Biodiversity Within a Community: AQA A Level Biology Exam Questions by Topic

AQABiodiversity Within a CommunityExam Questions
Written by Tom Whitburn

Biodiversity within a community (AQA 3.4.6) is one of the shortest sections of the Year 12 specification, but it turns up on AS and A-level papers almost every year, usually as data from a field study. You need to know that biodiversity can relate to anything from a small local habitat to the whole Earth, define species richness and an index of diversity, calculate d = N(N − 1) ÷ Σn(n − 1), and explain how farming techniques reduce biodiversity and how conservation and farming are balanced.

The examiners' reports keep finding the same slips. Students write 'population' instead of 'community', count individuals when only the number of species is needed, ask for the total number of organisms instead of the number in each species, and say a low index means every species is rare. On farming questions they write 'more food' or 'less shelter' instead of linking plant species to food sources and niches, and stop before saying what a lower yield means for the farmer.

Start with the definitions, then the habitat and farming questions, then the data and P values, and finish with the calculations. Answer each question on paper with a calculator before you open the mark scheme. If you'd like help with this topic, my AQA masterclasses run online on Tuesdays at 5.15pm for Year 12 and on Wednesdays or Thursdays at 6.30pm for Year 13.

What you need from GCSE and Year 12

Each question on this page assumes you're secure on these GCSE and Year 12 ideas. If any of them feels shaky, revise it before you start.

  • GCSE: a population is all the organisms of one species in a habitat; a community is all the populations of different species living in that habitat.
  • GCSE: biodiversity is the variety of all the different species of organisms on Earth, or within an ecosystem.
  • GCSE: random sampling with quadrats to estimate the abundance of a species, and why more samples give a more representative mean.
  • GCSE: hedgerows and field margins help to keep biodiversity on farmland, but farmers also need high yields.
  • Year 12 (AQA 3.4.5): two organisms belong to the same species if they are able to produce fertile offspring.

Key terms

These words come up in the questions and mark schemes. Examiners expect you to use them exactly.

  • Biodiversity: the variety of living organisms; it can relate to a range of habitats, from a small local habitat to the Earth.
  • Community: all the populations of different species living in the same place at the same time.
  • Population: all the organisms of one species in a habitat; species richness is never measured 'in a population'.
  • Species richness: a measure of the number of different species in a community.
  • Index of diversity: describes the relationship between the number of species in a community and the number of individuals in each species.
  • N: in d = N(N − 1) ÷ Σn(n − 1), the total number of organisms of all species.
  • n: the total number of organisms of each species; Σn(n − 1) adds up n(n − 1) for every species.
  • Habitats or niches: more plant species give animals more habitats or niches and a greater variety of food sources; 'homes' and 'shelter' don't score.
  • Conservation: protecting species and habitats; it has to be balanced against farming, where a lower yield means less food or less profit.
  • Significant difference: a difference between two means that is unlikely to be due to chance, for example P less than 0.05, or standard deviations that don't overlap.

What these questions cover (AQA 3.4.6)

The questions test these statements from the AQA AS and A-level Biology specification (7401/7402):

  • Biodiversity: Biodiversity can relate to a range of habitats, from a small local habitat to the Earth. (the rainforest question is the only part that asks about biodiversity across a whole ecosystem)
  • Species richness: Species richness is a measure of the number of different species in a community.
  • Index of diversity: An index of diversity describes the relationship between the number of species in a community and the number of individuals in each species.
  • Calculation of an index of diversity (d) from the formula d = N(N − 1) ÷ Σn(n − 1), where N = total number of organisms of all species and n = total number of organisms of each species. (the 2023 fish question asks you to work backwards from N and Σn(n − 1) to find the years on a graph)
  • Farming and conservation: Farming techniques reduce biodiversity. The balance between conservation and farming.

How to use this page

Write your answer on paper before you open the mark scheme. Allow about 1.3 minutes per mark: the 18 questions are worth 38 marks, so about 49 minutes in total. Then mark your answer strictly against the mark scheme and read the examiners' tip underneath it. If you'd rather print the questions, download the PDF pack.

