Answer:
In order to find out whether the oxygen in CO2 comes from the sugar or from oxygen gas, we will perform radioactive labeling one by one on oxygen of sugar and oxygen of gas.
After this, we will observe the results and find that labelling of oxygen done in case of sugar produces radio labelled CO2 whereas labelling done in atoms of oxygen gas did not give a radio labelled CO2.
From this, it is concluded that in the process of cellular respiration ( oxidation of sugar to give energy in the form of ATP while producing water and CO2 as waste products), CO2 comes from the sugar molecule and not from oxygen gas.
