The cell is the essential element of any organism. The cell is enclosed by either a cell wall or cell membrane. This outer covering surrounds the cellular components. The cellular components are freely suspended in part called cytoplasm.
The cytoplasm is a gel-like fluid present inside the cell that consists of various cellular organelles. It is widely distributed and separates the membrane-bound internal organelles of the cell. It consists of membrane-bound as well as non-membrane-bound organelles. Its principal function is to support cells during growth and metabolism and give structural integrity to cells.
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History of Cytoplasm
Robert Hooke discovered the cytoplasm in 1665, and Rudolf Von Kolliker gave the name in 1874. The term protoplasm was believed to be the synonym of cytoplasm, but later on, it was known that the two terms have different meanings. Protoplasm is the term used for cytoplasm with the nucleus.
Composition of Cytoplasm
The cytoplasm comprises four components; cytosol, organelles, cytoskeleton, and inclusions.
The cytosol is the liquid part of the cytoplasm called the cytoplasmic matrix. It is formed of water, dissolved minerals, and cytoskeleton filaments. It holds the cell organelles within the cell. 70% of cytosol consists of water. The organic minerals and ions are dissolved in the water. The ions present in mammal’s cytosol are K+. Cl–, Mg++, Ca++, and HCO3–. The organic compounds present in the cytosol are amino acids (the protein derivative).
In eukaryotes, it is the site for many cell chemical reactions. In prokaryotes, almost all metabolic reactions take place in the cytosol. Its prominent role is osmoregulation and cell signaling because of its dissolved ions. It also helps generate an action potential in the endocrine, nervous, and muscular cells.
The cytoskeleton is the part of the cytoplasm that helps maintain the cell’s shape and internal organization. It also supports the cell mechanically and helps to carry out essential functions like division and movement. It is made up of fibrous proteins divided into three classes that differ in size and concentration. The three classes are actin filaments, intermediate filaments, and microtubules.
The membrane-bound specialized structures inside the cells carrying specific tasks are called the organelles. The organelles are present inside the eukaryotic cells only as prokaryotic cells lack membrane-bound organelles. The organelles include the nucleus, chloroplasts, mitochondria, endoplasmic reticulum, ribosomes, Golgi apparatus, and lysosome. These organelles are like organs of the body that perform various cell tasks.
- The mitochondria are the cell’s powerhouse that synthesizes energy required for the cell.
- The ribosome is the house for protein synthesis, which is made up of proteins and RNA (ribonucleic acid)
- The endoplasmic reticulum is the network of flattened sacs, the site for lipid synthesis, carbohydrate metabolism, and cell detoxification. It is also helpful for the intracellular transport of products from an organelle to another organelle.
- Chloroplasts are green-colored plastids necessary for photosynthesis in plants. It is present in plants.
- Golgi apparatus is the membrane-bound stacks involved in glycosylation, packaging molecules for secretion, lipid transportation, and forming lysosomes.
- The lysosome is involved in the protection of the cell from foreign bodies and is also involved in cell death.
- Vacuoles are the cell organelles involved in exocytosis (removal of toxic substances) and storage of foods.
The other cellular components not membrane-bound in the cell are called inclusions. Proteins synthesized for forming the membranes and cytoskeleton, lipid droplets, and carbohydrates suspend freely in the cytoplasm. The plant cell has starch (a carbohydrate derivative) suspended in its cytoplasm required for photosynthesis, but animal cells lack it. The lipid droplets are present in plant and animal cells, which help store lipids as fatty acids.
Functions of Cytoplasm
The functions of cytoplasm include cell growth, metabolism, and expansion. Cell growth and development occur by cell division. The chemical reactions in breaking down the large and complex compounds into simpler ones also occur in it. Besides these, it also has other functions, which are:
- Support and structure: The cytoskeleton in the cytoplasm helps maintain the cell’s integral structure and shape. It also helps in preventing unnecessary movement of the organelles present in the cell. The empty parts of the cell (parts without cellular organelles) are filled with cytosol.
- Protection: It acts as the shock absorber during attacks by foreign bodies. It also protects the components of the cell by keeping those stable in their position.
- Storage: The cytoplasm stores enzymes, carbohydrate derivatives, lipids, and other compounds necessary for various metabolic processes. In plant cells, it stores starch, a very important component required for photosynthesis.
- Transport: The process of cytoplasmic streaming helps the transport of organelles and inclusions within the cell. It also helps in the removal of waste materials from the cell.
Cytoplasmic streaming is the process of movement of the cytoplasm within the cell membrane.
Difference Between Cytoplasm and Cytosol
The cytoplasm and cytosol are two terms often used as synonyms which is not true. Both these terms have many differences, which are as follows:
- The cytoplasm is the part present inside the cell membrane. The cytosol is the gel-like fluid and part of the cytoplasm.
- The cytosol consists of water, dissolved ions, more significant water-soluble compounds, and smaller proteins. But, 80% of the cytoplasm comprises nucleic acid, enzymes, lipids, non-organic ions, amino acids, and carbohydrates.
- The metabolic activities of prokaryotes occur in the cytosol. Whereas in eukaryotes, cell organelles in the cytoplasm carry out many metabolic activities.
Difference of Cytoplasm in Plant and Animal Cells
Although the cytoplasm of animal and plant cells are similar in many different ways, there are some key differences. Since both these habitat cell organelles, some cell organelles differ in plant and animal cells. The plant cells harbor plastids, mostly chloroplasts, but animal cells do not hold these.
Similarly, cytoplasm in plant cells often has a dominant vacuole that fills most of the cytoplasm, which is not the case in animal cells. During the late cell division phase, phragmoplast is exclusive to plant cells. Also, cytoplasmic inclusions differ in animal and plant cells. As a difference, many plant cells have starch as cytoplasmic inclusions, whereas few animal cells have glycogen. These both serve the same purpose of storing energy.
- Cytoplasm. Retrieved 21 August 2022, from https://www.genome.gov/genetics-glossary/Cytoplasm
- E. Ismaeel, F. The Cytoplasm. Retrieved 21 August 2022, from https://uomustansiriyah.edu.iq/media/lectures/2/2_2020_01_07!08_39_24_AM.pdf
- Oberling, C. (1959). The Structure of Cytoplasm. International Review Of Cytology, 1-31. DOI: 10.1016/s0074-7696(08)62726-6
Iwasa, J., & Marshall, W. (2018). Karp’s cell biology (8th ed.). Hoboken, NJ: Wiley.