How Does Metabolism Relate to Respiration?
Learn how respiration transfers energy for metabolism, why respiration is a metabolic reaction, and the key distinction for AQA GCSE Biology exams.
Respiration is part of metabolism, and it transfers the energy needed for many other metabolic reactions.
This explanation assumes AQA GCSE Biology at Higher tier, but everything here applies to both Foundation and Higher tiers and is shared with Combined Science.
What is metabolism?
Metabolism is the sum of all the chemical reactions in a cell or the body. These reactions are controlled by enzymes and include:
- building larger molecules from smaller molecules
- breaking down molecules
- respiration
- converting glucose into storage molecules such as glycogen
- forming lipids from glycerol and fatty acids
- using amino acids to make proteins
- breaking down excess amino acids to form urea
Respiration is therefore one of the reactions included in metabolism, but metabolism is much broader than respiration alone.
How does respiration support metabolism?
Cellular respiration is an exothermic reaction that occurs continuously in living cells. Exothermic means energy is transferred to the surroundings. Respiration transfers energy from glucose. In aerobic respiration:
glucose+oxygen→carbon dioxide+water\text{glucose} + \text{oxygen} \rightarrow \text{carbon dioxide} + \text{water}glucose+oxygen→carbon dioxide+waterCells use the energy transferred by respiration for enzyme-controlled processes, including synthesising larger molecules. Organisms also use energy for movement and maintaining body temperature.
Worked example
A cell joins amino acids to synthesise a protein. This is a metabolic reaction and requires energy. Respiration transfers energy from glucose, allowing this enzyme-controlled process to occur.
The relationship is:
respiration transfers energy→energy supports metabolic reactions\text{respiration transfers energy} \rightarrow \text{energy supports metabolic reactions}respiration transfers energy→energy supports metabolic reactionsWhy the distinction matters
Respiration is both a metabolic reaction and a source of transferred energy for other reactions.
Common exam mistake
Do not say respiration creates or produces energy. Energy is transferred from glucose during respiration. Also, do not confuse respiration with breathing: breathing moves air into and out of the lungs, whereas respiration is a chemical reaction in cells.
A strong exam answer is: Respiration is a metabolic reaction that transfers energy for other enzyme-controlled reactions in cells.
