Q. Describe the Discovery of the Cell?

Ans: The discovery that living organisms are composed of cells was made by an Englishman, Robert Hooke, in 1665. Hooke used the light microscope, which had been recently invented. He had been studying sections of cork under the microscope, and he coined the term "cell" to describe the cells making up the cork tissue. He felt they resembled the tiny rooms found in monasteries, which at the time were called "cells." Not surprisingly, living cells were first observed by one of the first microscope makers, Anton van Leeuwenhoek, in 1675. These first living organisms he observed were microorganisms found living in pond water.

Over a century later, in the early 1800s, the German scientists Schleiden and Schwann reaffirmed these early discoveries, and another German, Rudolph Virchow, found that cells originate by division of preexisting cells. Schleiden, Schwann, and Virchow are credited with contributing to the formulation of a "theory of cells." This Cell Theory describes the fundamental principles underlying the understanding of cell structure and function. It states: 1.) Cells make up all living things. 2.) The cellular unit makes up the basic structure and function of all living things. 3.) Every cell comes from another preexisting cell.

Since the maximum magnification of light microscopes is only about 1500X, close examination of the contents of the cell awaited the arrival of modern instruments such as transmission and scanning electron microscopes. Scanning and electron microscopes are able to produce much more powerful images of microscopic structures because they utilize electrons rather than light. Resolution refers to the ability to see two objects that are very close together as separate objects, and so, resolving power determines the lower size limit viewable under a microscope. However, the wavelength of the radiation used determines the resolution of the microscope. Since electrons have much smaller wavelengths than light waves, microscopes using electrons are able to resolve objects 1000 times smaller than light microscopes. This translates to an increase in functional magnification of about 1 million times greater than light microscopes. Scanning electron microscopes (SEM) produce 3-dimensional images as opposed to transmission electron microscopes, which produce 2-D images. Electron microscopes are restricted to using non-living prepared specimens, whereas light microscopes can use live material. There are much more powerful microscopes in use today like the scanning tunneling electron microscope that is able to produce images of atoms and molecules.