Osmosis

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Define osmosis

Describe the effect of osmosis on animal and plant cells.

Osmosis

Definition

Water can move across cell membranes by a process called osmosis.

Osmosis is the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.

Partially permeable membranePartially permeable membrane

A partially permeable membrane will allow some molecules to pass through such as water, but prevents other molecules from crossing e.g. solutes such as sugar or salt.

membrane

solute molecules unable to cross

water molecules can cross membrane

Dilute and concentrated solutions

solute

water

dilute solution concentrated solution

Dilute solutions contain high concentrations of water and concentrated solutions contain high concentrations of solutes.

Osmosis in cellsOsmosis in cells

cell cellcell

Water will move from high to low into the cell.

As the concentration is equal, there is no overall movement.

Water will move from high to low out of the cell.

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Osmosis...

In animal cells the cytoplasm is a concentrated solution. If animal cells are placed in water, they will absorb water by osmosis. They can swell up and burst.

If animal cells are placed in a concentrated solution, water leaves the cell by osmosis and the cell will shrivel.

dilute solution (water) concentrated solutionred blood cell

waterwater

Osmosis in red blood cells

waterwater

waterwater

waterwater

Osmosis in plant cells

If a plant cell is placed in water, then water will enter the cell and cause it to expand. The cell wall will prevent the cell from bursting. A swollen cell is called turgid.

If plant cells are placed in a concentrated solution water will leave the cell. The cell shrivels. A shrivelled cell is called flaccid.

plant cell concentrated solutiondilute solutionturgid flaccid

waterwater

waterwaterwaterwater

waterwater

dilute solution concentrated solutionwater moves

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