Dark+Reactions+Notes

The dark reactions are also called the Light Independent Reactions because they do not need light to function. Carbon Fixation is the addition of Carbon into organic compounds. The most common Dark Reaction is the Calvin Cyclen named after Melvin Calvin. Calvin checked the Biochemistry of a leaf every 8 seconds in order to discover his cycle. Since the intermediate molecules of the Calvin cycle (PGA and PGAL) have 3 Carbons, the Calvin Cycle is sometimes called the C3 pathway the biggest drawback of the Calvin Cycle is water loss. Plants in Hot or Dry areas would lose too much water using only the Calvin Cycle so they have alternate pathways.

C4 Pathway Plants that live in Dry areas, Plants like Corn, Crabgrass and Sugarcane. Partially close their stomata during the hottest part of the day, convert Carbon DDioxide into a 4C compound then undergo the Calvin cycle. The C4 plants lose about 1/2 the water of a typical C3 plant. CAM Pathway - Crassalucean Acid Metabolism Plants that live in HOT and DRY areas, Plants like Cacti and Pineapples. Close their stomata during the day and open them at night. Convert Carbon dioxide into organic acids at night and use them during the day for the Calvin Cycle.

Things to Think About: What is the function of the stomata? What is the purpose of the ATP that goes into the Calvin cycle? What determines the "OR" in the Calvin cycle? Why can't grass from your lawn grow in the desert?