Cells and Tissues
Cell Structure Almost every part of a plant or an animal is made of very tiny structures called cells. Thousands of cells packed together in an orderly way make up the tissues of living organisms which are skin, bone or muscle tissue of an animal or the leaf and stem tissue of a plant. Cells may be very different shapes and sizes, however, all cells have a cell membrane , enclosing the living substance called cytoplasm , which contains a nucleus . Cell membrane. This is a very thin, flexible layer around the cell. Although it is very thin it keeps the cell contents from escaping and mixing with the surroundings. The cell membrane also has control over the substances which are allowed to enter or leave the cell. Cytoplasm. Seen under an ordinary microscope, this looks like a thick liquid with particles in it. Cytoplasm contains enzymes which control the chemical changes taking place in it. There are also a number of tiny structures which play a part in building u...