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In this article we will discuss about Protoplasm:- 1. Meaning of Protoplasm 2. Nature of Protoplasm 3. Properties.
Meaning of Protoplasm:
The term protoplasm (Gr., protos = first + plasma = anything formed) was first coined in 1840 by who used the word to designate the living substance in the embryo of animals. Earlier the protoplasm was first of all observed by (1772) and the French zoologist (1935) first of all recognised its significance and called it “sarcode”. Later, Hugo Von Mohl applied this term to embryonic cells of plants.
In 1861, Schultze established the similarity which exists in the protoplasm of animal and plant cells, thus, offering a theory which was later called the “protoplasm theory” which states that the cell is an accumulation of living substances having a nucleus and limiting cell membrane. Gradually, protoplasm came to mean all living matter out of which plants and animals are formed.
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Huxley (1868) referred to protoplasm as the “physical basis of life”. It was first thought that protoplasm was a definite chemical substance, but investigations have shown that it is not a single chemical substance but is made up of different compounds and that it differs in every species of plant and animal life and probably in every different kind of cell.
For quite a long time, the protoplasm and cytoplasm were regarded to be synonyms. However, after recent investigations the protoplasm is a term used for the transparent, homogeneous and colloidal substance found in whole of the cell. The cytoplasm (Gr., kytos = hollow + plasma = form) is defined as the part of the cell which occurs between the plasma membrane and nuclear envelope.
Nature of Protoplasm:
Physical Nature of Protoplasm:
The protoplasm is a polyphasic colloidal system. The colloidal (Gr., kolla = glue) system of protoplasm contains abundance of water in which certain solutes remain dissolved and certain solute particles of various sizes remain suspended in it. The suspended particles may be of 0.001 µ to 0.1 diameter.
These particles are of two kinds hydrophilic and hydrophobic. The hydrophilic or water loving substances are the carbohydrates, proteins and inorganic salts and the hydrophobic or water repulsive substances are the lipids, etc.
The colloidal system of the protoplasm may be in semisolid or liquid state. The semisolid state is known as gel phase or jellylike state, while the liquid state is known as sol phase. In gel phase the molecules of solutes remain held together by various types of chemical bonds or bond between H-H, C-H or C-N. The stability of gel depends on the nature and strength of chemical bonds.
The colloidal system of the matrix usually changes its phase according to various metabolic and other physiological activities of the cell. A gel can change into sol by solation and a sol can change into gel by gelation. This property of colloid is known as phase reversal. The property of phase reversal provides many shapes or phases to the colloidal system of protoplasm.
In the past, there has been a lot of controversy about the physical nature of protoplasm. Different workers advanced different theories about the physical characteristics of the protoplasm.
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These theories have been represented as follows:
1. Reticular theory suggests that the protoplasm is composed of reticulum of fibres or particles in the ground substance (Fig. 3.2 A).
2. Alveolar theory was proposed by Butschili in 1892 and according to it the protoplasm consists of many suspended droplets or alveoli or minute bubbles resembling the foams of emulsion (Fig. 3.2 B).
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3. Granular theory was propounded by Altmann in 1893. This theory supports the view that the protoplasm contains many granules of smaller and larger size arranged differently. These granules were known as bioplasts (Fig. 3.2 C).
4. Fibrillar theory was proposed by Flemming very recently after the electron microscopical observations of the protoplasm. It holds that the protoplasm is fibrillar in nature. It is the most accepted view now-a-days (Fig. 3.2 D).
5. Colloidal theory has been forwarded very recently after the electron microscopical observations of the protoplasm. According to the recent concept, the protoplasm is partly a true solution and partly a colloidal system.
Chemical Nature of Protoplasm:
The protoplasm is found to consist of about thirty-six (36) chemical elements out of the total ninety-two (92) elements. Out of 36 elements only 12 are predominant in the protoplasm. These 12 elements are the carbon (C), hydrogen (H), nitrogen (N), oxygen (O), phosphorus (P), potassium (K), sulphur (S), chlorine (CI), sodium (Na), calcium (Ca), magnesium (Mg) and iron(Fe).
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Of these first four (C, H, N and O) form the 99 per cent of the protoplasm, while the remaining elements form only one per cent of the matrix. Some elements, e.g., copper (Cu), cobalt Co), manganese (Mn), zinc (Zn), iodine (I), molybdenum (Mb), boron (B), vanadium (Vd) and silicon (Si) occur as tracer elements. In the protoplasm these elements occur in the form of inorganic and the organic compounds.
Properties of Protoplasm:
Physical Properties of Protoplasm:
The most of the physical properties of the protoplasm are due to its colloidal nature and these are as follows:
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1. Tyndall’s Effect:
When a beam of strong light is passed through the colloidal system of the protoplasm at right angles in the dark room, then the small colloidal particles which remain suspended in the colloidal system, reflect the light. The path of the light appears like a cone. This light cone is known as Tyndall’s cone because this phenomenon was first of all reported by Tyndall (1820-1893) in colloids.
