Question

Q. During photosynthesis, oxygen in glucose comes from
A oxygen in air
B water
(c) carbon dioxide
D both (b) and (c).

Answer 1

Solution:
Ruben and Kamen (1941) and Ruben et al (1941) suspended Chlorella in water having nonradioactive heavy isotope of oxygen, ${ }^{18} \mathrm{O}$, instead of natural oxygen ${ }^{16} \mathrm{O}$. The suspension was
illuminated. Oxygen evolved was tested by means of mass spectrometer. It was found to be heavy isotope, ${ }^{18}$ O.This is possible only if oxygen evolved during photos ynth es is comes from
splitting of water. The oxygen in glucose comes from carbon dioxide.
$6 \mathrm{CO}_{2}+12 \mathrm{H}_{2}{ }^{18} \mathrm{O} \underset{\text { chlorophyl, enzymes }}{\text { light }} \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}+6 \mathrm{H}_{2} \mathrm{O}+6{ }^{18} \mathrm{O}_{2} \uparrow$

Answer 2

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Answer 3

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