Chlorophyll that loses electrons undergoes photolysis or oxidation of water molecules to regain electrons. The proton combines with NADP to yield the assimilation energy NADPH+H+. If photolysis does not occur, assimilation energy will not be produced. The most powerful oxidant in biology is P680+.
With the help of enzymes, Mn++ and Cl- ions, two molecules of water (2H2O) are decomposed to produce four protons (4H+), four electrons (4e-) and one molecule of oxygen (O2).
In water NADH+H+ to e- combines spontaneously with oxygen to form water. In the process of photosynthesis, electrons move from water to NADP+ under the influence of energy. Water is produced from high energy NADH+H+ in plants. Again, high energy NADH+H+ is produced from low energy water in photosynthesis process. Oxygen and H+ are produced as byproducts. When the body lacks oxygen, nerve cells die first. Water splitting occurs only in the presence of light hence the name photolysis.