In fixation, the first stage of the Calvin cycle, light-independent reactions are initiated; CO2 is fixed from an inorganic to an organic molecule. In the second stage, ATP and NADPH are used to reduce 3-PGA into G3P; then ATP and NADPH are converted to ADP and NADP+, respectively.

Because the celvin cycle is the term used for the reaction of photosynthesis .

The Calvin cycle is a biochemical pathway that occurs in the stroma of chloroplasts in photosynthetic organisms. It is also known as the dark reaction, light-independent reaction, or carbon fixation.

The Calvin cycle leads to the reduction of CO2, which means that CO2 is converted into organic compounds such as sugars, amino acids, and lipids. This reduction of CO2 is achieved through a series of enzymatic reactions that use the energy and reducing power from ATP and NADPH, which are produced during the light-dependent reactions of photosynthesis.

The Calvin cycle can be divided into three stages:

1. Carbon Fixation
- CO2 is incorporated into a five-carbon molecule called ribulose bisphosphate (RuBP) by the enzyme Rubisco
- This results in the formation of two molecules of a three-carbon compound called 3-phosphoglycerate (3-PGA)

2. Reduction
- ATP and NADPH produced during the light-dependent reactions are used to convert 3-PGA into glyceraldehyde 3-phosphate (G3P)
- G3P is a three-carbon sugar that can be used to synthesize glucose and other organic compounds

3. Regeneration
- Some of the G3P produced in the reduction stage is used to regenerate RuBP, which is required for the carbon fixation step to occur again
- The remaining G3P molecules can be used for biosynthesis or exported from the chloroplast to the cytosol for use in other metabolic pathways

In summary, the Calvin cycle leads to the reduction of CO2 into organic compounds that can be used by the plant for energy and growth.