Use the information in the following paragraph to answer the next few questions.
A hypothetical bacterium swims among human intestinal contents until it finds a suitable location on the intestinal lining. It adheres to the intestinal lining using a feature that also protects it from phagocytes, bacteriophages, and dehydration. Fecal matter from a human in whose intestine this bacterium lives can spread the bacterium, even after being mixed with water and boiled. The bacterium is not susceptible to the penicillin family of antibiotics. It contains no plasmids and relatively little peptidoglycan.
-This bacterium derives nutrition by digesting human intestinal contents (in other words, food). Humans lacking this bacterium have no measurable reproductive advantage or disadvantage relative to humans who harbor this bacterium. Consequently, the bacterium can be properly described as which of the following?
1)symbiont
2)endosymbiont
3)mutualist
4)commensal
A) 4 only
B) 1 and 2
C) 1 and 4
D) 2 and 3
E) 2 and 4

Question

Quizplus · Accepted Answer

The bacterium is not providing any benefit to the host and is simply living alongside it without causing harm, making it a commensal organism. It is not an endosymbiont as it is not living inside the host's cells, and it is not a mutualist as it is not providing any benefits to the host. Therefore, the best choice is C, which includes only option 1 and 4 (symbiont and commensal).

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