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What is respiration?

Respiration is the enzyme-controlled release of energy from glucose in every living cell, transferring it to ATP.

Respiration explained

Aerobic respiration uses oxygen and releases far more energy per glucose molecule than anaerobic respiration, producing carbon dioxide and water.
In humans, anaerobic respiration produces lactic acid and an oxygen debt; in yeast it produces ethanol and carbon dioxide, which is the basis of brewing and baking.

Key formula

C6H12O6+6O2→6CO2+6H2O\mathrm{C_6H_{12}O_6} + 6\mathrm{O_2} \rightarrow 6\mathrm{CO_2} + 6\mathrm{H_2O}

Worked example

A sprinter respires anaerobically in the final seconds of a race, building up lactic acid in the muscles.

Examiner tip

Respiration is not breathing. Write 'respiration releases energy from glucose in cells' and avoid the word breathing entirely.

Respiration: common questions

Where does aerobic respiration take place?
It starts in the cytoplasm with glycolysis and completes in the mitochondria.
What is an oxygen debt?
The extra oxygen needed after exercise to oxidise the lactic acid that built up during anaerobic respiration.

Related terms

Photosynthesis

Photosynthesis is the process by which plants use light energy to convert carbon dioxide and water into glucose and oxygen.

Active transport

Active transport moves substances against a concentration gradient using carrier proteins and energy from ATP.

Enzyme

An enzyme is a biological catalyst — a protein that speeds up a specific reaction by lowering its activation energy.

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