Monday, February 25, 2019

Cell Unit Of Life

Cell Unit Of Life, Notes For SSC And Railway Exams

Cell unit of life, Cell the unit of life, cell is the basic unit of life

In this Post we will learn Biology notes on "Cell Unit Of Life" for upcoming Railway and SSC Exams. It will be very helpfull for the comptative Exams.

Why we consider "Cell the Unit Of Life" ?

All living beings Made up of cells. Cells are called "Building Blocks Of Body". All Physiological, Biological, Genetic, etc activity is done by the cells. That's why Cell is called as the "functional and structural unit of life". We can also say that Cell is the Basic Unit of Life.

  • The study of cells is called cytology.
  • All organism including ourselves, start life as a single cell call the zygote.
  • The first living cell was discovered by Antony van leeuwenhoek.
  • Robert Hook first discovered the cell. He coined the term cell when he saw honeycomb like structure in the section of cork. He only discovered dead cell wall.

Cell Theory

Cell Theory is one of the most Important generalisations of biology. It was put forward by Matthias Schlelden (German botanist) in 1838 and Theodore Schwann (British zoologist).
Cell theory as described today is as follows:-

  • All organisms are composed of one or more cells.
  • Cell is the most basic unit of structure, function and organisation in all organisms.
  • All cells arise from pre-existing living cells.
  • Viruses do not follow cell theory. 

Structure of cell

Cell is consist of three part :-

  1. Cell membrane,
  2. Cytoplasm,
  3. Nucleus

Cell membrane

the cell is enclosed by a thin membrane called the cell membrane or Plasma membrane. It is composed of protein and phospholipid molecules in animal cell. It is selectively permeable in nature.

  • Plant cell have a cell wall surrounding the cell membrane.
  • It is made up of cellulose, a non-living substance.
  • Cotton, jute and coconut fibres are the cell wall of their dead cells.


All the part together inside the plasma membrane excluding nucleus is known as cytoplasm. All metabolic activity occur in it.
each cell has certain specific components within it, known as cell organelles. Various cell organelles perform special function.

These cell organelles are described below in detail

Endoplasmic Reticulum (ER)

  • It was discovered by KR Porter and Albert Claude in 1945.
  • They are the irregular network of tubular double membrane.
  • There are two type of ER i.e smooth ER (No Ribosomes attached) and Rough ER (Ribosomes attached).
  • It support Framework for the cell.It work for synthesis and transport of protein and fat.


  • It was discovered by Richard Altman in 1980 and the term mitochondria was coined by Carl Benda.
  • It release energy from pyruvic acid produced in cytoplasm in the form of ATP and also called as Powerhouse of the cell.
  • It has various shapes but usually sausage like.
  • It has own DNA containing several genes.

Golgi Apparatus (Golgi Body)

  • It was first discovered by camillo Golgi in 1898.
  • It is stacks of flattened membrane sacs.
  • It main function is to carry out the processing of proteins generated in ER.
  • It helps in the transportation of lipids around the cell.
  • It help in synthesis and secretion of enzyme, hormones, etc.


  • Ribosomes were discovered by George Plade in 1953.
  • These are basically composed of RNA and Proteins.
  • It is the smallest cell organelle.
  • It major function is to synthesise proteins in the cell, due to which it also known as factory of Protein in the Cell.


  • A region surrounding the centrioles, located near nucleus.
  • It initiates and regulates cell division.
  • It form spindle fibres with the help of aster during cell division.


It is a major organelle found in the cell of plant and algae.
Based on the type of pigment present , plastid can be classified into the following three types:-


Greenish plastid due to the presence of Chlorophyll and carotenoid, takes part in photosynthesis.


Yellow or reddish in colour due to presence of carotenoid pigment, found in coloured part like flowers, fruits, etc.

Various pigment found in plant - Tomato ( lycopene), carrot ( carotene), beetroot (betanin), bringle (xenthronin), etc.


Colourless, occurs near the nucleus, in non-green cell like roots, underground stems, etc.

They stores starch, fat and protein.


It stores water, food, pigment and waste product.

Plant cell have large vacuoles, while the animal cells have fewer and small vacuoles.


These are certain small particles, crystal in the cytoplasm.

Starch (in plant cell), Glycogen( in animal cell) and fat containing granules serves as food for the cell.


  • It is also known as “Suicidal bags” of the cell, due to presence of powerful hydrolytic enzymes which are able to digest every organic substance in the cell.
  • It destroy foreign substance in body defence system.
  • Intracellular and extracellular digestion is performed by lysosomes. 
  • It help in disposing useless cell and replace them with new cell. 
  • It PH value is 5


Nucleus was discovered by Robert Brown in 1831. It is an important component of the living cell. It is generally spherical or elliptical in shapes and is located in the centre of the cell.

  • It act as major controlling centre of the cell and also called as brain of the cell.
  • It contains network of thread like structure called Chromatin Fibers which contain DNA. 
  • It contain Chromosomes (bears genes that control hereditary characters).


  • Each cell has one or more round shaped nucleoli inside nucleus surrounded by nucleoplasma.
  • It produces ribosomes
  • Participating in protein synthesis by forming and storing RNA. 
  • Dictate Ribosomes to synthesise protein.

Chromatin fibres

Chromosomes carry the genetic character, made of chromatin, which is composed of hereditary units called genes.

It is made up of DNA thereds.

Types of Cell

On the basis of structure, cells are of two basic type -

Prokaryotic cell

Prokaryotic cells are cells that do not have a true nucleus or most other cell organelles. Organisms that have prokaryotic cells are unicellular and called prokaryotes.

Bacteria and archaea are prokaryotes.
Cell unit of life, RRB, SSC, Biology notes

Eukaryotic cell

Eukaryotic cells are cells that contain a nucleus and organelles, and are enclosed by a plasma membrane.

Cell unit of life, biology notes, RRB, SSC exams

Organisms that have eukaryotic cells include protozoa, fungi, plants and animals 

1 SIZE 0.5 - 3 um 2 - 100 um
2 KIND OF CELL single Cell Multicellular
3 NUCLEUS Well defined
nucleus is absent
Well defined
nucleus is present
4 CELL WALL Cell wall is present Cell wall usually absent
5 MITOCHONDRIA Absent Present
6 GOLGI APPARATUS Absent Present
7 E.R Absent Present
8 REPRODUCTION Asexual Most commonly sexual
9 CELL DIVISION Binary fission Mitosis
10 CHLOROPLAST Scattered in
Present in plant and
11 EXAMPLE Archaea, Bacteria Plant and Animals

These are the common differences between Prokaryotic and Eukaryotic cells.

This post "Cell Unit Of Life" is for the students who preparing government Jobs in India and i think this post will help you very much in any comptative exams likes SSC and RRB (RAILWAYS).

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