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Module 1: Communication and Homeostasis
Stimulus and response
Enzymes in the body require certain specific conditions. These include:
A suitable temperature
A suitable pH
An aqueous environment that keeps the substrates and products
in solution
Freedom from toxins and excess inhibitors
External environment
All organisms live in an external environment which is made up by air, water of soil. This environment
can change and this could place stress on the living organism. This is known as a stimulus.…read more

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Maintaining the internal environment of the cell…read more

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The composition of the tissue fluid is maintained by the…read more

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This is the transport medium for products to and from the cells. In order to prevent build-up of
toxic products they are taken away by the blood and preceded from excretion. It is very important
for the concentrations of all substances in the bodies to be monitored so to prevent accumulation of
any substance. And all the cells in the bodies need to be provided with the substances that they
need.…read more

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Blood pressure…read more

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Carbon dioxide concentration
Negative feedback
To maintain a constant internal environment the following processes will occur.
Any change in the internal environment must be detected.
The change must be signalled to other cells
Carbon dioxide concentration.
Stimulus receptor communication pathway (cell signalling) effector response
Positive feedback
When positive feedback occurs the response is to increase the original change. This destabilises the
system and is usually harmful.
Sometimes positive feedback can be good.…read more

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Temperature regulation in Ectotherms…read more

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Adaptation How it helps Example
Expose body to the Enables more heat to Snakes
sun be adsorbed
Orientate body to Exposes larger Locusts
sun surface are from
more heat absorption
Orientate body Exposes lower Locusts
away from the sun surface are so that
less heat is absorbed
Hide in burrow Reduces heat Lizards
absorption by
keeping out of the
Alter body shape Exposes more or less Horned lizards
surface are to sun
Increase breathing Evaporates more Locusts
movement water
Endotherms use…read more

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Hairs on skin Hairs lie flat Hair stands on end
providing little trapping air pockets
insulation in air as insulation
Arterioles leading Pre capillary Pre capillary
to skin capillaries sphincters of sphincters
arterioles leading vasoconstict
to skin capillary's
Liver cells Rate of metabolic Heightened
action is reduced metabolic reactions
Skeletal muscles No spontaneous Shivering causes
contracts heat
Behavioural mechanism to maintain body temperature
Behaviour if too hot Behaviour if too cold
Move into shade or hid in burrow Move into sunlight
Orientate body to…read more


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