1. Lipid Membrane Model – Gorter & Grendel (1925)
2. Sandwich Model or Bilayer Model – Danielli and Davson (1935)
3. Micellar Model – Hiller and Hoffman (1953)
4. Single Screen Hypothesis – Robertson (1959)
5. Benson’s model (1966)
6. Lenard & Singer’s model (1966)
7. Protein crystal model – Venderkoff and Green (1970)
8. Fluid-mosaic model – Singer and Nicholson (1972)

The fine, thin, elastic and permeable membrane that surrounds the protoplasm is called the plasma membrane. It is composed of lipids and proteins. It is called cytoplasmic membrane, cytomembrane, cell membrane, plasmalemma, biomembrane etc. It is called biomembrane as it exists in plant and animal body i.e. in all living cells. Chemically it consists of three layers: protein-lipid-protein. Carl Nageli and Cramer (1855) first discovered the cell membrane and named it plasma membrane. J. Q. Plower (1931) called it plasmalemma.

1. Protoplasm is the physical basis of life. It acts as the physical basis of life.
2. It is the main component of cells. Contains all the organelles of the cell.
3. It holds water for cells.
4. It causes reproduction.
5. It causes physical growth.
6. Maintains ionic balance in cells.

Protoplasm always exhibits dynamic movement. The dynamic movement of protoplasm is called cyclosis or cyclosis. It exhibits zig zag oscillations, called Brownian oscillations. It exhibits two types of movement.
1. Unidirectional Cyclosis: The movement in which the protoplasm rotates in one direction in a specific direction around a single cavity is called unidirectional cyclosis. The movement of the protoplasm of leafhoppers is unidirectional.
2. Multidirectional Cyclosis: The movement in which the protoplasm rotates irregularly in different directions around several cavities is called multidirectional cyclosis. The movement of the protoplasm of Tradescantia is unidirectional.

1. Reticular theory: According to the scientist Frommann (1865), protoplasm is formed by reticular fibers on the base material.
2. Granular theory: According to the scientist Altman (1886), protoplasm is a granular fluid with numerous small and large biomass.
3. Alveolar theory: According to the scientist Butschli (1892), protoplasm is like soap foam with numerous alveoli or tiny bubbles.
4. Colloidal theory: According to scientists Wilson and Fisher (1894), protoplasm is partly liquid and partly colloidal.

1. The main chemical constituent of protoplasm is water. It contains 70-90% water.
2. Dry protoplasm contains 45% proteins, 25% lipids, 25% carbohydrates and 5% other substances.
3. The main organic constituents of protoplasm are proteins and nitrogenous compounds.
4. It contains small amounts of liquid fats and oils.
5. Its minerals are calcium, magnesium, potassium, sodium, iron etc.

1. Protoplasm is translucent, colorless, gelatinous and sticky.
2. It is granular and colloidal.
3. Its colloidal particles carry homogeneous electrical charges.
4. Its relative importance is greater than that of water.
5. It performs all the basic functions of the body. The basic functions of organisms are photosynthesis, growth, movement, digestion, excretion, growth, reproduction, absorption, diffusion, respiration etc.
6. It coagulates under the influence of heat, acid and alcohol
7. It is always in motion and its dynamic movement is called cyclosis (eg Tradescantia).
8. It exhibits a zig zag pattern. It is called Brownian movement.
9. Plasmagel is formed from plasmasol of protoplasm and plasmasol from plasmagel.
10. Particles of protoplasm can be separated by Millipore filter paper.
11. It responds to any stimulus. Responds to light, heat, pressure, touch etc.
12. Its density is always variable.
13. After a certain period of time the protoplasm dies.

The word Protoplasm is derived from the Greek word Protos meaning origin and plasma. The translucent, sticky, colorless and jelly-like colloidal living matter inside the cell membrane is called protoplasm. It is called the physical basis of life or vivum fluidum as it performs all the functions of the organism.

The word Protoplast is formed from the Greek word Proto meaning origin and plasma meaning organization or matter. Protoplast means primitive matter. All parts of the cell except the cell wall are called protoplasts. German botanist Robert von Hanstein first used the term protoplast in 1880. According to I. K. Vasil (1980), the protoplast is the inner part of the cell wall that can be separated from the cell wall mechanically or by enzymes. Protoplasts that are produced artificially are called isolated protoplasts. Protoplast consists of two parts. Protoplasm and non-living matter.