F214 Module One

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F214 Module One - Communication and 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:

Organism need to maintain a set of conditions inside their cells, this is because the activities of the cells rely on enzymes. Enzymes need specific conditions in order to work efficiently:

Suitable temperature

Suitable pH

Freedom from toxins and excess inhibitors. 

Living organisms need to keep many conditions constant:

Body temperature

Blood glucose concentration

blood salt concentration

water potential of blood

blood pressure

External Environment

An organisms surrounding environment consists of air, water or soil around them. The external environment changes and this may place stress on the organism so it needs to be able to respond to the changes in the environment. For example, a cooler environment will cause greater heat loss so the organism needs to monitor the changes and change its behaviour or physiology to reduce the stress. Stimulus= Change in environment, Response= The way in which the organism changes its behaviour or physiology.

Internal Environment

Multicellular organisms need to respond to changes in their internal environment to ensure optimal conditions for metabolism. Cells release toxins such as carbon dioxide which are wanted and need to be removed in order to maintain the optimum conditions for metabolism. Build up of toxins will disrupt enzyme activity. Stimulus= Accumulation of excess toxins Response= Excretion of excess toxins. 

Good Communication System:

Covers whole body

Enables cells to communicate with each other

Enables specific communication

Enables rapid communication

Enables short-term and long-term responses.

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

Cell Signalling- The process in which cells communicate with each other.

State that neuronal and hormonal systems are examples of cell signalling

Communication Systems

Neuronal- Interconnected network of neurones that signal across synapse junctions. Can conduct a signal very quickly and enable rapid responses to stimuli.

Hormonal- Uses blood to transport signals, a hormone is released into the blood and is carried all over the body to be recognised by specific target cells, Enables long-term responses to be coordinated.

Define the terms negative feedback, positive feedback and homeostasis

Homeostasis- Keeping the internal environment constant despite external changes

Negative Feedback

A response to a stimuli which reverses a change.

A change to the internal environment is detected, then the change is signalled to other cells and a response occurs which reverses the change.

Positive Feedback

Positive feedback amplifies a change, rather than reversing it. 

Not part of homeostasis as it does not act to keep the internal environment constant.

Usually harmful E.G When the body gets too cold enzymes become less active which allows the body to cool further.

Sometimes beneficial E.G in childbirth

Explain the principles of homeostasis in terms of receptors, effectors and negative feedback

Receptors- Detect a specific stimulus.

Effectors- Bring about a response to a stimulus.

The Process of Negative


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