1 class periods of 45 minutes each
Small Groups
Observations of pond water help students to form classifications of microorganisms.
Each group of 2-4 students will need:
The purpose of this activity is to observe, describe, and classify microorganisms found in water sources (such as ponds, puddles, or lakes).
Protozoa cultures can be ordered from a biological supply house, collected from local water sources, or you can make your own.
The protozoans are excellent microorganisms for students to observe. Protozoans were one of the first forms of animal-like life. They are found in lakes, seas, oceans, rivers, and ponds. They are animal-like in that they must find outside sources of food and can move around freely, but they are so small (single-celled) they are placed in their own kingdom.
Amoeba are very simple and look much like a blob of jelly. Some amoebas can be seen without a microscope, but most are microorganisms. Amoebas have no cell wall, but, with their cell membrane, they can extend themselves. Their extension is called a pseudopod . The amoeba uses its pseudopod to pull itself along and also to catch food.
Ciliates are a group of protozoans that have hair-like projections on the outside of their cells called cilia. Cilia help these protozoans move and collect food particles. Paramecia are the most well know, of the ciliates.
Flagellates have a whip-like structure to help them move. There are two kinds. One contains chlorophyll and can make its own food. The other does not contain chlorophyll and must find its food. Euglena and Volvox are protozoans that move with flagella. Euglena are unusual protozoans in that they have chloroplasts, a lot like those found in plants, that allow them to carry out photosynthesis. But unlike plants, their flagella allow them to move from one sunny spot to another.
Sporozoans are protozoans that cannot move on their own. They are parasites and feed off the cells and body fluids of other organisms. Sporozoans form spores which contain their hereditary materials; by releasing these spores into the environment, new sporozoans are formed. For example, the disease malaria is caused by a sporozoan that is carried by the mosquito. You should not expect to see sporozoans in your protozoa cultures, because they are parasitic and do not reside in water.
This lesson may also be repeated in other variations. One such variation would be to use 3-5 different samples of Protozoa cultures from different sources. Students can then observe each sample and compare the number and types of Protozoa found in different areas.
Evaluate student classification systems to check for logical reasoning, and their ability to defend their method of classification.