Minerals in plant tissue culture are divided into macro and micronutrients. Ca, P, S, Mg, N and K are considered macro-elements, while Fe, Cu, Mn, Co, Mo, B, I, Ni, Cl and Al are considered micro-elements. The categorization of macro and micro-elements is based on necessary quantities for healthy cell growth. All macro and micronutrients must be provided in balance to allow for equally available cations and anions to support cell growth. Nutrients must also be supplied in a pure form, free of other elements and heavy metal contaminants.