A2 Biology

Outline the need for communication systems within multicellular organisms, with reference to the need to respond to changes in the 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.

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How do cells communicate with each other

Cell signalling

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2 examples of cell signalling

Hormonal and neuronal

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Define negative feedback

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.

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Define positive feedback

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

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Define homeostasis

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

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

Physiological: 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.

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

Behavioural: Snakes expose their body to the sun so more heat is absorbedLocusts orientate their body towards the sun to expose a larger surface area & so more heat is absorbed. Lizards hide in burrows to prevent heat absorption away from sun.

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A2 Biology

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