1. Colloids and colloidal dispersion

2. Colloids Molecules can cluster together to form particles of mater whose over all size is larger than the size of atom or molecules in aqueous solution. In general the normal solution are homogenous mixture of solute and solvent molecule. The size range of atoms or molecules is ordinary solution is 0.05-0.25 nanometer. Some time attraction between molecules forms cluster their size rang (1-100nm.). So matter containing particles of this size called (colloid). A uniform dispersion of a colloid in water called (a colloidal dispersion) which appear cloudily.

3. The colloid in acolloidal dispersion called dispered substance, the matter in which the colloid dispersed called dispersing substance). The dispersed and dispersing substance can in (9) nine different way to form colloidal dispersion, only 8 of these 9 combination are known because A mixture of 2 gases can't be colloidal dispersion because the particles of agas are individual molecules and when the molecules form cluster, the gas changed to a liquid. Many compounds of high m.wt is living system form colloidal dispersion rather than the solution in water like starch and protein.

4. Question If colloidals are clusters of molecules why don't the clusters increase in size until they get large enough to settle out.? Answer All particles have most stable colloidal dispersion have the same electrical charge, these charge can be caused by adsorption of ions to the surface of the particles so the particle's repel each other and can't form particles large enough to settle out.

5. Other colloids are stabilized in water by the action of a third substance called amulsifying agent (e.g) (mixture of oil+water), oil is immisible with water, if we added emulsifying agent) (soap) to the mixture, the oil is emulsified by the soap. The soap break up the oil into small drops, the soap molecule form anegativly charge layer on the surface of each oil drop, this cause the oil's drop to repel each other, and they disperse through out the water. (Bile salt) another example of emulsifying agent in living system. These salts break up the Fat's we eat in to small globules that can be more effectively digested. The fluid of living system are a complex mixture of colloids & dissolved and molecules the behaviour of these fluid in the body is vital to life. Apparticlary important property of these fluids is dialysis which is similar to osmosis.

6. Dialysis in living systems Osmotic membrane allow water molecules, to pass through it but not solute particles membranes that allow small molecules & ions to pass while holding backs large molecules and colloidal particles called (dialyzing membrane). Plasma membrane are example of such membrane. The selective passage of small molecules and ions in either direction by dialyzing membrane called dialysis. The kidney is an example in living system that use dialysis to maintain the solute of electrolyte balance of blood, dialysis differs from osmosis in that osmotic membranes allow only solvent molecules to pass. The main purpose of the kidney is to clean the blood by removing the waste product of metabolism and control the concentration of electrolyte. The kidney does this job very efficiently approximately 180L of blood