Saturday, December 7, 2013

Cells,Discovery of cells & Cell theory

Much of the diversity of forms and functions in living organisms results from small atoms being combinedin different ways to form a number of molecules and molecules form macromolecules. Eventually, thesemacromolecules build cells, tissues, organs and finally, an entire organism.

A cell is the smallest unit of life that can survive and reproduce on its own, given
information in DNA, energy, and raw materials. Some cells live and reproduce
independently. Others do so as part of a multicelled organism.

Discovery of cells
In the middle of the 17th century, one of the pioneers of microscopy, Robert
Hooke (1635–1703), decided to examine a piece of cork tissue with his home-built
microscope. He saw numerous box shaped structures that he thought resembled
row of empty boxes or rooms, so he called them ‘cells’.

Cell theory
Matthias Schleiden and Theodor Schwann, hypothesized that a plant cell is an independent living unit even
when it is part of a plant and both concluded that the tissues of animals as well as plants are composed of
cells and their products. Together, the two scientists recognized that cells have a life of their own even
when they are part of a multicelled body.
Later, physiologist Rudolf Virchow realized that all cells he studied descended from another living cell.
These and many other observations yielded three generalizations that today constitute the cell theory:
1) Every organism is composed of one or more cells
2) Cell is smallest unit having properties of life
3) Continuity of life arises from growth and division of single cells
Thus, Cell theory is that all organisms consist of one or more cells, which are the basic unit of life.

A cell is the smallest unit that shows the properties of life.
These properties include -
• Can survive on its own or has potential to do so
• Is highly organized for metabolism
• Senses and responds to environment
• Has potential to reproduce