How do light-independent reactions function in photosynthesis?

Light-independent reactions in photosynthesis convert carbon dioxide into glucose using ATP and NADPH.

Light-independent reactions, also known as the Calvin cycle, are the second stage of photosynthesis that occurs after the light-dependent reactions. These reactions do not require light to function, hence the name 'light-independent'. They occur in the stroma of the chloroplast, where they utilise the products of the light-dependent reactions, ATP and NADPH, to convert carbon dioxide into glucose.

The Calvin cycle begins with carbon fixation, where a molecule of carbon dioxide combines with a five-carbon sugar called ribulose bisphosphate (RuBP), facilitated by the enzyme RuBisCO. This results in an unstable six-carbon compound that quickly splits into two molecules of 3-phosphoglycerate (3-PGA).

In the next step, known as reduction, these 3-PGA molecules are converted into glyceraldehyde 3-phosphate (G3P) using the energy from ATP and the electrons from NADPH. This is the stage where glucose is actually produced. However, not all of the G3P is used to make glucose. Some molecules are used in the regeneration of RuBP, which is crucial for the cycle to continue.

The final stage is the regeneration of RuBP. Here, the remaining G3P molecules undergo a series of reactions that require further ATP. This results in the production of RuBP, which can then combine with another molecule of carbon dioxide, allowing the cycle to start again.

In summary, light-independent reactions are a crucial part of photosynthesis, converting carbon dioxide into glucose. They utilise the energy and electrons provided by the light-dependent reactions to power the conversion process. The Calvin cycle is a complex series of reactions, but each step is vital for the overall process of photosynthesis.