Plant Pigments and Photosynthesis
Problem: We are going to separate and identify pigments and other molecules from cell extracts through a process called chromatography. We will also test the theory that light and chloroplasts are required for light reactions to occur. Background: Pigments are chemical compounds which reflect only certain wavelengths of visible light. This is what makes them seem colorful. Many things contain pigments including flowers, corals, and even skin. More important than their reflection of light is their ability to absorb certain wavelengths. Because pigments interact with light, they are very useful to autotrophs. These pigments help the user gain energy. Because pigments only absorb a narrow range of light, many different color pigments are needed to capture more of the sun’s energy. There are three basic classes of pigments which are chlorophylls, carotenoids, and phycobilins. There are several kinds of chlorophyll and they are greenish pigments. The most important one is chlorophyll A which is very important in making photosynthesis possible. Carotenoids are red, orange or yellow pigments and phycobilins are water soluble pigments found in the cytoplasm. (www.berkely.edu) Chromatography comes from the Greek words chroma and graph for Color Writing. The technique was developed by Mikhail Tsvet who used it for separating pigments that made up plant dyes. Chromatography is a very valuable technique used for separating mixtures. It can be used for many things including find traces of drugs in urine and analyzing components of pollutants. (www.exploratorium.edu) Chloroplasts are special organelles found in plant cells. These organelles contain the plant cells chlorophyll providing it its green color. Because chlorophyll is important in making photosynthesis possible, it is a very important organelle in keeping the plant alive. (www.cellsalive.com) Light reactions are the photo part of photosynthesis. These steps convert solar energy into chemical energy which then goes to the Calvin Cycle. (Campbell 189) Procedures: Exercise 4A- In this lab we separated the pigments from a spinach leaf. We started off by obtaining a long strip of paper and cutting it into a point. Then, we rubbed the crushed cells from the spinach leaf in a line 1.5 cm from above the point. The paper strip was then put into a graduated cylinder with 1 cm of solvent in the bottom. We put a stopper over the top of the cylinder and watched as the solvent moved up the paper. When it got to about 1 cm from the top of the paper we removed it and marked the bottom of each pigment band. We marked 5 different pigment bands which showed us the different pigments in the plant. We also marked where the solvent stopped, or the solvent front. Then we used this data to find out which pigments were which color. Exercise 4B- In this lab we chloroplasts were extracted from spinach leaves and incubated with DPIP in the presence of light. We started out by labeling 5 cuvettes and covered cuvette 2 because it was the control for the experiment. Then, we put 1 ml of phosphate butter into each cuvette and into cuvette 1 we added 4 ml of distilled water. Then, we added 3 ml of distilled water and 1 ml of DPIP into cuvettes 2, 3, and 4. Finally, in cuvette 5 we added 3 ml plus 3 drops of distilled water and 1 ml of DPIP. To finish off cuvette 1 we added 3 drops of unboiled chloroplasts and inserted it into the spectrophotometer. All other tubes will be measured as a percentage of light transmitted through this tube. After that was measured, we added 3 drops of unboiled chloroplast to cuvette 2, removed it from its foil sleeve and read the percent transmittance. We put it back in the foil sleeve and placed the cuvette in the incubation rack in the light. We measured the percent transmittance every 5 minutes until we reached 15 minutes. The same thing was done to cuvette 3, however cuvette 3 did not have a covering over it. After measured we place it...
References: “Photosynthetic pigments” 09 July 1997.
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Owl Books. The Science Explorer. Henry Holt & Company, New York. “Black magic.” 1996.
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Quill Graphics. “Cell Organelles: The Chloroplasts.” 1994. http://www.cellsalive.com/cells/chloropl.htm. 12 November 2011.
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