This free quiz has 11 real AQA A-level Biology exam questions on respiration (25 marks, about 35 minutes). It marks itself: the tick-box and table questions are marked for you, and for written answers you check your work against the real AQA mark scheme.
What the quiz covers (AQA 3.5.2)
the process that happens in anaerobic respiration but not in aerobic respiration
why converting pyruvate to lactate lets ATP production continue
the substances that enter and leave the link reaction
why six carbon dioxide molecules are released from each glucose molecule
why inhibitors of the Krebs cycle or electron transfer chain affect oxygen uptake and ATP production
how uncoupling proteins help to keep body temperature constant
using a respirometer: why the liquid moves, what to measure and a suitable control
describing the process of glycolysis (4 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. Name each stage of respiration and say where it happens, and use precise terms such as oxidised, reduced and decarboxylation rather than “converted”. For the respirometer questions, say what happens to the oxygen, the carbon dioxide and the pressure inside the apparatus.
Where students lose marks (from AQA examiners’ reports and mark schemes)
Each point below is followed by wording that gained marks.
Energy is released, not produced. A significant number of students wrote about the “production of energy”, or said energy is needed for respiration. “Produces heat energy” was rejected.
✔ Gains credit: respiration releases energy, which is used to form ATP; when protons pass through uncoupling proteins, the energy is released as heat.
Oxygen is the final acceptor. A common uncredited answer was that less oxygen is taken up because only anaerobic respiration happens. Others said a lack of ATP reduces oxygen uptake.
✔ Gains credit: oxygen is the final electron acceptor in the electron transfer chain, so if fewer reduced coenzymes (reduced NAD or FAD) pass electrons to the chain, less oxygen is used.
Regenerating NAD. Wrong answers brought in the electron transport chain, the Krebs cycle or the link reaction, or said ATP is made directly from forming lactate. Many confused oxidation with reduction, and NADP or FAD were rejected.
✔ Gains credit: reduced NAD is oxidised, regenerating NAD so that glycolysis can continue.
Glycolysis, step by step. A third of students scored nothing, some describing glycogenesis, glycogenolysis or gluconeogenesis instead. Most wrote “conversion” or “breakdown” of triose phosphate, and mitochondrion was a common wrong answer for where glycolysis happens.
✔ Gains credit: glycolysis happens in the cytoplasm: glucose is phosphorylated using ATP, triose phosphate is oxidised (hydrogen is removed) and there is a net gain of ATP.
Decarboxylation, not carboxylation. A few students wrote “carboxylation” when carbon dioxide is released. Weaker answers confused the Krebs cycle with the Calvin cycle.
✔ Gains credit: per glucose, two carbon dioxide molecules are released by decarboxylation in the link reaction and four in the Krebs cycle.
Chemiosmosis makes ATP. Some students said oxidative phosphorylation is the setting up of a proton gradient rather than the production of ATP, or only said fewer electrons move down the chain. Protons diffusing in mitochondria was rejected for bacteria, which have none.
✔ Gains credit: protons (H⁺) diffuse through ATP synthase, providing the energy to add phosphate to ADP (oxidative phosphorylation).
Respirometer pressure changes. There was confusion over pressure and volume: a significant number of students suggested an increase in volume or pressure, or that a vacuum formed. Only 22% gave both measurements needed for a rate, and “volume of the tubing” was a common wrong answer.
✔ Gains credit: oxygen is taken up and carbon dioxide is absorbed by potassium hydroxide, so the pressure and volume of gas inside decrease; the rate needs the distance the liquid moves and the diameter of the tubing.
Keep practising
The other AQA 3.5 self-marking quizzes: Photosynthesis · Energy and ecosystems · 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.