2. Brownian Movement:
The suspended colloidal particles of the protoplasm always move in zig-zag fashion. This movement of molecules is caused by moving water molecules which strike with the colloidal molecules to provide motion to them. This type of movement was first of all observed by Scottish botanist Robert Brown in 1827 in the colloidal solution.
Therefore, such movements are known as Brownian movement. The Brownian movement is the peculiarity of all colloidal solutions and depends on the size of the particles and temperature.
3. Cyclosis and Amoeboid Movement:
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Due to the phase reversal property of the protoplasm, the intracellular streaming or movement of the protoplasm takes place. This property of intracellular movement of protoplasm is known as the cyclosis. The cyclosis usually occurs in the sol-phase of the protoplasm and is effected by the hydrostatic pressure, temperature, pH, viscosity, etc.
The intracellular movements of the pinosomes, phagosomes and various cytoplasmic organelles such as lysosomes, mitochondria, chromosomes, centrioles, etc., occur only due to cyclosis of the protoplasm. The cyclosis has been observed in most animal and plant cells.
The amoeboid movement depends directly on the cyclosis. The amoeboid movement occurs in the protozoans, leucocytes, epithelial, mesenchymal and other cells. In the amoeboid movement, the cell changes its shape actively and gives out cytoplasmic projections known as pseudopodia. Due to cyclosis, protoplasm moves these pseudopodia and this causes forward motion of the cell.
4. Surface Tension:
The molecules in the interior of a homogeneous liquid are free to move and are attached by surrounding molecules equally in all directions. At the surface of the liquid where it touches air or some other liquid, however, they are attached downward and sideways or inward, more than upward consequently they are subjected to unequal stress and are held together to form a membrane.
The force by which the molecules are bound is called the surface tension of the liquid. The protoplasm being a liquid has the property of surface tension. The proteins and lipids of protoplasm have less surface tension, therefore, occur at the surface and form the membrane, while the chemical substances such as NaCl have high surface tension, therefore, occur in deeper part of the protoplasm.
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5. Adsorption:
The increase in the concentration of a substance at the surface of a solution is known as adsorption (L., ad = to; sorbex = to draw in). The phenomenon of adsorption helps the protoplasm to form protein boundaries.
6. Other Mechanical Properties of Protoplasm:
Besides surface tension and adsorption, the protoplasm possesses other mechanical properties, e.g., elasticity, contractility, rigidity and viscosity which provide the protoplasm many physiological utilities.
7. Polarity of the Egg:
The colloidal system due to its stable phase determines the polarity of the cell protoplasm which cannot be altered by centrifugation or other mechanical means.
8. Buffers and pH:
The protoplasm has a definite pH value and it does not tolerate significant variations in its pH balance. Yet various metabolic activities produce small amount of excess acids or bases. Therefore, to protect itself from such pH variation, the protoplasm contains certain chemical compounds as carbonate bicarbonate system known as buffers which maintain a constant state of pH in the protoplasm.
Biological Properties of Protoplasm:
The protoplasm is a living substance and it has following biological properties:
1. Irritability:
The irritability is the fundamental and inherent property of protoplasm. It possesses a sensitivity to stimulation, an ability to transmission of excitation and ability to react according to stimuli. The heat, light, chemical substances and other factors stimulate the protoplasm to contract.
2. Conductivity:
The conductivity is the process of conduction or transmission of excitation from the place of its origin to the region of its reaction. The protoplasm of many cells possesses the property of the conductivity.
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3. Movement:
The protoplasm possesses movement due to cyclosis. The cyclosis depends on the age, water contents, heredity factors and composition of the cells.
4. Metabolism:
The protoplasm is the seat of various chemical activities. These activities may be either constructive or destructive in nature. The constructive processes such as biosynthesis of proteins, lipids, carbohydrates and nucleic acids are known as anabolic processes, while the destructive processes such as oxidation of foodstuffs, etc., are known as catabolic processes.
The anabolic and catabolic processes are collectively known as metabolic process.
5. Nutrition:
Nutrition involves taking in of the food, its digestion and assimilation. Protoplasm exhibits the power of nutrition.
6. Respiration:
The gaseous exchange, i.e., intake of oxygen and giving out of carbon dioxide is an important property of protoplasm. The oxidation of the food materials for the production of energy needed for various activities of life.
7. Excretion:
Protoplasm possesses the power of excretion. Waste products are passed out of body of the organisms.
8. Growth:
Due to the secretory activities of the cell, new protoplasm continuously increases in its volume. The increase in the volume of the protoplasm causes into the growth of the cell which ultimately divides into daughter cells by the cell divisions.
9. Reproduction:
The protoplasm has the property of asexual and sexual reproduction and producing exactly similar substances.
