More impressive than their sheer number, though, is the diversity of bacterial lifestyles. All organisms based on the complex eukaryotic cell (plants, animals, fungi) survive thanks to one of two basic metabolic strategies: photosynthesis and aerobic respiration. There may be astonishing diversity in the world of multicellular life—whales and black widows and giant redwoods—but beneath all that diversity lie two fundamental options for staying alive: breathing air and capturing sunlight.
