We are coral reefs.
We secrete these structures of calcium. We live within and upon them.
We pull against these structures to move them about.
It's a pretty good gig. It's luxurious enough that we can afford to blow a significant chunk of our energy on a knot of coral that just talks to itself. And comes up with ways for us to pull against our calcium structures to make the world around us even more luxurious for us.
Or at least that's the way I like to look at my body sometimes. (Yes, I know we are not descended from coral. It sounds a lot prettier than “colonies of cells”.