Microorganisms – Protists: Paramecia
Paramecium are unicellular protozoans classified in the Genus Paramecium, and the Kingdom Protista. The Paramecium is commonly found throughout the world in fresh and marine water containing bacteria and decaying organic matter.
Freshwater Paramecium live in quiet or stagnant ponds and are an essential part of the food chain. They feed on algae and other microorganisms, and other small organisms eat them. Freshwater paramecium are described below.
Paramecium are shaped like the sole of a shoe and move by tiny hair-like projections called cilia. The posterior (back) half is slightly wider than the anterior (front) half and is bluntly pointed, while the anterior end is rounded. The entire outer surface of the organism is covered with many hundreds of cilia. Color and label the cilia black.
The paramecium cannot change its shape like the ameba because it has a thick outer membrane called the pellicle. The pellicle surrounds the cell membrane. Color (trace) and label the pellicle navy blue.
There are two types of nuclei (plural of nucleus). The relatively large macronucleus is located near the center of the organism. The macronucleus controls most of the metabolic functions of the cell like respiration, protein synthesis and digestion. Color and label the macronucleus light blue.
The much smaller micronucleus lies partly within a depression on the oral (mouth) side of the macronucleus. The micronucleus is involved primarily in reproduction and hereditary functions. Reproduction in paramecium involves the exchanging of DNA within the micronucleus. In order to do this, two paramecia lie side by side and join at the mouth pore. This process is called conjugation and is a method of sexual reproduction in other microorganisms as well. Color and label the micronucleus dark blue.
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The paramecia that live in freshwater require an organelle to pump out excess water so they do not lyse (burst). These organelles are contractile vacuoles, and there is usually one at each end. The contractile vacuole is surrounded by several radiating canals which collect water from the surrounding cytoplasm (making it appear like a star when filled with water). The contractile vacuoles serve a critical function of osmoregulation, which is balancing the amount of water that accumulates inside the cytoplasm. Color and label both contractile vacuoles purple.
Paramecium are heterotrophs, meaning they must consume food for their energy. The area of the paramecium that appears pinched inward is called the oral groove, which runs about half the length of its body. Cilia sweep food into this area and into the gullet, where food vacuoles are formed. Color and label the oral groove light pink. Color and label the gullet red.
Food vacuoles remain in the cytoplasm until the food is digested. The round food vacuoles contain enzymes to digest the other smaller protozoans that the paramecium feeds on. Undigested food particles are eliminated through the anal pore. Color all food vacuoles yellow Label one food vacuole. Color and label the anal pore brown.
Paramecium can respond to temperature, food, oxygen and toxins and they have a very simple defense mechanism. Just inside the pellicle are threadlike organelles called trichocysts. The paramecium can shoot tiny threads out of the cell to entangle a predator or to make themselves appear bigger. Paramecium are also known to exhibit avoidance behavior, which is where the paramecium moves away from a negative or unpleasant stimulus. Color and label the trichocysts dark green.
There are 2 kinds of cytoplasm in the paramecium. The cytoplasm around the edges is light or clear in color and is called ectoplasm. The rest of the cytoplasm is more dense and appears darker. This is called the endoplasm. Remember that the word "ecto" means outside, and the word "endo" means inside. Color and label the ectoplasm medium green. Color and label the endoplasm light yellow-green.
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Questions:
1. Is the paramecium a unicellular or multicellular organism?
2. To what Genus and Kingdom do paramecium belong?
3. Define heterotroph.
4. What do paramecium eat?
5. How do all Paramecium move?
6. Why can't the paramecium change shape like the amoeba?
7. What do the macronucleus and micronucleus do?
8. Define conjugation.
9. What is the function of the contractile vacuole?
10. What is the oral groove?
11. Wastes exit the paramecium through what structure?
12. What is the function of the trichocysts?
13. Define avoidance behavior.
14. Where do paramecium live?
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