Lesson 5:
Protozoa
Amoebae
Amoebae, like those shown above, are protozoans which move by extending finger-like protrusions of their cells called pseudopodia. Amoebae are slow-moving and possess a cytoplasm that "flows" against a thin,flexible cell membrane. The flowing action "pushes" the cell membrane and provides the organism with locomotion. Extenstion and contraction of the cell membrane caused by the flowing action of the cytoplasm is referred to as a pseudopodia ("false foot") mode of locomotion, which is used to engulf or capture substances and bring them into the cell. This is called endocytosis (a type of active transport). There are two types of endocytosis. These are phagocytosis (eat) and pinocytosis (drink). You can see several engulfed food particles as circles within each amoebae cell above.
Amoebae itself is found in freshwater, typically on decaying vegetation from streams, also found in salt water, in wet soil, and in animals (including people); but large, naked Amoebae are not especially common in nature. However, because of the ease with which they may be obtained and kept in the lab, they are common objects of study, both as representative protozoa and to demonstrate cell structure and function.
A good method of collecting amoebae is to lower a jar upside down until it is just above the sediment surface. Then one should slowly let the air escape so the top layer will be sucked into the jar. Deeper sediment should not be allowed to get sucked in. It is possible to slowly move the jar when tilting it to collect from a larger area. If no amoebae are found, one can try introducing some rice grains into the jar and waiting for them to start to rot. The bacteria eating the rice will be eaten by the amoebae, thus increasing the population and making them easier to find.
Amoebae usually are present in high numbers during start up of a treatment plant recovery from a toxic discharge to the treatment plant or low dissolved oxygen levels. If amoebae are present as the dominant protozoan group, this could indicate an unstable wastewater environment and a sludge that is in poor health.
