Final answer:
Chlorophyll is the molecule that loses an electron during the light-dependent reactions of photosynthesis, when it absorbs light and becomes excited. The electron vacancy is then filled by an electron from the splitting of water.
Step-by-step explanation:
During the light-dependent reactions of photosynthesis, the molecule that loses an electron is chlorophyll. This occurs when chlorophyll absorbs the energy from a photon and becomes excited, at which point it transfers an electron to a nearby primary electron acceptor. To replace the missing electron in the chlorophyll molecule, a water (H₂O) molecule undergoes photolysis, splitting into oxygen, hydrogen ions, and providing the replacement electrons.
Therefore, while water is indeed split during this process, it is chlorophyll that directly loses the electron as a result of light absorption. The electrons from water then replenish the electron 'vacancy' in chlorophyll, permitting the molecule to continue absorbing light and participating in photosynthesis.
When a photon is absorbed by chlorophyll, it causes an excited electron to leave the chlorophyll. This electron is then replaced through a process called photolysis, where a water molecule is split into oxygen atoms, hydrogen ions, and electrons. The electrons released from water molecules replace the lost electrons in chlorophyll.