Describe cellular respiration as an exothermic reaction which occurs…

The idea

Cellular respiration is the set of enzyme-controlled reactions in living cells that transfers energy from glucose to the cell. It is exothermic: the reactions release energy to the surroundings, and the energy released drives metabolic processes such as building proteins, active transport, muscle contraction and keeping body temperature steady. Respiration happens continuously in all living cells, day and night, in plants and animals, because cells constantly need energy. It takes two forms. Aerobic respiration uses oxygen and releases more energy per glucose molecule; anaerobic respiration happens without oxygen and releases less energy. Both forms start from glucose and both release energy, so a cell respires whether or not oxygen is present.

What earns the marks

• Cellular respiration is an exothermic reaction: it releases energy to the surroundings.
• Respiration occurs continuously in living cells, not only during exercise or in the daytime.
• The energy released is used for metabolic processes such as active transport, protein synthesis, muscle contraction and maintaining body temperature.
• Respiration includes both aerobic respiration (using oxygen) and anaerobic respiration (without oxygen).

Common mistakes and how to put them right

• Thinking respiration only happens during exercise or breathing.

  Put it right by stating it occurs continuously in every living cell.

• Confusing respiration with breathing (ventilation).

  Put it right: Respiration is a chemical reaction inside cells, whereas breathing moves air in and out of the lungs.

• Calling respiration endothermic because it 'takes in' glucose.

  Put it right: It is exothermic because it releases energy to the surroundings.

• Believing anaerobic respiration does not release energy.

  Put it right: It does release energy, just less than aerobic respiration.

Exam tips

• Link the word 'exothermic' to 'releases energy' whenever you explain respiration.
• Remember the phrase 'continuously in living cells' — it is a common distractor in multiple-choice questions.
• When a question asks why a cell respires, name a specific metabolic use of the energy, such as active transport or protein synthesis.