Calvin cycle

Calvin Cycle

The Calvin cycle is a set of light-independent chemical reactions that occur in photosynthesis in the chloroplasts of plant cells. Named after Melvin Calvin, who won a Nobel Prize in Chemistry for his work on the cycle, it is also known as the Calvin-Benson cycle or the light-independent reactions.

Overview

The Calvin cycle takes place in the stroma of the chloroplasts, where it uses the energy stored in ATP and NADPH during the light-dependent reactions to convert carbon dioxide into glucose. This process is crucial for life on Earth, as it is the primary route by which carbon dioxide is converted into organic compounds.

Stages of the Calvin Cycle

The Calvin cycle can be divided into three stages: carbon fixation, reduction, and regeneration of the starting molecule.

Carbon Fixation

In the first stage, a molecule of carbon dioxide is combined with a five-carbon sugar called ribulose bisphosphate (RuBP) by the enzyme RuBisCO. This reaction produces a six-carbon compound that immediately splits into two three-carbon compounds.

Reduction

In the second stage, the three-carbon compounds are reduced to glyceraldehyde 3-phosphate (G3P) using the energy from ATP and NADPH. Some of the G3P is used to produce glucose, while the rest is used in the next stage of the cycle.

Regeneration

In the final stage, the remaining G3P is used to regenerate RuBP, allowing the cycle to continue.

Significance

The Calvin cycle is a fundamental process in the global carbon cycle, as it allows plants to convert carbon dioxide into organic compounds. This not only provides the energy that plants need to grow, but also forms the basis of the food chain for all other organisms.