Isotopes: Biological Applications
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Isotopes: Biological Applications

Biological applications of isotopes.

Isotopes are atoms having the same atomic number but different atomic weights. They are varieties of the same chemical element but with different physical properties. As an example we have hydrogen which has three isotopes. Namely, H1 or ordinary hydrogen consisting of a nucleus containing a proton around which revolves an electron; H2 or heavy hydrogen (deuterium) which contains an additional nuclear particle, a neutron, and H3 or tritium which has two neutrons .(See illustrations below.)

Since the atomic number is given by the net nuclear charge, these three atoms are evidently varieties of the same element. But deuterium is twice as heavy as ordinary hydrogen while tritium is three times heavier and is radioactive.

Classes of Isotopes

There are two classes of isotopes. The stable isotopes which is distinguished only by its mass, like deuterium. And the radioactive isotopes which differ not only in mass but also by possessing an unstable nuclei which cause them to decompose spontaneously, thus emitting radiation (electron and gamma radiation).

This variation in the mass of certain isotopes and the radioactivity of others allow the accurate determination of minute amounts of these elements in the body. Example: If deuterium is made to react with O2, water with twice the specific gravity of the ordinary water is formed. Minute amounts of this heavy water, when administered, can be detected readily. Again, radioactive isotopes in very minute quantities (one gram C14 diluted to 1,000,000) can be detected in the body by the use of a sensitive instrument (Geiger-Muller counter). By incorporating therefore one or more isotopes into a given substance, the latter becomes labeled or tagged and can be followed or traced in the body. Hence, isotopes are called tracer substances.

Isotopically labeled compounds are used for biological investigations. Isotopes are introduced into definite groups of a given molecule of a foodstuff, and the fate of the group can be followed throughout its travel in the animal body. By this, it is possible to demonstrate the intricate mechanism of the conversion of one compound into another. It has been demonstrated by these studies, that the biochemical reactions are more of a dynamic nature, and that many substances are first incorporated in the protoplasm before they are being utilized.

“Isotope analysis determines the relative abundances of isotopes of a given element in a particular sample. For biogenic substances in particular, significant variations of isotopes of C, N and O can occur. Analysis of such variations has a wide range of applications, such as the detection of adulteration of food products. The identification of certain meteorites as having originated on Mars is based in part upon the isotopic signature of trace gases contained in them.”


1. Biochemistry by Belen Espino Cabatit. 1959 Manila, Philippines

2. Applications of Isotopes. http//

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