Osmotic vs. Ionic

OBJECTIVE: The student shall demonstrate their ability to follow instructions and make careful observations of living material by making a series of different dilutions and studying the effects on fertilization.

PURPOSE: This "technique" lesson is a starting point for further experiments to be proposed by the students themselves.

SET: Why is seawater the composition that it is and what does this mean to the plants and animals in it? In the last lesson we played with changing individual components such as leaving the calcium out. Here we will change the overall concentration of salts and ions to study OSMOTIC and IONIC effects.


MODEL: Show students again how to make dilutions [can be done dry?]

STRUCTURED PRACTICE: Ask the students to help you do this. They should already be able to do this easily from having done the SIMPLE DILUTION lesson.

GUIDED PRACTICE: Watch students as they set up their dilutions and carry out the experiment.

CLOSURE: What happened? How low a salt concentration could you go and still get fertilization? What did the cells look like at low and high concentrations? Etc.

INDEPENDENT PRACTICE: Have students propose and carry out further experiments along this line on their own.

NOTES: This can be a one day to one week lesson depending on how far you wish to carry it.