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 up new cytoplasm, producing substances to be used outside the cell or breaking down food material in order to produce energy.

Nucleus. Each cell has one nucleus, and this is usually a spherical structure (shape of a ball like or globe) contained in the cytoplasm. The function of the nucleus is to control the chemical changes which take place in the cytoplasm. 

Cell wall in plants cell. All plants have cell wall surrounding the cell membrane. This is non-living layer of cellulose, which allows liquids and dissolved substances to pass freely through it.

Vacuole. Most plant cells have a large, fluid-filled space called a vacuole. The vacuole contains cell sap, a watery solution of sugar, salt and sometimes pigments (colored material). This large, central vacuole pushes the cytoplasm aside so that it forms just a thin lining inside the cell wall.

Each structure plays a huge role in building the cells in plants and animals. They perform different specific functions necessary for cell survival.