What is released when one water molecule is split at photosystem II?
AOne electron, one hydrogen atom, one oxygen atom
BTwo electrons, two hydrogen atoms, one oxygen atom
CTwo electrons, one hydrogen atom, two oxygen atoms
DFour electrons, four hydrogen atoms, two oxygen atoms
Answer & Solution
Correct answer: B. Two electrons, two hydrogen atoms, one oxygen atom
1. Splitting one water molecule releases two electrons, two hydrogen atoms and one atom of oxygen.
2. A single oxygen atom is not the gas that leaves the leaf.
3. Splitting two molecules is required to form one molecule of diatomic oxygen gas.
4. So the released oxygen must be paired up before it can escape as a gas.
5. Counting four electrons describes two water molecules rather than one.
6. The hydrogen atoms released here join those pumped across, building the gradient in the lumen.
_Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 8 "Photosynthesis", section 8.2 The Light-Dependent Reactions of Photosynthesis_
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