5.3 Calvin Cycle and Photosynthesis Notes

Calvin Cycle

• Reactions of photosynthesis use energy from light-dependent reactions to form glucose and other carbohydrates.

• Carbon atoms come from carbon dioxide.

Interworkings of the Calvin Cycle

• CO2 enters leaves through stomata, diffuses into mesophyll cells, and enters the stroma of chloroplasts.

• The Calvin cycle has three stages: fixation, reduction, and regeneration.

• Fixation: RuBisCO catalyzes a reaction between CO2 and RuBP, forming a six-carbon compound that is immediately converted into two three-carbon compounds.

  • Carbon fixation: CO2 is fixed from its inorganic form into organic molecules.

• Reduction: ATP and NADPH use their stored energy to convert the three-carbon compound, 3-PGA, into another three-carbon compound called G3P.

  • Reduction is the gain of an electron by an atom or molecule.

• One G3P molecule leaves the Calvin cycle to contribute to the formation of a carbohydrate molecule, commonly glucose (C6H{12}O_6).

• It takes six turns of the Calvin cycle to make one carbohydrate molecule.

• The remaining G3P molecules regenerate RuBP.

Photosynthesis

• The shared evolutionary history of all photosynthetic organisms is conspicuous, as the basic process has changed little over eras of time.

• Photosynthesis in dry-climate plants has evolved with adaptations that conserve water.

• Photosynthesis in Prokaryotes: Prokaryotic photosynthetic autotrophic organisms have infoldings of the plasma membrane for chlorophyll attachment and photosynthesis.

Energy Flow

• Carbohydrates are storage molecules for energy in all living things.

• Photosynthesis and cellular respiration function in a biological cycle.

• Overall reaction for photosynthesis: 6CO2 + 6H2O \rightarrow C6H{12}O6 + 6O2

• Overall reaction for cellular respiration: 6O2 + C6H{12}O6 \rightarrow 6CO2 + 6H2O