Flexi Says: A cell is the smallest structural and functional unit of an organism. Some organisms, like bacteria, consist of only one cell. Big organisms, like humans, consist of trillions of cells. Cell theory is a scientific theory that explains scientific observations of cells. As with other scientific theories, many hundreds, if not thousands, of experiments support the cell theory. The modern version of the Cell Theory includes:
all known living things are made up of one or more cells,
all living cells arise from pre-existing cells by division,
the cell is the fundamental unit of structure and function in all living organisms,
the activity of an organism depends on the total activity of independent cells,
energy flow (metabolism and biochemistry) occurs within cells,
cells contain hereditary information (DNA) which is passed from cell to cell during cell division,
all cells are basically the same in chemical composition in organisms of similar species.