Required Practicals 10 and 12, Animal Behaviour and Species Distribution: AQA A Level Biology Exam Questions by Topic

AQARequired PracticalsExam Questions
Written by Tom Whitburn

Required practicals 10 and 12 are both A-level only, so you'll meet them in Year 13. In practical 10 (AQA 3.6.1.1) you use a choice chamber or a maze to see how an environmental variable, such as light intensity, affects the movement of an animal. In practical 12 (AQA 3.7.4) you investigate how a named environmental factor affects the distribution of a species, using the sampling methods from 3.7.4: random quadrats or a belt transect for plants and slow-moving animals, and mark-release-recapture for animals that move around.

The examiners' reports show where the marks go. Only 6% got full marks for finding mean percentage cover, because most never said how to work out the mean, and 'scale up' on its own never gains the final mark for a population estimate. On mark-release-recapture, students forget to leave time for the animals to spread out, say marks shouldn't 'cause harm' without explaining why, and subtract the samples instead of multiplying them. In choice chambers, they list features without saying how each makes the conclusion valid.

Start with the quadrat and mark-release-recapture methods, then the choice chambers, and finish with the calculation and the chi-squared test. Answer each question on paper 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: using quadrats placed at random to estimate the population size of a common species, and a transect to see how its distribution changes across a habitat.
  • GCSE: abiotic factors such as light intensity, temperature, moisture and pH, and biotic factors such as predation, affect where organisms live.
  • GCSE: a hypothesis is tested by changing one variable and keeping the others the same; a larger sample gives more representative results.
  • Year 12 (AQA 3.4.6): species richness and the index of diversity are worked out from samples, so sampling must be random and the sample large. See the Biodiversity within a community page.
  • Year 12 (AQA 3.4.7): quantitative investigations of variation within a species collect data from random samples and calculate a mean and standard deviation. See the Investigating diversity page.

Key terms

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

  • Choice chamber: a container divided into sections with different conditions, such as light intensity, so you can count how many animals move into each.
  • Taxis: a directional movement towards or away from a stimulus, such as light.
  • Quadrat: a square frame of known area used to sample plants or slow-moving animals.
  • Random coordinates: positions on a grid laid over the area, chosen with a random number generator or table, so the quadrats are placed without bias.
  • Belt transect: quadrats placed at regular intervals along a line, used to see how a species' distribution changes with an environmental factor.
  • Percentage cover: the percentage of a quadrat's area covered by a species; used when individual plants are hard to count.
  • Mean number per quadrat: the total count in all the quadrats divided by the number of quadrats; multiply by (area of the habitat ÷ area of one quadrat) for the population.
  • Mark-release-recapture: a method for motile animals: capture a sample, mark and release them, wait for them to spread through the population, then take a second sample.
  • Population estimate: (number in first sample × number in second sample) ÷ number marked in the second sample.
  • Null hypothesis: a statement that there is no difference or no effect, for example that light intensity has no effect on the distribution of shrimps.
  • Chi-squared test: a statistical test for categoric data that tests whether there is a significant difference between observed and expected results.

What these questions cover (AQA required practicals 10 and 12)

The questions come from the tenth and twelfth required practicals in the AQA A-level Biology specification (7402), and the sampling methods in section 3.7.4, and test these statements and practical skills:

  • Required practical 10: Investigation into the effect of an environmental variable on the movement of an animal using either a choice chamber or a maze (both choice chamber questions test animals' responses to light; no available part uses a maze)
  • Required practical 12: Investigation into the effect of a named environmental factor on the distribution of a given species (no available written part asks about the effect of a named environmental factor on a species' distribution, for example along a belt transect, so the quadrat questions here are the sampling skills that practical relies on)
  • AT k use sampling techniques in fieldwork
  • Quadrats (3.7.4): randomly placed quadrats, or quadrats along a belt transect, for slow-moving or non-motile organisms
  • Mark-release-recapture (3.7.4): the mark-release-recapture method for motile organisms. The assumptions made when using the mark-release-recapture method.
  • Population size calculation (3.7.4): use given data to calculate the size of a population estimated using the mark-release-recapture method.
  • PS 2.4 Identify variables including those that must be controlled
  • PS 2.1 Comment on experimental design and evaluate scientific methods
  • MS 1.9 Select and use a statistical test

How to use this page

Write your answer on paper before you open the mark scheme. Allow about 1.3 minutes per mark: the 11 questions are worth 29 marks, so about 38 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.

Quadrats and percentage cover

Question 1

A level Paper 2 · June 2024 · Q05.1 · 5 marks · Easy

Describe how to estimate the number of fat hen plants in a field.

