Phospholipids (suggested by Grant)

osmotic processes
the ebb and flow
of nutrients and fluids
cellular membrane
defending
gatekeeper
biochemistry
at its most elegant

I had NO idea what phospholipids were a few years ago when I took microbiology. After taking micro, I had some familiarity with this term. But it didn’t mean anything. So when I was asking for ideas for topics and my son suggested it, I asked him. And he explained that it was something in the cell membrane that regulated the transference of nutrients and water from outside to inside. I also asked my friend Krista via IM, and she underscored its importance — it is in EVERY cell on the planet, apparently.

I didn’t find very many websites that were satisfactory to my level of knowledge in the time I had available, other than one from Western Kentucky University. This explained things pretty well for someone at my level. With a few pictures! Otherwise, wikipedia seems to be accurate, and there are basic definitions on the dictionary sites as well.