Chicano Studies - Steve Choi, Nena Connelly, Dan Flinn,...

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Steve Choi, Nena Connelly, Dan Flinn, Nicole Shin Life Science XL2 Deepthi Sudhakar 05/02/2010 The Pigments of Photosynthesis Lab INTRODUCTION The classic experiment of growing two plants in light and dark is significant, because it reveals the importance of photosynthesis and the environment’s role in its processes. Photosynthesis is a process that converts trapped solar energy to chemical energy that is then stored in bonds of organic molecules. Pigments are molecules that absorb light energy in light dependent reactions and play a major role in photosynthesis. There are various kinds of pigments which fall into three classes: chlorophylls, carotenoids, and phycobilins. All three types absorb light energy, but only chlorophyll can convert energy directly into chemical energy. Carotenoids and phycobilins are accessory pigments that merely pass an excitation onto another molecule until it reaches a chlorophyll molecule. These different pigments absorb different wavelengths of light resulting in a distinguishable color. A technique called thin layer chromatography (TLC) will be used to separate the pigments in order to observe the different colors and absorbance levels of existing pigments. This technique will be coupled with the use of a spectrophotometer, which will measure the absorbance values and peaks of the different pigment compositions in each sample. By comparing the different pigment compositions and their absorbance values, we can investigate how environmental conditions and the organism’s evolutionary history can affect pigment composition In this experiment we are analyzing the pigment composition of light barley and dark barley. We hypothesize that the growing environment will have an effect on the barley’s pigment composition, specifically that the light barley will have a higher composition of
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chlorophylls. Our null hypothesis states that the growing environment will not have an effect on the pigment composition, specifically that light and dark barley will have similar pigment compositions. Since each pigment has a characteristic R f in a particular solvent-matrix system, we will use R f values and color observations obtained through TLC as a point of comparison. In addition, since different pigments absorb different wavelengths of light, we will utilize spectrophotometry in order to analyze the pigment composition of different samples. Through the use of TLC and spectrophotometry, we hope to observe the pigment composition of different photosynthetic organisms and thus better understand the effects of the environment and evolutionary origin on pigment composition. MATERIAL AND METHODS: For the first part of the experiment, we used a mortar and pestle to grind eight dark barley leaves in 3 ml of methanol. After transferring the liquid into the capillary tubes, it was centrifuged. This process was repeated for four light barley extracts. On the TLC plate, we spotted the light barley and dark barley extracts 20 times each. We placed our TLC into a small
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Chicano Studies - Steve Choi, Nena Connelly, Dan Flinn,...

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