Review on Diffusion & Osmosis in Cells

Plant and animal cells behave differently when exosmosis or endosmosis occurs, due to their structural differences:

1. Plant cells have a cell wall, which allows for only slight changes in size, and also prevents lysis of the cells.

2. Plant cells have large central vacuoles, which are not present in animal cells. Hence during osmosis, water moves between cell sap in central vacuole and the solution surrounding the cells. For animal cells, water moves between cytoplasm and the solution surrounding the cells.

Cell surface membranes affect the entry and exit of water and substances.
Factors that affect diffusion and osmosis are:

1. Surface area available: An increase in surface area leads to an increase in rate of diffusion and osmosis.

2. Permeability of membranes: Usually cell membranes are partially permeable. However, when membranes are exposed to organic solvents which dissolve the lipid bilayer (eg. ethanol or ether), or when cells are heated, the structure of the lipid bilayer is disrupted. This means that the membrane becomes fully permeable, which allows larger molecules inside the cell (eg. proteins) to diffuse out of the cell.