Cell: Definition, Types, Functions and Division (Part 1)

Cell, in biology, is the basic membrane-bound unit that contains the fundamental molecules of life and of which all living things are composed of. Cells are the smallest structural units of living matter and make up of all living things. A single cell is often a complete organism in itself, such as a bacterium or yeast. Other cells acquire specialized functions as they mature. These cells cooperate with other specialized cells and become the building blocks (Tissue) of large multicellular organisms, such as humans and other animals. Although cells are much larger than atoms, they are still very small.

In 1655, Robert Hook, an English Scientist was inspecting a dried portion of the cork tree with a crude light microscope. during this examination, he came across several microscopic compartments that he termed "cells." This was such a significant discovery that it forever altered basic biology theory and research. 

The smallest known cells are a group of tiny bacteria called mycoplasmas; some of these single-celled organisms are spheres as small as 0.2 μm in diameter (1μm = about 0.000039 inch), with a total mass of 10⁻¹⁴ gram—equal to that of 8,000,000,000 hydrogen atoms. Cells of humans typically have a mass 400,000 times larger than the mass of a single mycoplasma bacterium, but even human cells are only about 20 μm across. It would require a sheet of about 10,000 human cells to cover the head of a pin, and each human organism is composed of more than 30,000,000,000,000 cells.