Notesale: Turn your study into money

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Take, for example, viruses –
which to this day scientists have still not agreed on whether or not they are to be considered life forms
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Communication
Animals are an example of a multicellular organism
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Stimulus and response is required, to allow the different tissues to
communicate with each other
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It provides a link between the receptor, detecting a stimulus, and the
effector being triggered to carry out an appropriate response
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The communication which
takes place between the detection of a stimulus and the implementation of the response relies on two systems: the
nervous system and the endocrine system (hormonal system)
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The endocrine system uses hormones, which travel around in the bloodstream and trigger a response
when they bind with target cells or target tissues
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Negative feedback
One mechanism, called negative feedback, operates by detecting the external change (stimulus), communicating with
other cells, and reversing the change (response)
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This type of
feedback usually doesn’t lead to homeostasis, as the effector actually increases the change detected by the receptor, and
so it can be seen as a ‘vicious cycle’ approach
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One example of this is, again, using temperature
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Normally, if the external temperature decreases slightly, our bodies
can react to the change, but when our bodies get too cold:
external
temperature drops

optimum
temperature

body temperature
decreases greatly
exothermic reactions
release even less heat
exothermic reactions
release less heat
enzymes become
even less active

When the internal body
temperature falls below a certain
level, enzyme action decreases
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The effect is that the body
temperature falls even lower, and
so this causes even less enzymes to
function properly, so even fewer
exothermic reactions release heat,
so body temperature falls again, and
so on
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This is an example of where positive feedback is actually beneficial
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Of course, this cycle will eventually end at some point, but this cannot always be said for
every type of positive feedback, which is why (for example, with the temperature) it can be very dangerous

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