Video: Protists Locomotion Overview & Methods

Definition and Classification of Protists

Protists are not plants, animals, or fungi. They are classified as eukaryotes. Eukaryotes are organisms with a nucleus and other organelles enclosed in cell membranes. Slime molds, protozoans, and unicellular algae are all eukaryotes. Protists are grouped according to how they move in their environment. These classes are the ciliates, flagellates, and amoeboid.

Ciliates: Locomotion and Feeding

Ciliates use cilia to move through water. Cilia are hair-like projections extending from the cell surface, covering the membrane called the pellicle. Coordinated movement of their cilia enables ciliates to move around in their environment. Ciliates also use their cilia to create currents that carry food to their mouth. Being the largest of the protists, their food consists of bacteria and other smaller protists. Paramecium is an example of a ciliate.

Flagellates: Tail-like Movement and Nutrition

The flagellates are the smallest of the protists. They move using a whip-like projection called a flagellum. Flagellates move their flagella back and forth or rotate them to propel them forward. There are two kinds of flagellates based on how they find their food. Some flagellates move around to find their food; these are heterotrophic flagellates. Others are capable of producing their food through a process known as photosynthesis, and these are called autotrophic flagellates.

Amoeboid Movement and Pseudopodia

Some protists, called amoeboid organisms, have no definite shapes. They move by using false feet or pseudopodia. Amoeboids form these false feet by extending their membrane forward. When the fluid in the membrane fills up the projection, this pulls the rest of the body forward. There is another kind of pseudopodia called axopodia. They are shaped like rods and are covered with membranes. To move, amoeboids project these axopodia forward, causing the axopodia on the opposite side to retract. When cytoplasmic flow occurs, amoeboids roll forward.