Answer
Isotopes are variants of chemical element which differ in neutron number. Carbon isotopes act as chemical element even in their radioactive state. Chemical behavior of a radioactive carbon isotope is essentially the same as that of the stable isotope because they have the same number of protons, so it is still carbon.
Work Step by Step
Melvin Calvin used a radioactive form of carbon called carbon-14 to trace the path that carbon took through the algae's chloroplast, the part of the cell where photosynthesis occurs. With this method, he discovered the steps plants use to make sugar out of carbon dioxide (photosynthesis).
When you have the addition of a small quanity of radioactive isotope, it becomes a tracer, which traces molecular changes.
