The Calvin Cycle: Building Sugars
The Calvin cycle uses the ATP and NADPH produced during the light reactions to convert carbon dioxide into glucose. This process occurs in the stroma and consists of three main phases: carbon fixation, reduction, and regeneration.
During carbon fixation, the enzyme RuBisCO attaches CO₂ to a five-carbon sugar (RuBP). The resulting six-carbon compound immediately splits into two three-carbon molecules. These molecules undergo reduction using NADPH and ATP from the light reactions, eventually forming glucose.
Example: Think of the Calvin cycle as a factory assembly line: CO₂ enters, gets processed through multiple steps using energy from the light reactions, and exits as sugar molecules that the plant can use for growth and energy storage.
The cycle must turn three times to produce one molecule of three-carbon sugar (G3P), which can then be converted into glucose. This intricate process demonstrates how plants efficiently convert inorganic carbon into organic molecules essential for life.