What Is Homeostasis? GCSE Biology

Homeostasis is the regulation of an organism’s internal conditions to maintain optimum conditions for its cells, despite internal or external changes.

In humans, homeostasis controls conditions such as:

• blood glucose concentration
• body temperature
• water levels

This is important because enzymes and cells function most effectively under particular conditions. If conditions change too much, cells may not work efficiently.

How does homeostasis work?

A homeostatic control system usually involves three main parts:

1. Receptors detect a stimulus. A stimulus is a change in the internal or external environment.
2. A coordination centre, such as the brain, spinal cord or pancreas, receives and processes the information.
3. Effectors produce a response that helps restore the optimum condition. Effectors can be muscles or glands.

The pathway can be remembered as:

stimulus → receptor → coordination centre → effector → response

These control systems may involve nervous responses or chemical responses involving hormones.

Worked example: blood glucose

After eating a carbohydrate-rich meal, blood glucose concentration may become too high.

• The pancreas detects the increase.
• The pancreas produces the hormone insulin.
• Insulin causes glucose to move from the blood into cells.
• Excess glucose is converted to glycogen in liver and muscle cells for storage.
• Blood glucose concentration therefore decreases towards its optimum level.

A hormone is a chemical messenger carried in the blood to a target organ.

Common exam mistake

Do not say that homeostasis keeps internal conditions completely constant. Conditions naturally fluctuate, but homeostasis keeps them within suitable limits and restores them towards optimum levels.

This explanation assumes Higher Tier and separate AQA GCSE Biology because no tier was specified. However, the core homeostasis content explained here is also studied at Foundation Tier and in Combined Science.