LEVEL 1

What does 'species richness' measure in a given community?

  • The number of different species present in the community.
  • The total number of individual organisms present in the community.
  • The relative abundance (number of individuals) of each species present.
  • The genetic diversity within the most dominant species.
Show clue

It is a simple count of the types of organisms, ignoring how many of each there are.

Show answer and explanation

Answer: The number of different species present in the community.

Species richness is a measure of the number of different species in a community.

QUESTION 6 · 3.4.6 · LEVEL 3

Why is an 'index of diversity' often considered a more useful measure of biodiversity than species richness alone?

  • It accounts for both the number of different species and the number of individuals within each species (relative abundance).
  • It calculates the exact mutation rate for every species in the habitat.
  • It completely ignores rare species, focusing only on the dominant organisms.
  • It measures the genetic diversity of a single species across multiple different habitats.
Show clue

A habitat where one species dominates $99\%$ of the population is less diverse than one where $10$ species are evenly split.

Show answer and explanation

Answer: It accounts for both the number of different species and the number of individuals within each species (relative abundance).

An index of diversity describes the relationship between the number of species in a community and the number of individuals in each species, providing a better picture of community balance.

QUESTION 7 · 3.4.6 · LEVEL 2

Which agricultural practice most heavily contributes to a reduction in biodiversity by replacing diverse plant communities with a single species?

  • The cultivation of monocultures.
  • The preservation of existing hedgerows.
  • The use of biological control agents instead of chemical pesticides.
  • The planting of genetically modified crops with high genetic diversity.
Show clue

This practice involves growing vast fields of just one crop, like wheat or corn.

Show answer and explanation

Answer: The cultivation of monocultures.

Farming techniques reduce biodiversity. The creation of monocultures (growing a single crop species over a large area) drastically reduces species richness and destroys habitats for other organisms.

QUESTION 8 · 3.4.6 · LEVEL 2

A forest is cleared to plant a massive field of single-crop wheat. What happens to the species richness and genetic diversity of the area?

  • Both species richness and genetic diversity drastically decrease.
  • Species richness decreases, but the genetic diversity of the wheat crop increases immensely.
  • Species richness increases due to the large number of wheat plants, but genetic diversity decreases.
  • Both species richness and genetic diversity naturally increase due to the added fertiliser.
Show clue

A monoculture replaces a complex web of life with billions of identical clones.

Show answer and explanation

Answer: Both species richness and genetic diversity drastically decrease.

Farming techniques reduce biodiversity. Monocultures lower species richness (only one species is grown) and genetic diversity (the crops are often genetically uniform).

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