During Photosynthesis, When Is CO2 Utilized?

During photosynthesis, carbon dioxide (CO2) is utilized in the Calvin cycle, which is the second stage of the process. This stage occurs in the stroma of the chloroplasts in plant cells.

Here’s a step-by-step explanation of how CO2 is used:

1. Carbon Fixation: CO2 molecules are attached to a five-carbon sugar called ribulose bisphosphate (RuBP) by the enzyme RuBisCO. This forms an unstable six-carbon compound that immediately splits into two molecules of 3-phosphoglycerate (3-PGA).
2. Reduction Phase: ATP and NADPH, produced during the light-dependent reactions, are used to convert 3-PGA into glyceraldehyde-3-phosphate (G3P), a three-carbon sugar. Some G3P molecules are used to regenerate RuBP, while others are used to form glucose.
3. Regeneration of RuBP: The remaining G3P molecules are used to regenerate RuBP, allowing the cycle to continue.

In summary, CO2 is utilized during the Calvin cycle to produce sugars that the plant can use for energy and growth. This process is essential for the plant’s survival and contributes to the global carbon cycle.