A2 Biology F214

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  • Created on: 17-06-12 23:31

Communication, Homeostasis & Energy

Communication & 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.

Organisms need to respond to external stimuli, e.g. temperature, oxygen concentration and levels of

sunlight. These may be over time, e.g. winter fur to summer fur, or quickly, e.g. changing size of pupils.

Internal environments change too- the build up of carbon dioxide as a result of respiration changes the pH

of the tissue fluid, and therefore inhibits enzyme activity. Multicellular organisms need to coordinate

different organs, so this requires a good communication system which will:

• Cover the whole body

• Enable cells to communicate with each other

• Enable specific communication

• Enable rapid communication

• Enable both short and long-term responses.

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

State that neuronal and hormonal systems are examples of cell signalling.

Define the terms negative feedback, positive feedback and homeostasis.

Negative feedback- A process in which any change in a parameter brings about the reversal of that change

so that the parameter is kept fairly constant.

Positive feedback- A process in which any change in a parameter brings about an increase in that change

Homeostasis- The maintenance of a constant internal environment despite external changes

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

Any change is detected by receptors, the communication system transmits a message from the receptor to

the effector and, through negative feedback, the effectors reverse the change.

Describe the physiological and behavioural responses that maintain a constant core body temperature in ectotherms

and endotherms, with reference to peripheral temperature receptors, the hypothalamus and effectors in skin and


To maintain a constant core body temperature, ectotherms have physiological and behavioural responses;


The horned lizard expands its ribcage and the frilled lizard uses its frill to expand its surface

area to absorb more heat from the sun

Locusts increase their abdominal breathing movements to increase water loss when hot


Snakes expose their body to the sun so more heat is absorbed

Locusts orientate their body towards the sun to expose a larger surface area & so more

heat is absorbed. By orientating their body away from the sun, more heat is lost.

Lizards hide in burrows to prevent heat absorption by staying out of the sun.

To maintain a constant core body temperature, endotherms have physiological and behavioural



Sweat glands

When hot they secrete sweat onto the skin. Water evaporates using heat from the

blood to supply latent heat of vaporisation.

When cold, less sweat is secreted, less water evaporates and so less loss of latent heat

Lungs, nose and mouth

When hot, panting increases water evaporation from lungs, tongue and moist

surfaces. Loss of latent heat as above.

When cold, no panting, less water evaporates, no loss of latent


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