OCR F214 Communication and Homeostasis

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Emily Hearn US2V
Biology A2 Revision: Communication
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.
Most animals and plants are complex, multicellular organisms
All living things need to maintain a certain set of conditions inside their cells as cellular activities rely on the action of
enzymes, which includes temperature, pH, an aqueous environment to keep the substrates and products in solution
and freedom from toxins and excess inhibitors.
Stimulus: any change in an environment which causes a response.
Response: a change in behaviour or physiology as a result of change in the environment.
All living organisms have an external environment which will change and as it changes it may place stress on the
organism. For instance, a cooler environment will cause greater heat loss. For the organism to stay alive and active
the changes must be monitored as well as the organism's behaviour and physiology.
The environmental change is the stimulus and how the organism changes its behaviour and physiology is the
The environment may change slowly (global warming) and this change will elicit a gradual response. However, it may
change quickly e.g. from day to night and the organisms' response much quicker.
Most multicellular organisms have a range of tissues and organs, which are protected by epithelial tissues and
organs such as skin or bark. In animals the internal cells and tissues are bathed in tissue fluid, this is the cells
During cellular metabolic activities they use up substrates and produce products, which may be unwanted or toxic.
These diffuse out into the tissue fluid. Carbon dioxide is a waste product so if it builds up in the tissue fluid it can alter
the pH level and disrupt the action of the enzymes.
Accumulation of excess waste or toxins must act as a stimulus in order to create a response, removing the wastes
so the cell can survive and reducing the cell activities so less waste is produced.
The composition of the tissue fluid is maintained by the blood, any wastes or toxins that enter the blood are likely to
be carried away and removed from the body via excretion. However, our body must be monitored in order to not
excrete too many useful substances but remove enough of the wastes to stay healthy and provide all cells with the
substances they need.
Different parts of the organism have different functions, and it is important to have a communication system
between theses so their activity can be coordinated.
Sometimes the purpose of this information transfer is to respond to changes in the internal environment of the
The accumulation of waste products such as carbon dioxide in tissue fluid around cells could change the pH of the
environment, disruption enzyme activity.
Therefore, the build up of toxins must act as a stimulus to cause the removal of these wastes so that the cells can
The external environment of an organism must also be monitored as changes may place a stress on the organism.
For example, a cooler environment will cause greater heat loss, and so the organism must change its behaviour or
physiology in response to this stimulus.
In both plants and animals, chemicals known as hormones help transfer information.
In many animals, nerves can also transfer information in the form of electrical impulses.
State that cells need to communicate with each other by a process called cell signalling.
Multicellular organisms' cells can be differentiated so they can perform specific functions. Groups of cells specialised
in this way form tissues and organs. Therefore a good communication system is required which would:
- 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 communicate through cell signalling where one cell releases a chemical which diffuses into the immediate
surroundings and is detected by another cell.
State that neuronal and hormonal systems are examples of cell signalling.
There are two major systems that work by cell signalling, the neuronal system. An interconnected network of
neurones that signal to each other across synapse junctions. They signal very quickly and gain a rapid response. The

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Emily Hearn US2V
Biology A2 Revision: Communication
hormonal system uses the blood to transport signals. Cells in an endocrine organ release a hormone directly into the
blood it travels around the body but only specific target cells recognise the signal. This allows longer-term responses
to be enabled.
Define the terms homeostasis, negative feedback and positive feedback.
Homeostasis is the maintenance of the internal environment in a constant state despite external changes.…read more

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Emily Hearn US2V
Biology A2 Revision: Communication
Some disadvantages are that they are less active in cooler temperatures and need to warm up before they can be
active, therefore in winter they may not be capable of activity so need sufficient stores of energy to survive the
When an ectotherm is cold/hot its behaviour or physiology will change to increase or decrease the absorption of
heat and loss of heat to its environment.…read more

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Emily Hearn US2V
Biology A2 Revision: Communication
Behavioural Mechanisms to
Maintain Body Temperature
Behaviour if too hot Behaviour if
too cold
Move into shade or hide in a Move into
burrow) sunlight
Orientate body to decrease Orientate
surface area exposed to sun body to
surface area
exposed to
Remain inactive and spread Move about
out the limbs to increase to generate
surface area heat in
when in
cold, it is
better to not
move and
roll into a
ball to…read more


Taj Dogra

very helpful :)

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