What Is the Primary Function of the Calvin Cycle?

The Calvin Cycle, Plants, and Photosynthesis

The Calvin cycle is responsible for carbon fixation.
The Calvin cycle is responsible for carbon fixation. Frank Krahmer, Getty Images

The Calvin cycle is the final step of photosynthesis. Here is an explanation of the primary function of this important step:

Purpose of the Calvin Cycle - Carbon Dioxide and Water Converted into Glucose

In the most general sense, the primary function of the Calvin cycle is to make organic products plants need, using the products from the Light Reactions of photosynthesis (ATP and NADPH), These products include glucose, the sugar made using carbon dioxide and water, and also protein (using nitrogen fixed from the soil) and lipids (e.g., fats and oils).

This is carbon fixation, or 'fixing' inorganic carbon into organic molecules that the plant can use:

3 CO2 + 6 NADPH + 5 H2O + 9 ATP → glyceraldehyde-3-phosphate (G3P) + 2 H+ + 6 NADP+ + 9 ADP + 8 Pi   (Pi = inorganic phosphate)

The key enzyme for the reaction is RuBisCO. Although most texts simply say the cycle makes glucose, the Calvin cycle actually produces 3-carbon molecules, which are eventually converted into the hexose (C6) sugar, glucose.

The Calvin cycle is a set of light independent chemical reactions, so you may also hear it referred to as the Dark Reactions. This doesn't mean the Calvin cycle only occurs in the dark -- it just doesn't require energy from light for the reactions to occur.

Summary

The primary function of the Calvin cycle is carbon fixation, which is making simple sugars from carbon dioxide and water.

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Helmenstine, Anne Marie, Ph.D. "What Is the Primary Function of the Calvin Cycle?" ThoughtCo, Feb. 13, 2017, thoughtco.com/the-purpose-of-the-calvin-cycle-608904. Helmenstine, Anne Marie, Ph.D. (2017, February 13). What Is the Primary Function of the Calvin Cycle? Retrieved from https://www.thoughtco.com/the-purpose-of-the-calvin-cycle-608904 Helmenstine, Anne Marie, Ph.D. "What Is the Primary Function of the Calvin Cycle?" ThoughtCo. https://www.thoughtco.com/the-purpose-of-the-calvin-cycle-608904 (accessed November 24, 2017).