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B4: Homeostasis Revision Notes
Receptor: Detects change inside the body a stimulus
Processing centre: This receives the information that there has been a change inside the body.
Effector: This produces an automatic response (reflex).
In an incubator
The temperature sensor is the receptor
The processing center is a thermostat with switch
The effector is the heater
Normal body temperature is sometimes called core body temperature and is often quoted as 37°C but
the normal range is 36 to 37.5°C.
The active site of an enzyme can only fit a certain molecule inside it; it is called the lock and key
hypothesis because the molecule fits into the active site like lock and key. The enzyme speeds up
reactions by breaking molecule down (e.g. Hydrogen peroxide = Hydrogen + Oxygen). Once the enzyme
breaks down one molecule it can be used again for another chemical reaction with the same type of
Enzymes work the best at body temperature. If it is heated any more it becomes denatured. Denatured
means the shape of the active site changes and when the enzyme cools down it stays like this.
Inputs of water are:
The water content in food = 25%
The water content in water = 60%
And water made in respiration = 15%
Outputs of water are:
Water content in exhaled air = 65%
Sweat = 15%
Urine = 15%
And faeces = 5% (tears also = trace)
If inputs stay the same and sweat production falls to 10% the percentage of urine will increase to 70%.
This is because inputs and outputs must balance. The kidneys maintain the balance by varying the amount
of urine they produce. Kidneys also remove urea and excess salts.
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The amount of sweat produced varies with temperature and amount of exercise.
ADH is Anti Diuretic Hormone which controls the permeability of the tubules in the kidneys.
The human body keeps a steady internal environment. This must happen so that cells can work properly.
For example, body temperature and water levels are both kept constant. Keeping a constant internal
environment is called homeostasis.
Denaturing = the changing of the shape in an enzyme's active site when it is heated.…read more
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Kidneys filter urea, water, glucose and ions of salt out of your blood.
Blood cells or protein in a person's urine is a sign of kidney damage because it means that the kidneys
are not doing what they are meant to. This is because protein and blood cells are needed in the body and
should not be given out. No large molecules in urine.
Caffeine and tea causes a greater volume of dilute urine to be produced.…read more