Communication and Homeostasis Unit 1.1.1

Multicellular organisms need communication systems to respond to changes in the internal and external environment and to co-ordinate the activities of different organs.

External Environment - A change in the environment may put stress on the organism e.g. cooler the environment, the greater the heat loss.

The environment needs to be monitored so any changes that occur in the environment (stimulus) can be detected and the organism can act accordingly. This could be to change its behaviour, or to change its physiology (response).

The stimulus can be gradual, so therefore the response would also be gradual e.g. the change in seasons. The stimulus can happen more quickly, so therefore the response would happen more quickly e.g. from light to dark (day to night).

Internal Environment - Organs and tissues inside multicellular organism are surrounded by tissue fluid and not exposed to the external environment. This is their environment. They are protected by skin or epithelial tissue.

Activities of the cell can alter their environment e.g. releasing unwanted/toxic substances. This could disrupt enzyme activity by disturbing the pH. This acts as a stimulus and the response would be to remove the waste.

This could be direct as in lowering cell activity to produce less waste - not beneficial for the whole organism.

Blood needs to be monitored so enough waste can be excreted and useful substances are remained in the body/blood.

Multicellular organisms need communication systems to respond to changes in the internal and external environment and to co-ordinate the activities of different organs.

Coordination - Multicellular organisms are more efficient than singled cell organisms as their cells can be differentiated and specialised to perform different and specific functions.

 Specialised groups of cells form tissues and groups of tissue form organs.

Therefore the monitor in the body can be in other places other than where the body needs to be monitored. 

A good communication system will:

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

Cells need to communicate with each other by a process called Cell Signalling. Neuronal and Hormonal systems use cell signalling.

Cell signalling - One cell releases a chemical which is deteced by the second cell. The second cell will respond to the signal sent by the first cell.

Major systems that uses cell signalling:

Neuronal systems - Large interconnected network of neurones that send signals to each other across synapse junctions. They can send a signal very quickly and enable a response to a stimulus can be chaning quickly.

Hormonal systems - It uses the blood for transport of the signal. A cell in an endocrine orgasn releases the signal (hormone) and is transported in the blood around the body. However, it is deteced and recognised by a specific receptor on target cells. this enables a long term response to be corordinated.