9th Class Science The Fundamental Unit of Life Introduction

       Introduction

We know that there are different kinds of living organisms found on the earth surface. It varies from unicellular to multicellular organisms. These organisms are bacteria, protista, fungi, virus, plant and animals. The bodies of all the organisms are made up of smallest unit called cell. Thus, cell are the basic unit of all life forms found on the earth surface. The cell was first observed by Robert Hook in 1665. He saw that the cork resembled the structure of honey comb consisting of many compartments. He observed this cell for the first time in the self made microscope. At that time the structure was not clear as the microscope was not of very high power. Later on with improved microscope in 1674, Leeuwenhoek discovered the free living cell in ponds. It was Robert Brown in 1831 who discovered the nucleus of the cell. The term protoplasm was proposed by Purkinje in 1839. Later in the same year the cell theory was proposed by two biologists Schleiden and Schwann. This was expanded by Virchow in 1855 saying that all the cell arises from preexisting cell..