Activity:
You give the kids a block of agar (slightly basic prep with BTB so it's blue). They get to carve it
or cut it down to achieve this goal:
** diffuse vinegar to the center within 25 minutes while maximizing the size of the cell. The cell
with the biggest cell mass/diffusion time ratio wins!
RULES: NO holes all the way through. Structural integrity: cell can't fall apart upon
handling. Only 1 cell is measured (no dicing your agar and weighing all of it!) No stirring,
poking, prodding of cell once it's in the vinegar.
cell survives: 10 points
cell doesn't survive*: 0 points
Winning cell: 15/10 points
* To earn 10 points, write a paragraph describing how you would make your cell the next time to
make it successful.
Prep for kids: Read 10-1, VIPS or section assessment Qs or reading quiz.
teacher prep: Make agar: 3 L is plenty for 7 sections. Pour prepared agar into ice cube trays and
let stand overnight. (No refrigeration needed.) (The ice cube trays make a good size, they pop
out easily and the clean up is minimal.)
AGAR RECIPE:
20 g agar/ 1 L DI water, stir and dissolve in a big pot on the stove between 213-214.
Add 50 ml stock BTB solution (0.04%)/ 1 L agar solution.
Add 0.1 M NaOH until stable blue color is achieved. (It's kind of a cornflower blue....)
Stir almost constantly. Agar burns easily!
Bring to a rolling boil for approximately one minute.
It's done!
Obtain smaller quantities of the agar solution using a beaker, then fill ice cube trays. If students
work in pairs, you will only need (less than) one tray per class.
Also, we had trays on their desks with a beaker containing ~ 150 ml vinegar, using a petri dish as
a lid. (We just reused the same vinegar all day.) Also, a plastic knife and metal spatula for
carving purposes.
Recommendation: have something for the kids to do while they're waiting, a worksheet,
homework assignment, reading, whatever. If you want to use the learning cycle, they could
actually read about SA:V during the wait. I wonder how many would go "A-ha!"
Attached is the record sheet. Only weigh those that turn clear in 25 minutes or less. Figure the
rate. Best rate wins!