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GCSE Biology
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Slide 2

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What is this unit about?
In order for our enzymes to function at full capacity, our
internal state must be kept constant. Every moment,
there is some sort of chemical reaction taking place and
keeping a constant internal environment is vital for
survival. This unit all about the internal environment of
your body and how it is kept constant.
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Slide 3

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A table to show the inputs and outputs of the
human body
Oxygen passes from the Energy is transferred
air in the lungs into the between your body and
blood. It is taken in the your environment
bloodstream to the body
cells where it is needed
for respiration
Molecules from digested
food pass through the gut Carbon dioxide is a waste
wall into the bloodstream. product of respiration. It is
They are transported to transported by the
the body cells to use for bloodstream to the lungs
growth and repair. where it is breathed out
Glucose is used in
Water and waste products Water from food and
for example urea, are drink passes through the
filtered out of the blood gut wall and into the
and are excreted in the bloodstream
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Slide 4

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Key Terms:
Homeostasis ­ when your internal environment is kept at a
constant state
Receptor ­ An action or behaviour that is caused by a stimulus
Processing centre ­ The part of a control system that receives
and processes information from the receptor and triggers
action by the effectors
Effector ­ The part of the control system that brings about a
change to the system
Negative feedback ­ When a change in a system results in an
action that will reverse the change, bringing the system back
to it's normal state
Antagonistic effectors ­ Antagonistic effectors have the
opposite effect
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Slide 5

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The general control system
The general control system is the nervous system. This is
controlled by your brain which sends signals through
your body in order for you to react. For example, if you
placed your hand onto a hot stove, your brain would
pick up that you are being burned and send a signal
through your nervous system and make you move you
hand away. This would all happen in the space of <1
second and would mean that less damage is done to
your hand.
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Slide 6

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What is an enzyme and how does it work?
An enzyme is a small protein molecule that speeds up
chemical reactions in cells. An example of a enzyme
breaking a substrate down would be starch being broken
down into glucose. However, an enzyme can also build up
substrates into products*. The active site of an enzyme is a
complimentary shape to the substrate and will only fit one
shape of substrate.
*Reactant + Reactant Product
Active Site
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