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a) Outline the need for communication systems within multicellular organisms.
Internal Environment:
Need to respond to changes to make sure the conditions are always optimal for metabolism.
E.g. If CO2 builds up in tissue fluid outside the cells, changing the pH of the environment
around the cell could disrupt the action of enzymes.
The accumulation of excess waste/toxins acts as a stimulus to cause a response, the removal.
External Environment:
This consists of air, water or soil.
Changes include: seasonal weather, day and night, global worming.
Changes may place stress on living organisms.
The way in which the organism changes its behaviour or physiology is the response.
A multicellular organism can have calls that are differentiated ­ the cells can be specialised
to perform particular functions.
Groups of specialised cells form tissues, which form organs.
Good communication systems will:
Cover the whole body.
Enable communication between cells.
Enable specific communication.
Enable rapid communication.
Enable short-term and long-term communication.
b) State that cells need to communicate with each other by a process called cell signalling.
Cell signalling is the process in which one cell will release a chemical that is detected by
another cell. The second cell will respond to the signal released by the first cell.
c) State that neuronal and hormonal systems are examples of cell signalling.
Neuronal System: an interconnected network of neurones that signal to each other across
synapse junctions. The neurones can conduct a signal very quickly and enable rapid
responses to stimuli that may be changing quickly.
Hormonal System: uses the blood to transport its signals. Cells in an endocrine organ
release the signal (a hormone) directly into the blood. It's carried all over the body but is

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This system enables longer-term responses to be
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