These are detailed Revision Notes for Topic Four (Homeostasis and Response) of AQA GCSE Biology. They are written by me, using a combination of class notes, text books and revision guides. I have also uploaded the other chapters in my store.
Homeostasis and Response
Homeostasis:
The body has to maintain certain conditions in the body in order to
survive.
o Blood glucose concentration – you need to have enough glucose
in your blood for your cells to respire. Not enough would leave
you with insufficient energy and too much would send you into a
coma.
o Body temperature – too hot or cold and your enzymes wouldn’t
be able to control your cellular reactions.
o Water balance – to little or too much would kill you.
The maintenance of these factors is called homeostasis. This is the
detection of changes to these conditions and responses to return the
body to normal. These changes are automatic, and you don’t know that
they are happening.
Negative Feedback:
The internal maintenance is done by negative feedback. When the
level of something gets too high or too low, your body uses negative
feedback to bring it back to normal.
1. Receptor detects a stimulus – level is too high
2. The coordination centre receives and processes the information,
then organises a response.
3. Effector produces a response, which counteracts the change and
restores the optimum level – the level decreases.
This is the same but opposite when the level is too low.
The effectors will carry on producing responses for as long as they’re
stimulated by the coordination centre. This might cause the opposite
problem – making the level change too much, but the receptor detects
if the level becomes too different and negative feedback starts again.
This process is automatic.
Nervous System:
The nervous system controls its voluntary and involuntary actions and
is responsible for transmitting and receiving impulses in different parts
of its body. It is comprised of the Central Nervous System
Receptors in your body detect a change
inside or outside the body Your Sens Organ Stimuli
central nervous system coordinates e
Sight Eyes Light
your body’s response Effectors cause
a response by moving part of your body Heari Ears Sound (and
ng position of
or secreting a hormone.
head)
Taste Tongue Chemicals in
food
Smell Nose Chemicals in air
Touch Skin Touch, pressure,
temperature,
pain and itch
, All messages sent along nerves are electrical. These are generated by
cells called receptors and travel to your brain and/or spinal cord. There
are many different types of receptor that measure and respond to
different stimuli.
There are 3 types of neurone or nerve cell in the nervous system:
o Sensory neurones – carry impulses from the receptor to the
spinal cord or the brain.
o Relay neurones – carry impulses through the spinal cord to the
brain and from the brain back along the spinal cord.
o Motor neurones – take impulses from the spinal cord to an
effector.
Electrical impulses cannot pass from neurone to neurone. When an
impulse reaches the end of a neurone, a neurotransmitter is released.
This chemical diffuses across the gap between this neurone and the
next and initiates an impulse in the second neurone. This gap is called
a synapse.
Stimulus Receptor Sensory Neurones Relay Neurones Motor
Neurones Motor Neurones Effector Response
Reflexes are rapid, automatic responses to certain stimuli that don’t
involve the conscious part of the brain – they can reduce the chances
of being injured.
The passage of information in a reflex is called a reflex arc.
1. The neurones in reflex arcs go through the spinal cord or through
an unconscious part of the brain.
2. When a stimulus (e.g. a bee sting) is detected by the receptors,
impulses are sent along a sensory neurone to a relay neurone in
the CNS.
3. When the impulses reach a synapse between the sensory
neurone and the relay neurone, they trigger chemicals to be
released. These chemicals cause impulses to be sent along the
relay neurone.
4. When the impulses reach a synapse between the relay neurone
and a motor neurone, the same thing happens. Chemicals are
released and cause impulses to be sent along the motor neurone.
5. The impulses then travel along the motor neurone to the effector
(usually a muscle).
6. The muscle then contracts and moves your hand away from the
bee.
7. Because you don’t have to think about the response it’s quicker
than normal responses.
The Brain:
The brain is made up of billions of interconnected neurones. The brain
is in charge of all of our complex behaviours. It controls and
coordinates everything you do.
Different regions of the brain carry out different functions:
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