Which term describes an organism that cannot live in the presence of oxygen?

• A. Anaerobic
• B. Aerobic
• C. Prokaryote
• D. Eukaryote

Answer: (A)

An organism that cannot live in the presence of oxygen is described as anaerobic. These organisms don’t require oxygen and are often harmed by it because they lack the enzymes needed to detoxify reactive oxygen species. Anaerobes excel in oxygen-free environments, like deep soils or the gut. The term aerobic, by contrast, refers to organisms that need oxygen to survive. The other terms describe cellular organization rather than how an organism handles oxygen: prokaryotes are organisms without a true nucleus, while eukaryotes have a nucleus and membrane-bound organelles. Some organisms are facultative anaerobes and can grow with or without oxygen, but they are not restricted to living without oxygen, so they don’t fit the description the question specifies.