DESPERATELY SEEKING CHLOROPHYLL
The year is 2065, and all of the green plants have died on earth. As you know, in 2033, we found that chlorophyll a has special anti-cancer properties. Consequently, all of the green plants were destroyed for food and medicine. We now need your help to assist a secret S.W.A.T. team (Students Who Ate Trees) find another source of chlorophyll a.
You remember from your youth that certain bacteria have chlorophyll a, and that bacteria still grow in every conceivable niche (the Bacteria-Eaters have not yet taken over the planet). You remember making a Winogradsky column, as a way to enrich for phototrophic bacteria. You search your bedroom, and luckily find your old Winogradsky column, still sitting on your window sill for all these years. You can still see the distinct layers of multi-colored phototrophic bacteria, each with their own unique pigments. In no time at all, you are able to isolate a cyanobacterium, a purple non-sulfur bacterium, a purple sulfur bacterium and a green sulfur bacterium.
The question is: Which one contains chlorophyll a?
You dust off your old notes from BioMi 290 and flip to the following page:
(You now regret dozing off during this lecture.) You do remember (you have a good memory for the age of 92) that phototrophic bacteria have characteristic absorption spectra based on their pigments. And that photosynthetic bacteria are phototactic, that is, they can swim towards the wavelength of light that their pigments absorb the best. (Why is this, do you think?)
You manage to find the absorption spectra for the four different pigments found in your four different bacteria: Chlorophyll a, Bacteriochlorophyll a, Bacteriochlorophyll b, and Bacteriochlorophyll e (you also have a large reference library). They are shown below on one graph which you made by superimposing the four individual graphs upon one another.
Does this give you an idea for an experiment to find the chlorophyll a using a prism and a microscope?