AQA GCSE Biology · Topic 12
Aerobic and anaerobic respiration, oxygen debt, the response to exercise, and metabolism.
156 questions 3 subtopics Spec 4.4
Every subtopic below has its own questions, mark schemes and notes once you start.
Respiration is the set of chemical reactions that transfers energy from glucose, going on continuously in every living cell. It can happen with oxygen or without, and the difference between those two routes decides how much energy the cell gets and what waste it is left with.
Exercise increases the demand for energy, so the body works harder to deliver oxygen. When even that is not enough, muscles switch to anaerobic respiration and build up a debt that has to be repaid once the exercise stops.
Metabolism is the whole of a cell's chemistry, every reaction happening in it, building up and breaking down, all controlled by enzymes and all ultimately powered by the energy respiration transfers.
Key definitions, in exam-ready wording.
The mistakes that come up again and again in this topic.
Never write that respiration 'produces', 'makes' or 'creates' energy. Energy is transferred, and examiners take marks off for the other wording.
Respiration is not breathing. If a question asks about respiration and your answer mentions lungs, check you have not answered the wrong question.
In the symbol equation the 6 goes in front of the whole formula (6CO₂), and glucose is C₆H₁₂O₆, both subscripts and balancing numbers are marked.
Anaerobic respiration still needs glucose. What it does without is oxygen.
Animal and plant/yeast anaerobic products are different. Lactic acid in muscle; ethanol and carbon dioxide in plants and yeast.
Oxygen debt is oxygen owed and repaid *after* exercise, not the oxygen used during it.
During vigorous exercise muscles respire anaerobically *as well as* aerobically, aerobic respiration does not stop.
For percentage increase, divide the increase by the *original* value, not the new one.
The liver converting lactic acid back to glucose is Higher tier only, but the rest of oxygen debt is needed by everyone.
If asked to explain an anomalous result, say the reading should be repeated first, do not simply say it should be deleted.
Define metabolism as *all* the reactions, not just the ones that release energy or just the ones that build molecules.
Starch is the plant storage carbohydrate and glycogen the animal one, getting them the wrong way round is the most common slip here.
A lipid is one glycerol plus three fatty acids. The number three is worth a mark on its own.
Nitrate ions are needed as well as glucose to make amino acids; leaving them out loses the mark.
156 questions on Respiration, marked against the scheme. Anything you get stuck on will be scheduled to come back sooner.