scientific method labs

Ross Koning koning at ECSUC.CTSTATEU.EDU
Thu Aug 7 09:07:19 EST 1997

At 9:37 AM -0400 8/7/97, Anne Heise wrote:
>The first lab for the soph. level general botany course I teach is often
>on the first day of class, so I like having a lab that students don't need
>to have prepared much for.  For the past sev. years it's been a scientific
>method lab.  The one I've tried a few times is to have students put a leaf
>in some boiling water, hopefully observe the bubbles escaping from the
>leaf, and ask them to test as many hypotheses as they can about that
>observation (e.g. it's the water, not the heat of the water, that causes
>the bubbles to escape).  But this hasn't been as reliable as I've hoped.


This project works like a charm for me.  I use
primary leaves of kidney bean seedlings (about
10-14 days from sowing).  The water has to be
just sub-boiling...boiling water generates its
own water-vapor bubbles which spoil it all.  The
control has to be sub-room temperature because
the leaf is sub-room temperature (evaporative
cooling!).  The project has to be done in large
glass beakers so the students can see the epidermi
while the leaf is held submerged.  I provide huge
forceps for this.  The leaf has to go in suddenly
and STAY submerged for the observation.  The gas
expansion is rapid and a leaf that surfaces will
lose its attached bubbles.  Kidney bean primaries
have stomata almost exclusively on the lower epidermis,
but other leaves have them more evenly distributed
which would NOT serve the purposes of my exercises.
A plant with thicker leaves has more trapped gases
to release (barring succulents!) so these primaries
are quite nice.  It is good to let students discover
some of these truths on their own.

>A few days ago I thought of asking students instead to investigate the
>browning that occurs when you cut open an apple.  Is it exposure to air,
>is it the damage due to cutting, what about lemon juice prevents it from
>occuring (e.g., is it the wetness of the lemon juice, its pH, or what?)
>Not having tried this w/ students, I naturally think this problem could
>work really well! It doesn't require much knowledge of plants, it should
>be a familiar phenomenon to most, it won't cost a lot, etc.  I'm tossing
>this little embryonic idea out to the group to see what other ideas people
>have about scientific method labs, and whether you have any particular
>comments about messing around w/ apples.

This is cool, particularly if you are going to do the
polyphenoloxidase exercises later.  My only comment
here is that not all cultivars of apple generate much
in the way of a polylphenoloxidase reaction.  Their
juices are too acidic maybe?  They lack substrate?
They lack enzyme?  Who knows?  I'd just think if you
bought a bag of the wrong apples to class it might
just be an exercise in frustration.  However, after
you did the exercise with "good" apples, you might
give them one of the non-responder types to try to
figure out why it fails.

>At the end of such a lab I have students do a very quick "poster session".
>I supply overheads and markers s  and have  them  present one of their
>experiments to the rest of the class.  They don't love this, but I think
>it helps make the lab seem a little more important.

Anne, what a good idea!  I haven't tried this but
I think I will.  It sounds like an excellent approach!
I routinely have them make one presentation, but this
is usually after a week of preparation.  An impromptu
one in the same lab period sounds GREAT!  I make lab
seem important by making it worth 60%+ of the total grade
in my course.

>Another thing we do, I guess in the second lab, is critique a lab write-up
>done by a student a few years ago.  This write-up has some good things and
>some that aren't terrific, and my hope is that if students take the time
>to figure out for themselves what is good and bad about someone else'e
>write-up, they'll start producing good ones of their own a little sooner.
>What else do you all do to help students write up labs well?

I've given up on more than one full-blown lab report
and generally require two submissions of that one
so that they get the idea of drafting.

For the rest of my exercises in Plant Phys, I have
them hand in a one-page abstract and the corresponding
diagrams, charts, calculations, etc.  It works well for
me.  In one page I can tell if they understand what they
did and what it meant.  It focuses their effort on a
complete understanding and concise writing.  It reduces
the pile of papers!  It speeds feedback before they write
the next one, etc.


Ross Koning                 | koning at
Biology Department          |
Eastern CT State University | phone: 860-465-5327
Willimantic, CT 06226 USA   | fax: 860-465-4479

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