Physics 132, Reminders from 3/13/2015 TA Training, for week of 3/23 (Lab 8, Part 2)

1) Recitation: Salting Out and Denaturing DNA

(Break--Pass Back graded Lab 7 reports, if not already done....)

2) Lab 8, Part 2: Modeling Signal Transmission Along Nerve Axons

(In room 3312 from now on; students have been sent a notice via ELMS.)

Link to documents: NEXUS Physics Labs, 2013-2014

a) Reminder of safety instructions (give to ALL students, as a class, at the start of this week's lab): The resistors can get HOT, so have the students close the switch only when taking data (opening the switch again immediately after the data is taken) and handle the resistors carefully.  The students should be careful to avoid a short-circuit--build the circuits carefully and have a TA check them (at least the first one) before the students close the switch and take data.  Students should be especially careful to make sure that the alligator clips do not touch each other--a short-circuited battery will get HOT VERY QUICKLY and will also cause the burnt metal smell in the air--disconnect the battery immediately if you notice this and then let the battery cool before you touch it and before you try to use it again (a hot battery does not function properly).  NO ADDITIONAL EQUIPMENT, beyond what is present in each plastic bin, is needed for these labs--students should not 'borrow' equipment from other bins; the more equipment they have the more likely they are to cause a short-circuit!  Please make sure that the equipment is put away properly at the end of the lab--having 'extra' equipment or too little equipment in a bin may confuse the next group of students.

b) Check the circuits the students build carefully.  The membrane resistor should be larger than the axon resistor.  The trays for the resistors include both the color code and the value for each of the resistances.  There is also a resistor chart at the front of the room.  If a circuit does not appear to be working, check that the wires are all placed in the correct holes, that the wires are all pushed into the holes fully, and that the circuit the students have created is correct and complete (the pictures in their lab document can guide their circuit-building and their use of the Logger Pro software).  If you haven't yet done so, review with the students the construction of the circuit/bread board--the central two columns of holes (red line and blue line) are electrically connected in a vertical line; the other holes in the board are connected in horizontal rows, and the dip in the breadboard is an electrical break between the rows, as are the red and blue lines.  Students should ensure that the START of their circuit is correct--including screwing the red and black knobs tight on the wires and making sure that the high voltage leads through an axon resistor before first crossing a membrane resistor to the low voltage/ground (extra cellular fluid). 

c) Ask the students regularly to connect the multiple representations/different models together--which part of the circuit is the axon?  Which part the membrane?  How do the different parts of the physical circuit match up to the circuit diagram?  To the drawing of the nerve?  Is the data they collect in Part 3 consistent with the graphical model they predicted in Parts 1 and 2?  Remind students to include in their report discussions of the exclamation points (!) in all parts (1 through 4) of the student document AS WELL AS a discussion of how this relates to things they have learned in their other biology/chemistry classes.  Diagrams, drawings, pictures and other representations of their models should also be included in their report.  (If any are beautiful and great in color, have the students also email the report to you and then forward it to me!)

d) Please have students put their equipment away neatly when they have finished taking data.  This includes taking apart their circuits, sorting and straightening their resistors (there should be 10 of each kind, replacement resistors are on the TA table at the front of the room), placing all equipment neatly in the plastic bin, and placing the bins neatly in the back-left cabinet.  "All equipment" means: 3 trays of different resistors, two circuit boards, 1 battery, 3 banana plug wires, two alligator clips, one switch, and one voltage probe (with micrograbbers).  Have the students leave the LabPro (ULI) on their group's lab table.

e) Please, bring me the completed Lab 8 reports for scanning (room 1322).

f) If you run out of printer paper/staples, see Don or Bill.

g) Organize papers and clean up tables after recitation/lab.  Place sorted papers in the back of the room by the printer.

That's all for now.  Good luck!

~KIM