Colloidal Theory- "Fisher 1894, Hardy" ] 899 and "Wilson" 1925.
This is most acceptable theory for protoplasm. According to this theory, the protoplasm is a Polyphasic
Colloidal System.

(1) Protoplasm is a translucent, odourless and polyphasic fluid.

(2) Protoplasm is a crystallo-colloid type of solution.
Protoplasm is a mixture of such chemical substances among which some form crystalloid i.e. true solution (Sugars, Salis, Acids, Bases etc.) and others which form colloidal solution (Proteins, Lipids etc.)

(3) Size of colloidal particles (0.001 to 0.1 ~m.) is between true solution and suspension.

(4) Colloidal systems composed of two stages. (i) Dispersion phase or continuous form or intermicelleus and
(ii) Dispersed phase or discontinuous phase or Micellus
On the basis of dispersion and dispersed phases there are four types of colloids-
(A) Sol Dispersion phase is liquid and dispersed phase is solid. In sol staf._Je, protoplasm is less viscous.
Protoplasm in sol stage occurs in majority of living cells.

(B) Gel= Dispersion phase is solid and dispersed phase is liquid. Protoplasm is more viscous e.g. Skin cells.

(C) Emulsion -Both stages are liquid i.e. fluid colloidal particles are dispersed in a liquid matrix e.g. blood
plasma composed of both sol and emulsion.

(D) Aerosol - solid particles remain suspended in gas e.g. smoke. Aerosol does not occur in living system

(5) Protoplasm mainly composed of either sol or gel.

(6) Sol stage provides cyclosis, Brownian movements and high reactivity to protoplasm.

(7) Gelation of protoplasm provides elasticity, contractibility, rigidity and viscosity.

(8) Colloid particles have electric charge and due to charges these remain in a continuous random motion , called
Brownian movement.

(9) Environmental conditions like temperature, pressure and pH cause changes in the properties of protoplasm.
This change brings endocellular movement of protoplasm called cyclosis.

(10) Brownian movement and cyclosis are more significant in sol stage of protoplasm.

(11) Being a liquid mixture, the protoplasm has a surface tension. Solutes (Proteins and lipids) having less surface.
tension, form a delimiting membrane at surface. This membrane is called Interface membrane (plasma mem-brane).
Interface membrane has power of rapid regeneration.


(12) Being colloid, protoplasm exhibits "Tyndal effect" i.e. Scattering of incident light rays.

(13) Sol and gel stages of protoplasm are in1erconvertible so the protoplasm is a reversible colloidal system. Non
living colloids are irreversible.

(14) Ageing- With age, charges of colloid particles diminishes, brownian movements stops so ultimately it becomes
non reactive (death of protoplasm).

(15) Viscosity of protoplasm = 2-20 centipoises

(16) pH= 6-8

(17) Refractive index = 1.4

Protoplasm is a living substance so it posseses biological properties also.
(1) Protoplasm has motion due to cyclosis, amoeboid and Brownian movement. These movements depend on a~Je of cells, amount of water, genetic factors and chemical composition of protoplasm.

(2) Protoplasm exhibits irritability when provided stimuli.
Sensitivity of protoplasm to external stimuli is called irritability. Transmission of stimuli from one place to another is called conductivity.
Besides irritability, conductivity also occurs in protoplasm of many cells e.g. nerve cells, muscle cells etc.

(3) Different chemical readions takes place in protoplasm. Constructive reactions are called Anabolic processes like synthesis of different types of biomolecules. Destructive reaction like oxidation of food is called catabolic processes. Anabolic and Catabolic Processes collectively called metabolism.

(4) Protoplasm has the capacity to take external material and resynthesize them in a new form (assimilation).

(5) Respiration and excretion.

Approximately 34 elements participate in the composition of protoplasm but only 13 elernents are main or universal
elements in protoplasm i.e. C, H, 0, N, Cl, Ca, P, Na, K, S, Mg, l, Fe.
Carbon, Hydrogen, Oxygen and Nitrogen form the 96% part of protoplasm.

Rest of the elements of protoplasm occur in very small quantity (0.756%). These are, therefore called Trace
elements. These includes Copper, Cobalt, Manganese, Zinc, Boron, Vanadium, Chromium, Tin, Silicon, Fluorine,
Molybdenum, Nickel, Selenium, Arsenic.

Although some elements occur in protoplasm as free ions but mostly two or more elements are variously
combined to form different kinds of compounds.
Biomolecule-) All the carbon compound that Present in living tissue.
Lipids is exceptionary micromolecule but present in acid insoluble pool.