GROUP PROTOZOA

The group protozoa includes the phyla that are considered animal-like because most members of these groups live by ingesting food, rather than synthesizing their own food, as in plants. Protozoans are classified primarily by their means of locomotion.

Amoebas

Amoebas are characterized by the possession of pseudopodia (singular: pseudopodium). These are flowing extensions of the cell which are used for feeding in all members of the group and for locomotion in some. This group includes the familiar amoebas, as well as shelled forms. They are either asymmetrical or have spherical symmetry. Amoebas reproduce asexually, but they do not show the typical stages of mitosis. There is no meiosis among amoebas, and they do not form spores.

Amoeba

Examine the stained prepared slide of Amoeba, shown on the right. Study the general form and structure by observing the slide at low, medium, and high magnification. In the mid-magnification view, locate (by moving the arrow over the structures described) the nucleus, endoplasm, ectoplasm, and pseudopodia. Using the high-magnification view, also locate contractile vacuoles and food vacuoles.

Next, observe a video clip of living amoeba from culture. Examine these cells as you did the fixed cells. Although it will be more difficult to see some of the organelles on a living animal, identify as many organelles as possible. Observe the amoeba feeding and moving. How are the pseudopodia used? Draw a sequence showing how one of the organisms you observed moves or feeds.

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