Question

During photosynthesis, oxygen in glucose comes from

• A. oxygen in air
• B. water
• C. carbon dioxide
• D. both (b) and (c).

Answer 1

Answer: (C)

carbon dioxide

Answer 2

Ruben and Kamen (1941) and Ruben et al (1941) suspended Chlorella in water having nonradioactive heavy isotope of oxygen, O , instead of natural oxygen O. The suspension was illuminated. Oxygen evolved was tested by means of mass spectrometer. It was found to be heavy isotope, 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. ${6CO2 + 12H2 ^18O ->[{light}][{chlorophyll, \,enzymes}] C6H12O6 + 6H2O + 6 ^18O2 ? }$