Cytoplasm : Defination, Meaning, Structure & Functions of Cytoplasm

Cytoplasm : Defination, Meaning, Structure & Functions of Cytoplasm 

What is cytoplasm?

The cytoplasm is a colloidal dispersion , a granular fluid present inside the cell and between the cell nuclear membrane and the plasma membrane. It is part of eukaryotic cells and prokaryotic cells. The cytoplasm is composed of the cytosol or cytoplasmic matrix, that contains cytoskeleton and cell organelles. It also contains several nutrients that, once they have crossed the plasma membrane to reach the cell organelles.

For this reason, various important molecular reactions are carried out in the cytoplasm for the proper functioning of the cell. The cytoplasm is located inside the membrane of a cell. A gelatinous substance composed mainly of water, salts and proteins that locates inside the nucleus, eukaryotic cells, the endoplasmic reticulum and the mitochondria. All of this is made up of a set of proteins that give it a structure called the cytoskeleton.

The cytoplasm contains:

  1. Salt (1%)
  2. Sugar (4-6%),
  3. Amino acids and proteins (10-12%),
  4. Lipids and fats (2-3%) enzymes,
  5. Up to 80% water.

Read : Cell structure & Function

Defination of Cytoplasm

Cytoplasm is the inner colloidal semi-liquid environment of the cell, separated from the external environment by the cell membrane, in which the nucleus and all membrane organelles and the non-membrane structure are located.

Cytoplasm Meaning 

At the beginning of cytology (the branch of science that studies cells), it was believed that a living cell housed a viscous liquid in which the nucleus was immersed. This liquid took the name of cytoplasm. What do you  Cytoplasm mean : "Cyto" means "cell", "plasma" means "material", so it is the "material of the cell". It means plasma or forming substance. cytoplasm is also known as protoplasm.

History of cytoplasm:

Who discovered the cytoplasm was the scientist Robert Hooke in the year 1665 . He looked at the cytoplasm through a microscope and it seemed like he was looking at a honeycomb through a microscope.

Robert Hooke: cytoplasm

Cytoplasm Location :

The cytoplasm is located inside the membrane of a cell. The cytoplasm is found in both eukaryotic and prokaryotic cells . But it is within eukaryotic cells that this cytoplasm is composed of:

Smooth endoplasmic reticulum.

Rough endoplasmic reticulum. It is present in eukaryotic cells. Not in prokaryotes. The combination of both is known as a membrane network.

Cytoplasm in Prokaryotic cells

The cytoplasm of prokaryotic cells is composed of cytosol and has no membrane structures or membrane systems. It is worth remembering that this type of cell, typical of bacteria and archaea, has no nucleus and its organization is relatively simple, with the genetic material directly immersed in the cytosol. This, in turn, contains thousands of ribosomes, granulations connected to RNA , whose function is to produce protein. The prokaryotic cell cytoplasm also contains the primary genetic material, since there is no specific nuclear membrane. These cells are usually smaller compared to eukaryotes, and their cytoplasm is simpler organism.

Read : Structure and function of prokaryotic cells 

Cytopkasm in Eukaryotic cell / Cytoplasm in plant cell and animal cell 

The eukaryotic cells  such as plant cell, animal cell, protozoa and fungi) are much more complex structure than prokaryotes. Its cytoplasm, in addition to being filled with cytosol, has several membranous structures, known as cytoplasmic organelles, and a network of tubes and filaments of protein called the cytoskeleton .

Read :  Structure and function of  Eukaryotic cells 

Structure of Cytoplasm 

Structure of Cytoplasm

The cytoplasm is multifunctional as it does not resemble any liquid found in the physical world, as it contains the fluids that are usually studied to understand the diffusion of some materials dissolved in an aqueous environment. The cytoplasm is a complex and crowded system that contains a wide range of particles; From electrolytes and small molecules, to proteins and mega-complexes, multi-protein and organelles.

These components are transported through the cell according to their requirements, according to a detailed cytoskeleton, and with the help of specialized motor proteins, the movement of such large particles also changes the physical properties of the cytosol.

The physical nature of the cytoplasm changes, so sometimes it spreads rapidly through the cell, making the cytoplasm resemble a colloidal solution, and at other times, it manifests properties similar to gel or glass, it is said That it possesses the properties of both viscous and elastic materials, so its shape is gradually changed by applying external force, and then be able to recover its original shape with minimal energy loss.

Parts of the cytoplasm close to the cell membrane are more durable than those in the interior that resemble free-flowing fluids. These changes in cytoplasm depend on metabolic processes within the cell and play an important role in completing certain functions and protecting the cell from stress factors.

