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Page 1

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Osmosis
The solutions inside the cells are separated from those outside the cells by the cell
membrane.

Membranes which only let some types of particles through are called partially
permeable.

Partially permeable membranes let water flow across them.




A dilute solution of sugar contains a high concentration of water (the…

Page 2

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Osmosis in animals
The solutions inside the cells are separated from those outside the cells by the cell
membrane.

Membranes which only let some types of particles through are called partially
permeable.

Partially permeable membranes let water flow across them.

If a cell uses up water in its reaction ,…

Page 3

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Active Transport
Dissolved substances need to move in and out of cells.

Substances move by diffusion along a concentration gradient.

Sometimes the substances needed by a cell have to be moved against a
concentration gradient, or across a partially permeable membrane.

This is known as active transport.

low concentration --------->…

Page 4

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Exchanging Materials - the lungs
In many larger organisms there are special surfaces where has and solute exchange
take place. They are adapted to be as effective as possible.

Adaptations

The effectiveness of an exchange surface can be increased by :

· having a large surface area
· being thin,…

Page 5

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Ventilating the lungs
For a gas exchange system to work efficiently you need a steep
concentration gradient.

Humans move air in and out of the lungs regularly.

They maintain a steep concentration gradient of both oxygen in and carbon
dioxide out.

This is known as ventilating the lungs or breathing.…

Page 6

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When you breathe in:

· muscles contract

· volume of thorax increases

· pressure in thorax decreases

· air enters lungs




When you breathe out:

When the intercostal muscles relax , your ribs drop down and in again.

When the diaphragm relaxes it curves back up into your thorax.

The…

Page 7

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Exchange in the gut
Absorption in the small intestine

Digested food molecules move from inside your small intestine into your blood
stream by a combination of diffusion and active transport.

The digestive food molecules are small enough to move freely through the
walls of the small intestine into the blood…

Page 8

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Transpiration
The loss of water vapour from the surface of plant leaves is known as
transpiration.

Water is lost through the stomata , which are opened and closed by the
guard cells to let in carbon dioxide for photosynthesis.

When the stomata are open plants loose water vapour through them…

Page 9

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Controlling water loss

Leaves have a waxy , waterproof layer to prevent uncontrolled
water loss.

Most stomata are found on the bottom of leaves. This protects
them from the direct light and energy from the sun reducing the
time that they are open.

If a plant looses water too quickly…

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