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Homeostasis/Growth and development/Brain and Mind
Biology Revision
What is homeostasis, the importance of
homeostasis, maintaining body temperature,
maintaining water balance…read more

Slide 2

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What is homeostasis?
Our bodies need to control things like body temperature and water level to keep them
from changing. The process of keeping things the same is called homeostasis.
Homeostasis is how the body keeps conditions
inside it the same. Scientists describe it as the
maintenance of a constant internal
Two examples of things that the body keeps
the same are:
body temperature at 37°C
the amount of water inside our body
Keeping these two the same is not always easy
when the outside environment is changing
constantly. But it is important so that all our
cells function properly.
Strenuous exercise, or living in a hot or cold
environment, affect our body temperature and
water balance.…read more

Slide 3

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What is homeostasis?
How we keep things the same
First, we need receptors to detect when
things such as temperature change.
Then we need a processing centre to receive
this information and coordinate our response.
Finally, we need effectors to produce a
response that ensures our body temperature
stays at 37°C.
It is easier to understand how this works by
using a model. Think of an incubator in a
premature baby unit:
The incubator needs sensors to monitor the
temperature. It also requires a computer or
processing centre to monitor and process the
data from the sensors and switch the heater Control of a room temperature
on or off. When the incubator is too cold, the
heater switches on. When it is too hot, the
heater switches off. In this way, it maintains
an almost constant temperature within the
incubator.…read more

Slide 4

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What is homeostasis?
Negative feedback - Higher
Negative feedback ensures that, in
any control system, changes are
reversed and returned back to the
set level.
For example, negative feedback
keeps our body temperature at a
constant 37°C. If we get too hot,
blood vessels in our skin vasodilate
(become larger) and we lose heat
and cool down. If we get too cold
blood vesssels in our skin
vasoconstrict (become smaller),
we lose less heat and our body
warms up. Negative feedback
makes sure this happens.
The other factors also controlled in
the body by negative feedback are:
blood oxygen levels
salt levels…read more

Slide 5

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The importance of homeostasis
Cells depend on the body environment to live and function. Homeostasis keeps the body
environment under control and keeps the conditions right for cells to live and function.
Without the right body conditions, certain processes (eg osmosis) and proteins (eg
enzymes) will not function properly.
Why is homeostasis important for cells?
Living cells depend on the movement of chemicals around the body. Chemicals such as
oxygen, carbon dioxide and dissolved food need to be transported into and out of cells.
This is done by the processes of diffusion and osmosis, and these processes depend on the
body's water and salt balance, which are maintained by homeostasis.
Cells depend on enzymes to speed up the many chemical reactions that keep the cell alive
and make it do its job. These enzymes work best at particular temperatures, and so again
homeostasis is vital to cells as it maintains a constant body temperature.
Particles in liquids and gases move about randomly in all directions.
In an area of high concentration, particles will escape from the concentrated area to
places where there are fewer or no particles. Very few particles leave an area of low
concentration to go to an area where the concentration is higher.
Diffusion is the movement of particles from an area of high concentration to an area of
low concentration. This is described as moving down a concentration gradient.…read more

Slide 6

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The importance of homeostasis
Osmosis is simply a special type of diffusion. It occurs when water molecules
pass through a partially permeable membrane.
Some membranes in plant and animal cells allow certain particles to pass
through them but not others. They are partially permeable membranes.
During osmosis, more water molecules pass from the pure water into the
dilute solution than pass back the other way. This is because there is a higher
concentration of water molecules in the pure water than in the solution. This
results in more water molecules diffusing across the concentration gradient
from the water to the solution. Eventually, the level on the more concentrated
side of the membrane will rise, while that on the less concentrated side falls.
Osmosis is the overall movement of water from a dilute solution to a more
concentrated solution through a partially permeable membrane. This is still
like diffusion, as the water is moving from a higher concentration of water to a
lower concentration of water.
Higher only
If red blood cells are placed in pure water, water enters them by osmosis and
the red blood cells swell up and burst.
If cells are placed in a concentrated solution, water leaves them by osmosis
and they are unable to function.…read more

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