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Photosynthesis: Dark Reactions
Ms. Bush, Ms. CohenPlants and Photosynthesis Unit
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Photosynthesis OverviewWhat is the chemical equation for photosynthesis?
_____ + ______ _____ + _______
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Calvin Cycle (light -Independent cycle)
The Calvin cycle usesATP and NADPH to producehigh energy sugars.
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ATP and NADPH power sugar synthesis in the Calvin Cycle.
• Occurs in the stroma of the chloroplast.
• For every two turns of the Calvin Cycle one glucose molecule is formed.
• Total input needed: 6CO2 and many ATP and NADPH molecules.
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Light Reactions Summary
• Light activates P680 and excites an electron in Photosystem II.
• Water is split to produce oxygen and to replace the lost electron.
• The excited electron goes through the electron transport chain creating ATP.
• Light then activates P700 so that an electron is excited in Photosystem I.
• This electron travels through a short electron transport chain to produce NADPH.
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Dark Reactions Summary
• CO2 enters the cycle and is fixed (attached to six 5-carbon molecules) by the enzyme Rubisco. The result is twelve 3-carbon molecules.
• The twelve 3-carbon molecules are converted to higher energy forms by input of ATP and NADH.
• Two of the twelve 3-carbon molecules are removed from the cycle to be converted to sugars and other compounds.
• The remaining ten 3-carbon molecules are converted back to six 5-carbon molecules thus restarting the cycle.