Response to Exercise and Metabolism — AQA GCSE Biology
During exercise the body works harder, changing how it supplies energy. Metabolism is the sum of all the body's chemical reactions.
Response to exercise
During exercise, muscles need more energy, so the body responds:
- Heart rate increases — to pump blood faster.
- Breathing rate and depth increase — to take in more oxygen and remove more carbon dioxide.
- These supply muscles with more oxygen and glucose and remove carbon dioxide.
Anaerobic respiration and oxygen debt
If oxygen cannot be supplied fast enough, muscles respire anaerobically, producing lactic acid. This allows energy release to continue but is inefficient and causes muscle fatigue.
After exercise, the body needs extra oxygen to break down the built-up lactic acid (it is transported to the liver and converted back to glucose). This extra oxygen required is the oxygen debt, which is why you keep breathing hard after stopping.
Metabolism
Metabolism is the sum of all the chemical reactions in a cell or the body. These reactions are controlled by enzymes and need energy from respiration. They include:
- converting glucose to starch, glycogen and cellulose,
- forming lipids from glycerol and fatty acids,
- using glucose and nitrate ions to make amino acids and then proteins,
- respiration, and
- breaking down excess proteins to form urea for excretion.
Exam tips
- List how the body responds to exercise (heart rate, breathing rate and depth).
- Explain the oxygen debt and the role of the liver in removing lactic acid.
- Define metabolism and give examples of metabolic reactions.
- Link increased breathing/heart rate to supplying oxygen and glucose.