n., plural: protoplasms
Definition: The living substance within a cell
Table of Contents
The protoplasm is regarded as “the living material or the living content of a cell“. It is fluid where various biological processes occur. The term protoplasm was coined by Czech physiologist Johannes Evangelista Purkinje to denote the gelatinous fluid found in living tissue. Take note that a tissue is made up of cells and the cell is the structural, functional, and fundamental unit of all organisms. A typical cell structure contains a biological membrane that surrounds the protoplasm to separate it and protect it from the external environment.
What is a protoplasm and what is not?
Do the terms protoplasm, protoplast, and cytoplasm are one and the same?
- Protoplasm vs. Cytoplasm: In some references, the word protoplasm is used synonymously with the term cytoplasm (especially when dealing with prokaryotes). However, in a stricter sense, a protoplasm is more inclusive by including not only the cytoplasm but also the nucleoplasm. The nucleoplasm is the fluid content of the nucleus surrounded by the nuclear envelope, including the nuclear materials, such as chromosomes, nuclear bodies, and nuclear matrix.
- Protoplasm vs. Protoplast: Protoplast refers to any of the plant cells with the cell wall removed.
Watch this vid about the protoplasm of living cells:
Features of Protoplasm
Here are the common features of the protoplasm of living organisms:
- The protoplasm is “alive”, meaning it is capable of performing various living processes, such as cell division and metabolism, thus, it is often regarded as the physical basis of life. As specified in the protoplasmic theory, all life forms possess a protoplasm. (In modern biology, this conceptual framework is expounded in the Biological Cell Theory)
- It is composed primarily of organic and inorganic substances. Organic substances include various biomolecules, such as nucleic acids, proteins, lipids, and carbohydrates. Examples of inorganic substances are inorganic salts and water molecules.
- The protoplasm is surrounded by the cell membrane.
- Protoplasm may exist in two forms:
- A liquid-like sol state, wherein the protoplasm exhibits a more fluid-like consistency
- A jelly-like gel state, wherein the protoplasm has a more viscous and semi-solid consistency.
The protoplasm is the site of many biological processes. Cells after dividing will undergo growth. The growth of the cell is enabled by metabolism. Metabolism may be categorized into two: catabolism and anabolism. Catabolism includes a series of degradative chemical reactions that break down complex molecules into smaller units, usually releasing energy in the process.
Anabolism includes a sequence of chemical reactions that constructs or synthesizes molecules from smaller units, usually requiring the input of energy (ATP) in the process. Thus, biomolecules, such as nucleic acids, proteins, carbohydrates, and lipids are produced, stored, and degraded inside the cell.
Protoplasm of Prokaryotes and Eukaryotes
Prokaryotes do not have a distinct nucleus and other cytoplasmic organelles. Thus, the protoplasm refers to the materials contained inside the cell membrane, i.e. the prokaryotic cytoplasm.
In certain prokaryotes, particularly Gram-negative bacteria, the protoplasm extends to the periplasmic region between the cytoplasmic membrane and the outer membrane. This region contains a gel-like material called periplasm, which is part of the protoplasm in Gram-negative bacteria.
In eukaryotes, the protoplasm consists of two major divisions: the cytoplasm and the nucleoplasm (cell nucleus). The cytoplasm is the jelly-like substance of the eukaryotic cell. It is made up of the cytosol, the vesicles, the cytoskeleton, the inclusions, and the organelles except for the nucleus. Thus, the cytoplasm of a eukaryotic cell is that part of the cell between the cell membrane and the nuclear envelope. The material contained inside the nuclear envelope is called nucleoplasm. The nucleoplasm is the protoplasm of the nucleus.
The cytoplasm of both eukaryotes and prokaryotes is where the functions for cell expansion, growth, and metabolic processes are carried out. However, in eukaryotic cells, the cytoplasm contains cellular organelles, which are not present in prokaryotic cells. So while the metabolic processes occur in the cytoplasm of the prokaryotes, these processes occur in specialized compartments of eukaryotes called organelles.
The nucleus, for instance, is the organelle that contains the genetic material and therefore it controls cellular activities such as metabolism, growth, and reproduction by regulating gene expression. Chloroplasts are plastids containing green pigments essential for photosynthesis. Mitochondria are the organelles that synthesize energy for multifarious metabolic processes.
The endoplasmic reticulum occurs as an interconnected network of flattened sacs and tubules involved in lipid synthesis, carbohydrate metabolism, drug detoxification, and attachment of receptors on cell membrane proteins. It is also involved in intracellular transport, such as the transport of the products (of rough endoplasmic reticulum) to other cell parts like the Golgi apparatus.
Charles Darwin and his 19th-century contemporaries viewed the protoplasm concept as the holistic content of a cell; in other words, cells were composed of a mysterious “proto-plasm”, a living substance with the ability of self-replication.
- Merriam-Webster Dictionary. (2023, August 28). Merriam-Webster.com. https://www.merriam-webster.com/dictionary/protoplasm
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