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Biology 4 Revision Notes
Homeostasis means the maintenance of a constant internal environment.
The body needs to keep certain things the same to stay healthy. There are six things that need
to be controlled:
1) Body Temperature
2) Water levels - if not, too much water could enter/leave cells by osmosis
3) Ion content
5) Carbon dioxide
6) Blood Pressure
7) Glucose Levels
From Mrs. GRENCH Movement, Respiration, Sensitivity, Growth, Reproduction,
Excretion, Nourishment, Cells, and Homeostasis all organisms are sensitive to their
Living organisms can detect changes in their environment and co ordinate their
responses to enhance survival.
Plants do it without a nervous system.
Keyword Stimuli Change in an animal's surroundings this can be internal or
Detection H20 Amount, direction
Light brightness, wave length, duration, direction
Positive = grow towards
Negative = grow away
Photo = Light
Hydro = water
Geo = gravity
E.g. `phototropism positive = response towards light e.g., shoot tips
`Negative geotropism'= response away from gravity e.g. stem / shoot tips.
These responses are a result of directional growth i.e. a relatively slow response caused
by growing towards/away Eucalyptus, Sunflower, touch me not, Venus flytrap.
The thermoregulatory centre is the part of the brain that monitors and controls body
The pancreas meanwhile monitors and controls blood glucose concentration.
It produces a hormone called insulin that reduces blood glucose levels.
Diabetes is a disease which can be caused by insufficient insulin.