AQA · GCSE · Biology
Course version: 8461 · Version from Sept 2018
Homeostasis maintains optimal conditions for enzyme action and all cell…
Full specification wording
Homeostasis: Homeostasis maintains optimal conditions for enzyme action and all cell functions.
Enzymes are proteins that catalyse metabolic reactions, and their activity depends on temperature and pH.
Checked against the AQA 8461 specification (opens in a new tab) on .
- Point 2 of 5
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Enzymes are proteins that catalyse metabolic reactions, and their activity depends on temperature and pH. 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.
What earns the marks
- 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.
Common mistakes and how to put them right
Saying enzymes are killed by high temperature.
Put it right by saying they are denatured, because enzymes are molecules, not living cells.
Stating that denaturation changes the substrate.
Put it right by stating that the active site changes shape so the substrate no longer fits.
Claiming homeostasis keeps every condition perfectly constant.
Put it right by saying it keeps conditions near the optimum within narrow limits.
Exam 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.
Try the lesson
The start of the Homeostasis: Homeostasis maintains optimal conditions for enzyme action and all cell functions. lesson, made from checked teaching notes for this specification point.
Have a go first
What is the main purpose of homeostasis in the human body?
Listen
Enzymes are proteins that catalyse metabolic reactions, and their activity depends on temperature and pH. 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. A strong answer earns marks for these 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. A common slip: Saying enzymes are killed by high temperature. Instead, saying they are denatured, because enzymes are molecules, not living cells. Exam tip: Link temperature and pH to active site shape when explaining why enzyme activity falls.
Key words
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Enzyme structure and active site specificity
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Effect of temperature and pH on enzyme activity
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Denaturation as a permanent change
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Homeostasis as protection for cell processes
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See every definition
- Enzyme structure and active site specificity
- Enzymes are proteins that catalyse metabolic reactions, and their activity depends on the active site fitting the substrate.
- Effect of temperature and pH on enzyme activity
- Enzyme activity depends on temperature and pH, with an optimum for each enzyme, and conditions away from the optimum reduce enzyme activity.
- Denaturation as a permanent change
- Extreme conditions denature enzymes by altering the active site, so the substrate no longer fits and the change is permanent.
- Homeostasis as protection for cell processes
- Homeostasis maintains optimum temperature and pH so enzyme-controlled reactions continue at a suitable rate, and because enzymes control cell processes this maintains all cell functions.
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