There are many different ways in which living organisms can be classified. Methods are constantly changing with the advent of new technologies and theories. No classification system is accepted universally although the following is a very popular version. If you are a student at the University of Manchester you will be able to access a more detailed CAL package on this subject. Protista is a large and variable group containing both plant and animal characteristics.
Protists are mostly microscopic and have no organs or tissues.
They are single-celled but may occur in colonies. They may be free-living on land or in water, or live in association with other plants and animals. An amoeba is an organism that is readily found in pond water. The outline of the single-celled body changes constantly as it moves and has no permanent shape. Amoebas feed themselves by trapping food particles in the surrounding water.