AQA Biology 4.5.1
Homeostasis
Your body keeps its inside steady while the outside changes. Push a level off normal and watch it come back.
Triple Science · Higher tier
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Midday in a heatwave.
You have been walking in full sun for twenty minutes.
If you had to guess, when you get hot, does your body try to warm you up more, or cool you down?
Homeostasis
Keeping conditions steady.
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. It matters for enzyme action and all cell functions. Tap each condition it controls in the human body.
These automatic control systems may involve nervous responses or chemical responses. Nerves: The nervous system. Hormones: The endocrine system.
Control system
Receptor, coordination centre, effector.
Every control system has three parts. Receptor cells detect stimuli. Coordination centres, such as the brain, spinal cord and pancreas, receive and process the information. Effectors, muscles or glands, bring about responses which restore optimum levels. Step a temperature rise through, then break one part.
Body temperature sits at the optimum. Press Next step to push it up.
Negative feedback
This kind of control is called negative feedback: the response opposes the change. If the level rises, the response brings it down; if it falls, the response brings it up. The level moves a little either side of the optimum and is brought back each time.
Read a feedback diagram by following the arrows: change, detect, respond, back towards the optimum. Low blood glucose raised again by glucagon: Blood glucose and diabetes.
How sweating and shivering work: Thermoregulation (Triple).
Think again · exactly the same?
“Homeostasis keeps everything exactly the same.”
Your call
ChooseWhat does homeostasis do to a level such as body temperature?
Sort
Which part?
Place each one.
Tap a card, then tap the box it belongs in. Tap a placed card to take it back.
Command words in this lesson
- Define
- Homeostasis, in the spec’s words.
- Describe
- What each part of a control system does.
- Explain
- Why a level returns to normal, link by link.
Key fact
Homeostasis keeps internal conditions at the optimum. A receptor detects a change, a coordination centre processes it, and an effector responds.
Key note · AQA 4.5.1
Homeostasis
- Homeostasis regulates internal conditions to keep them at the optimum, for enzyme action and all cell functions.
- In humans it controls blood glucose concentration, body temperature and water levels.
- Receptor detects, coordination centre (brain, spinal cord, pancreas) processes, effector (muscle or gland) responds.
- Control can be nervous or chemical. Negative feedback: the response opposes the change.
Photograph this card. Tomorrow, cover it and say each line first.
Previous and next
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Not sure which part is the effector?
The temperature trace is schematic.