tl;dr: E. coli performs chemotaxis—foraging for nutrients—by alternating "runs" and "tumbles" driven by flagellar motors, with the signaling molecule CheY-p carrying information from membrane receptors to rotors in about a tenth of a second. The system achieves remarkable sensitivity (detecting a 2% change in receptor occupancy) and five orders of magnitude of dynamic range via a methylation-based adaptation mechanism that functions as chemical memory. The article walks through the molecular machinery in detail—receptor arrays, phosphorylation cycles, the self-assembling flagellar motor, and direction-switching mechanics—arguing that a single cell is essentially a sophisticated physical computer.