Question

A plant is exposed to water labeled with a radioactive isotope of oxygen that can be traced as it moves through the plant. The plant is then exposed to sunlight. Once photosynthesis occurs, where will the radioactive oxygen from the water end up?

Answer 1

In photosynthesis water is the source of oxygen. Carbondoxide is not the source of oxygen but t is fixed as sugar molecules.The oxygen from water is released in the light reaction of photosynthesis. It is done by the water splitting complex present in PSII ( Reaction centre II) in chloroplast. Water is splitted up by the water splitting complex to produce H+(protons) and electrons and oxygen is released.

  
_{21,0 + 4H+ + 4e +02}

^{_{The protons and electrons enter into the electron chain to generate ATP and NADPH .The oxygen evolved is released out of the plant. It is released through the stomatal pores along with water vapour by the process called transpiration.}}

^{_{In this experiment, after the plant is exposed to water with radioactive oxygen,and provided with sunlight, photosynthesis will be carried out. Water containing radioactive oxygen will be splitted up by the water splitting complex at PSII and will generate the protons and electrons. The oxygen evolved will be released out through stomatal pores of the leaves.}}