Cytoplasm: Definition, Structure, Functions and Biochemical Reactions

It is a colorless gel-like fluid that fills the area between the cell membrane and the nucleus.

Being a gel-like substance, the cytoplasm is made up of water (70% to 90%) and salt.

Cytoplasm has two types, namely endoplasm and ectoplasm. Endoplasm is the granular region (consisting of small grains) on the inside of the cell. Ectoplasm, on the other hand, is the non-granular part found in the outer region of the cytoplasm.

Within the cytoplasm there are several structures with different functions. As such, this semitransparent cell space plays a vital role in various metabolic pathways and cellular processes such as glycolysis and cell division.

However, that is not the only function of the cytoplasm. It has numerous roles.

Cytoplasm structure

As mentioned, within the cytoplasm there are several structures that have important functions in the proper functioning of the cell, including the following:


The cytosol is the aqueous space between the various organelles present in the cytoplasm, which is approximately 70% of the total volume of a cell.

Several molecules are present in this part of the cell, such as soluble proteins (proteasomes), salt, and water. Furthermore, the cytosol also contains fatty acids, amino acids, carbohydrates, and enzymes.

In addition to molecules, filaments (a long chain of proteins) are also found in this fluid substance that form the cytoskeleton, which shapes a cell and contains the various organelles.

The cytoskeleton has two structures, which are microfilaments and microtubules. The main role of microfilaments is to help the movement of various substances in the cell, while microtubules help organelles to move.


An organelle is a small organ that has a specific role in cell survival. The various organelles in the cytoplasm are the Golgi apparatus, endoplasmic reticulum, mitochondria, ribosomes, vacuoles, and lysosomes.

A plant cell has an additional organelle, which is a chloroplast.

Golgi apparatus

The Golgi apparatus or Golgi complex is made up of cisterns or flattened tubes or sacs. The main role of this organelle is to pack and transport proteins to various places inside and outside the cell. Furthermore, this cytoplasmic structure plays a role in the transport of lipids in the cell.

Endoplasmic reticulum (ER)

The endoplasmic reticulum is the sac organelle present in the cytoplasm, which is also composed of cisternae. This organelle has two types:

  • The rough ER where ribosomes bind.
  • The soft ER that does not have any ribosomes.

One of the main functions of this organelle is to transport proteins to the Golgi complex. In addition, it also helps in the synthesis of steroids and proteins.

Lastly, it also has a role in the production and storage of glycogen, the stored form of glucose.


Known as the cell’s energy source, the mitochondrion is present in most eukaryotic cells. The main function of this organelle is to produce and store adenosine triphosphate (ATP), the energy-carrying molecules of living organisms.


Ribosomes are the organelles where protein synthesis occurs. These structures can be found moving freely within the cytosol or attached to the rough ER.

A ribosome has two components, namely the small and large ribosomal subunit. The large subunit forms polypeptide chains by binding to amino acids, while the small subunit reads mRNA.


Vacuoles are sac-like organelles that have no definite shape and contain water, enzymes, and molecules. Vacuoles have variable functions depending on the type of cell.

Usually the main function of this structure is to isolate and store waste materials. In addition, it also maintains the acidic pH of the cell.


Commonly found in animal cells, lysosomes have enzymes that break down waste products and dead organelles.


As the vital structure of a plant cell, the chloroplast is responsible for carrying out the process known as photosynthesis.

This process occurs when chlorophyll gets energy from the sun and transforms the energy into an organic molecule. Apart from photosynthesis, this organelle has a role in the production of fatty acids and amino acids.

Cytoplasmic inclusions

In the cytosol there are tiny, insoluble molecules known as cytoplasmic inclusions. These molecules are grain-like particles, however, they are not enclosed in a membrane. These particles will vary depending on the type of cell.

The most common inclusion is lipid droplets that act as the storage area for lipids like sterols and fatty acids. In a plant cell, its cytoplasm has inclusions ranging from crystals of silicon dioxide or calcium oxalate that store glycogen and starch.

Cytoplasmic inclusions contain nutrients that a cell can use when needed. Apart from that, it can also store waste materials, a cell can eliminate through exocytosis.

Cytoplasm functions

Although the cytoplasm is a simple structure of the cell, it provides numerous important functions, including the following:

Cell shape

Without the cytoplasm, a cell is an empty membrane with a flat shape. Note that this gelatinous substance contains the various organelles and protects these small structures from colliding with each other.

The cytosol has several compartments enclosed by a membrane, so each organelle has its own space.

Transportation of different materials

This semi-fluid part of the cell allows the occurrence of cytoplasmic transmission, a process of transporting nutrients, proteins, metabolites and genetic information from one organelle to another. This process is possible due to the microfilaments of the cytoskeleton.

Also, a cell can move due to cytoplasmic transmission. Some cells can change position with the help of cilia, the hair-like structures outside a cell.

However, for a cell without cilia, movement is only possible through cytoplasmic transmission.

Site of various biochemical reactions

Various biochemical reactions occur in the cytoplasm that is vital for the proper functioning of the cell. Examples of these processes are protein synthesis, cytokinesis, anaerobic glycolysis, and cell reproduction.

Other than that, each organelle in the cytoplasm has specific functions necessary for cell survival and optimal performance. Cell division, growth and expansion are examples of the processes carried out by these organelles.

Finally, the cytoplasm has enzymes that help break down the macromolecules required by organelles. An example is the enzyme pyruvate, which breaks down the glucose needed by the mitochondria.

In addition to glycolysis, pyruvate is also a catalyst in the synthesis or production of amino acids and fatty acids.


Due to cytoplasmic inclusions, a cell can store surplus nutrients that the organelles can use when needed. Furthermore, these inclusions can also store metabolic waste products until the cell dissolves and removes these substances.