Components of the cytoplasm : 

This state can not only vary from one organism to another  but it can also present variations from one cell to another of the same organism. Within the cytoplasm there are different elements that fulfill different functions:

1. Cytoplasmic matrix 

2. Cytoskeleton 

3. Cell Organelles 

4. Cell Inclusions 

Cytoplasmic matrix/ Hyaloplasm - 

  1. Cytoplasmic matrix is also known as hyaloplasm or cytosol.
  2.  It is the clear fluid part of the cytoplasm which can exist in two States, sol and gel
  3. Plasmasol is internal part of the cytoplasm and called endoplast.
  4. Plasmagel is present below the plasma membrane and that's why called as ectoplasm.
  5. Its colloidal cell structure is colorless. 
  6. Cytoplasmic consists of soluble proteins, RNA, polysaccharides, lipids and cellular structures present in a certain way: membranes, organelles, inclusions.

Functions of cytoplasmic matrix

  1.  The matrix contains raw materials and provide the same to the cell organelles for their functioning. 
  2.  The products of cell organelles are passed out into the cytoplasmic matrix.
  3.  The matrix is the seat of synthesis of number of biochemical products such as fats, nucleotides, coenzymes etc
  4.  Many catabolic reactions are occurs in the cytoplasmic matrix like anaerobic respiration and pentose pathway type of Aerobic respiration occurs in the matrix of cytoplasm.
  5.  The cytoplasmic matrix always in motion this helps in distribution of various materials inside the cell.

The cytoskeleton , or the intracellular skeleton

The term cytoskeleton was first given by Russian scientist Nikolai K Koltsov in 1903. The cytoskeleton is an important component of the cytoplasm. It is a network of intertwine protein fibers. The cytoskeleton is very dynamic in nature as it maintains breakdown and rebuilding in parts. It is present in all prokaryotic cells and eukaryotic cells which are plant, animal and fungi cells. The proteins that make up the cytoskeleton in the cells of different organisms are different and have varied properties and interactions.

The cytoskeleton of human and animal cells contains three main protein components - microfilaments called actin, which are microtubules called tibulin and intermediate filaments. The cytoskeleton is the part of the cytoplasm that helps provide shape and structure to the cell. It also provides mechanical resistance that prevents the cell from collapsing. The cytoskeleton contracts and relaxes that allows the cell and its environment to change shape while it passes through narrower areas of the body. This feature helps with cellular migration.

The cytoskeleton plays a major role in the exchange of signals between cells, the absorption of ions from the extracellular fluid (endocytosis), the separation of chromosomes during cell division and the division of the mother cells into two daughter cells (cytokinesis). The cytoskeleton aids in cellular movement of molecules and nutrients. The cytoskeleton is also believed to serve as a template for building the cell wall, and it also forms certain structures of cellular movement such as sella, cilia, lamipodas and podosomes.

A system of protein configurations - microtubules and microfibers - performs a supportive function in the cell, is involved in changing the cell's shape and movement, and provides a specific arrangement of enzymes in the cell.

Cell Organelles - 

These are stable cellular structures that perform certain functions that guarantee all the processes of cell life (movement, respiration, nutrition, synthesis, transport, preservation, and transmission of genetic information).

Eukaryotic organelles are divided into:

  1. Two membranes Structure like mitochondria, plastids, Nucleus 
  2. Single membrane like endoplasmic reticulum, Golgi apparatus (complex), lysosomes, vacuoles);
  3. Non-membranous  like flagellum, cilia, pseudomembranous, myofascial).

Cell Inclusions :

Cell inclusions are nonliving present in the cell whether they are soluble or insoluble inorganic or organic and present in vacuoles, cytoplasm or cell wall. They are also called ergastic bodies or duetoplamic material. Cell inclusions are of three types :  

  1. Reserve food material 
  2. Secretory and excretory material and 
  3. Mineral matter
Cellular inclusions may include a wide range of biochemicals, such as small crystals of proteins, dyes, carbohydrates, and fats, as all cells, especially those in tissues such as adipose tissue, contain droplets of lipids in the form of triglycerides used to create cellular membranes, which are excellent stores of energy. Lipids can generate twice as much adenosine triphosphate (ATP) per gram compared to carbohydrates But the process of releasing energy from triglycerides is abundant with oxygen consumption, so all cells also contain glycogen stores as cytoplasmic inclusions, 

Crystals are another type of cytoplasmic inclusions found in many cells, and have a special function in the inner ear cells (maintain homeostasis), and their presence in testicular cells appears to be associated with morbidity and fertility.

Read : Ribosomes 

Theories regarding physical structure of cytoplasm : 

(a) Granular Theory (Altmann 1893): The cytoplasm consists of tiny granules evently suspended in a fluid medium.

