DIFFUSION and OSMOSIS

The plant cell possesses a cell wall as well as a cell membrane. Cell wall has the permeability of the solute molecules and water and so is not an obstacle to the movement of solute molecules. The cells of the plants have a large vacuole at the center consisting of the vacuolar sap. The sap of the vacuole offers the solute potential of the cell. The cell membrane and the vacuolar membrane called the tonoplast are majorly involved in the molecular movement on either side of the membrane of the cell.

Osmosis is the process that refers to the diffusion of water through the membrane that is differently permeable or semipermeable. The net rate of osmosis is dependent on the concentration gradient and pressure gradient. The movement of water from the region of its higher chemical potential to the region of its lower chemical potential till the equilibrium is maintained is called osmosis. The water potential of the two regions should reach the equilibrium.

Potato osmometer: This is a simple experiment to understand and visualize the osmosis process in potato. The potato tuber with a cavity created in it is filled with sugar solution. This tuber with sugar solution, when placed inside the water, will allow the movement of water into the sugar solution.

Some interesting experiments on Osmosis

The above diagram explains the experiment in which the funnel consists of sucrose solution separated from the pure water taken in the beaker by a semipermeable membrane.

The egg can be used for making the semipermeable membrane. The yolk and albumin present in the egg can be removed from the egg. The shell can be located in the dilute hydrochloric acid solution for some time. The membrane is left intact after the eggshell is dissolved. The pure water will move into the funnel and enhances the solution level in the funnel. The movement towards inside the funnel will continue until the equilibrium between the beaker and funnel is reached.

The pressure that can be applied externally from the funnel will be able to prevent the entry of water into the funnel. The pressure that prevents the water to diffuse into the funnel through the membrane is the osmotic pressure which is the measure of the solute concentration.