When you cover transpiration in Spring, Summer, or Fall, you can have the
students put zip-loc plastic bags over real leaves on real plants, leaving
them there for awhile, then collecting them later. Weigh the bags before,
marking the wt on the bag with a waterproof marker. Put the bags over the
leaves, seal the zip loc around the petiole, leave for x minutes/hours.
Collect the bags and seal them immediately. Take them back to lab and
weigh them again. Subtract the dry wt from the wet wt to see how much
water was captured. Now comes the difficult part... the analysis. What
were the variables? Variables could be: Species (mark the name of the
plant on the bag when you put it on the tree or collect the leaf for later
identification), leaf area (trace each leaf on graph paper and count the
squares), sunny leaf vs shade leaf (again, mark this on the bag). You get
the idea. If the experiment is to compare species, be sure to include a
needle-leaved conifer (geometry necessary calculate leaf area).
Maybe this can work in winter too....with houseplants or greenhouse plants?
I have never done this at this time of year.
This is a good experiment to teach scientific method: Control vs variable,
hypothesis formation, data analysis, etc. Let the students, individually
or in teams, design their own experiment, do it, gather and analyze data,
draw conclusion (results do/do not support hypothesis), write report, give
oral report to class. They might have design errors which they discover
later. Just like real science! Re-design the experiment and start over...
or at least tell how you would do it differently if you were to repeat it.
>Dear Plant-ed folks:
>>I received this request from Carol Lafave at the U of Pittsburgh. Can
>anyone help?
>>My name is Carole LaFave and I am the coordinator of the Introductory
>Biology Program at the University of Pittsburgh. I have been trying to
>do a
>transpiration experiment with the students and it has not worked well at
>all. Ellen York told me that you might be able to give me some insight.
> Do
>you have a procedure that works easily?
*********************
David W. Kramer, Ph.D.
Asst. Prof. of Evolution, Ecology, and Organismal Biology
Ohio State University at Mansfield
1680 University Drive
Mansfield, OH 44906-1547
Phone: (419) 755-4344 FAX: (419) 755-4367
e-mail: kramer.8 at osu.eduhttp://www.mansfield.ohio-state.edu/~dkramer/
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