The Oxygen Came Out of the Water

A leaf is not one machine. It is two rooms and a relay. In the thylakoid membrane, light knocks an electron out of chlorophyll — and to replace it, the plant tears water apart. That is where the oxygen you are breathing right now came from: not the carbon dioxide, the water. Next door in the stroma, an enzyme called RuBisCO spends the ATP and NADPH that first room made, bolting carbon out of the air into sugar. It never sees a photon. It stops anyway, seconds after the lights go out. Follow the atoms and the energy through both rooms, and every classic mistake in this topic runs out of places to hide.

AP BIOLOGY · 8 STEPS · 6 QUICK CHECKS · O₂ FROM H₂O, NOT CO₂ · LIGHT-INDEPENDENT ≠ IN THE DARK · PLANTS RESPIRE ROUND THE CLOCK · v1