Protoplasm: During the 19th century, the concept of the cell as the fundamental particle of life was complemented by the “protoplasm” concept, which holds that the protoplasm within the cell is responsible for life. Is protoplasm another name for the plasma membrane or cytoplasm? Well, protoplasm includes both the contents of nucleoplasm and cytoplasm. Let’s learn more about protoplasm, its definition, discovery, physical and chemical nature of protoplasm for a clear concept.

Definition

The living substance of cells that is surrounded by the plasma membrane is known as protoplasm (Greek: protos = first, plasma = form). It is a complex polyphasic crystallo-colloidal complex that contains all of the features of life and can be found inside living cells. However, because protoplasm contains numerous living elements, not everything found in it is alive. Protoplasm is divided into nucleoplasm (within the nucleus) and cytoplasm in eukaryotic cells. Protoplasm produces deutoplasm, which is a non-living material generated during metabolism.

Discovery of Protoplasm

1. Protoplasm is found in all cells. Huxley identified protoplasm as the physical substrate of life.
2. Dujardin researched the contents of cells in various Protozoa in 1835, and he defined the cell-matrix as a homogeneous mass that he termed sarcode.
3. J.E. Purkinje coined the term protoplasm to describe this cellular matrix in 1840. In 1846, H. Von Mohl described protoplasm as a clear, homogeneous, gelatinous substance (under a light microscope).
4. He also highlighted protoplasm’s relevance in cell division. Schultz showed the resemblance between plant and animal protoplasm in 1861, resulting in the protoplasm theory, which states that a cell is made up of a basic living ground substance with a nucleus and a limiting cell membrane. Hyaloplasm is the ground substance left after all the major particle components or organelles have been removed.
5. After the invention of electron microscopy in 1939-40, protoplasm was redefined as a multiphased complex system including various membranous elements rather than a homogenous transparent colloidal suspension.

Physical Nature of Protoplasm

Fig: Protoplasm

1. Protoplasm is a jelly-like fluid that is viscous, transparent, stretchy, and odourless. It has a viscosity of 2-10 times that of water.
2. It is a polyphonic colloidal system that can appear in a variety of states (phases).
3. Protoplasm can transform from a thick gel to a more fluid sol condition and back.
4. Protoplasm has the ability to grow and divide.
5. It is elastic, meaning it can be stretched and compressed.
6. It is irritable, meaning it is sensitive to many stimuli.
7. Brownian movement, amoeboid movement, ciliary movement, and cyclosis or cytoplasmic streaming are all examples of protoplasmic movement.
8. Protoplasm can swell when it takes in water and shrink when it loses it.
9. It is made up of both nonpolar and charged particles. The electrical conductivity of the material is low.
10. It has the ability to coagulate. Heating, electrification, contact with hazardous substances, and other factors cause protoplasm to coagulate. The protoplasm dies as a result of this, and all of its physical and biological features are lost.
11. Long chains of molecules are held together by forces such as Van der Waals bonds, which hold the numerous particles or molecules of protoplasm together.
12. Contractility characteristic is important in a variety of plant stomatal operations. Protoplasm contractility is necessary for the absorption and elimination of water, which are both common in protoplasm.
13. Viscosity is the most important property of the protoplasm by which it exhibits three main phenomena, i.e., Brownian movement, amoeboid movement and cytoplasmic streaming or cyclosis.
14. Brownian movement is characterized by the zigzag motion of suspended colloidal particles, occurring due to the bombardment of one particle or molecule by others. This type of movement of particles was first of all observed by Robert Brown in the colloidal solution, and hence such movements are known as Brownian movements.
15. The higher the temperature, the more rapid the movement and – thus viscosity of cell is decreased. This means that high viscosity indicates a more gel-like state of protoplasm and low viscosity, a more sol-like condition.
16. Viscosity also causes amoeboid movements in Amoeba and other protozoans, as well as leucocytes and other cells. Sol-constant gel’s alteration and vice versa are the cause for such motions. The cell produces cytoplasmic projections, known as pseudopodia, and protoplasm enters the pseudopodia by cyclosis, causing the cell to migrate forward.
17. It’s the cytoplasmic mobility within the cell, as demonstrated by Paramecium. It usually happens while the cytoplasm is in the sol phase. Its true cause is unknown; nevertheless, if cell metabolism decreases, cyclosis decreases as well. In the same way, an increase in metabolic rate leads to an increase in streaming.
18. In the protoplasm, surface tension is also visible. The presence of cytoplasmic proteins and lipids at the membrane’s surface is due to their lower surface tension. Chemical substances with high surface tension, such as NaCl, are present at a deeper level in the cell protoplasm.

Different Types of Theories

Protoplasm is the most basic component of all living organisms. Fisher (1894) and Hardy (1895) proposed the colloidal theory of protoplasm (1899). Protoplasm is a heterogeneous polyphasic colloidal structure that exists in several phases such as reticular, fibrillar, granular, and alveolar.

1. Granular Theory: According to this theory, protoplasm is made up of minute granules suspended in a bioplast or basic organism fluid. Altmann had proposed it (1893).

2. Alveolar Theory: Butchlli proposed the alveolar nature of protoplasm in 1892. Protoplasm, he claims, is made up of many suspended droplets, alveoli, or minute bubbles that resemble emulsion foams.

3. Fibrillar Theory: The protoplasm, according to this hypothesis, is made up of fibres embedded in the matrix’s core mass. The fibrillae are referred to as spongioplasm, whereas the ground substance is referred to as hyaloplasm. Flemming had proposed it.

