So here we have an example problem that asks, which of the following is not a function of lymph nodes? And we've got these 4 potential answer options down below. And option A says filtration of lymph or filtering out pathogens from the lymph, or in other words, removing disease-causing agents from the lymph. And, of course, this is definitely a function of lymph nodes. It's probably the main function of lymph nodes, if you will. And so we can eliminate answer option A because we are looking for the option that is not a function of lymph nodes.
Now option B says, providing a site for lymphocytes to mature. Now on first glance, this might seem like a function of lymph nodes. However, recall that lymphocytes mature in the primary lymphoid organs, which are the red bone marrow for B cells and the thymus for T cells. And so lymph nodes are not primary lymphoid organs; they are secondary lymphoid organs, which means that lymph nodes already have mature lymphocytes, and the lymph nodes do not provide a site for lymphocytes to mature, which means that answer option B is not a function of lymph nodes. So we can indicate that answer option B is the correct answer that we are looking for.
Now just to be sure, let's check option C and D. Option C says initiating the immune response when a foreign antigen is detected. And, of course, we know that this is also a function of lymph nodes, so we can cross off option C. And then option D says, these are all functions of lymph nodes, but, again, we've already identified option B as not a function of lymph nodes, so we can also cross off option D. And, again, option B is the correct answer to this example problem. That concludes this example, and I'll see you all in our next video.