Calvin Cycle and Reduction of CO2

The Calvin cycle, also known as the Calvin-Benson cycle or the C3 cycle, is a series of biochemical reactions that occur in the stroma of chloroplasts during photosynthesis. It is an essential part of the dark reaction or light-independent phase of photosynthesis.

Function of the Calvin Cycle

The primary function of the Calvin cycle is to convert carbon dioxide (CO2) into glucose, a high-energy molecule that can be used by plants for growth and development. This process is also known as carbon fixation. The Calvin cycle occurs in three main stages: carbon fixation, reduction, and regeneration.

Reduction of CO2

During the reduction phase of the Calvin cycle, the energy-rich molecules ATP and NADPH, which are produced in the light-dependent reactions of photosynthesis, are utilized to convert the unstable 3-phosphoglycerate (3-PGA) molecules into more stable molecules. This reduction process involves the addition of electrons and hydrogen ions (H+) to the 3-PGA molecules.

The reduction of 3-PGA involves a series of enzyme-catalyzed reactions, resulting in the formation of glyceraldehyde 3-phosphate (G3P). For every three molecules of CO2 that enter the Calvin cycle, six molecules of G3P are produced. One of the six G3P molecules is used to synthesize glucose, while the remaining five G3P molecules are used to regenerate the starting molecule of the Calvin cycle, ribulose 1,5-bisphosphate (RuBP).

Final Outcome

In summary, the Calvin cycle leads to the reduction of CO2 by utilizing ATP and NADPH to convert 3-PGA into G3P. This reduction process ultimately results in the production of glucose, which can be used by plants for energy storage and various metabolic processes. Additionally, the Calvin cycle also regenerates RuBP, ensuring the continuous functioning of the cycle.

Conclusion

The correct option for the question is (A) CO2. The Calvin cycle is responsible for the reduction of CO2, which is converted into glucose and other organic compounds necessary for the growth and survival of plants. This process plays a crucial role in the overall process of photosynthesis and is essential for the sustenance of life on Earth.