Osmosis and Diffusion

Osmosis

 

  Osmosis is the net movement of water across a selectively permeable membrane driven by a difference in solute concentrations on the two sides of the membrane. A selectively permiable membrane is one that allows unrestricted passage of water, but not solute molecules or ions.
Different concentrations of solute molecules leads to different concentrations of free water molecules on either side of the membrane. On the side of the membrane with higher free water concentration (i.e. a lower concentration of solute), more water molecules will strike the pores in the membrane in a give interval of time. More strikes equates to more molecules passing through the pores, which in turn results in net diffusion of water from the compartment with high concentration of free water to that with low concentration of free water.
The key to remember about osmosis is that water flows from the solution with the lower solute concentration into the solution with higher solute concentration. This means that water flows in response to differences in molarity across a membrane. The size of the solute particles does not influence osmosis. Equilibrium is reached once sufficient water has moved to equalize the solute concentration on both sides of the membrane, and at that point, net flow of water ceases.

  Diffusion

Diffusion is the movement of particles (atoms, ions or molecules) from a region in which they are in higher concentration to regions of lower concentration.  A good example of diffusion is food colouring. If you place a drop of red food colouring in a beaker of water eventually the entire beaker of water will have a red tint. The food colouring moved through the water until it was equally distributed throughout the beaker. Diffusion takes place along a concentration gradient. A concentration gradient exists until the diffused substance is evenly distributed.

Other everyday examples of diffusion are:

1.   Sugar will diffuse through tea until the entire cup of tea is sweet. (We stir the tea to speed up the diffusion.)

2.   The odour of food cooking diffuses throughout the kitchen. If you open the kitchen door it will spread into the next room.

The movement of these molecules is said to be passive. No energy is needed to be provided. The natural kinetic energy of the particles supplies the energy.

For more information:http://wizznotes.com/biology/diffusion-and-osmosis