F214 OCR Biology: Homeostasis, Communication and Thermoregulation

F214 OCR Biology

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  • Created on: 15-06-11 11:22
Preview of F214 OCR Biology: Homeostasis, Communication and Thermoregulation

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Communication / Thermoregulation Summary
Communication within a multi-cellular organism is essential to co-ordinate activities
Communication is between receptors and effectors
This allows an organism to :
1. Monitor changes in internal and external environments
2. Respond adaptively to such changes
3. Co-ordinate the activities of different organs
Cells communicate with one-another by cell-signalling
The signal may be :
Electrical, by means of neurones
Chemical by means of messengers called hormones
Homeostasis - The maintenance of a relatively stable internal environment within an organism
Eg maintenance of body temperature, plasma glucose concentration, water potential
Negative feedback - A change in a system causes actions to take place that counteract that change,
attempting to restore the original state. i.e if body temperature falls actions take
place to cause it to rise
Positive feedback - A change in a system causes actions that increase that change further
e.g when the potential across an axon changes Na + channels open. This causes
further change in potential, which then causes more Na channels to open
Homeostasis requires :
A receptor that receives information
A control mechanism that responds to stimulus
An effector that performs the appropriate action
Control of body temperature
Ectotherms ­ e.g. reptiles
1. Have no physiological mechanism to control their temperature.
2. They must rely on behaviour eg lying in sun to warm up
3. They absorb heat in this way, raising their temperature
4. Kinetic energy of molecules within the cells increases
5. Molecules move faster, so collide more often
6. More enzyme-substrate complexes will form
7. Reaction within the cells will happen at a faster rate
8. Eg respiration at a faster rate, so more ATP made
9. So muscles can now contract to allow movement of the organism

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Endotherms ­ e.g. mammals
Receptors in skin detect changes in external temperature
Receptors in hypothalamus detect changes in internal temperature
If internal temperature rises : If internal temperature falls :
1. Hypothalamus detects change 1. Hypothalamus detects change
2. Hypothalamus is connected to effectors 2. Hypothalamus is connected to effectors
by neurones by neurones
Effectors cause a drop in internal temperature : Effectors cause an increase in internal
temperature :
1. Smooth muscle in skin arterioles relaxes 1. Smooth muscle in skin arterioles
2.…read more


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