How is the light energy absorbed by chlorophyll transferred to ATP molecules during photophosphorylation? How is the resulting ATP used?

Answer 1

Electrons in the chlorophyll molecule become energized by photons of light. The electrons are captured by a primary electron acceptor and travel down the the electron transport chain in the thylakoid membrane. As the electrons flow they provide energy for the active transport of H ions from the stroma into the thylakoid space. The thylakoid membrane is not permeable to H ions so that there is a dramatic concentration difference between the thylakoid space and the stroma. But....H ions can pass through an enzyme called ATP synthase via chemiosmosis . As H ions pass through ATP synthase, the enzyme catalyses the formation of ATP from ADP and Pi utilizing the energy (electromotive force) of the H ions . The resulting ATP is used by many plant metabolic processes but particularly in the Calvin Cycle, along with NADPH, to fix CO2 and produce sugar.