Cell - A unit of life (Explained)

Do you want to know What is a Cell and its types? What is cell theory? Do you want to learn about different types of cell organelles? want to download Full diagram of Cell organelles?

So, your need is going to be fulfilled. Here is a short brief details about Cell and its parts? You will also read Feature and Function of cell organelles. Let's dive into this article of knowledge about Cell - A unit of Life.

Also Read - Photosynthesis in Plants (Full Explanation with diagram)

What is a cell?

A cell is a functional and structural unit of all living organisms.

  • Functional:- All the functions of life complete inside the cell.
  • structure:- Body of organisms is composed of the cell.


Therefore, it is known as the basic unit of life. It was first discovered by Robert Hook in dead cork cells. He has explained his observation in his book "MICROGRAPHIA". Anton Von Leeuwenhoek first observed and described the living cells. 

Cell theory:-

Mathias Schleiden-paisarani-com

Cell theory was given by a German botanist Mathias Schleiden and British zoologist Theodore Schwann.

  • Schleiden studied the plant cell and observed that all plant is composed of the cell. 
  • Schwann studied both plants and animals and concluded that all the animals had a thin outer layer, today this layer known as 'plasma membrane', 'cell membrane' or 'plasmalemma'. he also studied plant cells and conclude, the presence of a cell wall is a unique character of the plant. Both studies are in the form of cell theory.


Schleiden and Schwann were not told about how the cell formed?

  • For this answer, new scientist Rudolf Virchow (1855) explained that anew cell is formed from Pre-exciting cells (Omnis cellula-e-cellula).

Cell theory understood in a new form:-

  1. All living organisms are composed of cells & products of cells.
  2. A new cell formed from pre-existing cells.


Type of Cell

There are two types of cell on the basis of organelles.

  1. Prokaryotic Cell
  2. Eukaryotic Cell


Celltypes -paisarani-com


On the Basis of

Prokaryotic Cell

 Eukaryotic Cell

1. Nuclear Membrane Absent Present
2. Membrane-Bound Cell Organelle Absent Present
3. Cell Wall Present Present
4. Flagella Present Present
5. Histon Protein Absent Present
6. Chromosome False True
7. Examples Bacteria, Mycoplasma, BGA, PPLO....etc Plants, Animals, Fungi, Algae....etc


Now, let's discuss cell parts

Plasma membrane

The cell membrane possesses lipid, Protein, Carbohydrates. The composition of lipids and proteins varies in different cell types. It is a universal structure because present in both Prokaryotes and Eukaryotes.  

Structure of cell membrane:-


It is described by fluid mosaic theory and given by a scientist's Singer and Nicolson(1972). This is a new and most famous model for the cell membrane. According to this proteins are embedded or arranged in the phospholipid bilayer. The phospholipid is the main component of the plasma membrane, it forms the continuous boundary. The phospholipid layer gives fluidity to the plasma membrane. The fluid nature of the membrane is important in many functions like cell division, cell growth, the formation of the intracellular junction, secretion, endocytosis, etc.

Proteins are arranged in two manners. 

  1. Totally buried through the complete thickness of the membrane.
  2. Superficially arranged on the surface of lipid. This protein has enzymatic roles.

Cholesterol is also present in the membrane which is more rigid and hard than phospholipid, it provides stability to the plasma membrane.


Cell wall

A non-living outermost covering of Bacteria, Some protistan, fungi, algae, and plants. It is rigid and hard structure. The composition of the plant cell wall is cellulose, hemicellulose, pectins, and proteins.



Type cell wall:-

  1. Primary cell wall:- Thin, elastic, capable of growth, diminished when  cell mature, composed of cellulose, hemicellulose & pectins
  2. Secondary cell wall:-  Rigid and thick, Inner side of the primary cell wall, composed of cellulose, hemicellulose & pectins.
  3. Middle Lamilla:-  Common boundary b/w two cells. It is consists of mainly Ca & Mg pectates. Ca↑.

Functions of cell wall:-

  • Gives the shape of the cell.
  • helps in the cell to cell interactions. 
  • protect the cell from mechanical damage and infections.
  • provides a barrier to undesirable macromolecules.





This term was given by 'Strasburger'. Inside the cell, It is present b/w the Nucleus and Cell membrane. the cytoplasm is the main arena of cellular or biological activity of both plants and animal cells.


Endoplasmic reticulum (ER)

A network of tiny tubular structures present in the cytoplasm. It is only present in Eukaryotic cells.


