Diffusion of water molecules through a semi permeable membrane from a higher concentration to a lower concentration until the concentration on both sides is equal.
Osmosis in animal cells:
The cell membrane is the partially permeable membrane in animal cells. If the cells were placed in distilled water they gain water, swell and burst. This is known as haemolysis.
Osmosis in plant cells:
The cellulose cell wall of plant cells is fully permeable. Therefore it’s the cell membrane of a plant cell which acts as the semi-permeable membrane, deciding what gets into and out of the cell.
When plant cells are placed in water the following happens:
• Water enters the cell, the reason is that the cell sap in the permanent vacuole is concentrated and therefore has a low water concentration compared to the water on the outside of the cell.
• The cellulose cell wall stretches slightly but most importantly it prevents the cell bursting. (Plant cell is turgid)
• The permanent vacuole fills with water, pushing the cytoplasm against the cell wall.
• The cell membrane is not visible anymore.
When plant cells are placed in concentrated sugar solutions the following happens:
• Water leaves the cells, the reason is that the cell sap in the permanent vacuole is now less concentrated and therefore has a high water concentration compared to the water on the outside of the cell. The amount of water lost from the cell depends on the concentration of the solution in which it was placed. If only a small amount of water is lost the cell cannot remain turgid and wilting of the plant occurs. Cells which aren’t turgid are described as being flaccid.
• If a...