Organisms can be divided into two main groups based on fundamental differences in their cell structure. Animals, plants, fungi, and protists are eukaryotes. Bacteria and archaea are prokaryotes. All prokaryotes are unicellular while eukaryotes may be single-celled or multicellular.
The term "prokaryote" refers to single-celled organisms that lack nuclei. The term "eukaryote" refers to organisms that may be single-celled or multicellular, but whose cells are distinguished by nuclei that contain genetic informaiton.
This is because muscles of human cells are made up of proteins filaments of actin and myosin, which contain nitrogen molecule. Definitely this should contain the radioactive nitrogen incorporated.