Species richness and index of diversity (3.4.6)

Question 1

A level Paper 1 · June 2018 · Q03.1 · 1 mark · Easy

Explain what is meant by species richness.

Figure 4: two line graphs over days 50 to 250 of the year for natural, town and farmland habitats, showing the mean number of bees collected and the mean bee species richness. Question asks what is meant by species richness, 1 mark.
Show the mark scheme Mark scheme: (a measure of) the number of different species in a community. Accept habitat, ecosystem or one area for community; reject 'in a population'.

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From the examiners' report: 67.1% got it. Say community, not population, and don't mix species richness up with the index of diversity.

Question 2

AS Paper 2 · June 2016 · Q04.2 · 1 mark · Medium

State what other measurement is needed to calculate an index of diversity for dung beetles.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Figures 4 and 5: bar charts with standard deviation bars of the mean number of species of dung beetle and the mean total number of dung beetles on intensive, rough grazing and organic farms. Question asks what other measurement is needed to calculate an index of diversity, 1 mark.
Show the mark scheme Mark scheme: number of individuals in each species; accept population of each species.

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From the examiners' report: Fewer than 50% got it. The total number of beetles is already in Figure 5; you need the number of individuals in each species.

Question 3

AS Paper 1 · June 2019 · Q04.2 · 2 marks

Explain why an index of diversity is more useful than species richness.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Table 2: numbers of five invertebrate species caught at two river sites (48 and 45 in total); Table 3: index of diversity 4.7 at site 2 and the rate of water flow at each site. Question asks why it is more useful to calculate an index of diversity than to record species richness, 2 marks.
Show the mark scheme Mark scheme: the index of diversity also measures the number or population of each species; useful because there may be many of some species, or few of other species.

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From the examiners' report: No examiners' report for this paper. The mark scheme wants the number of individuals of each species, then why that matters: some species may be common and others rare.

Question 4

A level Paper 3 · June 2017 · Q04.2 · 3 marks

Outline a method to determine plant species richness at one site.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Question text: ecologists studied changes in mean species richness and mean index of diversity in grasslands on Scottish islands between 1975 and 2010; outline a method to determine the plant species richness at one site, 3 marks.
Show the mark scheme Mark scheme: a method of selecting sampling sites at random, such as a grid with coordinates from a random number table; use of a quadrat (frame or point); identify or count the number of different plant species. Reject percentage cover or counting individuals.

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From the examiners' report: The commonest error was counting individuals or the percentage cover of each species. For species richness you only identify and count the species; mention both and you lose the mark.

Question 5

AS Paper 1 · June 2023 · Q07.1 · 4 marks

Define species richness and index of diversity and use SDs to compare two farming methods.

Table 4: soil prokaryotes under two farming methods: mean species richness 517 (±17) and 560 (±24); mean index of diversity 0.251 (±0.011) and 0.230 (±0.014); plus prokaryotic biomass, carbon stored and wheat yield. Values are mean ±2 standard deviations. Question asks for both definitions and the differences in biodiversity, 4 marks.
Show the mark scheme Mark scheme: species richness is the number of species in a community; index of diversity is the relationship between the number of species and the number of individuals in each species; no SD overlap for species richness, so a significant difference; SD overlap for index of diversity, so no significant difference.

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From the examiners' report: The index of diversity was defined less well than species richness. 'Number of species in a population' was wrong. No overlap of SDs means a significant difference; overlap means the difference may be due to chance.

Biodiversity, habitats and farming (3.4.6)

Question 6

AS Paper 1 · June 2023 · Q07.3 · 2 marks · Hard

Evaluate the balance between conservation and farming for two farming methods.

Question text: evaluate the balance between conservation and farming for the two farming methods, using Table 4 (soil prokaryote species richness, index of diversity, biomass, stored carbon and wheat yield), 2 marks.
Show the mark scheme Mark scheme, any two: method 2 has better conservation with higher species richness, biomass and stored carbon; more organisms for food webs; more stored carbon so less CO2 in the atmosphere; lower yield so less food or less profit. Accept the converse for method 1.

