Re: what is meant by an action spectrum as opposed to an absobrtion spectrum

Rest of question:

of a suspension of chloroplasts and how would you produce it experimentally

i have searched my libary and have been searching the internet for about
two weeks now and i cant find an answer could you recommend a specific
book then i could order it from the bookstore if my libary does not have
it??   

Reply:

A photosynthesis action spectrum is a graph of photosynthesis rate on the 
vertical axis versus wavelength on the horizontal axis. To make one for algae, 
you can shine light of different wavelengths on the algae and measure the rate 
of photosynthesis by oxygen evolution or other method. 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).


An absorption spectrum is a graph of the light absorption of a pigment, often 
chlorophyll. You first extract the chlorophyll usually by boiling in an organic 
solvent such as ethanol or acetone. Then the extract is placed in a 
spectrophotometer and its absorbance measured at wavelengths usually between 
400 and 700 nanometers.

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.

Most introductory college botany textbooks and college plant physiology 
textbooks discuss action and absorption spectra. An absorption spectrum is 
easier to produce and is often confused with the action spectrum. 

References

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.


                        

Response:

Re: what is meant by an action spectrum as oppossed to an absobrtion spectrum
of a suspemsion of chloroplasts and how would you produce it experimentally


_______________________________________________________________
Greetings - Your question was not submitted to the
MAD Scientist Network for the following reason:

Your question may be answered by basic references such as
an encyclopedia, or a reference science text. 

In this case, any good plant physiology book (which you can probably find at 
your university's library) should explain this.  

	Elizabeth Millard, Admin MadSci Network

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