Diffusion and Osmosis

These should help explain more about diffusion and osmosis. I am trying to revise for Biology unit 2, and at first i really didnt get this subject, but now i have got it i thought i would share my revision cards :)

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  • Created by: lucy
  • Created on: 15-10-11 12:07


Dissolved substances move across our cell membranes constantly. They do this through 3 ways.



-Active Transport


A good example of difusion is the way a shark smells its prey in water. It uses diffusion. Diffusion is where a subsatnce in a soultion spreads out, (in this case blood in water.) In this, particles from a high contration move to a low concentration. For example first the blood stays in the area then it spread out in the sea ll the time its particles moving and bumping into each other as they move around.

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Diffusion continued

At first during diffusion of blood in water, particles from the sea and blood do not mix at all, but over time as the partciles move around randomly they begin to mix with one another, eventually spreading out into one another. We say diffusion is complete when they are fully mixed up together, and spread out.

To make diffusion happen quickest you can make a bigger difference between two concentrations before mixing. The difference between concentration is called concentration gradient.

For example- If there was a steep diffusion, then at the beggining of the experiment both concentrations would be in two groups, not mixed together, and then after steep gradient would mix together.

Concentration isnt the only thing that affects diffusion, so does tempeture. An increase in tempeture means the particles will more quicker with more energy and therefore diffusion will happen more quickly.

Increasing the surface area, will also make diffusion occur more quickly.

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Diffusion takes place where particles can spread freely form one place to another. Osmosis on the other hands happens when substance are separated by a partially permable cell membrane.


Partially permable cells allow water to move across them. Usually a cell contains a mixture of water and sugar. Water moves from a high concentration to a lower concentration, across the membrane of a cell. This type of diffusion is called OSMOSIS.

Animal and plant cells use OSMOSIS, because there are very different concentrations of liquid in each cell, so water is moved from cell to cell using the method of osmosis.

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Osmosis in animal and plant cells

How Osmosis is used in cells

If a cell uses up its water in a chemical reaction, the cytoplasm in a cell becomes too concentrated, and water is moved back in from another cell through osmosis. Also if there is to much water in a cell, then water will leave the cell through osmosis.

Problems with Osmosis

Osmosis although good in plant cells, can also cause problems. If a soultion outside the cell is more dilute than inside the cell, water will move into the cell sometimes causing it to burst.

Sometimes, also if there is too much water in a cell, water will move out, and sometimes this can cause too much cytoplasm, making the cell shrivel up.

Maintaining conditions in cell is very important if you want to avoid this ^

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Osmosis in Plants

Osmosis in Plants

Plants rely on Osmosis for their stems and leaves. Water moves into plants through Osmosis, making the cytoplasm in the plant swell against plant walls, making the cells hard and rigid.

This swollen state of plants makes the plants strong and osmosis is therefore important for keeping the fluid surronding of the cells have a higher ocncentration of water than the cytoplasm in cells.

Plants also use ACTIVE TRANSPORT to move sunstances in and out of the cells including glocuse. They do this through active transport.

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