Question

What is the hydrogen donor in green plants?

Answer 1

Green plants:

1. Green plants carry out ‘photosynthesis’, a physicochemical process by which they use light energy to drive the synthesis of organic compounds.
2. In green plants, ${\mathrm{H}}_2\mathrm{O}$ is the hydrogen donor and is oxidized to ${\mathrm{O}}_2$.
3. Some organisms do not release ${\mathrm{O}}_2$ during photosynthesis.
4. When ${\mathrm{H}}_2\mathrm{S}$ instead is the hydrogen donor for purple and green sulfur bacteria, the ‘oxidation’ product is sulfur or sulfate depending on the organism, and not O₂ .
5. Hence, ${\mathrm{O}}_2$ evolved by the green plant comes from ${\mathrm{H}}_2\mathrm{O}$, not from carbon dioxide.
6. This was later proved by using radio isotopic techniques.
7. Photolysis is the reaction involving the splitting of water during photosynthesis.