What are the differences between light-dependent and light-independent reactions in photosynthesis?

Light-dependent reactions occur in the thylakoid membranes of chloroplasts and require light energy to produce ATP and NADPH. Light-independent reactions, also known as the Calvin cycle, occur in the stroma of chloroplasts and use the ATP and NADPH produced in the light-dependent reactions to fix carbon dioxide into glucose.

During light-dependent reactions, light energy is absorbed by pigments such as chlorophyll and converted into chemical energy in the form of ATP and NADPH. This process is known as photophosphorylation and involves the transfer of electrons along the electron transport chain. Water is also split during this process, releasing oxygen as a by-product.

In contrast, light-independent reactions do not require light energy and instead use the ATP and NADPH produced in the light-dependent reactions to fix carbon dioxide into glucose. This process is known as carbon fixation and involves a series of enzyme-catalysed reactions that convert carbon dioxide into organic compounds. The first step in this process is the fixation of carbon dioxide into a three-carbon molecule called 3-phosphoglycerate, which is then converted into glucose.

Overall, light-dependent and light-independent reactions are both essential for photosynthesis to occur. Light-dependent reactions produce the ATP and NADPH needed for carbon fixation in the light-independent reactions, which in turn produce the glucose needed for plant growth and metabolism.