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GCSE Revision 101
Guide to Biology
AQA Specification A
Unit Biology B3 BLY3H

Daniel Holloway

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1 Exchange of Materials 3

2 Transporting Substances Around the Body 9

3 Microbiology 16

End of Unit Questions 22

Copyright © 2009 Daniel Holloway
Significant contribution Nelson Thornes AQA Science [GCSE Biology]


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Active Transport

Two of the main ways in which diffused substances are transported across cells are osmosis
and diffusion. Diffusion is the movement of a fluid across a concentration gradient useful to
the cells; osmosis is the movement of water across a semi-permeable membrane. However,
sometimes substances need to be…

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Active transport is an important process in plants. The uptake of mineral ions through the
soil requires active transport because the ions are found in very dilute solutions, whereas
the solution inside the plant cells is a lot stronger. This means the ions have to be taken in
against the…

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The diagram here shows an alveolus (singular of alveoli). It has been adapted to make
gaseous exchange as efficient as possible in the following ways:

spherical shape gives large surface area
moist surface makes diffusion easy as gases can dissolve
thin walls make diffusion easy
good bloody supply (explained before)…

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The lining of the small intestine is folded into thousands of tiny villi (above). These greatly
increase the uptake of digested food by diffusion. This is because only a certain amount of
digested food molecules can diffuse over a certain surface area at a given time ­ so the villi…

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open when oxygen is needed and close when it is not. This also prevents water loss, much
like plant stomata. Spiracles lead to a tube system which delivers the oxygen straight to the
tissues where it is needed. Most of the gas exchange takes place in the tracheoles, tiny

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The loss of water vapour through the surface of
the leaves is called transpiration. As water is lost
through the opening in stomata, more water is
pulled up through the xylem to take its place. This
constant movement of water around the plant is
known as the transpiration stream.…

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The Circulatory System

The blood circulation system we have is made up of three main
components: blood vessels, the heart and the blood. It is made up
of two different blood systems ­ a double circulation. The diagram
shows that one transports blood from the heart to the lungs and…

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The veins carry blood towards the heart, usually low in oxygen and hence are deep purple-
red in colour. No pulse in veins, but they do contain valves usually which prevent the
backflow of blood.

The capillaries are found in junctions between the arteries and veins. These are found in…





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