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Biology Revision
Exchanging Materials
Osmosis and Diffusion
Water and dissolved substances automatically move along a concentration
gradient. They move from high concentration to low concentrations. They move
by osmosis and diffusion.

Active Transport
Substances are sometimes absorbed against a concentration gradient. But this
means using energy from respiration. This is…

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Humans have organ systems which are specialised to help the exchange of
materials. For example...
the villi in your small intestine
the alveoli in your lungs

Villi in the Small Intestine
Villi line the walls of your small intestine. They have a massive surface area and
an extensive network of…

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Exchanging Materials in Plants
Leaves are broad, thin and flat with lots of internal
air spaces. This provides a large surface area,
making them efficient at photosynthesis.

Leaves have stomata on their under surface in order
let carbon dioxide in
let oxygen out (by diffusion)
(The exchange of substances…

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The Circulatory System
The Circulatory System
A transport system is vital to our bodies
as we have cells in every part of us. This
transport system is called the
circulatory system.
Three important elements:
the medium (blood),
the pump (heart)
the pipes (blood vessels)
Humans have two circulatory systems:

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your lungs to form oxyhaemoglobin. In other organs, oxyhaemoglobin splits into
haemoglobin and oxygen.

Blood Vessels
You have three main types of blood vessels. They are adapted to carry out
particular functions within your body, although they are all carrying the same

Blood Vessels Distinctive Features
Your arteries carry…

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Aerobic Respiration
When glucose is combined with oxygen inside living cells, it breaks down and
releases energy. (The energy is contained inside the glucose molecule)
This process is called aerobic respiration.
The energy released during aerobic respiration is used to make your muscles
Aerobic respiration occurs during normal day-to-day…

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If no oxygen is present, glucose in living cells can't break down completely.
Instead, a little energy is released very quickly inside your cells. This is anaerobic
The waste product from anaerobic respiration is lactic acid which accumulates in
your tissues. When this happens, your muscles become fatigued.

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If the kidneys fail, the body has no ways of removing excess substances. This will
ultimately result in death.
Each kidney is made up of two important issues:
blood vessels

How the Kidneys Function
Blood vessels take the blood through the kidney,
where unwanted substances end up in millions…

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Kidney Transplants
A kidney transplant allows a diseased kidney to be replaced by a healthy one from
a donor. This is only performed if both kidneys fail (one kidney can do a good job).
The main problem with kidney transplants is the
possibility of rejection by the immune system.

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o a membrane
o a cell wall

How Yeast Works
Yeast can't respire without oxygen (anaerobic respiration) to produce ethanol
(alcohol) and carbon dioxide.

This is called fermentation and it has many industrial applications.
Yeast can also respire with oxygen (aerobic respiration) to produce water and
carbon dioxide.

Aerobic respiration…


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