OBJECTIVE: The student shall demonstrate their ability to handle embryos and hazardous materials by fixing eggs in Carnoy's fixative and making observations.
PURPOSE: The major plus of using fixatives, is not so much there preservation ability or even the "stopping" of further action, but their ability to selectively extract the material you don't want to see. This lesson gives students the chance to experience the "Ah Ha!" effect of seeing something in a new way. Most scientific research involves the use of hazardous materials and this lesson also provides important early training in the safe handling of these materials.
SET: The embryo is so opaque, it is hard to see some of the finer structures that we might be interested in. Fixation provides a means of selectively extracting material were are not interested in to allow us to see what we are interested in.
MODEL: Demonstrate how to do the extraction, using safe handling technique.
STRUCTURED PRACTICE: Have students do "dry" runs without solutions until you are confident they are able to handle the hazardous materials.
GUIDED PRACTICE: Watch carefully as students perform the operations.
CLOSURE: What could you see that you could not see before? How would this be useful in asking questions about development?
INDEPENDENT PRACTICE: This lesson is best done after Modified Seawater and Artificial Activation so that students can then apply this technique to furter study the effects of the previous lessons in experiments of their own design.
NOTES: PLEASE NOTE THE TIME NEEDED FOR THIS PROCEDURE. Best extended over a longer period and several days.