Question text: a weed is a plant growing where it is not wanted; fat hen is a weed which grows in some crop fields; describe how you could estimate the number of fat hen plants in a field, 5 marks.
Show the mark scheme Mark scheme: use a grid or divide the field into squares; obtain random coordinates with a calculator, computer or random numbers table or generator; count the number in a quadrat; large sample and calculate the mean number per quadrat (at least 10 if a number is given); multiply the mean per m² by the area of the field, or divide the field area by the quadrat area and multiply by the mean per quadrat. 'Scale up' alone isn't enough; a belt transect with quadrats at regular intervals is accepted.

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From the examiners' report: About 24% got all five and 97% at least one. Say how you get random coordinates, use 10 or more quadrats, and finish with the sum: field area ÷ quadrat area × mean per quadrat.

Question 2

A level Paper 2 · November 2021 · Q09.1 · 3 marks · Hard

Describe a method to find the mean percentage cover of algae on a coral reef.

Question text: a coral reef is an underwater ecosystem formed as a ridge of mainly calcium carbonate deposits; some algae grow on coral reefs; describe a method that could be used to determine the mean percentage cover of algae on a coral reef, not including the difficulties of working underwater, 3 marks.
Show the mark scheme Mark scheme: a method of randomly positioning the quadrats, such as a random numbers table or generator; a large number of quadrats (10 or more if a number is given); divide the total percentage by the number of quadrats. Ignore line or belt transects and point quadrats; accept squares or frames of a grid for quadrats.

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From the examiners' report: 63% got at least one mark but only 6% all three. Give a method for random positions, not just 'randomly', use many quadrats, and divide the total percentage cover by the number of quadrats.

Mark-release-recapture

Question 3

A level Paper 2 · November 2021 · Q10.4 · 4 marks · Medium

Explain how the mark-release-recapture method estimates the size of a fish population.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Passage about Lake Malawi: it has more fish species than any other lake, deforestation and farming have caused soil erosion and loss of nutrients into the lake and reduced some fish populations; lines 13 to 15 say mark-release-recapture can be used to estimate a fish population but can give unreliable results in very large lakes. Question: the mark-release-recapture method can be used to estimate the size of a fish population; explain how, 4 marks.
Show the mark scheme Mark scheme: capture a sample, mark and release; make sure the marking isn't harmful and doesn't affect survival; allow time for the fish to distribute randomly before collecting a second sample; population = number in first sample × number in second sample ÷ number marked in the second sample.

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From the examiners' report: Four in five got at least one mark and 15% all four. Don't forget 'release' and the time to spread out. Most lost the last mark on the formula: multiply the two samples and divide by the marked ones.

Question 4

A level Paper 2 · June 2024 · Q10.5 · 3 marks · Hard

Describe and explain two precautions for a valid mark-release-recapture estimate of geckos, and give the formula.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Passage about the wall gecko in southern Italy: pale geckos live on walls and are nocturnal, dark geckos live on olive tree trunks and are diurnal; lines 12 to 13 say scientists used mark-release-recapture to estimate the population. Question: describe and explain two precautions needed for the estimate to be valid, not including sample size, and include the formula, with spaces for Precaution 1, Precaution 2 and Formula, 3 marks.
Show the mark scheme Mark scheme: marking not toxic so it doesn't affect survival, or not visible to predators, or doesn't wash or rub off so recaptured geckos are identified; time after release so the geckos spread through the population; population = first sample × second sample ÷ number marked in the second sample. Ignore births, deaths, immigration and emigration.

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From the examiners' report: About 62% got at least one mark but only 7% all three. Explain each precaution: the mark mustn't rub off so recaptured geckos are identified. Many subtracted the samples instead of multiplying.

Question 5

A level Paper 2 · November 2021 · Q10.5 · 1 mark

Suggest why mark-release-recapture gives unreliable results in very large lakes.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Passage about Lake Malawi, one of the largest lakes in the world; lines 14 to 15 say mark-release-recapture can produce unreliable results in very large lakes. Question: suggest why, 1 mark.
Show the mark scheme Mark scheme: less chance of recapturing marked fish, or fish are unlikely to distribute randomly or evenly (accept fish may stay in one area or congregate). Ignore 'harder to capture fish'.

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From the examiners' report: About one in four got it. Stick to the large lake: marked fish are less likely to be recaptured, or won't mix evenly. Marks washing off, births and deaths, and migration didn't score.

