<h3>
	Overview</h3>
<p>
	In Unit 1 we introduced the students to mercury.<span>&nbsp; </span>They learned that it is toxic and they should by now have at least a rough idea of the kinds of quantities that we might expect to find in human hair and in fish.<span>&nbsp; </span>They should also have a general familiarity with the way that mercury, in its different forms, moves through the environment; more specifically they should think about how it moves through their study site and organism.</p>
<p>
	In this second unit we begin work on the notion of bioaccumulation.<span>&nbsp; </span>Bioaccumulation means that mercury magnifies as you move up a food chain to higher trophic levels.<span>&nbsp; </span>The mechanism is, in some ways, the inverse of the &ldquo;pyramid&rdquo; structure that you introduce to students when you explain how only a small fraction of the energy at one trophic level is transferred to the next, higher level.</p>
<p>
	Understanding the way that bioaccumulation works is essential before students can begin to ask meaningful questions about mercury levels in different organisms, including themselves.<span>&nbsp; </span>It is also a great way to pull together ideas that you are introducing elsewhere in a biology, environmental science, or health science course.</p>
<p>
	Are you what you eat? What about all the toxins and other substances contained in what you eat? These activities provide an understanding of how mercury biomagnifies through food webs, and allow students to construct a mercury diagram for their own study site. Additional background material specific to each activity is presented within the text for each activity.</p>
<p>
	This unit also provides a brief background fact sheet about dragonfly larvae and why scientists suspect they might be good indicators for mercury in our region. The fact sheet and site visit should begin to spark some concrete questions that students might turn into their hypotheses in the next unit.</p>
<p>
	Note:<span>&nbsp; </span>Much of the important material that you will need is referenced through &ldquo;links&rdquo; within this document.<span>&nbsp; </span>Links are indicated through use of colored, underlined text.<span>&nbsp; </span>That means that you will want to use this document in electronic form as well as in printed form, at least some of the time, so you can follow these links.</p>
