Homeostasis — AQA GCSE Biology
Test yourself on Homeostasis with AQA GCSE practice questions.
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Homeostasis explained
Enzymes are proteins that catalyse metabolic reactions, and their activity depends on temperature and pH.
Read the full explanation
If conditions drift too far from the optimum, enzyme molecules change shape, the active site no longer fits the substrate, and the rate of reaction falls; extreme changes denature the enzyme permanently. Homeostasis therefore protects enzyme action by holding core temperature near 37 °C and controlling pH and substrate levels. Because enzymes drive processes such as respiration, digestion and protein synthesis, maintaining optimum conditions for enzymes also maintains all cell functions. For example, a high fever can slow or stop enzyme-controlled reactions, which is why body temperature is regulated so carefully.
Your focus
- Explain how temperature and pH affect enzyme activity and active site shape.
- Describe why homeostasis is needed to maintain optimum conditions for enzymes.
- Link enzyme-controlled reactions to the maintenance of all cell functions.
Homeostasis exam tips
Marking Points
- Enzymes are biological catalysts that control the rate of metabolic reactions.
- Enzyme activity depends on temperature and pH, with an optimum for each enzyme.
- Conditions away from the optimum reduce enzyme activity, and extreme conditions denature enzymes by altering the active site.
- Homeostasis maintains optimum temperature and pH so enzyme-controlled reactions continue at a suitable rate.
- Because enzymes control cell processes, maintaining optimum conditions for enzymes maintains all cell functions.
Examiner Tips
- 💡Link temperature and pH to active site shape when explaining why enzyme activity falls.
- 💡Use the term denatured precisely and state that the change is permanent.
- 💡Connect enzyme optimum conditions to one named process, such as respiration or digestion, to show the link to cell function.
Common Mistakes
- Saying enzymes are killed by high temperature; correct this by saying they are denatured, because enzymes are molecules, not living cells.
- Stating that denaturation changes the substrate; correct this by stating that the active site changes shape so the substrate no longer fits.
- Claiming homeostasis keeps every condition perfectly constant; correct this by saying it keeps conditions near the optimum within narrow limits.