Effects of osmosis on plant and animal cells

The diffusion of water into a solution leads to an increase in volume of this solution. If the solution is in a closed system, such as a cell, this results in an increase in pressure. This pressure is called hydrostatic pressure and has the same units as water potentiaL kPa. All the cellular level this pressure is relatively large and potentially damaging.

Animal cells: If an animal cell is placed in a solution with a higher water potential than that of the cytoplasm, water will move into the cell by osmosis, increasing the hydrostatic pressure inside the cell. All cells have thin cell-surface membranes (around 7nm) and no cell walls. The cell-surface membrane cannot stretch much and cannot withstand the increased pressure. It will break and the cell will burst, an event called cytolysis.
Plant cells: Like animal cells, plant cells contain a variety of solutes, mainly dissolved in a large vacuole. However. unlike animals, plants are unable to control the water potential of the fluid around them, for example, the roots are usually surrounded by almost pure water.
Plants cells have strong cellulose walls surrounding the cell-surface membrane. When water enters by osmosis the increased hydrostatic pressure pushes the membrane against the rigid cell walls. This pressure against the cell wall is called turgor.

	Created by Emily Rowland-Rawson about 6 years ago

Notes for chapter 5, plasma membranes, of the OCR A-level biology specification.