Photosynthesis160-page8

Photosynthesis160-page8 - involve using light energy to...

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Photosynthesis - 8 Photosynthetic Pathways - Overview. The two "stages" of photosynthesis (light-dependent and Calvin cycle) are linked by the products of the first stage, the light-dependent reactions. These products are ATP and NADPH. The Calvin cycle uses ATP and NADPH and returns ADP and NADP + . Stage I: Light-Dependent Reactions. The light-dependent reactions transform light energy into chemical energy that is trapped and carried by ATP and NADPH to the Calvin Cycle. The light-dependent reactions require chlorophyll and occur in the thylakoid membranes of the grana of the chloroplast. Light energy is also used to split water (Photolysis) in Photosystem II to: H 2 O -----> 2H + + 2e - + 1 / 2 O 2 This produces oxygen and provides electrons and hydrogen for the reduction of NADP to NADPH (NADP gains H + and electrons; the water is oxidized because it loses the H + and e - ). The light-dependent reactions are photophosphorylations because they
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Unformatted text preview: involve using light energy to make ATP. • The light reactions consume H 2 0 and produce ATP, NADPH and O 2 as a byproduct. Stage II: Calvin Cycle • The photosynthetic reactions of the Calvin cycle do not use light energy for their energy source. They use the ATP produced in the light-dependent reactions for their energy source, and the energy transfer molecule, NADPH to provide hydrogen and electrons for a high-energy reduction. • Carbohydrate molecules are produced in Calvin Cycle in the stroma of the chloroplast. • In the Calvin cycle, carbon dioxide combines with a 5-carbon sugar (Ribulose bisphosphate) and undergoes a reduction to form 3-carbon molecules. These 3-carbon intermediates can be used to regenerate the 5-carbon sugar or metabolized to form the carbohydrate, glucose or other needed organic molecules....
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