Photosynthesis: Dark Reactions

Ms. Bush, Ms. CohenPlants and Photosynthesis Unit

Photosynthesis OverviewWhat is the chemical equation for photosynthesis?

_____ + ______ _____ + _______

Calvin Cycle (light -Independent cycle)

The Calvin cycle usesATP and NADPH to producehigh energy sugars.

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.

4

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.

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.