Living cells are highly compartmentalized. Thus, most biological processes involve intricately regulated flows of matter, energy, and information across membranes. Our research focuses on understanding and controlling energy and information fluxes in biology. New tools such as super-resolution light microscopy now make it possible to investigate these fluxes on the single cell level. I'll briefly discuss some new imaging tools we have developed, such as extremely small sources of coherent visible radiation. Mostly, however, I'll discuss how to create cells that harvest light energy by extruding protons through their cell membrane and how bacteria sense chemicals in their environment. In both cases, our experiments allowed us to construct simple physical models that work unexpectedly well.