Question

Certain bacteria living in a human's large intestine help to produce vitamin K. The intestines are a safe place for the bacteria to live, with plenty of food available. This relationship is an example of

a) animal parasitism.
b) plant parasitism.
c) commensalism.
d) mutualism.

Answer 1

A. mutualism
Both organisms benefit from this relationship, which is why it is called mutualism. The human gets vitamin K and the bacteria get a place to live. Commensalism is when one organism benefits and the other is not affected. Parasitism is when one organism benefits at the other organisms expense.