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Communication & Homeostasis Basics
Responding to their Environment Helps Organisms Survive
1) Animals increase their chances of survival by responding to changes in their
external environment e.g. avoiding harmful environments too hot/cold places.
2) And respond to changes in their internal environment to make sure that
conditions are always optimal for their metabolism (all the chem. reactions that go
on inside them).
3) Plants increase their chances of survival by responding to changes in their
4) Any change in the internal or external environment is called a stimulus.
Receptors Detect Stimuli and Effectors Produce a Response
1) Receptors detect stimuli.
2) Receptors are specific they only detect one particular stimulus, e.g. light, pressure
or glucose concentration.
3) There are many different types of receptor that each detect a different type of
4) Some receptors are cells, e.g. photoreceptors are receptor cells that connect to the
nervous system, some are proteins on cell surface membranes e.g. glucose receptors
are proteins found in the cells membranes of some pancreatic cells.
5) Effectors are cells that bring about a response to a stimulus, to produce an effect.
Effectors include muscle cells and cells found in glands, e.g. pancreas.
Receptors Communicate with Effectors via Hormones and Nerves
1) Receptors communicate with effectors via the nervous system or the hormonal
system or sometimes both.
2) Nervous and hormonal communications are both examples of cell signalling
(ways cells communicate with each other).
Homeostasis is the Maintenance of a Constant Internal Environment
1) Changes in your external environment can affect you internal environment the
blood and tissue fluid that surrounds your cells.
2) Homeostasis involves control systems that keep your internal environment
roughly constant (within certain limits).
3) Keeping your internal environment constant is vital for cells to function normally
and to stop them being damaged.
4) It's particularly important to maintain the right core body temperature. This is
because temperature affects enzyme activity, and enzymes control the rate of
If body temperature is too high (e.g. 40°C) enzymes may become
denatured. The enzyme's molecules vibrate too much, which breaks the
hydrogen bonds that hold them in their 3D shape. The shape of the
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means metabolic reactions are less efficient.
If body temperature is too low, enzyme activity is reduced, slowing the rate
of metabolic reactions.
The highest rate of enzyme activity happens at their optimum temperature
(about 37°C in humans).
5) It's also important to maintain the right concentration of glucose in the blood, so
there's always enough available for respiration.
Homeostatic Systems Detect a Change and Respond by Negative Feedback
1) Homeostatic systems involve receptors, a communication system and effectors.…read more