Bio-Mr.Willets
Lab-Protozoans
Kingdom Protista includes basically two types of organisms. One kind is the protozoans ("first animals") which are unicellular and heterotrophic. These were originally included in the Animal Kingdom. The other kind is the algae which are unicellular or colonial and autotrophic. These were originally in the Plant Kingdom. Algae will be covered at another time.
Protozoans are classified into 4 phyla based on how they move. Phylum Sarcodina includes protozoans that move by changing shape. The most famous member of this phylum is the ameba. Phylum Ciliophora are those protozoans that move using cilia. These are called ciliates. Phylum Zoomastigina are those protozoans that move using a flagellum. These are called flagellates or zooflagellates. The final protozoan phylum is Phylum Sporozoa. Members of this phylum do not move and are all parasites.
Slides of living ameba will be available from the front of the room. (Notice that the name 'ameba' is spelled differently when used as a scientific name.) Search for a living ameba using low or scanning power. The TV scope will have one to look at. The living ameba has a grey-black speckled appearance. The cytoplasm should be moving inside the cell. You may switch to high power when you have found one.
Notice that the edge of the cytoplasm looks clear. This is called ectoplasm. The grainier looking inner cytoplasm is called endoplasm. As the cytoplasm flows, portions of the ameba stick out to form pseudopods (false feet). As pseudopods surround food, they form food vacuoles inside the cell. These might be seen as circular areas. This method of feeding is called phagocytosis.
Since most ameba live in fresh water (hypotonic solution), excess water must be removed from the cell by a contractile vacuole. This is a clear circular structure that periodically disappears when it squeezes the water out. You probably will not see this happening.
The ameba has a nucleus but it probably is not visible. A stain could be used to make it darker but this would kill the ameba.
A) On a separate sheet, make an outline of the shape of the ameba. Use arrows inside the cell to show the direction of cytoplasm flow. B)Make a second diagram a few minutes later showing how it changed shape. These two diagrams should be small.
C) Make a larger diagram of the ameba and label the following parts: ectoplasm, endoplasm, pseudopod, nucleus, food vacuoles, contractile vacuole. Use the books to help draw parts not seen. Estimate the average distance from one side of the ameba to the other.
Compared to the ameba, the paramecium is a speedy little fellow and because of this, it is hard to get a good look at one unless we slow it down. We will use methyl cellulose (wallpaper paste) to do this.
Paramecium is a ciliated protozoan and a member of Phylum Ciliophora.
Slides of living paramecium will be available at the front of the room. Search for a paramecium using low power. With a little luck, you will find one that is stuck and can be observed using high power. The TV scope should have one to look at. The diagram in the book is helpful.
Look for the beating cilia along the edge of the cell. Note the scooped out section along one side. This is the oral groove. Cilia push food particles into the oral groove and through the mouth where they enter a tube (the gullet) and finally end up in a food vacuole where they are digested.
Look for food vacuoles throughout the paramecium. They are round and have bits of food in them. When the food is completely digested, any wastes are taken to the anal pore and released.
The paramecium has two contractile vacuoles to remove excess water. They are located at either end of the organism. If you watch for a minute or so, you should see them squeeze shut to remove the water. I am hopeful that this will be visible on the TV scope.
Paramecium has one large nucleus (macronucleus) and often has several smaller ones (micronuclei). These cannot be seen without staining.
Use your book to help draw the basic shape of the paramecium on a separate sheet. Draw in and label the following structures: cilia, both contractile vacuoles, food vacuoles, macronucleus, micronucleus, oral groove, anal pore. Use the book to help locate structures not seen. Estimate the length of the cell.
Euglena is a flagellated unicellular organism that has chloroplasts for making food but that can eat food when it is dark. Some books put this organism with the protozoans, others put it with the algae. Still others put it in both places.
The TV scope will show Euglena. Look for the flagella whipping about.