Living cells have one striking difference from such simple manmade devices as transistor radios: They have a history.

Every living cell developed from an earlier cell that was almost, but not quite, like its offspring. The further back one goes, the less alike a modem cell and its ancestor become. As we trace the lineage backward, we see the outlines of the evolution of life and ultimately the beginnings of life from nonliving chemical systems.

This will be, the ultimate chemical triumph: to understand in detail how this process came about. The present chapter is devoted to the role of structure and organization in a functioning chemical cell, and the final chapter will be addressed to the problem of the origin of life.

Right: A macrophage ingests bacteria as part of the immune response to infection. The white blood cell (a eucaryotic cell - yellow) is protecting its host by devouring the bacteria (blue).