Cell: Types, Composition, and Functions of Cell


The cell is a basic structural and functional unit of the body. It consists of two major parts.

  1. Cytoplasm
  2. Nucleus

Types of cell

i)   Nerve cell
ii)  Muscle cell
iii) Connective cell 
iv) Immune cell
v)  Blood Cell

Composition of cell

i)   Water 65-80%
ii)  Proteins
iii) Electrolytes
iv) Lipids
v)  Carbohydrates

Organelle of cell

1. Cell membrane/plasma membrane

The cell membrane/plasma membrane is the outer covering of the cell. It is very thin in nature about 8-10 nanometer.




  1. The cell membrane/plasma membrane provides the passage of the water-soluble substances.
  2. These act as transported by attaching to the cell membrane proteins.
  3. Permit the passage of ions and molecules outside the cell.
  4. The cell membrane/plasma membrane protects the cell organelles.
  5. Some carbohydrates in the plasma membrane are helpful for the binding of hormones (insulin).

2. Cytoplasm

The cytoplasm is part of the cell that covers/ surrounds the cell nucleus. It lies near to the cell membrane.

Zone of cytoplasm:
(i)  Ectoplasm →  near to the cell membrane
(ii) Endoplasm →  near to the nucleus



The cytosol is a clear fluid where all organelles are present.

Clarification of terms

  • Cytosol – the fluid (and suspended molecules of salts, sugars, amino acids, enzymes, etc.) around the organelles.
  • Cytoplasm – the cytosol PLUS the organelles suspended within it (i.e., everything EXCEPT the nucleus)
Cell = Plasma membrane + Cytoplasm (Cytosol + Organelles) + Nucleus

Endoplasmic reticulum

The endoplasmic reticulum is a series of tubular portions in the cytoplasm. 

Types of endoplasmic reticulum

A. Rough surface endoplasmic reticulum (Granular)
B. Smooth surface endoplasmic reticulum (A granular)

The rough-surfaced endoplasmic reticulum


  • Ribosomes are attached to the outer surface of the endoplasmic reticulum.
  • Proteins are synthesized by the ribosome and then transferred to the endoplasmic lumen.

B. Smooth surface endoplasmic reticulum


  • Lipid biosynthesis and intracellular transportation.
  • In the liver there is a large quantity of smooth endoplasmic reticulum is present.
  • It plays a major role in glycogen metabolism.
  • It also helps in the detoxification of various toxins and alcohol.

3. Ribosome

A cell contains a much tiny granular structure known as Ribosomes.
It is a non-membranous organelle in which protein and RNA are present.


Types of ribosomes are depending upon their functions.
i. Endoplasm reticulum ribosomes
               Protein synthesis
ii. Free-floating ribosomes
               Produce cytoplasmic proteins


  • Transcription: It is a formation of messenger RNA (mRNA) from DNA.
  • Translation: Formation of proteins. It is occurred due to messenger RNA (mRNA) and transfer RNA (tRNA).

4. Golgi apparatus

Golgi apparatus is also known as the Golgi body or Golgi complex. It is a membranous organelle, which is responsible for packaging and lysosomes formation.


  • To form lysosomes.
  • To form secreting cells
  • This is the additional distribution center of proteins and liquids from the endoplasmic reticulum to the plasma membrane, lysosomes, and secretin vesicles.
  • It modifies N-oligosaccharides.
  • This is the site for carbohydrates and protein.


Mitochondria is a self-replicating organelle, a thread-like membrane that synthesized high-energy phosphate. Therefore it is known as the powerhouse of cells.
It is composed of two lipid bilayer protein-membrane consist of two parts.
  • a) Outer membrane
  • b) Inner membrane


It has a different size and shape. It is Motile, localize at the intercellular site for maximum energy. It is wide 0.5 – 1 um and Length up to 10 um.


These are elongate in shape, like a cigar shape. These are single and branched.


Proteins and lipids in lower quantity and a small quantity of DNA and RNA are present in it.


A large amount of adenosine triphosphate (ATP) is formed in mitochondria.
Pyruvic acid, amino acids, and fatty acids are converted into acetyl CoA. The acetyl CoA is broken into hydrogen and CO2.

6. Nucleus

The nucleus is a control center of cells. It is responsible for all physiological, biochemical, and reproductive functions of cells. It is mostly present in eukaryotic cells.

Size & Shape:

The nucleus of each cell is usually in spherical size and shape is 4-10 mm in diameter.


It is made by the Nucleus membrane, Nucleus plasma, chromosomes, and Nucleolus.


It consists of Water = 80% and Dry weight = 20% in which DNA 18% and RNa 2% are present.


  • It is a control center of cells.
  • It controls protein synthesis by messenger RNA (mRNA). 
  • It helps in hereditary material transformation. 
  • It controls the cell division.
  • It controls the activity of the cytoplasm.

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