Osmosis is the passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration.
Oliver Putter
H/W
Osmosis
Definition
Osmosis is the passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration.
Plant cells always have a strong cell wall surrounding them. When the take up water by osmosis they start to swell, but the cell wall prevents them from bursting. Plant cells become "turgid" when they are put in dilute solutions.
Turgid = Swollen and hard. The pressure inside the cell rises; the internal pressure of the cell eventually becomes so high that no more water can enter the cell. This liquid or hydrostatic pressure works against osmosis. Turgidity is very important to plants because this is what makes the green parts of the plant "stand up" into the sunlight. When plant cells are placed in concentrated sugar solutions they lose water by osmosis and they become "flaccid"; this is the exact opposite of "turgid". If you put plant cells into concentrated sugar solutions and look at them under a microscope you would see that the contents of the cells have shrunk and pulled away from the cell wall: they are said to be plasmolysed.
