Final answer:
Water is the higher energy electron donor in the first half of the light reactions of the electron transport chain.
Step-by-step explanation:
The higher energy electron donor for the electron transport chain in the first half of the light reactions is water.
In photosystem II (PSII), energy from sunlight is used to extract electrons from water, which then travel through the chloroplast electron transport chain to photosystem I (PSI), where NADP+ is reduced to NADPH.
The splitting of water during photosystem II releases electrons, hydrogen atoms, and oxygen. Splitting two molecules of water is required to form one molecule of diatomic O₂ gas.