What term describes the lowest oxygen level that allows growth?

• A. Minimum permissive oxygen concentration
• B. Maximum permissive oxygen concentration
• C. Microaerophile
• D. Facultative aerobe

Answer: (A)

The idea being tested is that aerobic growth needs a certain minimum amount of oxygen to power respiration. The term that best captures the lowest oxygen level that still allows growth is the minimum permissive oxygen concentration. It signifies a threshold: below this level, the organism can’t grow because there isn’t enough oxygen for efficient energy production; at or above this level, growth is possible.

The other options don’t fit this threshold idea. A microaerophile describes a type of organism that prefers reduced oxygen, not a threshold value. A facultative aerobe is capable of growing with or without oxygen, which is about metabolic flexibility, not the lowest O2 needed to start growth. A maximum permissive concentration would refer to the highest level that still allows growth, which isn’t what’s being asked.