Explain the Osmosis

Osmosis, quite simply, is the physical process, wherein there is transfer of a liquid solvent (water) through a semi-permeable membrane that does not allow the dissolved solids (solutes) to pass. 1 et us understand this process with the help of an example. Suppose a semi-permeable membrane separates two compartments. The membrane allows water to pass through but it does not allow the solute to pass through. On side A, there is water and on the other side B, there is solute dissolved in water. The membrane is permeable only to water, and the concentration of water is higher on side A. Hence, water diffuses from A to B, but in this type of solution, water is said to be transported by 'osmosis'. Unlike simple diffusion, no matter how much water moves from A to B, the concentration of water will stay higher on side A because side B can have a more and more dilute solution of the solute.

However, transport of water by osmosis does not occur indefinitely because osmosis of water increases the hydrostatic pressure of side B. Osmosis is said to stop when the excess hydrostatic pressure on side B equals the hydrostatic pressure exerted by the solute. What do you mean by the term 'hydrostatic pressure'? Well to put in simple terms, hydrostatic pressure is a pushing pressure. Hence, the hydrostatic pressure on the side B tends to push the water from side B to A. While osmotic pressure is a pulling pressure, which in this case is exerted by the solute which pulls the water from A to B. When the pushing and pulling pressure become equal, there is no further movement of water. Finally, to summarize osmosis is the net movement of water from a region of high water concentration across a selectively permeable membrane to a region of low water concentration, driven by a difference in solute concentrations on the two sides of the membrane. Figure illustrates the osmosis process. We have looked at diffusion, osmosis and the facilitative diffusion process so far. We shall also look at the processes of ultra-filtration which is included under the passive transport system.