• Best to allow two periods for this lab. You will also want to fit in LabA2 either to precede this lab or as a review before Lab C loading step. (In this and all Teacher's Guides, "periods" are assumed to be 50-55 min. long). If students understand and have thoroughly practiced micropipeting, it will pay off later! Consider:
  
  
  1. Have students handle pipets with the Student Worksheets on first day (and do Lab A2?), then have students do the lab the next day, or
     
     
  2. Start lab first day, go slowly; maybe practice withdrawing certain volumes & dispensing on wax paper; pick up lab on second day where you left off.
     
     

• Check that food coloring solutions have been aliquoted. Solutions I-IV are in 1.5 mL reaction tubes; solution V is in 15-mL tubes (so students practice with both kinds of tubes).
  
  
• Set out supplies. Tips and tubes need NOT be sterile.
  
  
• Prepare X and Z assessment tubes (40 µL and 10 µL, respectively). These tubes, too, can be dried and reused.
  
  
• Have students dry out tubes A-E and save for next class.
  
  

• Review metrics units - particularly liter (L), milliliter (mL), and microliter (µL).
  
  
• Encourage students to really observe the volume of liquid in the pipet at each step -- also to note if there is liquid on the outside of the tip.
  
  
• Plan to demonstrate the use of a micropipet. Use a full page illustration (in plastic page protector). A set of 20 are in a notebook in the Gene Connection Teacher's Box 1.
  
  
• Demonstrate the use of the different microcentrifuges available -- your lab may have a 24-place microfuge, a 12-place microfuge, or a 6-place FOTODYNE Educational microfuge.
  
  

• Watch students' micropipeting technique, and lend assistance as needed. See micropipet cautions. The two most common mistakes are:
  
  1. depressing the plunger to the second stop before filling the pipettor ;
     
  2. releasing the plunger after dispensing the solution while removing the pipettor from the tube (keep the plunger depressed until free of the tube or liquid will be sucked back into the tip.)
  
  
• Some teachers require that each student demonstrate his/her proficiency at each step before going on...No air in the tip and no liquid left in the tube...Repeat until they get it right!
  
  
• A grading rubric: C for P20; B for both P20 and P200; A for all three; A+ if also do Lab A ext correctly.
  
  

• Have a student refill food coloring solutions I-V for the next class.

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