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HUNTING FOR PROTOZOA

Although there are about fifteen thousand species of them, most protozoa are too small to be seen without a microscope. To see some protozoa, prepare a microscope slide by placing a large drop of pond water on it and carefully covering it with a cover glass.

Set the slide on a microscope or a microprojector platform. When focused, move the slide slowly under as the animals are viewed. The protozoan most likely to be observed is the paramecium.

A diagram of this animal can guide students' observations. Students can make their own diagrams (or drawings).

You will see that it has a definite, permanent shape and moves rapidly by the coordinated beating of a great many fine, hair-like structures on its body. The structures are
called "cilia." (Isn't that what our eyelashes are called?)

The dark spots in the animal are nuclei. (The smaller nucleus controls reproduction, and the larger one controls most of the animal's other functions.)

As the animal swims, food is swept into the oral groove and eventually is passed out through the anal pore.

Also observe an amoeba -- a slow moving, clear animal with a constantly changing body shape. It has one nucleus and obtains food by engulfing it.

Obtain several samples of water from a pond, stream, puddle, and faucet. Make a slide for each type, label the slides so they will not get mixed up, then look for similarities and differences in the kinds and numbers of protozoa in the samples.

The idea of protozoa in our drinking water, as well as our bath water, is really gross. Maybe this yuck thought will cause us to be more careful. When we see a sign that says water is polluted, we will have enough sense not to swim in it; certainly we won't drink it.

Place a large drop from a rich culture of protozoa on a microscope slide, and place it under a microscope or on a microprojector. Move the slide slowly until a large
paramecium is found, then follow it. If the sample begins to dry, add more water. Rarely, you will see the paramecium divide to form two paramecia. This type of reproduction is called "fission" (simple cell division). [The next time somebody tells you they are "goin' fishin'," you can ask them why they are going to divide their cells!]

Protozoa can also reproduce by joining together, then dividing (a process called conjugation), but the chances of seeing this in the classroom are slight.

Algae can similarly be observed in hopes of seeing reproduction by fission or conjugation.

---oOo---

Pour equal amounts of pond water (or other water containing a protozoa culture) into three clean jars. Store one in a refrigerator, one in the classroom at room temperature, and one in a warmer location.

After 24 hours, use a medicine dropper to place a large drop from each jar onto different microscope slides. Place cover slips on them, and observe under a microscope or with a microprojector to see what effect the different temperatures had.

 
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