All forms of life, from the biggest trees to the microscopic organisms that swim in the smallest drop of water, are made up of cells.

Big or small, all living things are made of cells.

Most organisms are made up of many types of different cells. Some organisms, called single-celled organisms, have all they need for life in one single cell. They can move, breathe, feed, grow, reproduce, excrete and are sensitive even though each individual exists as a single cell. An example of a single-celled organism is a paramecium.

Organisms which have more than one cell are called multi-cellular organisms. Each type of cell in the organism has a special function. In plants, for example, some cells are in charge of making food using photosynthesis, other cells have the job of absorbing water in the roots and still others are responsible for making the plant rigid so it will not fall over.

© Paul Billiet, Shirley Burchill, Alan Damon and Deborah James 2008