Please see attached problem.
Animals obtain energy through a series of chemical reactions in which sugar ( ) and oxygen gas ( ) are reactants. This process produces water and carbon as waste products. How might you use a radioactive isotope to find out whether the oxygen in comes from sugar or oxygen gas.© BrainMass Inc. brainmass.com October 9, 2019, 8:55 pm ad1c9bdddf
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Sugar contains oxygen.
One can substitute these 16O natural oxygens with say 15O isotope (short one neutron) which has a half life of 122 seconds.
Say 10% of the oxygens in your sugar are now radioactive.
You then measure the amount of CO2 and you can calculate how many oxygen atoms are now present at the gas.
If you supply the sugar continuously to the plant, after a while the CO2 will have an equilibrium ...
The solution explains how one can use radioactive isotopes and their decay properties to track molecules in the chemical process.