Calvin Cycle and Carbon Fixation Mechanisms

The Calvin Cycle operates through three sophisticated phases in the chloroplast stroma, representing an anabolic process that consumes both ATP and NADPH to produce essential carbohydrates. The cycle requires three complete turns to produce one molecule of G3P, incorporating three CO₂ molecules in the process.

Definition: The Calvin Cycle is an anabolic pathway occurring in the stroma that uses ATP and NADPH to convert CO₂ into carbohydrates.

Highlight: The cycle requires 9 ATP and 6 NADPH molecules to synthesize one G3P molecule.

Example: During carbon fixation, RuBP combines with CO₂ through rubisco enzyme catalysis, forming a six-carbon intermediate that quickly splits.

Vocabulary: Photorespiration occurs when rubisco adds O₂ instead of CO₂ to the cycle, resulting in CO₂ release.

The document also explains alternative carbon fixation mechanisms in specialized plants:

Definition: C4 plants employ a modified pathway that initially fixes CO₂ into a four-carbon compound, with sugar production occurring in bundle-sheath cells.

Highlight: CAM plants demonstrate temporal separation of carbon fixation, opening stomata at night and storing organic acids until daylight hours when the Calvin cycle operates.