Cell Theory The Cell Theory states that all organisms are composed of similar units of organization, called cells. The concept was formally articulated in 1839 by Schleiden and Schwann and has remained as the foundation of modern biology. Formulation of the cell theory In 1838 Theodor Schwann and Matthias Schleiden were talking about their studies on cells. It has been suggested that when Schwann heard Schleiden describe plant cells with nuclei, he was stuck by the similarity of these plant cells to cells he had observed in animal tissues. The two published his book on animal and plant cells the next year.

Schwann summarized his observations into three conclusions about cells. 1. The cell is the unit of structure, physiology, and organization in living things. 2. The cell retains a dual existence as a distinct entity and building block in the construction of organisms. 3.

Cells form by free-cell formation, similar to the formation of crystals. We know today that the first two tenets are right, but the third is wrong. The cell theory include: 1. All known living things are made up of cells. 2. The cell is structural and functional unit of all living things.

3. All cells come from pre-existing cells by division. 4. Cells contains hereditary information whish is passed from cell to cell during cell division.

5. All cells are basically the same in chemical composition. 6. All energy flow of life occurs within cells. With any theory, its tenets are based upon previous observations and facts. The cell theory is no different being founded upon the observations of many.

For the first 150 years, the cell theory was just a structural idea. This structural view whish is found in most text books describes the components of a cell and their fate in cell reproduction. But cell biology has focused on DNA and its informational features. Today we look at the cell as a unit of self -control. The description of a cell must includes ideas about how genetic information is converted to structure. There are two different types of cells: Prokaryote: do not have a nucleus of membranes surrounding its organelles.

Example: Bacteria Eukaryote: do have a nucleus and organelles with membranes surrounding them. Example: plants, and animals.