Yogurt exists because Lactobacillus (heterotrophic) ferments milk sugar into lactic acid — you eat bacterial waste products daily. Cyanobacteria (photoautotrophs) oxygenated Earth's atmosphere 2.4 billion years ago — every breath you take is their legacy. Hospital sterilization works because endospores (Bacillus, Clostridium) survive boiling — autoclaves use pressurized steam at 121°C to kill them.