[Plant-education] Re: photosynthesis lab for nonmajors biology

David R. Hershey dh321 at excite.com
Tue Jul 11 18:05:23 EST 2006

1. You mentioned the leaf disk photosynthesis system using plastic
syringes and sodium bicarbonate. It  is one of the cheapest, simplest
and effective student photosynthesis labs. It can be used for
experiments on light level and temperature effects on photosynthesis
rate. Leaf disks from green and white sections of a variegated leaf can
be used to demonstrate that chloroplasts are required for
photosynthesis. Adding or omitting the sodium bicarbonate will
demonstrate that carbon dioxide is required for photosynthesis. One
could also start with leaf disks from plants that had been in the dark
for a day or two so that starch tests could be run on control leaves
and leaves exposed to light.

The technique also has an historical connection. About 1754, Charles
Bonnet, a Swiss scientist, was first to notice air bubble formation on
illuminated leaves submerged in water. In the 1770s, Dutch physician,
Jan Ingenhousz, used Bonnet's technique for some of his pioneering work
on photosynthesis, e.g. Inhenhousz wrote,

"If the sun caused this air to ooze out of the leaves by rarifying the
air in heating the water, it would follow that, if a leaf, warmed in
the middle of the sun-shine upon the tree, was immediately placed in
water drawn directly from the pump, and thus being very cold, the air
bubbles would not appear till, at least, some degree of warmth was
communicated to the water; but quite the contrary happens. The leaves
taken from trees or plants the midst of a warm day, and plunged
immediately into cold water, are remarkably quick in forming air
bubbles, and yielding the best dephlogisticated air."

Exploring Photosynthesis with Fast Plants

2. Another classic exercise is to visualize leaf starch with iodine.
Sometimes multicolor leaves are used, such as coleus, and students
correlate starch with green areas of the leaves. There is a white and
green variegated coleus often used for this purpose.

Reiss (1994) has a lab on "Whodunit - or - The influence of light
intensity on starch production in photosynthesis." Students made a leaf
starch print from a black and white negative of a "plantnapper" to help
the "botanical detective Cloro Plast." Hangarter and Gest (2004) also
describe the technique.

Reiss, Carol. 1994. Experiments in Plant Physiology. Englewood Cliffs,
NJ: Prentice Hall.

Roger P. Hangarter & Howard Gest. 2004. Pictorial demonstrations of
photosynthesis. Photosynthesis Research 80: 421-425.

3. Students can grow plants with and without CO2 in 2-liter soda bottle
systems that scrub CO2 from the air by bubbling it through calcium
hydroxide solution and see how lack of CO2 stops plant growth (Hershey
1994), but that takes longer than one class period. It makes an
effective demonstration.

Hershey, D.R. 1994. Solution culture hydroponics: history and
inexpensive equipment. American Biology Teacher 56:111-118. (email me
for a copy)

4. Students can seal a C3 and a C4 plant together in a terrarium or
clear, airtight container and see that the C4 plant lives longer
because it has a lower CO2 compensation point, but that takes longer
than one class period. It might be better as a demonstration.

5. Another quick and informative exercise is to have students use a
footcandle or PAR meter to measure the light level in various
locations, e.g. classroom, office, outdoors in sun, outdoors in shade,
plant growth chamber. The students then compare their data with
benchmarks such as full sunlight, ~10,000 foot candles or ~2,000
micromoles/square meter/second of PAR and leaf light compensation
point, ~5 to 100 footcandles or 1 to 20 micromoles/square meter/second
of PAR.

6. Friend (1990) has several simple exercises on CAM photosynthesis
using the succulent houseplant, Kalanchoe daigremontiana (devil's
backbone or mother of thousands). For one exercise, the instructor
collects leaves at several times during the day and freezes then.
Students then express the sap from the leaves and either measure the pH
or titrate the sap. A graph of pH or malic acid concentration versus
time is then created. Kalanchoe daigremontiana is one of the more
fascinating plants for teaching because it produces abundant
adventitious plantlets on its leaves. It can also be used for student
experiments in photoperiodism, mineral nutrition, water relations,
hormones, tropisms, asexual reproduction, etc.

Friend, D.J.C. 1990. Plant eco-physiology: Experiments on Crassulacean
acid metabolism, using minimal equipment. American Biology Teacher 52:

7. I liked to do a quick demonstration of the light spectrum using a
prism and a light source, such as sunlight or an overhead projector. It
is a way to introduce a discussion of some photosynthesis
misconceptions, like the one that plant leaves do not use green light
in photosynthesis.

Hershey, David R. 2004. Avoid Misconceptions When Teaching about Plants


8. With a spectrophotometer, students could make a chlorophyll
absorption spectrum and possibly leaf absorption and transmission
spectra. They could be compared with each other and to published
photosynthesis action spectra, such as the following:

Balegh, S.E. and Biddulph, O. 1970. The photosynthetic action spectrum
of the bean plant. Plant Physiology 46(1): 1-5.

Clark, John B. and Lister, Geoffrey R. 1975. Photosynthetic action
apectra of trees I. Comparative photosynthetic action spectra of one
deciduous and four coniferous tree species as related to
photorespiration and pigment complements. Plant Physiology 55(2):

Clark, John B. and Lister, Geoffrey R. 1975. Photosynthetic action
spectra of trees
II. The relationship of cuticle structure to the visible and
ultraviolet spectral properties of needles from four coniferous
species. Plant Physiology  55(2): 407-413.

David R. Hershey

gross at georgian.edu wrote:
> Greetings,
> My colleagues are looking for a simple photosynthesis lab for nonmajors
> biology that does not use sophisticated equipment.  We are looking for
> something other than a computer simulation, or separation/chromatography of
> pigments, or the Hill reaction lab using DCIP oxidation/reduction (which we
> teach in our botany course).   Those who teach the course have used a lab
> with Elodea and bicarbonate in a stoppered test tube with a pH indicator
> and movement of water through glass tubing and were hoping to find
> something other than that because they weren't happy with it for various
> reasons.   Does have something that works for them?
> I have looked at www.ableweb.org and this list's archives but may have
> missed something.  I did run into a leaf-disk lab with bicarbonate that we
> might try.  Anything else out there that you can recommend?
> Thanks,
> Mike Gross
> Georgian Court University
> Lakewood NJ

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