Osmosis in Plants
Biology: Cambridge International GCSE Supplement, topic 3.2.4
Osmosis and Plant Cells
Raw potato discs change mass after being left in solutions with different water potentials because of movement of water into or out of the plant cells. This also causes the cells to change shape.
Flaccid
- When water moves out of cells by osmosis, cell volume decreases, so the cell becomes flaccid (floppy).
- Unlike animal cells, the cells do not shrink very much in size because the cell wall maintains their shape, but the cell now exerts less turgor pressure on the cell wall.
- This causes the plant to wilt.
Plasmolysis
- If a plant cell loses a large amount of its water by osmosis, the cell volume may decrease so much that the cell membrane is pulled away from the cell wall.
- This process is called plasmolysis.
- This causes cell damage.
Turgid
- When water moves into cells by osmosis, cell volume increases, and the cell is said to be turgid (swollen).
- Unlike animal cells, which would burst, plant cells do not burst.
- This is because they have inelastic cell walls. The swollen cell exerts turgor pressure on the cell wall.
- This turgor pressure is very important to support the plant. Water is drawn up through the plant from the roots to maintain turgor pressure.
Test yourself on Osmosis in Plants
Which cells would not burst if left in distilled (pure) water?