MadSci Network: Botany

Re: Comparing chlorophylls action spectrum with its absorption spectrum

Date: Fri Jun 11 11:52:57 1999
Posted By: Maggie Guo, Grad student, Plant Physiologu and Molecular Biology Program, Dept.of Plant Biology, UIUC
Area of science: Botany
ID: 926939304.Bt


Actually spectrophotometer is up to now the only equipment we use to measure
absorption spectrum, and the older model is not very expensive. Without it 
you can not get valuable information about chlorophylls action spectrum.

--------- Admin note:

David Hershey adds the following:

To do a chlorophyll absorption spectrum requires a spectrophotometer which is not an uncommon instrument in American high schools.

A photosynthesis action spectrum was probably first generated in 1883 by T.W. Engelmann who used a prism to shine different colors of light on a filamentous algae (Spirogyra) on a microscope slide. The rate of photosynthesis with different colors of light was measured visually by observing bacteria that were attracted to oxygen. The colors that produced the most photosynthesis also produced the most oxygen and attracted the most bacteria. This experiment is often mentioned in botany textbooks such as Stern (1991) or Moore and Clark (1995).

You can do a qualitative photosynthesis action spectrum by using the leaf disk photosynthesis assay described in my book and using colored films around the syringe. The difficulty in doing a quantitative photosynthesis action spectrum is mainly in getting equal amounts of light of each color. To do that a botanist would use a quantum light sensor which measures photosynthetically active radiation (PAR) and make sure the PAR was the same for each color.


Hershey, D.R. 1995. Plant Biology Science Projects. New York: Wiley.

Moore, R. and Clark, W.D. 1995. Botany: Plant Form and Function. Dubuque, Iowa: Wm. C. Brown.

Stern, K.L. 1991. Introductory Plant Biology. Dubuque, Iowa: Wm. C. Brown.

David Hershey

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