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From the examiners' report: Students struggled. Use all three conservation measures for method 2, then finish each point: more stored carbon means less CO2 in the atmosphere, and a lower yield means less food or less profit.

Question 7

A level Paper 2 · June 2025 · Q10.1 · 3 marks · Medium

Explain why tropical rainforests have a high biodiversity of animal species.

Passage: tropical rainforests are among the most biologically diverse ecosystems in the world, and their varied plant communities support a high biodiversity of animal species; it also covers nutrient recycling, fires, succession and deforestation. Question asks why there is a high biodiversity of animal species, 3 marks.
Show the mark scheme Mark scheme: large number or variety of plant species; more or different habitats or niches; greater variety or sources of food. Ignore shelter, homes and 'more food'.

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From the examiners' report: Under 10% got all three. Start from the varied plants: many plant species give more habitats or niches and more types of food. 'More food' didn't score, and some wrote about succession instead.

Question 8

AS Paper 2 · June 2016 · Q04.5 · 3 marks · Medium

Explain why removing hedges decreased the diversity of birds on farms.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Figures 4 and 5: dung beetle species and numbers on intensive, rough grazing and organic farms. Question text: farmers removed hedges to increase land for grazing and the diversity of birds fell; explain why, 3 marks.
Show the mark scheme Mark scheme: removes species of plant or insect; fewer food sources; fewer habitats or niches. Ignore 'less food' and homes or shelters.

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From the examiners' report: Most got a mark for habitat loss, but few linked removing hedges to losing plant and insect species. 'Less food', 'less homes' and 'less shelters' didn't score, and this is about species, not genetic diversity.

Question 9

AS Paper 1 · June 2024 · Q05.4 · 2 marks · Hard

Explain why bee species richness is greater in a wild flower field than in a wheat field.

Question text: species richness of plants and of bees is greater in a field of wild flowers than in a field of wheat; suggest and explain one reason for the higher species richness of bees, 2 marks.
Show the mark scheme Mark scheme: more plant species or greater plant diversity; so more variety of food (nectar or pollen), more habitats or niches, or more protection from predators. Ignore more food, shelter and homes.

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From the examiners' report: Many found this hard. The first mark is for the higher plant diversity in the wild flower field; link it to more types of nectar or pollen as food for the bees.

Question 10

A level Paper 1 · June 2019 · Q03.4 · 2 marks

Suggest one advantage and one disadvantage to a farmer of replanting hedges.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Figure 4: bar chart of index of diversity, about 0.85 in the centre of a field, 0.92 at the edge of a field and 0.96 in a hedge between fields. Question asks for one advantage and one disadvantage to a farmer of replanting hedges, 2 marks.
Show the mark scheme Mark scheme: advantage, such as more predators of pests so more yield or less pesticide, more pollinators so more yield, or subsidies or tourists so more income; disadvantage, such as less land for crops, more pests, more competition, or harder to farm, so less income.

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From the examiners' report: No examiners' report for this paper. Each point needs a suggestion and its effect on the farm, for example more predators of pests so a higher yield, or less land for crops so less income.

Interpreting biodiversity data (3.4.6)

Question 11

AS Paper 1 · June 2017 · Q09.3 · 3 marks · Hard

Explain why 68% of fish in one sample doesn't show it had the highest index of diversity.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Figure 9: scatter graph of species richness of fish samples (0 to 16) against depth (0 to 1000 m), with sample A at about 400 m and 12 species. Question: 68% of all the fish came from sample A; give reasons why you can't conclude that A had the greatest index of diversity, 3 marks.
Show the mark scheme Mark scheme, max 3: number of individuals of each species not known; almost all of sample A could be of the same species; two other samples have a higher species richness but fewer fish; other samples may have more individuals of each species.

