CELLS

Cells are the basic unit of structure and function for all living things. All living things are made up of cells. Most cells are too small to see without the aide of a microscope. Biologists express their understanding of cells being the basis for structure and function in terms of the cell theory. The cell theory states that 1) all organisms are composed of cells; 2) all cells come from preexisting cells; 3) the cell is the basic living unit of all organisms. These basic principles of the cell theory serve as the foundation for ongoing investigations into cells and the roles of cells in the functioning of all organisms. When the classification of living things are considered, the cell types of the different living organisms serve as one way to place living things into categories. In the six kingdom classification system, Kingdom Monera and Kingdom Archaebacteria are composed of the simplest cells--prokaryotic cell types. The Kingdoms--Plantae, Animalia, Fungi, and Protista include living things composed of very complex cells--eukaryotic cell types.

All cells are composed of a cell membrane, cytoplasm, ribosomes, and nucleic acid (DNA or RNA). Other important structures inside the most complex cells include--nucleus, endoplasmic reticulum, Golgi Apparatus, lysosomes, vacuoles / vessicles, mitochondria--each carrying on a specific job to keep the cell alive, growing, developing and reproducing.