Biology · Photosynthesis in Higher Plants · NEET
It is associated with PS II. This is the single most tested point. NCERT says clearly: 'The splitting of water is associated with the PS II.' PS II loses electrons when light hits P680, and those lost electrons are replaced by electrons released when water is split. PS I does NOT split water. Any statement saying 'water splitting complex is associated with PS I' is INCORRECT (this exact wrong statement appeared in NEET 2026).
Water is split into three things: protons (H+), oxygen (O2), and electrons. NCERT writes it as water splitting into '2H+, [O] and electrons'. The balanced form is 2H2O gives 4H+ + O2 + 4e-. The O2 released here is the oxygen we breathe, and it is a net product of photosynthesis. The electrons go to replace the ones lost by PS II, and the H+ builds up in the lumen for ATP making.
On the inner side, that is, facing the lumen. NCERT states the water-splitting complex is on the inner side of the thylakoid membrane, so the H+ (protons) and O2 are released INTO the lumen. This is important because those protons build a proton gradient inside the lumen, which later drives ATP synthase. If you are asked where protons accumulate, the answer is 'in the lumen of the thylakoid'.
It needs light and is part of the light reaction (photochemical phase). The word 'photo' in photolysis means light. Water splitting, oxygen release, and the making of ATP and NADPH all happen only when light is absorbed by the photosystems. It is NOT part of the Calvin cycle (dark reaction), which does not split water.
Manganese (Mn). The oxygen-evolving / water-splitting complex uses manganese, along with chloride (Cl-) and calcium (Ca2+) ions. NEET 2023 asked exactly this and the answer was manganese, not magnesium, molybdenum or copper. Do not confuse manganese (Mn, splits water) with magnesium (Mg, the central atom of chlorophyll).
Which micronutrient is required for splitting of water molecule during photosynthesis?
Find the incorrect statement(s) about photosynthesis: A. The water splitting complex is associated with PS I. B. C4 plants use the C3 pathway of CO2 fixation as the main biosynthetic pathway. C. In C4 plants, photorespiration does not occur. D. C3 plants exhibit 'Kranz' anatomy. E. ATP synthesis in chloroplast occurs through chemiosmosis.
Which of the following statements about RuBisCO is true?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
2H2O gives 4H+ + O2 + 4e-. NCERT describes water being split into 2H+, [O] and electrons. The oxygen produced is released as O2, the protons stay in the lumen, and the electrons replace those lost by PS II.
Because when water is split at PS II, oxygen is released. The main aim of splitting water is to get electrons (to refill PS II) and protons (for ATP). The oxygen is simply left over, so it is called a by-product, yet it is a net product that all animals breathe.
Photolysis splits water and needs light (light reaction). The Calvin cycle (dark reaction) does not split water at all; it uses the ATP and NADPH made during the light reaction to fix CO2. So water splitting is only in the light reaction.
Into the lumen of the thylakoid, because water is split on the inner side of the membrane. These protons build up and create a proton gradient that later drives ATP synthase to make ATP.
Indirectly, yes. The electrons from split water first refill PS II. From PS II, electrons move along the Z-scheme (through carriers to PS I) and finally reduce NADP+ to NADPH. So water is the original source of electrons in non-cyclic electron transport.
