Final answer:
In photosynthesis, the light-dependent reactions convert sunlight into ATP and NADPH in the thylakoid membranes, and these molecules then drive the light-independent reactions in the stroma, which fix CO2 into sugar. ATP and NADPH link the two processes, cycling between 'full' and 'empty' states to sustain the synthesis of glucose.
Step-by-step explanation:
Photosynthesis occurs in two main stages: the light-dependent reactions and the light-independent reactions (also known as the Calvin cycle). During the light-dependent reactions, which take place in the thylakoid membranes, pigments like chlorophyll absorb sunlight and convert it into chemical energy in the form of NADPH and ATP. This process also generates oxygen from water. The light-independent reactions, occurring in the stroma, use the ATP and NADPH to convert carbon dioxide into glucose, a process known as carbon fixation. The energy-rich molecules of ATP and NADPH are essential for the Calvin cycle, and therefore, link the two stages of photosynthesis together.
These stages are interconnected as the energy carriers ATP and NADPH, which are produced during the light-dependent reactions, are necessary for driving the Calvin cycle. After the energy from ATP and NADPH is utilized in the light-independent reactions, they become 'empty' and return to the light-dependent reactions to be re-energized. This creates a continuous cycle that allows plants to convert light energy into a form that can be stored and used for growth, reproduction, and other life processes.