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From the examiners' report: 62% scored zero and only 0.2% got all three. Generic answers about fair tests, repeats or sample size didn't score. Use the definition: the index needs the number of individuals of each species, which isn't given.

Question 12

A level Paper 3 · June 2017 · Q04.3 · 3 marks · Medium

Use P values to decide whether changes in species richness and index of diversity were significant.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Table 2: change in mean species richness and in mean index of diversity between 1975 and 2010, with P values: Islay +8.89 (P ≤0.001) and +0.22 (P >0.05); Colonsay +14.70 (≤0.001) and +2.68 (≤0.01); Harris −5.13 (≤0.001) and −2.44 (≤0.01). Question asks whether there were any significant changes, 3 marks.
Show the mark scheme Mark scheme: significant increase in species richness on Islay and Colonsay and a significant fall on Harris; change in diversity on Islay not significant; probability of getting the difference by chance greater than 0.05 on Islay, or less than 0.001 or 0.01 for the others. Reject 'results are due to chance'.

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From the examiners' report: 46% scored zero. The test shows whether the difference between two means is significant, not whether the data are accurate. Read ≤ and > carefully, and say which changes were increases and which was a fall.

Question 13

A level Paper 1 · June 2022 · Q01.3 · 1 mark · Hard

Suggest why biomass was used instead of numbers of individuals to measure plant diversity.

Table 1: total shoot biomass (g m⁻²) of seven plant species in soil containing 14 fungal species, from 2 for Poa compressa to 51 for Fragaria virginiana. Question asks why biomass was used instead of the number of individuals of each species, 1 mark.
Show the mark scheme Mark scheme, one of: individual organisms could not be identified or separated; too small or numerous to count; too time consuming. Ignore 'too difficult to count' unless qualified.

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From the examiners' report: Many compared it with a pyramid of biomass, which isn't the point. Say why individuals can't be counted: they can't be separated, or they are too small or too numerous.

Calculating an index of diversity (3.4.6)

Question 14

AS Paper 1 · June 2024 · Q05.3 · 2 marks · Medium

Calculate the index of diversity for three bee species.

Table 4: bees trapped in a field of wild flowers over 6 months: cuckoo bee 250, domestic honeybee 800, clover bee 200, with the formula d = N(N − 1) ÷ Σn(n − 1). Question asks for the index of diversity, 2 marks.
Show the mark scheme Mark scheme: 2.11 for 2 marks (accept 2.1 or any correct rounding); 1 mark for the numerator 1 561 250 or the denominator 741 250.

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From the examiners' report: Three-quarters scored at least 1 mark. Each half of the formula earns a mark, so show N(N − 1) and Σn(n − 1) before you divide.

Question 15

AS Paper 1 · November 2021 · Q07.1 · 2 marks

Calculate the index of diversity for insects from a stacked bar chart.

Figure 7: stacked bar chart of the numbers of fly, beetle, bee and leaf hopper in an uncut plot 1 (79 insects) and a mown plot 2 (about 97 insects, mostly leaf hoppers). Question asks for the index of diversity for plot 1 to 2 significant figures, 2 marks.
Show the mark scheme Mark scheme: 2.7 for 2 marks; 1 mark for 79 × 78 = 6162, or 2286 for Σn(n − 1), or correct readings of 22, 41, 14 and 2.

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From the examiners' report: No examiners' report for this paper. The mark scheme expects readings of 22, 41, 14 and 2 for each species: read each segment of the stacked bar, not the running totals 22, 63, 77 and 79.

Question 16

AS Paper 1 · November 2021 · Q07.2 · 1 mark

Explain why mowing didn't increase insect species richness.

Question text: the student concluded that cutting plants with a lawn mower increased the species richness of insects; use Figure 7 to explain why this conclusion is incorrect, 1 mark.
Show the mark scheme Mark scheme: the same number of different species in both plots, 4.

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From the examiners' report: No examiners' report for this paper. Species richness is the number of species, and both plots have four; plot 2 has more insects, not more species.

