Homeostasis and negative feedback
Laura Armstrong & Joe Wolfensohn
Teachers
Contents
Recall Questions
This topic requires prior knowledge of enzymes and osmosis.
What is the optimum temperature for human enzymes?
Around 37°C – the body’s core temperature.
What is osmosis?
The diffusion of water across a partially permeable membrane from a dilute solution to a more concentrated solution.
Why do enzymes denature at high temperatures?
The enzyme’s active site changes shape due to breaking of bonds, meaning substrates can no longer bind.
Topic Explainer Video
Check out this @Lauradoesbiology video that explains homeostasis and negative feedback, then read the study notes. Once you’ve gone through them, don’t forget to try the practice questions!
Definition of Homeostasis
Homeostasis is the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes.
Homeostasis maintains optimal conditions for enzyme action and all cell functions.
Why Homeostasis Is Important
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Enzymes and cells work best at specific (optimum) conditions.
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If conditions such as temperature or pH change too much, enzymes denature, leading to failure of biological processes like respiration.
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Changes in water levels affect osmosis in and out of cells, which can lead to cells bursting or shrinking.
Definition of Negative Feedback
Negative feedback is a process where a change in a condition triggers a response that counteracts (reverses) the change to restore normal conditions.
Examples of Conditions Controlled by Negative Feedback
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Body temperature.
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Blood glucose levels.
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Water content of the body.
How Negative Feedback Works
Negative feedback uses automatic control systems that involve nervous responses or chemical responses.
All control systems include:
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Cells called receptors, which detect stimuli (changes in the environment).
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Coordination centres (such as the brain and spinal cord) that receive and process information from receptors.
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Effectors - muscles or glands, which bring about responses which restore optimum levels.
Example: Body Temperature
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The body gets too hot ➤ Receptors detect this.
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Effectors (e.g., sweat glands) are activated to cool the body.
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Once normal temperature is restored ➤ Effectors stop.
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If the body gets too cold ➤ Different effectors (e.g., muscles contracting) warm the body.
This cycle ensures internal conditions are kept near optimum.
Key Terms
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Homeostasis - Homeostasis is the regulation of the internal conditions of a cell or organism to maintain optimum conditions for enzyme action.
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Negative Feedback - A response mechanism that reverses changes.
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Optimum Conditions - Best conditions for enzyme activity.
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Effector - Muscle or gland that brings about a response.
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Receptor - Detects a stimulus (changes in the environment).
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Exam Tip
When asked about negative feedback, always describe how a receptor detects a change and an effector acts to reverse the change back to normal.
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Practice Question
Explain why homeostasis is important for enzyme-controlled reactions. (4 marks)
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Enzymes work best at specific conditions (temperature, pH, water levels).
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If the conditions move away from optimum, enzymes may work more slowly.
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Extreme changes (such as very high temperatures) cause enzymes to denature (active site changes shape).
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Homeostasis keeps conditions stable so enzyme-controlled reactions can happen faster.
More Practice
Try to answer the practice question from the TikTok video on your own, then watch the video to see how well you did!