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Euglena is a common group of freshwater single celled organisms in the Kingdom Protista. Euglena confused early scientists because it is green like a plant and thus carries out photosynthesis. However Euglena moves, something that in the mind of the average person is associated with animals, not plants. Also, unlike plants Euglena does not have a cellulose cell wall.

Early scientists were confused because they wanted to divide up the living world into plants and animals. But evolution is not so clear cut and the result do not always fit our preconceptions. So in science we constantly change our understanding of what things are are as new information becomes available. After all, living things are going to do what they do, evolution has happened and will continue to happen regardless of what we think and how we view the biological world at any given time.
This is what a typical Euglena looks like, The green ovoid structures are the chloroplasts where photosynthesis takes place. Notice the long whip-like structure on the right side of the organism. That is a flagellum which moves the Euglena through the water. Contrary to what you might think, the flagellum pulls the Euglena through the water, somewhat like the propeller of an airplane pulls it through the air. So this Euglenais moving from left to right. 
euglena movieHere is a movie of a Euglena so you can get an idea of how the flagellum moves. The movie is looped and the organism will be seen moving left to right then appear to move back to the left hand side of the frame. 
One really cool feature of Euglena and other related organisms, is the presence of a pigmented organelle, or eyespot, that allows the organism to orient toward or away from light. This is a sensible adaptation since these organisms carry out photosynthesis. The image to the left show the eyespot . The eyespot itself is not sufficient to help the organism turn toward light since the cell is transparent. So the outside of the eyespot is covered by a black pigmented area. The Euglena determines which way turn turn by turning to the direction in which the eyespot is receiving the least light. In this direction the pigmented eyespot is most directly shaded by the black pigmented area. 

Created 6/9/99 pgdVBS Home, Protista navigator Previous Page.