Notes from own school work and CGP AQA Biology Revision Guide

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  • Created on: 09-02-11 18:42
Preview of Homeostasis

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The process of keeping the internal environment constant.
Involves the nervous system and hormonal system.
Body levels that need to be controlled:
1. Body Temperature:
This is through thermoregulation ­ SEE A3 SHEET.
2. Water Content:
If the water content in the blood is:
a) Too high ­ the cells could burst.
b) Too low ­ they will dehydrate and the enzymes will stop working efficiently.
The body gains water through: eating, drinking and respiration.
The body loses water through: sweating, exhaling, urinating, and defecating.
On a cold day, if you don't sweat, you'll produce more urine which will be pale and dilute.
On a hot day, you sweat a lot, and you'll produce less urine which will be darkcoloured and
The kidneys control water balance.
3. Ion Content:
The body gains ions through: mineral ions from our diet ­ e.g. sodium.
If the correct balance isn't maintained cells can become shrivelled, swollen or burst ­ osmosis in
cells is affected.
The body loses ions through: sweat and urine ­ via the kidneys.
Excess ions are removed by the kidneys.
The kidneys control ion balance.
4. Blood Sugar Level:
Controlled by the pancreas, using the hormones insulin and glucagon.
Insulin allows glucose to move from the blood into the cells.
If your blood glucose concentration is too high insulin is released by the pancreas:
- Insulin causes your liver to remove any glucose which is not needed at the time from the blood
decreasing your blood glucose
concentration and returning blood
sugar concentration to the normal
- The soluble glucose is converted to an
insoluble carbohydrate called glycogen
which is stored in your liver.
If your blood glucose concentration is
too low glucagon is released by the
- Glucagon makes your liver break down
glycogen, converting it back into
- In this way the stored sugar is released back into the blood ­ increasing your blood glucose
concentration and returning blood sugar concentration to the normal range.

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Waste products that need to be removed:
5. Carbon Dioxide:
A product of respiration.
Toxic in high quantities and therefore must be released from the body.
Leaves the body by the lungs when you breathe out.
6. Urea
Proteins can't be stored by the body ­ so any excess amino acids are converted into fats and
carbohydrates, which can be stored.
This process occurs in the liver.
Urea is produced as a waste product from these reactions.
It is poisonous.…read more

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In the 1980s, human insulin made by genetic engineering became available. This didn't cause any
adverse reactions in patients, which animal insulin sometimes did.
3) Slow, intermediate and fast acting insulin's have been developed to make it easier for diabetics to
control their blood sugar levels.
4) Ready sterilised, disposable syringes are now available, as well as needlefree devices.
Improving methods allows diabetics to easily control their blood sugar. This helps them avoid some
damaging sideeffects of poor control, such as blindness and gangrene.…read more


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