Question

which best describes how the photosystems are used in the light - dependent reactions?
photosystem i is used first then photosystem ii
photosystem ii is used first then photosystem i
both processes are used at the same time.
both processes are used during the light - independent reactions.

Explanation:

In the light - dependent reactions of photosynthesis, photosystem II is activated first. It captures light energy and uses it to split water molecules, releasing oxygen and generating electrons. These electrons then pass through an electron - transport chain to photosystem I. Photosystem I further boosts the energy of the electrons and uses them to produce NADPH.

Answer:

photosystem II is used first then photosystem I