GCSE Combined Science revision · Biology: cells, organisation and disease

Respiration and metabolism

The idea

Respiration is an exothermic reaction that releases energy in all living cells. Aerobic: glucose + oxygen → carbon dioxide + water. Anaerobic in muscles: glucose → lactic acid. Anaerobic in plants and yeast (fermentation): glucose → ethanol + carbon dioxide. Aerobic respiration releases much more energy. During exercise heart rate, breathing rate and breath volume rise to supply more oxygen. Metabolism is the sum of all reactions in a cell or body.

Write the right equation for the organism.
Compare energy released.
Link exercise changes to oxygen supply.

Watch out Respiration is not breathing: it is a chemical reaction in every cell.

See it worked

Worked example

Explain why heart rate increases during exercise.

Muscles respire faster and need more oxygen and glucose.
A faster heart rate delivers these faster and removes carbon dioxide.

Answer To supply muscles with more oxygen and glucose for respiration

Your turn

Question 1Calculator allowed1 mark

What is produced by anaerobic respiration in human muscles?

Question 2Calculator allowed1 mark

Fermentation by yeast produces:

Question 3Calculator allowed2 marks

A runner's heart rate rises from 70 to 154 beats per minute. What is the percentage increase?

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