BIOLOGY

First topic : CELL MORPHOLOGY.STRUCTURAL COMPONENTS OF THE CELL

The cell theory, in its modern form, includes the following three principles :

1. All organisms are composed of one or more cells, within which the life processes of metabolism and heredity occur.
2. Cells are the smallest living things, the basic unit of organization of all organisms.
3. Cells arise only by division of a previously existing cell. Although life evolved spontaneously in the hydrogen-rich environment of the early earth, biologists have concluded that additional cells are not originating at present. Rather, life on earth represents a continuous line of descent from those early cells.
The conclusion is: all the organisms on earth are cells or aggregates of cells, and all of us are descendants of the first cells.