Biology: Homeostasis

A summary of homestasis for the unit 2 AQA exam on the 19th May.

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  • Created by: Rebecca
  • Created on: 11-05-11 17:28


Homeostasis: maintenance of a constant internal environment

What conditions are maintained?

  • Temperature: enzymes in body work at 37C
  • Water: too much or too little causes more osmosis and can damage cells
  • Ions: too few or too many causes more osmosis and can damage cells
  • Blood sugar: as above
  • CO2 must be removed through exhalation as it's toxic
  • Urea is removed in urine as it's toxic
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Body temperature

What happens when you get too hot?

  • Hairs lie flat so they don't trap insulating layer of air
  • Blood vessels dilate allowing more blood to flow so heat transfers to surroundings through radiation
  • Sweat glands secrete sweat so evaporation removes heat

What happens when you get too cold?

  • No sweat is produced
  • Hairs stand up to trap insulating layer of air next to skin, reducing heat loss
  • Capillaries near skin constrict to reduce blood flow so less heat is lost through radiation
  • Muscles contract causing shivering which involves more respiration so releases heat
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What do the kidneys do?

  • Filter urea from blood
  • Adjust water content
  • Adjust ion content

What is urea?

  • Proteins can't be stored so they're broken down in the liver into urea.
  • Kidneys filter it out of the blood
  • It's stored as urine in the bladder and then excreted

Ion and water content

  • Excess salts are removed by the liver and some is lost in sweat
  • Water is lost in urine, sweat and exhalation
  • Cold: less sweat, pale and dilute urine
  • Hot: more sweat, dark and concentrated urine
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Blood sugar

  • Blood sugar input: carbohydrates in food put glucose in blood
  • Blood sugar output: exercise and reactions in cells remove glucose

The PANCREAS monitors and controls blood glucose


  • Pancrease releases insulin
  • Insulin tells cells to store glucose as glycogen which is insoluble
  • Level returns to normal


  • Pancreas releases glucagon
  • Glucagon tells cells to convert insoluble glycogen into soluble glucose
  • Glucose dissolves in blood and level returns to normal
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The person with diabetes is unable to control their blood sugar levels as they have too little insulin

They can help the condition through:

  • Avoiding food rich in sugar
  • Doing more exercise
  • Injecting insulin

The right amount has to be injected to correspond with the person's diet, size and exercise. If not, they risk entering into a coma.

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Banting and Best

What did they do?

  • Removed the pancreas from a dog
  • This resulted in its urine becoming sugary
  • They obtained an extract from the pancreas
  • Injected the extract into diabetic dogs
  • This caused a temporary decrease in blood sugar levels
  • They later went on to isolate the insulin gene


  • Dogs are quite similar to humans
  • It avoided human experimentation


  • Animals rights: dogs were harmed
  • Dogs are not metabolically the same as humans
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Pancreas transplantation


  • Permanent solution
  • No longer have to inject insulin
  • Cheaper in the long term


  • Body can reject the tissue
  • You may need to take expensive immunosuppressive drugs which could have side effects
  • Operations always carry the risk of infection
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Eleanor Prescott

This is really helpful, thanks :)


my life = saved. thankyou so much

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