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Understanding the Calvin Cycle: Carbon Fixation in C3, C4, and CAM Plants

The Calvin Cycle, a crucial light-independent reaction in photosynthesis, occurs in the stroma of chloroplasts and is responsible for carbon fixation in C3 plants, which represent 80% of Earth's plant species. It utilizes ATP and NADPH generated from light reactions to convert CO2 into glucose over six cycles, requiring 18 ATP and 12 NADPH. The cycle can be affected by photorespiration under hot, dry conditions. To counter this, C4 and CAM plants have developed adaptations, optimizing photosynthesis in varying environments.

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Understanding the Calvin Cycle: Carbon Fixation in C3, C4, and CAM Plants

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  1. PHOTOSYNTHESIS

  2. Calvin Cycle • Carbon Fixation (light independent rxn). • C3 plants (80% of plants on earth). • Occurs in the stroma. • Uses ATP and NADPH from light rxn. • Uses CO2. • To produce glucose: it takes 6 turns and uses 18 ATP and 12 NADPH.

  3. Stroma Outer Membrane Thylakoid Granum Inner Membrane Chloroplast

  4. C3 Glucose Calvin Cycle • Remember:C3 = Calvin Cycle

  5. Photorespiration • Occurs on hot, dry, bright days • Stomatesclose • Fixation of O2 instead of CO2 • Produces 2-C molecules instead of 3-C molecules • Produces no sugar molecules or no ATP

  6. Photorespiration • Because of photorespiration: Plants have special adaptations to limit the effect of photorespiration. 1. C4 plants 2. CAM plants

  7. C4 Plants • Hot, moist environments. • 15% of plants (grasses, corn, sugarcane). • Divides photosynthesis spatially. • Light rxn - mesophyll cells. • Calvin cycle - bundle sheath cells.

  8. CAM Plants • Hot, dry environments • 5% of plants (cactus and ice plants) • Stomatesstay closed during day • Stomates open during the night • Light reactions occur during the day • Calvin Cycle occurs when CO2 is present

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