4. Reticular Theory:

1. Klein, Comoy, and others proposed this theory. It suggests that the protoplasm’s hyaloplasm is made up of a reticulum of fibres.
2. The organic material in suspension, which comprises proteins and carbohydrates, can be either hydrophilic or hydrophobic. Water molecules are surrounded by hydrophilic particles. The electric charges that bind protein and water are responsible for their attraction.
3. The bond’s stability is determined by the type and strength of the bond. It’s possible that the gel will become more liquid than solid. This is known as solation, and the liquid condition is known as a sol. 
4. Thus, through solation, colloidal protoplasm in gel form can be transformed into a sol, and the sol can be transformed into a gel by gelation. The mechanical behaviour of cytoplasm is mostly determined by the gel-sol conditions of the colloidal system.
5. Protoplasm is neither an excellent nor a bad electricity conductor. When it comes into touch with water, it produces a delimiting barrier that solidifies when heated.

Biological Properties of Protoplasm 

1. Cyclosis, Amoeboid, and Brownian movement all-cause protoplasm to move. These movements are influenced by cell age, water content, genetic variables, and protoplasm chemical composition. When exposed to stimuli, protoplasm becomes irritable.
2. Irritability refers to protoplasm’s susceptibility to external stimuli. Conductivity is the ability to transmit stimuli from one location to another. Conductivity is occurred in the protoplasm of many cells, including nerve cells, muscle cells, and so on, in addition to irritability.
3. Protoplasm undergoes a variety of chemical processes. Anabolic processes, such as the production of many types of biomolecules, are examples of constructive reactions. 
4. The catabolic process refers to a negative response such as food oxidation.  Metabolism refers to both anabolic and catabolic processes.
5. Protoplasm has the ability to resynthesize external materials into a new form (assimilation).

Chemical Nature

1. Carbon, hydrogen, oxygen, phosphorus, sulphur, calcium, and various other elements have been discovered in the protoplasm of many cells. Water (75-95%), carbohydrates, ions, proteins, lipids, nucleic acids (DNA and RNA), fatty acids, glycerol, nucleotides, nucleosides, and minerals are some of the substances they form. They can only live as long as they are in protoplasm. They are unable to carry out basic life activities on their own. Protoplasm has an inconsistency in its composition, and it is constantly changing.
2. Protoplasm reacts chemically as a mild alkali. It dissolves in dilute alkalis and acids but solidifies when exposed to strong acids or alcohols. During chemical analysis, it quickly decomposes into H2O, NH3, and CO2, among other things.
3. Many more trace elements are required for various physical (osmosis and diffusion) and biochemical (impulse conduction, etc.) activities. Protoplasm has an approximate water content of 85-90%. The dispersion medium is made out of the water, in which other materials are suspended.
4. It has been found that three main kinds of carbohydrates are present in protoplasm:
   a. Monosaccharides—glucose and fructose
   b. Disaccharides— sucrose, lactose and maltose and
   c. Polysaccharides— cellulose, glycogen and starch.
5. water makes up 95% of total cellular water and contains diverse inorganic and organic molecules dissolved in it. Water weakly coupled to protein molecules by hydrogen bonds or other factors makes up the remaining 5% of total cellular water.

Summary

The living matter of plant and animal cells is protoplasm, a complex, semifluid, translucent substance. Protoplasm is the medium in which a cell’s vital life functions take place. Proteins, lipids, and other substances suspended in water make up protoplasm. The contents of nucleoplasm and cytoplasm are included in protoplasm. J.E. Purkinje coined the term protoplasm to describe the cellular matrix. The genetic material of a cell is found in protoplasm. It also regulates the cell’s activity. Protoplasm is a heterogeneous polyphasic colloidal structure that exists in several phases such as reticular, fibrillar, granular, and alveolar theory. 

Protoplasm is subjected to a number of chemical reactions. Constructive responses include anabolic processes, including the synthesis of a variety of biomolecules. Many elements have been observed in the protoplasm of cells, including carbon, hydrogen, oxygen, phosphorus, sulphur, calcium, and others. Some of the molecules they form include water (75-95 per cent), carbohydrates, ions, proteins, lipids, nucleic acids (DNA and RNA), fatty acids, glycerol, nucleotides, nucleosides, and minerals.

Frequently Asked Questions (FAQs) on Protoplasm

Q.1. What is protoplasm?
Ans: Protoplasm is a jelly-like fluid that is viscous, transparent, stretchy, and odourless. It is a mixture of small molecules such as ions, monosaccharides, amino acids, and macromolecules such as proteins, polysaccharides, lipids, etc.

Q.2. What is the primary function of protoplasm?
Ans: The genetic material of a cell is found in protoplasm. It also regulates the cell’s activity.

Q.3. Who coined the term protoplasm?
Ans: J.E. Purkinje coined the term protoplasm.

Q.4. What is the difference between a protoplast and a protoplasm?
Ans: Protoplasts are cells that have been deprived of their cell walls. Plasmalemma encircles it. On the other hand, protoplasm is a translucent, complex substance that includes the life matter of plants and animals.

Q.5. Is the cell membrane a part of protoplasm?
Ans: The living core of the cell is protoplasm. The cytoplasm, nucleus, and other organelles are all included. Protoplasm is stored within the cell membrane but itself is not a part of protoplasm.

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