Which theory is acceptable for physical structure of protoplasm?
          (A) Granular theory
          (B) Reticular theory
          (C) Alveolar theory
          (D) Colloidal theory

Hint:
Protoplasm is optically homogeneous, elastic, colourless, jelly-like, semi-transparent to transparent and semi-viscous substance.

Complete step by step answer:
The ‘living structure’ present inside the cell is termed as protoplasm. There is about 80-90% of water in protoplasm. Many soluble materials like salts, sugars and minerals are suspended in protoplasm in the form of ions and molecules. It is evident that the protoplasm is a crystallocolloidal solution.
Basically, the protoplasm is a polyphasic colloidal system. The colloidal structure of protoplasm was explained by ‘Fisher’ and ‘Hardy’ in 1894 and 1899 respectively.
In Reticular theory, particles form a network of fibrils in a liquid medium. In granular theory, the protoplasm is composed of minute granules suspended in a fluid said bioplast or elementary organism.
In alveolar theory, particles consist of numerous suspended droplets or alveoli similar to form or emulsion called ‘uritomes’ and inter-alveolar as mioplasma. Also called ‘Emulsion theory’.
The protoplasm is a polyphasic colloidal system. The colloidal system of protoplasm contains abundance of water in which certain solutes remain dissolved and certain solute particles of various sizes remain suspended in it.
Protoplasm is found in solution and gel states which are reversible or inter—convertible. A gel is said to be a group of suspended particles in a jelly like state. This gel converts into a liquid solution called Sol.

Hence, the correct answer is option (D). Colloidal theory.

Note:
‘Purkinje’ term as Protoplasm. It is the ground substance of living matter found within the membrane of a cell. ‘Von Mohl’ in 1946 emphasized its role in cell division including other metabolic processes of the cell.