Final answer:
Copper (Cu) is not a major element of a microbial cell; it is a micronutrient needed in smaller quantities compared to Oxygen, Carbon, Hydrogen, and Nitrogen, which are macronutrients.
Step-by-step explanation:
The element that is not a major element of a microbial cell is Copper (Cu).
In the context of biology, particularly when studying microbial cells, it is essential to distinguish between macronutrients and micronutrients. Macronutrients are the elements required in large amounts, such as Oxygen (O), Carbon (C), Hydrogen (H), and Nitrogen (N), which are fundamental components of biomolecules and cellular structures.
In contrast, micronutrients or trace elements, like Copper (Cu), are necessary only in small amounts for specific functions, mainly in enzyme catalysis and maintaining the stability of proteins and nucleic acids. While copper is essential to certain biochemical reactions, it does not constitute part of the cell's core structural makeup or the bulk of its biomass like the macronutrients do.