Biology-2-diffusion.

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What is diffusion?

Diffusion is the spreading out of particles from an area of high concentration to an area of low concentration.

For example: 

When perfume is sprayed, the smell of perfume diffuses through the air in the room.

(http://www.occc.edu/biologylabs/Images/Cells_Membranes/diffusion.gif)

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Diffusion across cell membranes..

Cell membranes hold the cell together but they let stuff in and out too. 

Only very small stuff can diffuse through cell membranes- things like oxygen, glucose, amino acids and water. Big molecules like starch and proteins cant fit through the membrane.

If there are a lot more particles on one side of the membrane, there is a net(overall) movement from that side.

(http://img.sparknotes.com/content/testprep/bookimgs/sat2/biology/0002/diffusion.gif)

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the rate of diffusion...

The rate of diffusion is affected by the difference in concentration of the particles- the bigger the difference in concentration, the faster the diffusion rate.

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