The splitting of water and the generation of oxygen occur in the thylakoid membranes of chloroplasts, specifically in Photosystem II during the light- dependent reactions of photosynthesis.

Where it happens in the cell

  • In plants and algae, this reaction takes place inside chloroplasts.
  • Within chloroplasts, it is localized on the thylakoid membranes , not in the stroma or cytoplasm.

The exact site: Photosystem II

  • Water is split at a specialized protein complex called Photosystem II (PSII).
  • Inside PSII, the oxygen-evolving complex (OEC) contains a manganese–calcium cluster that catalyzes the splitting of water into oxygen, protons, and electrons.

What is produced when water splits

  • The reaction produces oxygen gas (O₂) , which is released as a by‑product.
  • It also releases protons (H⁺) and electrons , which are used to generate ATP and NADPH in the rest of the light reactions.

TL;DR: In photosynthesis, water splitting and oxygen generation happen in Photosystem II on the thylakoid membranes of chloroplasts.