1. Osmosis is the diffusion of water molecules across a semipermeable membrane from an area of lower concentration solution to an area of higher concentration. Certain biological and synthetic membranes appear as a continuous film or sheet, yet they contain a network of submicroscopic pores or holes. Small solvent molecules like water pass through these pores yet large solute molecules are hindered. Membranes with such properties are known as semipermeable membranes. The flow of solvent molecules from a pure substance to a concentrated solution is osmosis.
2. For comparing two solutions with unequal concentrations, the solution with higher concentration of solute is hypertonic and the one with the lower concentration is hypotonic. Once the solutions have equal concentrations through osmosis, state of equilibrium is reached and the solutions are called isotonic.
3. There are two types of osmosis which also explains the experiment below, (i) Endosmosis, which occurs when a substance with membrane or a cell is placed in a relatively hypotonic solution, the solvent molecules move through its membrane and the cell becomes turgid, and (ii) Exosmosis, which occurs when a cell is placed in a hypertonic solution, the solvent molecules move out of the substance into the surrounding solution, making the cell flaccid.
4. Raisins are grapes from which the water content has been evaporated. The dried fruit is made up cells covering its surface as well internally, which have a membrane surrounding the cytoplasm. When raisins are placed in water, the water acts as a hypotonic solution to the content of the raisin and its molecules will flow through the cell membrane which acts semipermeable and partakes in osmosis. The type of osmosis in this case is endosmosis, making the cells turgid and causing the raisin to swell.
5. There are various home as well as industrial applications of osmosis. Raw mango is placed in a highly concentrated salt solution, so it loses its water by osmosis and shrivels into pickles. Preservation of meat by salting and fruit by adding a high concentration of sugars cause bacteria in these foods to shrivel and die, thus helping to preserve the food. Blood cells or animal cells need to be stored in 0.9% saline solution as it is isotonic to physiological fluids and if the concentration is lower, water will flow inside the cells causing them to swell.
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