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a) Communication systems needed to respond to
internal and external environments to coordinate
activity of organisms.
· Nervous and hormonal systems coordinate
activity of organisms e.g. info transfer via cell
signalling
· Communication with receptors and effectors
allow organism to;
· Monitor internal and external environments
· Regulate substance levels in organism
· Respond adaptively to changes; change activity
of an organism in response to a stimulus
· Coordinate cell activity…read more

Slide 3

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C) State that neuronal and hormonal
systems are examples of cell signalling
· Neuronal- give rapid but cause short term effects within
the cell such as the Symphatecic nerve stimulating sweat
secretion. (animals)
· Hormonal- slower than neuronal but give long lasting
effects such as growth. (plants and animals)…read more

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b) State that cell need to communicate with each
other by a process called cell signalling
· Cell signalling is needed to coordinate cell activity
AS RECAP
-Signal molecules such as hormones are secreted by glands
-signal molecule shapes are complementary to their receptors so they fit like a lock fits a key
-Signal molecules dock their receptors and bind causing a reaction to occur…read more

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d) Define the terms negative feedback, positive
feedback and homeostasis
· Negative feedback= change in a system that sets in
motion a series of events that counteract the change and
restores to the original state; set point needed (e.g.
temp. regulation)
· Positive feedback= change in a system that sets in
motion series of events that results in further change
away from the original state (e.g. carbon dioxide
poisoning)
· Homeostasis= stable internal environment within an
organism providing constant conditions for cells…read more

Slide 6

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e) Explain the principles of homeostasis in
terms of receptors, effectors and negative
feedback
· Negative feedback maintains homeostasis by body sensing a
change and activating mechanisms to reverse that change
· Negative feedback requires receptors and effectors with good
communication between them
· Receptors monitors factors being controlled .e.g. temperature
of the blood passing through the hypothalamus. If the value is
not suitable for the factor, the receptor communicates with
the effecter
· Effecter causes an action which brings the factor back to the
normal value
· Negative feedback is not instant as short delay from change
in factor, receptor and effecter taking action causes an
oscillation value rather than a definite…read more

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