Osmosis And Osmoregulation

Introduction:

All the natural phenomena observed in nature and other surroundings display either shrinking or expanding in volume, all such phenomena have one thing in common; all these substances are bound by membranes. These membranes can be of any origin, they appear to be continuous sheets or films yet contain a network of submicroscopic holes or pores. Small solvent molecules like water can pass through these holes but the passage of bigger molecules like the solute is hindered. Membranes having such kind of properties are known as semi permeable membranes.

Principle:

Osmosis is process that takes place when a solution and solvent are separated by a semi permeable membrane. Such a membrane permits the movement of solvent molecules but not of solute molecules. In such a situation, the solvent molecules flow from the solvent side to the solution side through the membrane. This process of flow of the solvent is called as osmosis. This flow will continue till the equilibrium is attained. The flow of solvent from the dilute solvent to the concentrated solution across a semi permeable membrane is due to osmosis. Important point to note is that solvent molecules flow from lower concentration to higher concentration of solution. It is a vital cellular process. Plant roots absorb water by osmosis and plant cells are kept firm as a result of the uptake of water by osmosis (turgor), membranes of all living cells use it to control the passage of required substances.

Examples:

• Wilted plants, limp fruits where there is water loss into the atmosphere can be placed into the water to make them fresh, firm again. Water will move into them through osmosis.
• When placed in water containing less than 0.9 %(mass/volume)salt, blood cells collapse due to loss of water by osmosis
• The preservation of meat by salting and of fruits by adding sugar protects against bacterial action. Through the process of osmosis, bacterium on salted meat loses water, shrivels and dies.

The movement of solvent molecules in osmosis stops when the hydrostatic pressure on the solution side is sufficiently high to prevent the flow of the solvent. This extra pressure on the solution side necessary to counteract the forces of osmosis is called as osmotic pressure.

Osmo-regulation: Process by which the amount of water and concentration of salts are regulated in the bodies of animals and protozoan’s. In salt water environments, water tends to pass from an organisms body through the action of osmosis. This effect is counteracted by the kidneys. Similarly in fresh-water environments, the kidneys of higher animals and the contractile vacuoles of protozoan’s, prevent water from passing into the body.

Many processes which occur in living organism both animal and plants depend on osmosis through membranes of cell walls that surround them. One of the chief uses of osmotic pressure measurements is the molecular mass determination of high molecular mass compounds like polymers and biologically important molecules.