Friday, 21 January 2011

Communication, Homeostasis & Energy

Communication & Homeostasis
Outline the need for communication systems within multicellular organisms, with reference to the need to respond to changes in the internal and external environment and to co-ordinate the activities of different organs.

Organisms need to respond to external stimuli, e.g. temperature, oxygen concentration and levels of
sunlight. These may be over time, e.g. winter fur to summer fur, or quickly, e.g. changing size of pupils.
Internal environments change too- the build up of carbon dioxide as a result of respiration changes the pH
of the tissue fluid, and therefore inhibits enzyme activity. Multicellular organisms need to coordinate
different organs, so this requires a good communication system which will:
• Cover the whole body
• Enable cells to communicate with each other
• Enable specific communication
• Enable rapid communication
• Enable both short and long-term responses.

State that cells need to communicate with each other by a process called cell signalling.

State that neuronal and hormonal systems are examples of cell signalling.

Define the terms negative feedback, positive feedback and homeostasis.
Negative feedback- A process in which any change in a parameter brings about the reversal of that change
so that the parameter is kept fairly constant.
Positive feedback- A process in which any change in a parameter brings about an increase in that change
Homeostasis- The maintenance of a constant internal environment despite external changes
Explain the principles of homeostasis in terms of receptors, effectors and negative feedback.
Any change is detected by receptors, the communication system transmits a message from the receptor to
the effector and, through negative feedback, the effectors reverse the change.

Describe the physiological and behavioural responses that maintain a constant core body temperature in ectotherms and endotherms, with reference to peripheral temperature receptors, the hypothalamus and effectors in skin and muscles.

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