What process produces a steady supply of ATP in the presence of sunlight?

The process that produces a steady supply of ATP in the presence of sunlight is non-cyclic photophosphorylation. This process occurs during the light-dependent reactions of photosynthesis within the thylakoid membranes of chloroplasts.

In non-cyclic photophosphorylation, light energy is absorbed by chlorophyll, exciting electrons that then travel through a series of proteins known as the electron transport chain. As these electrons move, they promote the transport of hydrogen ions (protons) from the stroma into the thylakoid lumen, creating a proton gradient. This gradient is then used by ATP synthase to generate ATP from ADP and inorganic phosphate (Pi) through a process known as chemiosmosis.

Not only does non-cyclic photophosphorylation produce ATP, but it also results in the generation of NADPH, another crucial energy carrier used in the Calvin cycle for carbon fixation. This process is vital for plants to convert light energy into chemical energy.

In contrast, cyclic photophosphorylation only produces ATP without the generation of NADPH, and it generally serves more specialized roles in balancing ATP and NADPH levels in the chloroplast. Oxidative phosphorylation involves the production of ATP in mitochondria during cellular respiration