Question 6

A level Paper 3 · June 2025 · Q03.2 · 3 marks · Easy

Use the tansy beetle's life cycle to explain the timing of the first sample and why beetles were identified first.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Context: the tansy beetle, Chrysolina graminis, 8 to 10 mm long and green, lives on tansy; two other green beetles, the dock beetle (4 to 7 mm) and the mint leaf beetle (6 to 10 mm), share the habitat. Figure 2: life cycle, with adults emerging in April to feed, mate and lay eggs, eggs hatching into larvae in May, larvae burrowing into the soil in June to July, adults emerging and feeding in August, and adults burrowing underground for winter from September to March. Table 2: 405 captured and marked in the first sample; 248 unmarked and 124 marked in the second sample. Question: suggest two reasons why the first sample was captured in the second week of August, and one reason why the beetles had to be identified before marking, 3 marks.
Show the mark scheme Mark scheme, max 2 for timing: the beetles have emerged from the soil; time to distribute evenly before burrowing; time for recapture before burrowing; not disturbing mating or egg laying; no population increase from eggs or larvae. Max 1 for identification: all three beetles are green; they're a similar length; only the tansy beetle population is being investigated.

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From the examiners' report: About 75% got at least 2 marks, but few found a second reason for August. Use the life cycle: adults are above ground, and there's time to mix and be recaptured before they burrow.

Question 7

A level Paper 3 · June 2025 · Q03.4 · 2 marks · Easy

State two precautions to get comparable tansy beetle data each year over five years.

Context: the tansy beetle life cycle (adults emerge in April and again in August, larvae burrow in June to July, adults overwinter underground from September to March) and Table 2 of mark-release-recapture results: 405 marked in the first sample, 248 unmarked and 124 marked in the second. Question: the ecologists repeated the investigation over five years; state two precautions they would have taken each year to obtain comparable data, 2 marks.
Show the mark scheme Mark scheme, any two: sample in the second week of August or the same time of year; sample the same location; use the same method; use a different mark each year; marking doesn't affect survival, predation or recapture, or isn't toxic or removed.

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From the examiners' report: About half got both. Think about repeating the study fairly: same time of year, same place, same method. 'No migration' or keeping the population the same didn't score.

Choice chambers (required practical 10)

Question 8

A level Paper 2 · June 2025 · Q07.1 · 3 marks · Medium

Suggest and explain three features of a choice chamber investigation with freshwater shrimps that make its conclusions valid.

Figure 3: photograph of Gammarus pulex, a freshwater shrimp. The student collected 30 shrimps from a stream, added stream water and gravel to each segment, used black paper on the lid to reduce light intensity, placed the shrimps at the centre and waited 10 minutes before counting. Figure 4: circular choice chamber in four segments, A 0%, B 25%, C 50% and D 100% light intensity. Question: suggest and explain three features of this investigation that help ensure the validity of any conclusions, 3 marks.
Show the mark scheme Mark scheme, any three: stream water and gravel so a natural habitat, normal behaviour, or other variables such as oxygen and pH controlled; 30 or a large sample so representative; placed at the centre so the same distance to each segment, or no bias; 10-minute delay so the shrimps acclimatise or have time to distribute.

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From the examiners' report: About 20% got all three and 85% at least one. Explain each feature: centre so no bias, 30 shrimps so representative, and 10 minutes to acclimatise. 'Time to move' wasn't enough.

Question 9

A level Paper 3 · June 2019 · Q05.2 · 1 mark · Hard

Suggest two factors to keep constant in choice chambers so crown-of-thorns starfish behave normally.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Table 1: behaviour of crown-of-thorns starfish (COTS) in a choice chamber with flashing or constant light: towards the stimulus 22 and 12, away 28 and 38, P values 0.69 and 0.02. Question: the natural habitat of COTS is coral reefs of tropical oceans; suggest two factors that should be kept constant in the choice chambers so that COTS display normal behaviour, 1 mark.
Show the mark scheme Mark scheme, any two for 1 mark: salinity of the water; temperature of the water; amount or distribution of food; pH; oxygen or carbon dioxide concentration; intensity or wavelength of the light. Ignore humidity, type of coral and depth of water.

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From the examiners' report: Just over half got it. This is a lab choice chamber, not the reef, so give abiotic factors you can control, such as water temperature, pH or salinity, not 'a reef' or 'type of coral'.

Calculations and statistics

Question 10

A level Paper 3 · June 2025 · Q03.3 · 2 marks · Medium

Estimate the tansy beetle population from mark-release-recapture results.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Table 2: number of C. graminis captured and marked in the first sample, 405; number of unmarked beetles captured in the second sample, 248; number of marked beetles captured in the second sample, 124. Question: use the data in Table 2 to estimate the population size of C. graminis, showing working, 2 marks.
Show the mark scheme Mark scheme: 1215 for 2 marks; 1 mark for 810 (second-sample total not worked out), 608 (divided by unmarked rather than marked), or correct working such as 405 × 372 ÷ 124 with a wrong or missing answer.

