Which characteristic is true of axenic animals as compared to animals with normal microflora?

• A. Axenic animals have lower levels of tissue enzymes.
• B. Axenic animals have thicker intestinal walls.
• C. Axenic animals have a larger thymus.
• D. Axenic animals have a shorter life span.

Answer: (A)

Axenic (germ-free) animals lack the microbial signals that normally stimulate development and function of the digestive tract. Because of this absence, the intestinal mucosa doesn’t mature as fully, and the cells lining the gut produce fewer digestive enzymes. That results in lower levels of tissue enzymes in axenic animals compared with those that have a normal microflora. Other ideas like a thicker intestinal wall or a larger thymus aren’t characteristic outcomes of germ-free conditions, and life span differences aren’t a defining feature. So the best match is reduced tissue enzyme activity.