**Help with an AP Bio Question

Test Preparation AP Sciences
1

<p>Question reads: Nitrogen-fixing bacteria are abundant in soils and convert atmospheric nitrogen into nitrates. Plants are able to use the nitrates to synthesize plant proteins. This is an example of</p>

<p>(A) mutualism
(C) commensalism</p>

<p>The answer was A and I chose C. How is this relationship of any benefit to the nitrogen-fixing bacteria? By virtue of these bacteria, plants are able to make proteins for themselves, which doesn't seem like any reciprocation to me. Bacteria do their own task and while they do this, plants benefit: commensalism? Bacteria seem to be impervious to anything that plants do or make in this question..... Help?</p>

<p>Thanx in advance :)</p>

2

<p>The bacteria are located in these structures in the roots called nodules which protect the bacteria and provide them with food.</p>

3

<p>oh I guess the question presupposed my knowledge of nitrogen-fixing bacteria.
Thanx aldfig0!! :slight_smile: By any chance, does the real AP exam assume that students know some knowledge like this? I am still a fledgling AP student, so …</p>