EVOLUTION OF THE CELL
All the living organisms are made up of cells. A living cell may be defined as a compartment enclosed by a membrane that consists of several chemical constituents and is capable of propagating itself by division. Activity of an organism is dependent on the activities of its cells, individually and collectively. Basic structures and functions are common in all cells with certain differences according to their specific needs. As you have already studied in Unit 12 of the Foundation Course in Science and Technology, there are two stages in evolution of the cell; chemical evolution and biological evolution. Chemical evolution started with the formation of organic molecules on the earth which had no life until then. We call it pre-biotic earth. Some of these early molecules developed the ability of producing an exact copy of their own self by self-replication. We can mark this event as the origin of life. Later on, during the course of biological evolution, molecular aggregates organized and formed the cell which was different from the cell as it exists today. We shall trace these events which are based partly on speculation and partly on experimental evidence.