Active Transport

Marta D. de Jesus mdejesus at ventura.cc.ca.us
Wed Sep 15 19:35:32 EST 1999


Dear Dr. Perry,

    Here's another active transport lab:  I'll admit this sounds very
simplistic, but my college has been doing this with beginning Bio majors
for years:

1. Make a live yeast culture (bakers yeast with a little sugar dissolved
in water).
2. Have the students take 2 samples in test tubes.
3. Boil one of the tubes for ~ 1 min.
4. Add a small drop of Congo Red to each tube (explain that the dye is
actively transported; but not the direction of the transport).
5. Have the students examine the 2 samples macro- and microscopically
and then ask them to explain the color differences with regard to active
transport.

    Congo Red will be actively transported out of living cells (Trypan
Blue can also be used), so the uncooked sample is much darker red
macroscopically and the cells are less colored at the microscopic
level.  This tends to shake them up a little because while they know
that cells have to be alive to do active transport (thus non-boiled),
many of them assume (probably from the standard explanations in many
texts) that active transport has to be "into" the cell.  So some will
twist their observations to fit their assumptions (tell you that the
non-boiled cells are "really" darker red, or that the amount of Congo
Red added to the 2 samples was very different).
    I've modified this basic exercise a little by having them take
sequential samples at different time points so they can see the
progression in color change and have them use micropipetters so the
addition of Congo Red is more precise (could do a quantitative version
with a colorimeter I suppose) .

Marta D. de Jesus
Associate Professor
Ventura College
mdejesus at ventura.cc.ca.us





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