Paramecium caudatum

Used in: Diversity of Life
Paramecia—Paramecium caudatum

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Background. Paramecia are single-celled ciliated protists found in freshwater ponds. They feed on microorganisms such as bacteria, algae, and yeasts, sweeping the food down the oral groove, into the mouth. Their movement is characterized by whiplike movement of the cilia, small hair-like projections that are arranged along the outside of their bodies. They spiral through the water until running into an obstacle, at which point the cilia "reverse course" so the paramecium can swim backwards and try again. Paramecia have two nuclei and reproduce asexually, by binary fission. A paramecium can also exchange genetic material with another via the process of conjugation.

Acquiring paramecia. You can purchase Paramecium caudatum from Delta Education or a biological supply house. This species is a classic classroom organism, hardy and large enough for students to easily observe using a light microscope. Purchase enough to "spike" a sample of water that students will use for preparing slides of elodea leaves and to use in Part 2 of Investigation 3 when students will focus specifically on study of the organism itself.

What to do when they arrive. Open the shipping container, remove the culture jar, and loosen the lid on the jar. Aerate the culture using the pipette supplied, bubbling air through the water. Repeat several times to oxygenate the water. After about 15 minutes, use a dropper or the pipette to obtain organisms, gathering them from around the barley (or other food source). Prepare a wet-mount slide and look for paramecia using a microscope.

Caring for paramecia. Keep the culture in ambient light at room temperature with the lid placed lightly over the jar. Aerate the container daily. After several weeks, the food may be consumed, if you wish to maintain the culture, feed the paramecia with several grains of boiled barley or wheat seed. Add bottled water as needed. Do not add pond water unless you want other organisms to be introduced.

What to do with them when the investigations are completed. Do not dispose of paramecia outside. Slides can be rinsed off into the sink. If you do not wish to maintain the culture or pass it on to a colleague, you can allow the water to evaporate, seal the jar with the lid and toss in the garbage.