AP BIOLOGY

Detailed explanation-1: -During the light-dependent reactions, an electron that’s excited in PSII is passed down an electron transport chain to PSI (losing energy along the way). In PSI, the electron is excited again and passed down the second leg of the electron transport chain to a final electron acceptor.

Detailed explanation-2: -After electrons get excited by light a second time (at photosystem I), where do they go? They travel down a second electron transport chain and are donated to ADP, which is then converted to ATP. They remain excited and then travel to photosystem II where they get even more excited until they spontaneously combust.

Detailed explanation-3: -After the photon hits, photosystem II transfers the free electron to the first in a series of proteins inside the thylakoid membrane called the electron transport chain.

Detailed explanation-4: -From photosystem II, electrons are carried by plastocyanin (a peripheral membrane protein) to photosystem I, where the absorption of additional photons again generates high-energy electrons. Photosystem I, however, does not act as a proton pump; instead, it uses these high-energy electrons to reduce NADP+ to NADPH.

Detailed explanation-5: -The light excites an electron from the chlorophyll a pair, which passes to the primary electron acceptor. The excited electron must then be replaced. In (a) photosystem II, the electron comes from the splitting of water, which releases oxygen as a waste product.