OBJECTIVE: The student shall demonstrate their ability to think and work in a lab environment by careful observations on later stages of development of the sea urchin, writing up a lab report, and answering the Implications Questions.
PURPOSE: Sea urchins are very similar to humans up through gastrulation. However, we do not go through a pluteus stage. The sea urchin is different, having a different life strategy. Understanding differences helps us to see the necessity of having different organisms for different ecological niches in our environment.
SET: "Ontogeny recapitulates phylogeny." As an organism develops it often shows its phylogenetic heritage by the stages it goes through. See if, in your observations today, you can identify characteristics common to other phyla.
MODEL: 1) show overhead of development in sea urchins
STRUCTURED PRACTICE: Ask and answer questions while introducing the model to insure active participation and check understanding. [they should pretty much have it by now]
GUIDED PRACTICE: Students observe and draw dividing cells, blastula, gastrula, and plutei.
CLOSURE: You now have an introduction to the sea urchin system. Tomorrow we start our own experiments using this system. Carefully note the Criteria for a Good Experiment on the overhead. Start thinking about what your group might do.
NOTES: Remember to start cultures ahead of time! This lab is a LOT OF SET up for the teacher, in terms of timing.