This free quiz has 12 real AQA A-level Biology exam questions on energy and ecosystems (26 marks, about 35 minutes). It marks itself: tick-box, 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 3.5.3)
the equation for the net production of consumers
key terms for biomass and its chemical energy store
measuring dry mass with an oven and a balance
why most light falling on producers isn't used in photosynthesis
why energy transfer between trophic levels is inefficient, and why farming cattle is less efficient than farming crops
net primary production, and how temperature and light affect it
calculations from calorimetry data and energy transfer percentages
evaluating the effect of fungi and phosphate on plant productivity (4 marks)
How to use it
Write each answer in full before you open the mark scheme. Say energy is lost, not “used” or “produced”. For the calculations, show your working on paper and check the units the question asks for.
Where students lose marks (from AQA examiners’ reports and mark schemes)
Each point below is followed by wording that gained marks.
Dry mass to constant mass. Some students forgot to say the sample is heated, suggested burning it, or used methods such as paper towels or drying agents. Many didn't see why a constant mass matters, and some just took the final mass from the initial mass.
✔ Gains credit: heat the sample and weigh it, then keep heating and reweighing until the mass is constant.
The NPP equation. Weaker answers added losses in faeces to the equation for net primary production, and some didn't realise that NPP and GPP relate to plants, not animals.
✔ Gains credit: net primary production is gross primary production minus respiratory losses (NPP = GPP − R).
Temperature and NPP. Students often said that both photosynthesis and respiration would slow down, or simply wrote that “enzymes would denature”. “More energy used in respiration” was rejected.
✔ Gains credit: at a higher temperature respiration increases or photosynthesis (GPP) decreases, so NPP is lower.
Explaining NPP trends. Most students could say whether NPP stays constant or falls, but less than a third of them could explain why. Some thought NPP would rise just because there were more plants.
✔ Gains credit: NPP stays constant because GPP and respiration stay constant, or NPP falls because less light means less photosynthesis.
Energy is lost, not used. Writing that energy is “used in respiration” or that energy is “produced” lost the mark. Only 22% gained both marks in one question, mostly because they didn't say energy is lost between trophic levels.
✔ Gains credit: energy is lost between trophic levels, via respiration (as heat), excretion and faeces.
Faeces are not excretion. A significant number of students called faeces an excretory product, or wrote vague statements such as “energy is lost in waste”. Heat loss only gained credit when it was linked to respiration.
✔ Gains credit: heat loss from respiration, food that is not eaten or not digested (lost in faeces), and excretion (urine or urea) as separate reasons.
Why light isn't used. Almost 40% of students gained no mark in one question. Answers such as “light is not absorbed” or “light misses the producers” weren't detailed enough, and carbon dioxide rarely scored because its concentration wasn't mentioned.
✔ Gains credit: light is reflected, is the wrong wavelength, or misses the chlorophyll or chloroplasts; CO₂ concentration or temperature may be limiting.
Keep practising
The other AQA 3.5 self-marking quizzes: Photosynthesis · Respiration · Nutrient cycles
Next, topic 3.6: the stimuli and receptors 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.