Summary
Summary A level Biology communication and homeostasis
- Institution
- OCR
Detailed notes on communication and homeostasis including positive and negative feedback and thermoregulation for the OCR exam spec.
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HomeostasisHomeostasis – maintaining conditions internally within set limits
despite changes in the external environment e.g temperature, blood
glucose levels, water content, water potential of blood, blood
pressure, carbon dioxide concentration (pH)
Negative feedback – counteracts changes in internal conditions,
reversal of a change in the internal environment which returns to a
steady state or optimum position
1. Detect the change (stimulus)
2. Communicate – signal this change to other cells in the body
3. Response – initiate a mechanism to reverse the change
A change is detected and a mechanism is initiated that will reverse
the change and return conditions to optimum
e.g decrease in water potential below optimum detected by
osmoreceptors in hypothalamus.
ADH is released (endocrine system) from pituitary gland
Collecting duct reabsorbs more water
There is always oscillation as it takes time to detect stimulus and
cause a response
1. Enzyme controlled reactions – end product inhibition
2. Regulation of blood glucose concentrations
3. Regulation of body temperature
4. Regulation of the cardiac cycle
5. Regulation of blood pressure
6. Menstrual cycle (oestrogen and progesterone)
Positive feedback:
A process that increases the change detected by the sensory receptor
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