AP BIOLOGY

Detailed explanation-1: -As the electron from the electron transport chain arrives at photosystem I, it is re-energized with another photon captured by chlorophyll. The energy from this electron drives the formation of NADPH from NADP+ and a hydrogen ion (H+).

Detailed explanation-2: -NADPH is formed on the stromal side of the thylakoid membrane, so it is released into the stroma. In a process called non-cyclic photophosphorylation (the “standard” form of the light-dependent reactions), electrons are removed from water and passed through PSII and PSI before ending up in NADPH.

Detailed explanation-3: -The reaction center chlorophyll of photosystem I transfers its excited electrons through a series of carriers to ferrodoxin, a small protein on the stromal side of the thylakoid membrane. The enzyme NADP reductase then transfers electrons from ferrodoxin to NADP+, generating NADPH.

Detailed explanation-4: -The protons (H+ ions) that are used in photosynthesis come from molecules of water. When light hits chlorophyll it excites electrons, these electrons are used to split a water molecule and create a molecule of oxygen, leaving behind a free proton that can be transported across the membrane to create a proton gradient.