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Learning objectives – to learn about osmosis and

learn why it is important


Osmosis is the movement of water from an area of high water

concentration to an area of low water concentration across a

partially permeable membrane.


Definition – the above definition may need some explaining. A partially

permeable membrane is like a cell membrane which only allows certain

molecules pass. For example it will let water pass but it may not let other

large molecules like starch or protein pass.


High water concentration is simply an area that has a lot of water molecules

in it, the volume as such does not matter, and it is the concentration. So for

example one container may have 500ml of water but it is 100% water, whereas

the other container may have 600ml of water but there are some starch and

protein molecules in there so the total percentage or concentration of water

is at 80%. Therefore container A has a high concentration of water.


This diagram will help to explain:

The net movement of water


In the above diagram, the orange molecules are too big to pass through the

partially permeable membrane, however the concentration of water is higher

in the left compartment than the right compartment therefore the water moves.