Question 17

A level Paper 3 · June 2023 · Q05.1 · 1 mark · Medium

Use N and Σn(n − 1) to find which years had a given index of diversity.

Figure 7: species richness of fish (about 30 to 48) and Figure 8: index of diversity of fish (about 2 to 6.6), 1980 to 2010, near a power station. Question: with N = 624 and Σn(n − 1) = 64 792, which years had these values? 1 mark.
Show the mark scheme Mark scheme: 1982 and 2003; reject if any other year is given.

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From the examiners' report: 40% got it. The values give d = 6. Give only the years where a plotted point is at 6, not every place the line crosses 6, and read the x-axis scale carefully.

Question 18

A level Paper 3 · June 2023 · Q05.2 · 2 marks · Hard

Explain how a year had the highest species richness but the lowest index of diversity.

Question text: in 1997 the scientists recorded the highest species richness but the lowest value of d over the 29 years; describe and explain how these results were possible, 2 marks.
Show the mark scheme Mark scheme: many (48) species, the highest number; but one or a few species were present in very large numbers, or most species in very small numbers. Ignore each or all species in small numbers.

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From the examiners' report: Only 7% got both. Nearly half got the first mark, but 'all species were in small numbers' is wrong: the index is low because one or a few species dominate.

Where students lose marks (from AQA examiners' reports and mark schemes)

Each point below is followed by wording that gained marks.

  • Count the individuals in each species: Fewer than 50% knew what else was needed to calculate an index of diversity for dung beetles. Many asked for the total number of beetles, which the graph already gave.

    ✔ Gains credit: "Number (of individuals) in each species" or "population of each species".

  • Species richness is for a community, not a population: 67.1% defined species richness, but many confused population with community and species richness with the index of diversity. 'The number of species in a population' and 'the variety of alleles in a community' were both wrong.

    ✔ Gains credit: "(A measure of) the number of (different) species in a community."

  • For richness, only count the species: On the method for plant species richness, the commonest error was counting the number or percentage cover of each species. Writing about counting both species and individuals lost the mark too.

    ✔ Gains credit: "Select sampling sites at random; use a quadrat; identify or count the number of different plant species."

  • A few common species pull the index down: Only 7% explained how 1997 had the highest species richness but the lowest index of diversity. Nearly half got the first mark, but many said each or all species were present in small numbers.

    ✔ Gains credit: "Many (48) different species; but one or a few species were present in very large numbers."

  • Variety of food sources, not 'more food': Under 10% got all three marks on rainforest animal diversity, and few started from the variety of plant species. 'More food' wasn't credited; on the hedge question 'less food', 'less homes' and 'less shelters' didn't score either.

    ✔ Gains credit: "Large variety of plant species; more habitats or niches; greater variety of food sources."

  • Finish the conservation and farming argument: On evaluating two farming methods, many noted the lower wheat yield without saying it means less food or less profit, and noted more stored carbon without linking it to less carbon dioxide in the atmosphere.

    ✔ Gains credit: "Better conservation as higher species richness, biomass and stored carbon; more stored carbon, less CO2 in the atmosphere; lower yield so less food or profit."

  • A statistical test compares the two means: 46% scored zero on the island P values. Many thought the test shows whether the data are accurate or reliable, mixed up ≤ and >, or missed that species richness rose on two islands and fell on Harris.

    ✔ Gains credit: "Significant increase in species richness on Islay and Colonsay and fall on Harris; change in diversity on Islay not significant; greater than 0.05 probability that the difference is due to chance."

  • Lots of fish in one sample says nothing about d: 62% scored zero and only 0.2% got all three marks when told 68% of the fish came from sample A. Answers like 'not a fair test', 'no repeats' or 'not representative' didn't score.

    ✔ Gains credit: "Number of individuals of each species not known; other samples have a higher species richness but fewer fish."

Download the questions

Download the PDF pack (18 questions, mark schemes at the end)

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Questions, mark schemes and examiners' report extracts © AQA.

Tom Whitburn
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