Overview of Homeostasis
Biology: AQA A Level, topic 6.4.1
Homeostasis
Homeostasis is the maintenance of the internal environment within an optimum range. Homeostasis is necessary to control the following factors:
High temperature
- Homeostasis maintains optimum core body temperature. This is approximately 37°C in humans.
- If body temperature rises above the optimum range, enzymes denature.
- The higher temperature causes the hydrogen bonds that maintain the enzyme structure to break.
- This alters the enzyme active site so the enzyme can no longer catalyse reactions (e.g. respiration).
Low temperature
- If temperature falls below the optimum range, enzyme activity declines.
- Decreased enzyme activity causes the rate of important reactions (e.g. respiration) to slow down.
Blood pH
- Homeostasis maintains blood pH.
- If blood pH rises above (too alkaline) or falls below (too acidic) the optimum range, enzymes denature.
- Denatured enzymes can no longer catalyse important reactions.
- Optimum pH range is normally around pH 7. Some enzymes have very different optimum ranges (e.g. enzymes in the stomach have a very acidic optimum pH).
High blood glucose
- Homeostasis maintains blood glucose concentration.
- If blood glucose levels rise above the optimum range, the water potential of the blood is reduced.
- Low water potential in the blood causes water to diffuse out of the cells by osmosis and into the blood.
- This makes the cells flaccid and they die.
Low blood glucose
- Homeostasis maintains blood glucose concentration.
- If blood glucose levels fall below the optimum range, there is not sufficient glucose for respiration.
- Respiration rate declines and energy levels fall.
Negative Feedback
Negative feedback is the mechanism that restores systems to the original level. The steps involved in these mechanisms are:
1) Detect change
- Change in the internal environment (stimulus) is detected by receptors.
- Receptors (e.g. thermoreceptors) are stimulated when the level is too high or too low (e.g. temperature).
2) Counteract change
- Receptors send a signal to the effectors through the nervous system.
- The effectors counteract the change (e.g by restoring body temperature to 37°C).
- Negative feedback can only maintain the internal environment within a specific range. If a change is too dramatic, negative feedback may not be able to prevent it.
Multiple Negative Feedback Mechanisms
Multiple negative feedback mechanisms provide a greater degree of control of the internal environment.
More control
- Multiple feedback mechanisms provide more control because the body can respond to multiple changes away from the optimum.
- E.g. Body temperature can be reduced or increased by multiple mechanisms.
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Faster response
- Multiple feedback mechanisms also provide a faster response because the body can respond in more ways to a change away from the optimum.
- E.g. If body temperature decreases, negative feedback can increase body temperature by both shivering and vasoconstriction.
Test yourself on Overview of Homeostasis
If our internal conditions are not regulated, which of the following could denature?
Which of the following statements about homeostasis are true?
Which of these is NOT an example of homeostasis?
Which of the following statements about negative feedback are true?
What is the optimum human body temperature?