Topic 12.2 · Core + Supplement
Aerobic Respiration
Aerobic respiration is respiration that uses oxygen. Cells use that oxygen to break down nutrient molecules, and the energy released is what powers everything covered on the previous page — from muscle contraction to keeping your body temperature steady.
The definition Cambridge is actually checking
Aerobic respiration is the chemical process in cells in which oxygen is used to break down nutrient molecules and release energy. Glucose is the nutrient molecule used in the syllabus equation. Notice how many separate ideas that one definition is carrying at once: chemical reactions, happening in cells, using oxygen, breaking down a nutrient molecule, and releasing energy. Leave any one of those out — say, by defining aerobic respiration as simply “respiration with oxygen” — and you’ve stated something true without stating the biology an examiner is actually looking for.
The word equation
glucose + oxygen → carbon dioxide + water
Glucose and oxygen are the reactants; carbon dioxide and water are the products. Energy is released during the process, but it is not written as a product in this equation — that’s a detail worth being deliberate about, because it’s an easy place to lose a mark by adding “+ energy” to the right-hand side.
Treat the equation as a relationship rather than a line to recall from memory. If a cell is respiring aerobically, it follows automatically that it requires a supply of oxygen, that a nutrient molecule such as glucose is being broken down, that carbon dioxide and water are being produced, and that energy is being released — which lets you apply the same reasoning to an unfamiliar organism, tissue, or experimental setup a question might describe.
Supplement: the balanced chemical equation
Supplement candidates also need the balanced version:
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
One glucose molecule reacts with six oxygen molecules to form six carbon dioxide molecules and six water molecules. The coefficients are what make the equation balanced — the number of atoms of each element has to match on both sides, so six carbon atoms in glucose become six carbon dioxide molecules, and the twelve hydrogen atoms in glucose become six water molecules.
Where aerobic respiration happens
Mitochondria are the main site associated with aerobic respiration at this level. It’s worth keeping that as a supporting fact rather than importing more advanced pathway names or ATP accounting into an answer — neither is required for the current 0610 syllabus, and adding detail beyond what’s asked doesn’t earn extra credit here.
Don’t confuse
Don’t swap oxygen and carbon dioxide on either side of the arrow, and don’t write lactic acid or alcohol as products — those belong to anaerobic respiration in muscle and in yeast respectively, not to the aerobic equation. It’s also worth not reversing this equation with photosynthesis: carbon dioxide and water going in, glucose and oxygen coming out, is the opposite reaction, running in the opposite direction, and mixing the two up under exam pressure is a genuinely common mistake.