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Respiration using oxygen to break down food molecules is called aerobic respiration. Glucose is the molecule normally used for respiration – it is the main respiratory substrate. Glucose is oxidised to release its energy.

The word equation for aerobic respiration is:

glucose + oxygen → carbon dioxide + water + energy released

The reactants in this reaction are glucose and oxygen. The products are carbon dioxide and water.

Symbol equation - Higher

You need to be able to recognise the chemical symbols:

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O

Respiration is a series of reactions, but this summarises the overall process.

The first stages of respiration occur in the cytoplasm of cells, but most of the energy released is in the mitochondria.