This free quiz has 11 real AQA A-level Biology exam questions on populations in ecosystems (28 marks, about 35 minutes). It marks itself: the table and calculation questions are marked for you, and for written answers you check your work against the real AQA mark scheme.
What the quiz covers (AQA 3.7.4)
naming the type of competition between species, and why a weed affects crop growth
how releasing sterile males reduces a mosquito population
key ecology terms for populations, habitats and ecosystems
reasons for conserving rainforests
precautions when marking animals for mark-release-recapture, and estimating a population size from data
describing the mark-release-recapture method
random quadrat sampling to find the mean percentage cover
using sand dune data to explain succession (4 marks), and estimating the number of plants in a field (5 marks)
How to use it
Write each written answer in full before you open the mark scheme, then tick only the points you really made. For sampling methods, say how you would get random coordinates and how many quadrats you would use, and explain why each precaution matters rather than just naming it. For the calculation, show your working on paper.
Where students lose marks (from AQA examiners’ reports and mark schemes)
Each point below is followed by wording that gained marks.
Name the competition. Common wrong answers were “interspecies” and intraspecific, and a significant number of students didn't name the type of competition at all or named something the species compete for instead. Weaker answers said only that growth would be affected.
✔ Gains credit: interspecific competition, linked to less light so less photosynthesis, or less nitrate to make amino acids, proteins or DNA.
Competition in pest control. Most students understood that sterile males reduce breeding, but few mentioned competition, so only about 10% gained both marks. A significant number thought being infertile stopped the males passing on the virus.
✔ Gains credit: sterile males compete with fertile males to mate, so they do not reproduce and the mosquito population falls.
Random sampling needs a method. A significant number of students said quadrats should be placed randomly without saying how, or wrote only “use a generator”. Some suggested throwing quadrats, and Punnett squares were not credited.
✔ Gains credit: a grid over the area (e.g. using tape measures) with coordinates from a random numbers table or generator.
Many quadrats, then a mean. Most students did not say that a large number of quadrats should be used, and some gave too few, such as 1, 3 or 5. Many described the percentage cover in one quadrat without explaining how to get the mean, or counted numbers instead of percentage cover.
✔ Gains credit: a large number of quadrats (10 or more if a number is given), dividing the total percentage cover by the number of quadrats.
Scaling up to a total. Working out the total number of plants in the whole area was the hardest mark. A common answer was to “scale up” from the mean with no detail of how, and some left out the area of the quadrat.
✔ Gains credit: divide the area of the field by the area of a quadrat and multiply by the mean number of plants per quadrat.
Explain marking precautions. Answers such as “marking should not cause harm” or “the mark should not rub off” were not credited unless explained. Most students did not mention leaving time for the animals to disperse, and some forgot to release them after marking.
✔ Gains credit: the mark is non-toxic and not visible to predators so it does not affect survival, and time is left after release for the animals to disperse before the second sample.
Pioneer species change conditions. Some students wrote “pioneers”, “colonisers” or “primary species” instead of pioneer species, used “organism” or “plant” instead of species, and wrote “more hospitable” or “more habitable”. Over 11% of students scored zero on one question, often by describing natural selection or speciation.
✔ Gains credit: pioneer species change the environment (e.g. forming soil or humus), so it becomes less hostile or more suitable for other species.
Keep practising
The other AQA 3.7 self-marking quizzes: Inheritance · Hardy–Weinberg · Evolution and speciation
Next, topic 3.8: the gene expression quiz
The AQA topic index
weekly AQA group classes: Year 12 on Tuesdays at 5.15pm, Year 13 on Wednesdays or Thursdays at 6.30pm
Questions © AQA, from past A-level and AS Biology papers, with their mark schemes and examiners’ reports.