The electrons that chlorophyll loses to electron transport chain are replenished by

Electron Transport Chain or ETC is a series of compounds which transfer electrons to electron transfer from electron donors thru a redox reaction which in turn, couples this electron transfer with the proton transfer (H+ ions) through the membrane.
The negatively charge particles that chlorophyll loses to the transport chain or ETC are replinished by the molecules of water. Water is divided and electrons from it are used to replace the electron found in the chrlorophyll pigment.