Use of radioactive isotopes in study of mechanism of- Photosynthesis in plants → A small quantity of Radioactive C O ∗ 2 containing radioactive oxygen O 18 is mixed with ordinary carbondioxide and the process is carried out. It has been found that oxygen gas evolved along with sugar formation is non-radioactive. 6C O ∗ 2 +6H 2 O⇌C 6 H 12 O 6 +6 O ∗ 2 Thus O 2 produced comes from water and not from carbondioxide.
Hydrolysis of esters → The mechanism of ester hydrolysis can be studied by using water labelled with O 18 . The hydrolysis of an ester by water enriched with radioactive oxygen is indicated as : RCOOR+H O ∗ H⇌RCO O ∗ H+R−OH Thus it is the acid and not alcohol produced which is radioactive confirming the above mechanism.