Modern technology and medicine makes use of radioactive isotopes in numerous ways. The following video gives a brief overview of some of the prime uses of radioactive isotopes.
Give special emphasis to the use of radioisotopes, especially C14, in the working out of metabolic pathways. For example: How do we know that plants absorb CO2 from the atmosphere and use it to make glucose? It is done with radioactive tracing. The plant is placed in a chamber with air containing C14O2 for a few minutes. The leaves are then chemically analyzed. Glucose is isolated and found to be radioactive. The only explanation is that the glucose was made from the C14O2 in the air.
Recognize that for every metabolic pathway you learn about in your future schooling, its details were worked out by means of radioisotope tracing. The following video gives another example.
The answer to the question that is left hanging in this video is: nucleic acids. This experiment is the proof that phosphorous is part of nucleic acid molecules; it is not present in proteins.