two stages of photosynthesis

two stages of photosynthesis - its steps in the 1940s. The...

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two stages of photosynthesis. Photosynthesis is two processes, each with multiple stages. The  light reactions  (photo) convert solar energy to chemical energy. The  Calvin cycle  (synthesis) uses energy from the light reactions to incorporate CO 2  from  the atmosphere into sugar. In the light reactions, light energy absorbed by chlorophyll in the thylakoids drives the  transfer of electrons and hydrogen from water to  NADP +  (nicotinamide adenine  dinucleotide phosphate), forming NADPH. NADPH, an electron acceptor, provides reducing power via energized electrons to the  Calvin cycle. Water is split in the process, and O 2  is released as a by-product. The light reaction also generates ATP using chemiosmosis, in a process called  photophosphorylation. Thus light energy is initially converted to chemical energy in the form of two compounds:  NADPH and ATP. The Calvin cycle is named for Melvin Calvin who, with his colleagues, worked out many of 
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Unformatted text preview: its steps in the 1940s. The cycle begins with the incorporation of CO 2 into organic molecules, a process known as carbon fixation. The fixed carbon is reduced with electrons provided by NADPH. ATP from the light reactions also powers parts of the Calvin cycle. Thus, it is the Calvin cycle that makes sugar, but only with the help of ATP and NADPH from the light reactions. The metabolic steps of the Calvin cycle are sometimes referred to as the light-independent reactions, because none of the steps requires light directly. Nevertheless, the Calvin cycle in most plants occurs during daylight, because that is when the light reactions can provide the NADPH and ATP the Calvin cycle requires. While the light reactions occur at the thylakoids, the Calvin cycle occurs in the stroma....
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