GCSE · Biology · AQA · Spec 8461

Homeostasis overview

Hot day or cold, just eaten or starving, the conditions inside you stay about right for your cells. Nobody tells your body to do it. So how does it manage?

Control systems

Rebuild the loop, then break it

2 stages are missing. Use the rest of the loop to work out which goes where.

Stage 1: A change pushes a condition away from its optimum
The optimum is the level your cells work best at. The change can come from inside the body or from outside it.
Stage 3: A coordination centre processes the information
It receives the information sent from the receptors and processes it.
Stage 5: The condition is back at its optimum
The response has restored the optimum level, until the next change sets the loop going again.

…and stage 5 leads back to stage 1.

Why it matters

Reason it through

Why does your body bother keeping its internal conditions at the optimum?

Link 1 of 4

First link · your turn

Something changes, around you or inside you. What happens to the conditions inside your body?

Locked — reveal the link above first

What homeostasis really means

Which one sounds like you?

Four friends are revising. Each sums up homeostasis in one line.

Which one is closest to what you think right now?

It's how your body reacts to changes in the world outside, like the weather.When something inside or outside me changes, my body brings its conditions back to the best level for my cells.It keeps everything inside me exactly the same. Conditions never change.It keeps conditions as high as possible, because more is always better.

How sure are you?

I'm sureI think soI'm guessing

It's how your body reacts to changes in the world outside, like the weather.

This is a common misconception

Outside changes count, but they're only half the story. Changes inside the body can push a condition away from its optimum too, and control systems respond to internal and external changes alike.

When something inside or outside me changes, my body brings its conditions back to the best level for my cells.

This matches the evidence

Yes, that's it. Homeostasis is the regulation of the internal conditions of a cell or organism to keep them at the optimum for function, in response to both internal and external changes.

It keeps everything inside me exactly the same. Conditions never change.

This is a common misconception

Conditions do change: internal and external changes keep pushing them away from the optimum. Homeostasis is the body's response. Control systems detect the change and bring the condition back. That's regulation, not a freeze-frame.

It keeps conditions as high as possible, because more is always better.

This is a common misconception

The target is the optimum, the best level for enzymes and cell functions, not the maximum. A condition can move too high or too low, and either way it has moved away from the optimum and needs bringing back.

Things change, inside you and around you. Homeostasis keeps bringing your conditions back to the optimum. That's what 'regulation' means.

Who does which job?

Sort the parts into the loop

Which component is each part?

Still to sort

Receptor (0)

Detects the change (the stimulus).

Coordination centre (0)

Receives and processes information from receptors.

Where the line is: A coordination centre receives and processes information. It doesn't carry out the response itself.

Effector (0)

Brings about the response that restores the optimum.

Where the line is: An effector carries out the response. Processing the information is the coordination centre's job.

6 of 6 still to sort.

Every part here belongs to one of the three components. Decide by what it does, not by what it looks like.

Watch out: The pancreas trips people up. Don't sort by what kind of organ something is. Ask what job it does in the loop.

Put it all together

Write it, then mark it

What is homeostasis? Name two conditions in the human body that it controls, and the three components that every control system includes. [7 marks]

Your answer

0 words · your answer stays on this page and is not sent anywhere.

The mark scheme

Homeostasis is the regulation of the internal conditions of a cell or organism. (1 mark)
It keeps conditions at the optimum for function, in response to internal and external changes. (1 mark)
Any two of: blood glucose concentration, body temperature, water levels (one mark each). (2 marks)
Receptors. (1 mark)
Coordination centres. (1 mark)
Effectors. (1 mark)

Model answer

Homeostasis is the regulation of the internal conditions of a cell or organism to keep them at the optimum for function, in response to internal and external changes. In the human body it controls body temperature and blood glucose concentration (it also controls water levels). Every control system includes receptors, a coordination centre and effectors.

Check your definition says 'regulation' and 'optimum', not 'the same', and mentions both internal and external changes. Then count: two conditions, three components.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

How your body keeps its conditions just right for your cells, and the three-part loop that does it

What you need to know

Homeostasis keeps the conditions inside you at the optimum, the best level for your cells.
It responds to changes both inside and outside the body. It's regulation, not keeping things fixed.
Enzymes and all your other cell functions work best at the optimum.
Every control system runs one loop: receptors detect, a coordination centre processes, effectors respond.

The big picture

Homeostasis is the regulation of the internal conditions of a cell or organism, keeping them at the optimum for function in response to internal and external changes. It matters because enzyme action and all cell functions work best at the optimum. In humans it includes control of blood glucose concentration, body temperature and water levels. Every control system, nervous or chemical, has the same three parts: receptors detect stimuli, coordination centres (such as the brain, spinal cord and pancreas) process the information, and effectors (muscles or glands) respond to restore optimum levels.

Key points

1Homeostasis 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.

2Homeostasis maintains optimal conditions for enzyme action and all cell functions.

3In the human body, homeostasis includes control of blood glucose concentration, body temperature and water levels.

4These automatic control systems may involve nervous responses or chemical responses.

5Receptors are cells that detect stimuli (changes in the environment).

6Coordination centres, such as the brain, spinal cord and pancreas, receive and process information from receptors.

7Effectors are muscles or glands. They bring about responses that restore optimum levels.

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Worked example

Problem

You step out of a warm house into freezing air, and the cold starts to lower your body temperature. Explain how a control system brings your body temperature back to its optimum, and why that matters.

⚠ Watch out

Stopping at 'the effectors respond'. The whole point of the response is that it restores the optimum level. Say that, because it's what makes the loop regulation rather than just a reaction.

🧠

Memory hook

Detect, Decide, Do, and back to best. Receptors DETECT the change, the coordination centre DECIDES (it processes the information), effectors DO the response, and the condition is back at its best: the optimum.

✓

Check yourself

Blood glucose concentration, body temperature and water levels are very different things. So why can the same three-part loop describe how the body controls every one of them?

Flashcards

(12)

What is homeostasis?

The regulation of the internal conditions of a cell or organism to maintain optimum conditions for function, in response to internal and external changes.

Why does the body need homeostasis?

It maintains optimal conditions for enzyme action and all cell functions.

Which three conditions in the human body does homeostasis control?

Blood glucose concentration, body temperature and water levels.

Does homeostasis keep internal conditions exactly the same all the time?

No. Conditions keep changing. Homeostasis regulates them, bringing them back to the optimum after each change.

Does homeostasis only respond to changes outside the body?

No. It responds to internal changes and external changes.

What are receptors?

Cells that detect stimuli.

What is a stimulus?

A change in the environment. Receptors are the cells that detect stimuli.

What does a coordination centre do?

It receives and processes information from receptors.

Name three coordination centres.

The brain, the spinal cord and the pancreas.

What are effectors, and what do they do?

Muscles or glands. They bring about responses that restore optimum levels.

What two kinds of response can automatic control systems involve?

Nervous responses or chemical responses.

Put these in loop order: effector, receptor, coordination centre.

Receptor, then coordination centre, then effector, and the response brings the condition back to its optimum.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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Rebuild the loop, then break it

Which one sounds like you?

Sort the parts into the loop

Write it, then mark it

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