Axemic animals have an intestinal wall that is _____________ than in animals with a normal microflora.

• A. Thicker
• B. Thinner
• C. Less fibrous
• D. More porous

Answer: (B)

Microbial exposure drives development and maturation of the intestinal lining. In axenic (germ-free) animals, the absence of microflora means the mucosa does not receive the usual developmental signals from bacteria, so the intestinal wall remains underdeveloped. This results in a thinner mucosal layer with shorter villi and shallower crypts compared with animals that have a normal microbiota. The idea that the wall would be thicker, less fibrous, or more porous does not align with how microbial stimulation influences gut growth; the well-established effect of microbiota is to promote mucosal development, so removing that stimulus leads to a thinner intestinal wall.