• Created by: Ella
  • Created on: 26-05-15 15:44

Organisms to be able to respond to changes in the external environment to ensure survival, such as changes in light, oxygen concentration, and temperature. These responses happen very quickly, such as pupil dilation, or over a longer period of time, such as winter fur to summer fur. 
Organisms also need to be able to respond to changes in their internal environments, such as increasing carbon dioxide concentration as a result of respiration can lower the pH of the tissue fluid, which will effect enzyme action and could cause respiratory acidosis. Multicellular organisms also need to be able to coordinate the action of different organs, and so require a good communication system, that will:

  • Cover the whole body
  • Allow cells to communicate with each other
  • Enable rapid communication
  • Enable specific communication
  • Enable both short and long term responses

Cells need to communicate with each other by a process called cell signalling. 
Neuronal and hormonal systems are examples of cell signalling.

Negative feedback: A process in which…


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