Chapter 10 Notes Continued

Part 2: The light-independent reactions A.k.a “dark reactions” or “Calvin cycle” or “C3 cycle”; occurs in the stroma of the chloroplast. ATP and NADPH produced by the light reactions are used in the Calvin cycle to reduce carbon dioxide to sugar. ATP is the energy source, while NADPH is the reducing agent that adds high-energy electrons to form sugar. For the Calvin cycle to synthesize one molecule of simple 3-C sugar, three molecules of CO2 must enter the cycle.

Calvin-Benson Cycle Phase 1: Carbon Fixation (CO2 is attached to a sugar already in the cycle) Phase 2: Reduction (ATP and NADPH are used to produce simple sugars; two of these 3-C sugars will leave the cycle and form glucose) Phase 3: Regeneration (sugars within the cycle are rearranged for the next go-round)

Energy  Food For the net gain of one 3-C simple sugar molecule, the Calvin cycle uses the products of the light reactions: • 9 ATP molecules • 6 NADPH molecules Calvin cycle uses 18 ATP and 12 NADPH molecules to produce one glucose molecule. This glucose is used by the plant for its own energy needs. Excess glucose forms cellulose (for plant growth), starch (for energy storage), and other organic compounds (food for heterotrophs).

Calvin-Benson cycle animation (don’t worry about individual steps) Another clip… Chemosynthesis Song…