Question

Which substance splits in the beginning of the light-dependent reactions to contribute electrons to the Electron Transport Chain (ETC)?

1) Water
2) Oxygen
3) Carbon dioxide
4) Glucose

Answer 1

Water is the substance that splits during the light-dependent reactions of photosynthesis to provide electrons to the Electron Transport Chain.

Step-by-step explanation:

The substance that splits at the beginning of the light-dependent reactions to contribute electrons to the Electron Transport Chain (ETC) is water (H2O). In the reaction center of Photosystem II (PSII), identified as P680, light energy is used to extract high-energy electrons, which are then transferred through the ETC to Photosystem I (PSI). To replenish the missing electron in P680, a molecule of water is split, releasing two electrons, two hydrogen atoms, and one oxygen atom. The splitting of two water molecules is necessary to produce one molecule of diatomic oxygen gas (O2).