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William Holder
Communication & Homeostasis
a) 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 coordinate the
activities of different organs
Organisms need to respond to external stimuli e.g. Temperature, Oxygen conc. & levels of
sunlight. These may be over time e.g. winter or summer fur, or quickly e.g. changing size of
pupils.…read more

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Physiological: The horned lizard expands its ribcage & frilled lizard expands its frills to absorb
more heat due to a larger surface area exposed to the sun.
Behavioural: Snakes expose their body to the sun, so more heat is absorbed. Locusts
orientate their body in the direction of the sun to absorb maximum heat & orientate the body
the other way to prevent absorption. Also, lizards hide in burrows, to prevent heat absorption.
Endotherms can maintain the temperature within the body.…read more

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William Holder
· Sweat glands in skin. If body temperature is high, the sweat glands secrete sweat which
evaporates, cooling the body. If it is too cold, less sweat is secreted so less evaporated,
therefore less heat loss.
· There are hairs on the skin, if it is too hot, the hairs lay flat, providing less insulation so more
heat can be lost.…read more

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William Holder
a) Outline the roles of sensory receptors in mammals in converting different forms of energy
into nerve
Sensory receptors are specialised cells that can detect changes in our surroundings. They are
energy transducers ­ they convert energy from one form to another. Each transducer is
adapted to changes such as light levels etc.…read more


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