OBJECTIVE: The students shall demonstrate their ability to use dilution techniques by calculating sperm concentration in a serial dilution series.
PURPOSE: What is the ideal sperm concentration? Too much and the eggs will abort, too little and they will not all fertilize. The EPA uses a similar assay to determine the effects of environmental pollution on the very sensitive development of the sea urchin.
SET: What is the ideal sperm concentration? To be consistent in our experiments, how can we ensure we have the same concentration of sperm from day to day?
MODEL: Demonstrate how to use an hemacytometer.
STRUCTURED PRACTICE: The hemacytometer is the only new tool introduced. [See how to use a videomicroscope for class instruction.]
GUIDED PRACTICE: By this time students should be working pretty independently.
CLOSURE: What are some environmental factors that could affect a sperm's ability to fertilize an egg? How could we use what we have just done to test for this effect?