Micronutrients K, Mg, Ca, Fe required in small but significant amts. Marine microbes require sodium. Sugars are common energy sources, bacteria have evolved complex transport system to bring them across membrane whenever possible. Energy may be used in form of ATP More commonly, cells use energy in form of proton gradient or ion gradiend such as sodium gradient. These are usually present as trace contaminants in water, on glassware, or in chemicals used to make media.
Media can be liquid or solid.
Good for growing quantities of microbes needed for analysis or experiments. Unless inoculated with pure culture, cannot separate different organisms. Agar melts at 80-90 deg. C, will remain liquid until temperature cools to 40-42 deg. Very few microbes can degrade agar, so it is normally not a source of C, and acts as inert gelling medium.