Cells

Cells:- An overview

Diverse forms of living organisms are present in our surrounding.

Like ourselves, all of them are made up of tiny structure called "Cell".

Cells are building blocks of life, they are the basic structural and functional units from which life takes shapes. A cell is smallest living entity in living organism.

For example:-

Shape and structure of plants and animals are different, also shape and structure are different between animals, not only this shape and structure of different part of a same body is also different from each other, all these because of different types of cells.

Know the history of cell

Robert Hooke(1635-1703)

The term"cell" was introduced by Robert Hooke in 1665 after observing the cellular structure of cork(a substance obtained from the bark of a tree) while examining a thin slice of cork under a compound microscope . Hook observed many small compartments resemble honeycomb, these he termed as cell.

Robert Brown(1773-1858)

In 1831, Robert Brown discovered the presence of nucleus in the center of cell

Matthias schleiden (1804-1881)

In 1838, Matthias schleiden, a German physiologist discovered that all plants and tissue are made up of cells, ie ., Cells are fundamental units for all plants.

Theodore Schwann (1810-1882)

In 1839, Theodore Schwann, a German physiologist, discovered that all animal tissue are made up of cells, ie., Cells are fundamental unit of all animals.

Formation of cells

In 1838 and 1839, the two scientist Matthias schleiden (1838) and Theodore Schwann(1839) proposed the cell theory and formulated that all plants and animals are made up of cells.  They however, were unsuccessful in explanation, How new cells forms ?

Later in 1855, Rudolph Virchow further expanded the cell theory by suggesting that all cells arises from pre-existing cells.

According to cell theory:-

• All living organism are composed of cells and products of cells.
• Cells are the basic unit of structure and functions in an organisms.
• All cells arise from pre-existing cells.

Properties of living cells:

1. Generally,a cell is too small that it cannot be seen by nacked eyes.
2. Shape and size of cell varies both within an Organism and between different organisms. The shape and size of cell is related to the specific function it performs.
3. All living cells exhibits certain basic properties like respiration, growth and metabolism.
4. Nerve cells are  one of the longest cells.

Types of Organisms on the basis of cells:-

Organisms are classified into Unicellular organism and Multicellular organism.

Unicellular Organisms:- There are certain organisms that are made up of only a single cell ; such organism are known as unicellular organisms: Example of unicellular organisms are Amoeba and Yeast.

Did you know? The smallest unicellular organism we know is Mycoplasma, a type of bacteria. It's diameter is 0.1 μ.

Multicellular Organisms:- Those organisms which is made up of more than one cell is called multicellular organisms : Examples of Multicellular organisms are humans,trees and animals.

Multicellular organisms can performs a variety of task efficiently due to Division of labour which gives a wide range of adaptability to survive. In Multicellular organism's dead cells plays an important role . For example :- The dead epidermal cells in animals protects the underlaying cells.

Classification of cells:-

Cells are classified into

A) Prokaryotic cell.                   B) Eukaryotic cell

Characterstics	prokaryotes	Eukaryotes
size	cells are small in size	cells vary in size, are generally larger than those in prokaryotes
Nuceus	No nucleus with nuclear membrane	well defined nucleus with nuclear membrane
Membrane-enclosed organelles	Organelles having a membrane around them is absent	Organelles having enclosed membrane.
Cell wall	cell wall is usually present, it's composed of peptidoglycon	cell wall usually present in plants cell, which is composed of cellulose
Genetic material	The genetic materials is present in nucleotide, ie., a properly defined nucleus is absent	The genetic materials is present inside the well defined nucleus