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Lab #2 - Sacha Prashad James Chyu Shilpi Patel Group#2...

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Sacha Prashad James Chyu Shilpi Patel Group #2 Lab #3: The Pigments of Photosynthesis Introduction : Photosynthesis is the process by which solar energy is trapped and stored as glucose. This molecule’s bonds can be broken to release the store energy. All living organisms depend on the energy that the plants generate from photosynthesis, directly or indirectly. The overall process of photosynthesis is 6CO 2 + 12H 2 O -> C 6 H 12 O 6 + 6H 2 O + 6O 2 . During this process, carbon is fixed producing glucose, and oxygen is released as a product. Photosynthesis is divided into two sets of reactions: the light-dependent reaction and the light-independent reaction. Absorbed photos are used to produce ATP and electrons carried NADPH in the light-dependence. In this process, water molecules are broken and O 2 gas is produced. In the light-independent reaction, otherwise called the Calvin-Benson cycle, carbon dioxide is fixed and glucose is produced. Pigments are molecules that absorb light-energy and include chlorophylls, carotenoids, and phycobilins. Unlike carotenoids and phycobilins, known as accessory pigments, chlorophyll can directly convert the energy. Main chlorophylls a and b absorb red and blue wavelengths giving plants a green color. The two types of carotenoids, carotenes and xanthophylls, absorb violet and blue wavelengths giving them yellow, orange, and/or red color. Phycocyanin and phycoerythrin give red algae and cyanobacteria. Visible light includes wavelengths between 400 to 700 nanometers. The wavelengths absorbed by each pigment is its absorption spectrum, measured by spectrophotometer. Thin layer chromatography (TLC) is the process of separating organic compounds like pigments. Using a plate and a solvent, the components of a pigment are separated along a plate while placed in a solvent. What is produced is the retention factor R f , the relationship between the distance the pigments and solvent traveled. This can identify what pigments are in the compound. Spectrophotometry, is the process of using beams of light from the wavelengths of the visible light spectrum. What is produced is a graph of the absorbance versus wavelength. The absorption spectrum of some pigments can have one or more peaks because they may absorb several wavelengths. In this lab, we utilize TLC and spectrophotometry to explore how a plant’s (specifically barley’s) environment can affect its pigment composition. In TLC, non- polar pigments are examined, because they are able to dissolve in the non-polar solvent.
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