The maintenance of a constant internal environment inside the body in spite of changes inside it and around it.

Name three conditions that are held constant inside the human body.

Body temperature, blood glucose concentration and the water content of the blood.

Why must body temperature be held close to 37 °C?

Enzymes work fastest near this temperature and are denatured above it, so metabolic reactions would otherwise run at the wrong rate or stop altogether.

Explain why the body's chemical reactions slow down if a person becomes very cold.

Molecules move more slowly, so enzymes and their substrates collide less often and metabolic reactions proceed more slowly than the body needs.

What are the three parts of a control system in homeostasis?

A receptor that detects the change, a coordination centre that processes the information, and an effector that brings about the response.

OCR GCSE Combined Science Biology J250

Cell Level Systems

Topic overview Microscopy, and sub-cellular structures DNA structure: polymer, double helix and nucleotides Enzyme action, and investigating enzymes Cellular respiration as an exothermic process Aerobic and anaerobic respiration compared Synthesis and breakdown of carbohydrates, proteins and lipids Photosynthesis: producers and the process Photosynthesis as endothermic, and investigating it Limiting factors in photosynthesis

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Global Challenges

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Organism Level Systems

Topic overview The nervous system and coordinated responses The reflex arc Hormonal coordination, thyroxine and adrenaline Hormones in reproduction and the menstrual cycle Contraception and treating infertility Homeostasis and control systems in the body Insulin and glucagon in blood sugar control Type 1 and type 2 diabetes

Scaling Up

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Organism Level Systems

Homeostasis and control systems in the body

3 things to know
Paper 7 (Biology)

Overview

What homeostasis is, the conditions held constant inside the body, why body temperature stays close to 37 °C, the three parts of a control system, how the body corrects a change in temperature, and why the water content of the blood is controlled.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

A person's body temperature rises above normal and then returns to normal. Explain how this shows the body correcting a change.

Key term

Give an external change and an internal change that the body must respond to in order to keep conditions constant.

Key term

What is homeostasis?

Questions from this subtopic

Each one with the model answer underneath.

1
What is homeostasis?
Model answer
The maintenance of a constant internal environment inside the body in spite of changes inside it and around it.
2
Name three conditions that are held constant inside the human body.
Model answer
Body temperature, blood glucose concentration and the water content of the blood.
3
Why must body temperature be held close to 37 °C?
Model answer
Enzymes work fastest near this temperature and are denatured above it, so metabolic reactions would otherwise run at the wrong rate or stop altogether.
4
Explain why the body's chemical reactions slow down if a person becomes very cold.
Model answer
Molecules move more slowly, so enzymes and their substrates collide less often and metabolic reactions proceed more slowly than the body needs.
5
What are the three parts of a control system in homeostasis?
Model answer
A receptor that detects the change, a coordination centre that processes the information, and an effector that brings about the response.
6
A person's body temperature rises above normal and then returns to normal. Explain how this shows the body correcting a change.
Model answer
The rise is detected, and the responses it triggers, such as sweating and widening of the skin blood vessels, act against the rise and bring the temperature back down to its normal level.

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AA diet high in sugar and fat leads to obesity.

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