This matrix of cell was given the name of protoplasm by J.E. Purkinje in 1840. H. Von Mohl, in 1846, stated the protoplasm as a clear, homogeneous appearing (in the light microscope), gelatinous substance.
He also emphasized the importance of protoplasm in cell division. In 1861, Schultz established the similarity between the protoplasm of plants and animals, thus formulating the protoplasm theory, according to which cell consists of an essentially living ground substance having nucleus with limiting cell membrane. This ground substance after removing all the major particulate components or organelles is termed hyaloplasm.
After the discovery of electron microscope in 1939-40, the concept of protoplasm has been changed from a homogeneous clear, colloidal suspension to that of a multiphased complex system containing numerous membranous elements.
Physical Nature:
The protoplasm, under an ordinary microscope, seems to be a clear homogeneous fluid, called hyaloplasm, in which are distributed globules, granules, and various special differentiations. The hyaloplasm is also known as kinoplasm, cytoplasm, etc.
Physical properties of protoplasm include its function due to chemical nature, physiological activities and organization. It shows the following properties—
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[I] Protoplasm as a colloidal system:
Basically the hyaloplasm or cytoplasm is a complex colloidal system. Its colloidal structure was suggested by Fisher in 1894 and Hardy in 1899. It consists of high water contents containing various solutes of biological importance such as glucose, fatty acids, amino acids, minerals, vitamins, hormones and enzymes.
These solutes may be either soluble in water making it a homogeneous mass or insoluble in it, thus making it a heterogeneous mass. This suspension of particles in the protoplasm is the basis for its colloidal nature. The various components give the appearance to protoplasm of four different kinds:
1. Granular theory:
This theory was propounded by Altmann in 1893. According to this theory, protoplasm consists of numerous tiny granules as shown in Amoeba. Henle, Maggi, etc., considered these protoplasmic granules as plastidules. Altmann recognized them as ‘elementary organisms’, or bioplasts (or cytoplasts).
2. Alveolar theory:
The alveolar nature of protoplasm was suggested by Butchlli in 1892. According to him, protoplasm consists of many suspended droplets or alveoli or minute bubbles, resembling the foams of emulsion.
3. Fibrillar theory:
This theory was put forward by Flemming. According to him, protoplasm consist of fibres embedded in the inner mass of matrix. The fibrillae are called mitome or spongioplasm formed of proteins called micelles, and ground substance is termed paramitome or hyaloplasm.
4. Reticular theory:
This theory was postulated by Klein, Comoy, etc. It suggests that protoplasm consists of a reticulum of fibres in its hyaloplasm.
The organic material which consists of proteins and carbohydrates in suspension may be either hydrophilic (water-loving) or hydrophobic (water-hating). The hydrophilic particles occur surrounding the water molecules. The attraction between protein and water is due to electric charges that hold them together.
The physical properties of protoplasm are principally due to the various chemical inclusions in a gel phase. A gel is a group of suspended particles in a semi-solid condition or jelly-like state. The molecules of a gel are held together by various types of chemical bonds of varying strength.
The stability of bond depends upon the type of bond and strength of bond. The gel may become more liquid than solid. This process is called solation and the liquid state as sol. Thus, the colloidal protoplasm which is in gel form can change into sol form by solation and the sol can change into gel by gelation. These gel-sol conditions of colloidal system are prime basis for mechanical behaviour of cytoplasm.
Protoplasm is neither a good nor a bad conductor of electricity. It forms a delimiting membrane on coming in contact with water and solidifies when heated.