At 8:52 PM -0500 8/30/99, Jim Perry wrote:
>Well, I'm one of those people that cannot say "no" and figure I need to be
>involved in high school linkages, so I have agreed to do two 50-55 minute
>sessions of "non-trivial" hands on botany. The students are talented,
>taking "Bio. 2", and are mostly seniors. They can take the AP exam after
>completing the high school course. They probably will have had no botany at
>the time the activity takes place (early November). They are using a
>college text -- Starr and Taggart.
>>Any suggestions for a "hands-on, non-trivial" experience that we might be
>able to do in 50 minutes?
>
Hi Jim!
My favorite exercise for this one is the leaf-disc
photosynthesis exercise. You need black film cans,
20 mL syringe body (no needle), plain and bicarbonate
buffers, a hand punch, a light bulb (I prefer fluorescent
screw-in with socket adapter), and a power strip. For
the plant I use Dieffenbachia--a plant with wide, thick
leaves having dark green margin zones and white central
zones.
After going over the leaf anatomy and being careful to
point out the gas spaces (maybe doing the boiling water
experiment to be SURE they are gas spaces). And then
connecting to PV=nRT to explain both the water trick and
aspiration, you can have them design projects.
The syringe bodies stand on their plunger nicely. You can
put 10 discs in the body and insert the plunger. Fill the
body with bicarb buffer and expel any airspace. Then
covering the tip with a finger/thumb, back off the plunger,
swirl the discs, release the vacuum, and IMMEDIATELY expel
any new gas space. After a few moments the discs will start
to sink as they place buffer into the evacuated gas space.
You may have to repeat the vacuum/swirl step a few times
to get at least most (if not all) of the discs sunk. When
they have two syringes prepared, place them about 20 cm
from the lamp (to avoid heat I use the fluorescent...but
incandescent will work if you have a beaker of water or
somesuch as a heat sink between the lamp and syringes).
You cover one of the syringes with the black film can
immediately. The discs in the light produce oxygen and
float...the discs in the dark will not refloat. When all
the discs in the light are floating, move the film can
from the one syringe to the other. The ones in the light
for the first time will refloat nicely (the dark did not
"kill" them...just prevented PSN). The ones that floated
by PSN will now sink...the oxygen is used up in respiration.
You can do green discs in plain vs bicarb buffer to show
that you need "dark" reactions to permit "light" reactions.
You can show light dose effects by increasing the distance
from the source. You can show the need for chlorophyll by
comparing green and white discs in bicarb in light...etc.
The responses are fast and the "connections" made are dense
in this short exercise.
ross
________________________________________________________________
Ross Koning | koning at ecsu.ctstateu.edu
Biology Department | http://koning.ecsu.ctstateu.edu/
Eastern CT State University | phone: 860-465-5327
Willimantic, CT 06226 USA | fax: 860-465-4479
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