(b) Fibrillar theory (Flemming): Protoplasm consists of fine threads, suspended in a homogenous fluid ground substance, filbrillae, the hyaloplasm.

(c) Reticular theory (Heitzmann): Protoplasm consists of a network, the reticulum, formed by fibrillae and holding a fluid, the hyaloplasm, in the


(d) Alveolar theory (Butschli, 1892): Protoplasm consists of separate but often crowded fluid filled spheres, or vacuoles, called the alveoli, suspended in a continuous viscous fluid, the matrix.

(e) Colloidal Theory (Fisher, 1894): It is the generally accepted theory. The protoplasm is a complex mixture of two types of aqueous solutions: a colloidal solution of organic compounds and a molecular substance of both inorganic and organic compounds.

Read : Animal cell structure and function 

Main Functions of Cytoplasm 

● The cytoplasm provides  support to the cell and suspend cell organelles and cellular molecules within it.

● The cytoplasm is the site for most of the metabolic reactions of the cells.

● Many metabolic processes occur in the cytoplasm like  protein synthesis, the first stage of cellular respiration (known as glycolysis), mitosis, and meiosis etc.

● One of the important functions of cytoplasm is that it provides proper shape to cell. It fills the cells thus allowing the organelles to remain in place.

● The cytoplasm acts as a regulator and protects the cell's genetic material as well as cellular organisms from damage by motion and collision with other cells.

● Cytoplasm contains many enzymes that are crucial in the break down of the waste products and to perform enzymatic reactions.

● Another important function of cytoplasm is it is involved in the transportation and removal of waste products from the cells through vesicles.

● Glycolysis occurs in cytoplasm. This reaction provides intermediates used by mitochondria to generate ATP.

● The main function of cytoplasm  is it allows cells to maintain their turgidity, which enables the cells to hold their proper shape. 

● Translation of mRNA into proteins in ribosomes also occurs primarily in the cytoplasm.

● In cytoplasm cyclosis occurs also called Cytoplasmic streaming ( The process in which substances are circulated within a cell. ) Cyclosus occurs in a different types such as plant cells, amoeba, protozoa, and fungi etc. 

● Cytoplasm functions as storage site, Various chemical molecules like lipids, fats, starch, etc) can be found floating within cytoplasm.

● The cytoplasm is rapidly realigned during cell division and the microtubules are formed into a spindle that attaches to the chromosomes and separates them into two daughter cells.

● The cytoplasm also contains monomers that create the cytoskeleton, which is necessary for cells to have a specialized shape, in addition to being important for normal cell activities.For example, neurons with their long axons need intermediate filaments, fine tubes, and actin filaments to secure a frame.

FAQs about cytoplasm

What is the cytoplasm?

The cytoplasm is the gelatinous fluid that fills the inside of a cell. It is made up of water, salts, and various organic molecules. Some intracellular organelles, such as the nucleus and mitochondria, are surrounded by membranes that separate them from the cytoplasm.

How is the cytoplasm identified?

The cytoplasm is the internal environment of the cell. It is a colloidal system with a gelatinous and heterogeneous consistency, composed of organelles and hyaloplasm. It is located between the cytoplasmic membrane and the cell nucleus. The cytoplasm comprises the entire volume of the cell except for its nucleus.

How is the cytoplasm made?

It is made up of the cytosol, the cytoskeleton, and the cellular organelles. ... The cytoskeleton and ribosomes float in it. It is made up of 85% water with a high content of colloidal dispersed substances (protides, lipids, carbohydrates, nucleic acids and nucleotides as well as dissolved salts.

How do you see the cytoplasm of the cell under the microscope?

Under the light microscope, the cytoplasm of living cells appears as a relatively empty structure. However, even before the beginning of the 20th century, examination of stained sections of animal tissues suggested the existence of an extensive network of membranes within the cytoplasm.

What kinds of cell has DNA in the cytoplasm?

All cells, prokaryotic and eukaryotic, contain DNA in their cells. In eukaryotic cells, DNA is contained within the cell nucleus, while in prokaryotic cells, which do not have a defined nucleus, the genetic material is dispersed in the cell cytoplasm.

What is the role of the cytoplasm in the cell?

The cytoplasm is responsible for holding the components of the cell and protects them from damage. It stores the molecules required for cellular processes and is also responsible for giving the cell its shape.

What are the components of cytosol?

The cytosol consists mostly of water, dissolved ions, small molecules, and large water-soluble molecules (such as proteins). The majority of these non-protein molecules have a molecular mass of less than 300 Da.

What are the organelles found inside the cytoplasm? 



Golgi apparatus;

Lysis particles;

Vacuoles (in plants and fungi);

Cell center

Plastids (in plants);

Cilia and flagella;

Fine strands.

Microscopic tubes.