What are the substrates and products of the light-independent reactions of photosynthesis?

The substrates of the light-independent reactions of photosynthesis are carbon dioxide, ATP, and NADPH. The products are glucose and oxygen.

The light-independent reactions, also known as the Calvin cycle, occur in the stroma of the chloroplasts. These reactions do not require light, hence the name 'light-independent'. The main substrates or inputs for these reactions are carbon dioxide (CO2), adenosine triphosphate (ATP), and nicotinamide adenine dinucleotide phosphate (NADPH). These molecules are produced in the light-dependent reactions and are used in the Calvin cycle to produce glucose.

Carbon dioxide enters the leaf through tiny pores called stomata and diffuses into the stroma of the chloroplasts. Here, it combines with a five-carbon sugar called ribulose bisphosphate (RuBP) to form an unstable six-carbon compound. This compound quickly breaks down into two molecules of a three-carbon compound, glycerate 3-phosphate (GP).

ATP and NADPH, produced in the light-dependent reactions, are used to convert GP into another three-carbon compound, glyceraldehyde 3-phosphate (G3P). Some G3P molecules are used to regenerate RuBP, allowing the cycle to continue, while others are used to synthesise glucose.

The glucose produced can be used by the plant for energy or converted into other substances such as cellulose or starch. Oxygen is also produced as a by-product of these reactions, although it is not the main product. The oxygen is released into the atmosphere through the stomata.

In summary, the light-independent reactions of photosynthesis use carbon dioxide, ATP, and NADPH to produce glucose and oxygen. These reactions are a crucial part of the photosynthetic process, allowing plants to convert light energy into a form that can be stored and used for growth and reproduction.