The correct answer is a) replaced by electrons from water molecules.
During photosynthesis, chlorophyll molecules absorb light energy, which excites electrons and leads to their release. This process occurs in the thylakoid membranes of chloroplasts during the light-dependent reactions. To replace the lost electrons, chlorophyll molecules utilize electrons that are derived from water molecules. Water is split through a process called photolysis, producing oxygen and providing the necessary electrons to replenish chlorophyll’s electron supply. Thus, the cycle of electron transfer and water splitting is essential for sustaining the photosynthetic process and ensuring that energy is captured and transformed into chemical energy for plant growth.