Match the following prokaryotic classes with differing modes of metabolism with the appropriate descriptions - obligate anaerobes - Facultative anaerobes - Aerotolerant anaerobes - Obligate aerobes A. can shift their metabolism between anaerobic and aerobic modes B. Oxygen-sensitive, can only use anaerobic mode of nutrition C. unable to survive for extended periods in the absence of oxygen. They require oxygen for cellular respiration. D. cannot conduct cellular respiration but are not damaged by oxygen when it is present

Obligate anaerobes are microorganisms that dead in normal atmospheric oxygen (O2) levels (around 21%). Some examples of obligate anaerobes are procaryotic bacteria such as Clostridium, Fusobacterium, Actinomyces and Peptostreptococcus. Facultative anaerobes are organisms that can grow without O2 and produce energy by fermentation, but they can produce more energy (ATP) by the aerobic respiration mechanism. Facultative anaerobes include both prokaryotic (e.g., Escherichia coli) and eukaryotic (e.g., Saccharomyces cerevisiae) organisms. Aerotolerant anaerobes are microorganisms that can live in O2 atmospheric conditions, but they use fermentation as cellular mechanism to produce energy (ATP). Some examples of aerotolerant anaerobes are lactobacilli and streptococci (bacteria) found in the oral microbiota. Finally, obligate aerobes are organisms that can grow only in normal O2 conditions and metabolize foods through cellular respiration, a process more energetically efficient than fermentation. An example of an obligate aerobe is the human species.