Axenic animals generally have which of the following characteristics?

• A. Thick walled intestines
• B. Poor muscle development
• C. High tissue enzyme levels
• D. Strong immune systems

Answer: (B)

Without microorganisms, axenic animals miss out on the signals and nutrients produced by gut microbes that normally promote growth and tissue maturation. Those microbial cues help drive development of muscles and overall growth, so in their absence muscle formation and strength can be impaired. That’s why poor muscle development is the characteristic most associated with axenic status.

The other options don’t fit as well: there isn’t a reason to expect thick-walled intestines or high tissue enzyme levels simply because the animals are germ-free, and their immune systems are typically underdeveloped rather than strong, due to lack of microbial stimulation.