It has two types:-

  1. Smooth ER
  2. Rough ER

Smooth ER

Rough ER

  • Ribosomes are absent.
  • mainly composed of tubules.
  • Glycogen and lipid metabolism.
  • In animals, steroidal hormone synthesis.
  • 80s ribosome binds with its membrane.
  • mainly composed of cisternae.
  • Protein synthesis and its secretion.


The function of ER -

  1. Mechanical support.
  2. lipoprotein & glycogen synthesis by SER.
  3. protein synthesis & its section by RER.
  4. Intracellular Exchange.


Golgi Complex

Golgi Complex is densely stained structure found near Nucleus. It was first observed by Camillo Golgi who named its 'Golgi bodies'. Cisternae is disc flat shaped, saps like structure. Tubules are branched and irregular tube-like structures. Transition vesicles converted to Mature vesicles.


The function of the Golgi complex:- Performs the function of packaging materials to delivered intra or extracellular targets. Golgi bodies are an important suite for the formation of glycoproteins & glycolipids.



It is the membrane-bound vesicular structure formed by the packaging in the Golgi bodies. The lumen of the lysosome contains a hydrolytic enzyme of pH = 5. The enzyme of lysosomes capable of digesting carbohydrates, proteins, lipids, and nucleic acid. Lysosomes are polymorphic cell organelles.


Type of Lysosome:- 

  1. Primary Lysosome
  2. Secondary Lysosomes (Heterophagosomes)
  3. Residual Body
  4. Autophagic Lysosome

Functions of Lysosomes:-

  • Intracellular Digestion
  • Extracellular Digestion
  • Autolysis



The vacuole is the membrane-bound space found in the cytoplasm. It contains water, excretory products, and other materials that are not useful for the cell. Single Membrane of the vacuole is called Tonoplast. The Vacuole can occupy 90% of the volume of the plant cells. Vacuoles are absent in animal cells.

In the amoeba, the contractile vacuole is important for excretion and in protists, food vacuoles are used for engulfing the food particles.



Mitochondria are also named as -

  • The powerhouse of the cell
  • Cell within cell
  • Most busy and active cell organelles
  • Semi-autonomous cell organelles
  • Endo-symbionts of the cell.

It is the double membrane-bound organelle. It consists of an outer compartment and an inner compartment. The space between both compartments is called perimitochondrial. The outer compartment contains channel protein called porins whose presence makes the outer membrane more permeable. The inner compartment is folded in finger-like projections called cristae. It contains a 70s  type of ribosomes.


The number of mitochondria depends on the physiological activity of the cell. The main function of mitochondria is the site of aerobic respiration and ATP formation.



It is the granular structure first observed by George Palade (1953). They are composed of Ribonucleic acid(RNA) and proteins. It is a membrane-less cell organelle. Ribosome present in both prokaryotic (70s) and eukaryotic (80s) except mammalian RBC. The ribosome is the smallest Cell Organelles.



Ribosomes are also called 

  • Organelle within organelle
  • Protein Factory of cell
  • Cell Engine



The nucleus was first discovered by Robert Brown (1831). The material of the Nucleus stained by the basic dyes (acetocarmine) called chromatin. The nucleus is a double membrane-bound dense protoplasmic body that controls all cellular metabolism and contains the genetic information of the cell.



Important points on Nucleus of Cell:-

  • A eukaryotic cell contains one nucleus.
  • The nucleus is absent in mature phloem sieve tube and mature RBC.
  • Paramoecium has two nuclei.
  • Fungi have many nuclei inside the nuclear membrane.

Structure of Interphase nucleus:- 

  1. Nuclear Membrane - It consists of two parallel membranes with space between them called perinuclear space. It forms a barrier between the material of the nucleus and the cytoplasm. Both membrane combinedly formed a nuclear envelope. By the fusion of both membranes, nuclear pores are formed through which movement of RNA and proteins is possible.
  2. Nuclear Matrix - It is also called nucleoplasm and karyolymph. It is a ground substance of nucleus that contains a number of chemicals like nucleotides, nucleosides, ATP, Proteins, and Enzymes.
  3. Nucleolus - Nucleolus is a spherical and membrane-less structure. It is a site for active ribosomal synthesis. The nucleus is also called the Ribosome factory of the cell.



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Apr 11, 2020, 7:11 PM - Bablu Raj
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