I consider, in a Quantum Field Theory theoretical approach, the effects of an electromagnetic field on the components of the total angular momentum of an elementary fermion system, assuming the “minimal” form of the relative interaction. When the electromagnetic field can be treated as a classical one, these effects are particularly simple to be computed and exhibit a number of very general characteristic features in the case of a constant magnetic field. A qualitative possible analogy with similar features of an elementary organic system is finally proposed.