The major role of minor elements inside living organisms is to act as : -

Minor (trace) elements, i.e. micronutrients such as Mn, Zn, Cu, Mo, Fe, B, Cl and Ni, are needed in very small amounts.
Most of them act as cofactors or activators of enzymes: for example Zn for carbonic anhydrase and alcohol dehydrogenase, Mo for nitrogenase and nitrate reductase, Mn for the photolysis of water, Cu in plastocyanin and cytochrome oxidase.
Building blocks of amino acids and structural material are provided by major elements (C, H, O, N, S).
So the major role of minor elements is to act as cofactors of enzymes.