Osmosis in cells

Osmosis is the movement of a solvent through a semi-permeable membrane. In all living cells, membranes are dividers: they separate different parts of the cell from each other and impede movement of substances between compartments.

In pure water cells maintain their physiological turgor. The cell starting water potential is in equilibrium with the water potential.

Cells tend to lose water by increasing the concentration of the solution with a solute (Saccharose). The increased sucrose concentration lowers the solution water potential, draws out water from cells, and thereby reduces the cell’s turgor pressure.

The direction and rate of water flow across the membrane are determined not only by the concentration gradient of water or by the pressure gradient, but by the sum of these two driving forces.

• Beaker 500 ml — 1118.50
• Dropping pipette with teats — 1441.50+5448.00
• Tweezers — 8261.30
• Scalpel — 8262.02
• Microscope slides — 1388.00
• Cover glass — 1397.05
• Microscope — 8542.12
• Tin foil
• Onion
• Small alga (Nitella)

• Sucrose solution
• Distilled water

• Report your observations and try to recognise the cells in the different conditions.