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From the examiners' report: Just under a third got both marks. The second sample is 248 + 124 = 372 beetles, so 405 × 372 ÷ 124. Using only the 248 unmarked gives the common wrong answer, 810.

Question 11

A level Paper 2 · June 2025 · Q07.3 · 2 marks · Medium

State a null hypothesis for the shrimp choice chamber and explain why chi-squared was the right test.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Table 3: number of G. pulex counted after 10 minutes in segments A (0% light), 15; B (25%), 8; C (50%), 4; D (100%), 3. Table 4: critical values of chi-squared at P = 0.95, 0.5, 0.05, 0.01 and 0.005 for 1 to 5 degrees of freedom. The student calculated a chi-squared value of 11.87. Question: state a null hypothesis for this investigation and explain why the chi-squared test was the appropriate statistical test, 2 marks.
Show the mark scheme Mark scheme: there is no significant difference in the distribution or number of shrimps at different light intensities, or light intensity has no effect on the movement of shrimps; the data are categoric or discrete, or the test finds whether there is a difference between observed and expected results.

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From the examiners' report: About 35% got both marks. Put light intensity in the null hypothesis, then say the data are categoric, or that the test compares observed and expected results. Correlation and comparing means are wrong.

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

Each point below is followed by wording that gained marks.

  • Percentage cover, then divide by the number of quadrats: Only 6% got all three marks for the mean percentage cover of algae. Most never said how to calculate the mean; many counted algae or species instead of estimating percentage cover, or used one quadrat for the whole reef.

    ✔ Gains credit: "Method of randomly determining position (of quadrats) e.g. random numbers table/generator"; "Large number/sample of quadrats"; "Divide total percentage by number of quadrats/samples/readings."

  • Scale up with the area of the quadrat: About 24% got all five marks for estimating the number of fat hen plants. The final step was the hardest: 'scale up' wasn't credited without saying how, and some left out the area of the quadrat.

    ✔ Gains credit: "Divide area of field by area of quadrat x mean number of plants per quadrat" or "Multiply mean number of plants per m² by area of field."

  • Release them, then give them time to spread out: Students often left out releasing the animals, and most failed to say time was needed for them to disperse before the second sample. Re-joining the population on its own wasn't enough.

    ✔ Gains credit: "Capture/collect sample, mark and release"; "Allow (time for) fish to (randomly) distribute before collecting a second sample."

  • Multiply the two samples; never subtract them: Many couldn't give the formula. Common errors were subtracting the second sample from the first, adding the samples, multiplying by 100, or dividing by the whole second sample instead of the marked animals in it.

    ✔ Gains credit: "(Population =) number in first sample × number in second sample divided by number of marked in second sample/number recaptured."

  • Explain why the mark mustn't harm or rub off: About 7% got all three marks on the gecko precautions. 'Marking should not cause harm' or 'the mark should not rub off' wasn't credited unless the answer said why that matters.

    ✔ Gains credit: "Marking not toxic so does not affect survival OR Marking not visible to predators OR Marking does not wash/rub off so recaptured (geckos) identified."

  • The second sample is marked plus unmarked: Just under a third got both marks for the tansy beetle estimate. The most common wrong answer, 810, used only the 248 unmarked beetles instead of adding the 124 marked ones to give 372 in the second sample.

    ✔ Gains credit: "Correct answer of 1215 = 2 marks" (405 × 372 ÷ 124).

  • Say how each choice chamber feature makes it valid: About 20% got all three marks. Some listed features without explaining them, few explained putting the shrimps in the centre, and 'time to move' didn't score.

    ✔ Gains credit: "30/large sample so representative/reliable"; "(Placed at) centre so same distance to each segment/light intensity OR so no bias"; "(10 minute) delay so shrimps can acclimatise/equilibrate."

  • Chi-squared, because the data are categoric: About 35% got both marks. Null hypotheses without light intensity didn't score, and wrong reasons for the test referred to correlation or comparing means.

    ✔ Gains credit: "(Different) light intensity/intensities has/have no effect … on the distribution/movement/behaviour of shrimp(s)"; "The data are discrete/categoric OR (To determine) if there is a difference between the observed and expected (results)."

Download the questions

Download the PDF pack (11 questions, mark schemes at the end)

Keep practising

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

Tom Whitburn
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