To begin the lesson, I ask students to review the macro chart that they completed in the previous two lessons. A completed student example can be found here. In reviewing the organizer, I ask students to remind themselves about the different pollution-sensitive (mainly mayflies, caddisflies, stoneflies, and gilled snails) and pollution tolerant macroinvertebrates that they can expect to see in the sample bin. Because there are many snails I also ask them to review how they can determine whether a snail is pollution sensitive (gilled snail) or pollution tolerant (pouch snail)
I provide the students with a variety of new supplies. Since this is the first opportunity the student have to use these materials, I lead the class in a brief discussion of how the students can use their supplies to identify the macroinvertebrates.
I provide each students with a bin containing macroinvertebrates gathered at our stream site (in stream water), magnifying glasses, an ice cube tray, spoons, and pipettes. I allow students to work with their group members to isolate and identify the macroinvertebrates. As the students work, I circulate around the classroom to listen in to student discussions. I intervene with clarifying and probing questions when I hear students struggling to identify macros, incorrectly identifying the macros, or dealing with teamwork issues. As I walk around, I remind students to record their results on their pollution tolerance index. A sample of a student completed work can be found here.
After 10 - 15 minutes (as students have identified most of the macroinvertebrates in their bin), I ask students to return all macros to their tubs. I rotate the macro bins between the tables. I do this because each bin contains a unique mix of macros and I want the students to have the opportunity to observe and identify different types of macroinvertebrates.
After all macros have been returned to their bins, I ask all of the students to return to their work spaces to begin a class discussion. I ask students to identify the macro species that their group identified and to record any new species on their record sheets. I also ask students to begin to consider what the presence of the macros tells us about water quality.
My goals for this lesson are to have students correctly identify macro species based on their physical characteristics and to use the presence of pollution sensitive macroinvertebrates to determine water quality. This discussion serves as a quick formative assessment of student progress towards these goals.