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 Biology A J247

Cell Level Systems

Topic overview Microscopy, and sub-cellular structures DNA structure: polymer, double helix and nucleotides Protein synthesis and the triplet code 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

Community Level Systems

Topic overview Cycling materials, and the role of microorganisms The carbon and water cycles, and decomposition Levels of organisation, and abiotic and biotic factors Interdependence, competition and trophic levels Pyramids of biomass and the efficiency of transfer

Genes, Inheritance and Selection

Topic overview Genetic terms, and the genome Genome, environment and mutations How genetic variants influence phenotype Asexual and sexual reproduction compared Haploid, diploid and meiosis Single gene inheritance and Punnett squares Sex determination, multiple genes and Mendel's work Variation within a population, and classification Natural selection and evolution Evidence for evolution, and the work of Darwin and Wallace

Global Challenges

Topic overview Field investigations, and human impact on ecosystems Maintaining biodiversity, and evidence for environmental change Food security, agricultural and biotechnological solutions Selective breeding and genetic engineering Health, disease, and types of disease Interactions between diseases, and how they spread Reducing the spread of disease, and named examples Physical and chemical plant defences Detecting plant disease; white blood cells and platelets Non-specific defences and the immune system Monoclonal antibodies and their uses Vaccines, medicines and aseptic technique Developing new medicines, and non-communicable disease Treating cardiovascular disease, and lifestyle factors Cancer, and the use of stem cells in medicine Gene technology in medicine, and the human genome

Organism Level Systems

Topic overview The nervous system and coordinated responses The reflex arc The eye and its common defects The structure and function of the brain Investigating and treating the brain Hormonal coordination, thyroxine and adrenaline Hormones in reproduction and the menstrual cycle Contraception and treating infertility Plant hormones and their commercial uses Homeostasis, and the skin in temperature control Insulin and glucagon in blood sugar control Type 1 and type 2 diabetes Osmotic changes in body fluids, and the kidneys The kidney tubule and the effect of ADH Responding to temperature and osmotic challenges

Scaling Up

Topic overview Diffusion, osmosis and active transport Mitosis, the cell cycle and cell differentiation Stem cells in animals and meristems in plants Surface area to volume ratio and exchange surfaces The circulatory system, the heart and blood vessels Red blood cells and plasma Root hair cells, transpiration and translocation Xylem and phloem Factors affecting water uptake, and the potometer

Organism Level Systems

Homeostasis, and the skin in temperature control

3 things to know
Paper 3

Overview

What homeostasis is and the conditions it keeps constant, why body temperature and blood water content must be controlled, the receptor, coordination centre and effector of a control system, how the skin and hypothalamus detect temperature, and how sweating, vasodilation, vasoconstriction and shivering correct body temperature, with why sweating works poorly on a humid day.

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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Cell Level Systems

Community Level Systems

Genes, Inheritance and Selection

Global Challenges

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Algae and .

phytoplanktonfungianimals

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AThe blood becomes too dilute.

BLess ADH is released.

CThe collecting ducts become less permeable.

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Egestion means passing out of undigested food as faeces.

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