AP BIOLOGY

Detailed explanation-1: -TRUE 3. Electrons from water molecules replace the ones lost by photosystem II.

Detailed explanation-2: -Once an electron is lost, each photosystem is replenished by electrons from a different source. The PSII reaction center gets electrons from water, while the PSI reaction center is replenished by electrons that flow down an electron transport chain from PSII.

Detailed explanation-3: -The two electrons lost from photosystem II are replaced by the splitting of water molecules. Water splitting also releases hydrogen ions into the lumen. This contributes to a hydrogen ion gradient similar to the one created by mitochondrial electron transport.

Detailed explanation-4: -Photosynthesis is the process of synthesis of food by plants using carbon dioxide and water in presence of sunlight and chlorophyll. Oxygen (O2) is released during the process as a waste product. Hence, oxygen is not essential for the process of photosynthesis.