Concepts ● Microorganisms require about 10 elements in large quantities, in part because they are used to construct carbohydrates, lipids,proteins,and nucleic acids.Several other elements are needed in very small amount and are parts of enzymes and cofactors. All microorganisms can be placed in one of a few nutritional categories on the bases of their requirements for carbon, energy and hydrogen atoms or electrons. Nutrient molecules frequently cannot cross selectively permeable plasma membranes through passive diffusion. They must be transported by one of three major mechanisms involving the use of membrane carrier proteins. Concepts Microorganisms require about 10 elements in large quantities, in part because they are used to construct carbohydrates, lipids, proteins, and nucleic acids. Several other elements are needed in very small amount and are parts of enzymes and cofactors. All microorganisms can be placed in one of a few nutritional categories on the bases of their requirements for carbon, energy and hydrogen atoms or electrons. Nutrient molecules frequently cannot cross selectively permeable plasma membranes through passive diffusion. They must be transported by one of three major mechanisms involving the use of membrane carrier proteins