May have an outer covering over the envelope called a glycocalyx made of polysacchride. May have attached projecting appendages in the form of flagella, fimbriae, pili or spikes. Specialized membrane bound vacuoles are essential for a cell to store nutrients in the cytoplasm. Respiration can not be performed by procaryotes because they lack mitochondria and therefore can not generate a proton motive force. All microbes must be able to make their own energy and protein, or they must live in a host cell that will perform these functions for the microbe.
All microbes are too small to see with the unaided human eye.
The simpler the structure of the microbe, the fewer genes it carries. Facultative anaerobes use O 2 in respiration, but they can make energy through an anaerobic pathway if they are in an O 2 free environment. Aerotolerant anaerobes use O 2 in respiration, but lack superoxide dismutase and catalase or peroxidase. Obligate or strict anaerobes make energy through fermentation or anaerobic respiration, and they lack the necessary enzymes for detoxifying O 2 . Obligate aerobes use O 2 as the terminal electron acceptor in respiration, and they must have the enzymes superoxide dismutase plus either catalase or peroxidase.