THE CELL

      A cell is made up of repeating basic units, which inspired Robert Hooke to coin of the term “cell”. All living organisms are made up of these basic units of life i.e., “cells”.

     The cell has same central position to biology as the atom in physics.

     This concept was further developed by two German biologist- M. Schleiden and Theodore Schwann in 1839, who formulated the “Cell Theory”. According to this theory, cells are basic units of structure as well as function. Later on, one more idea that all the cells arise from pre-existing cells was added by Rudolph Virchow, a German Physician, in 1855.

All cells have some basic features:

(i)A selectively permeable membrane – the plasma membrane

(ii)A jelly-like, semi fluid substance – the cytosol (All the cellular organelles are present in this cytosol forming the matrix of the cell.)

(iii)Genes in the form of DNA (the hereditary molecule)

(iv)Tiny, rounded structure meat for protein synthesis –the ribosomes

 

      There are two types of cells – prokaryotic and eukaryotic cells. They differ in one major aspect which is the location of DNA. In prokaryotes, (Gr –pro before and karyon – nucleus), viz. found in bacteria and blue –green algae, (I) DNA is naked and concentrated in region that is not membrane bound, called the nucleoid region. (2) Further, they have no membranous organelles except ribosomes. They cells are some primitive.

      On the other hand, eukaryote, (Gr. ‘eu’ – true, ‘karyon’ – nucleus) which includes higher organism’s viz plants, animals and other multi-cellular organisms, have most of their DNA present in a double membrane bound organelle, called nucleus. Further, they have a number of other membrane-enclosed organelles as well.