Body site is sterile brain, completely sterile because of blood-brain barrier not stomach, which is almost sterile. Dna or rna or combination of both. Do not metabolize things, relatively inert, need host cells to take over and make progeny. Bacteria are cells: have own metabolism, have ribosomes, have rna/dna bacteria. Metabolism - break down what s ingested, turn it into something. Do not need host cell, in theory to reproduce: some bacteria require host but not using host rna and dna enzymes for reproduction. Can move autonomously have appendages, flagella or villi how move, how direct movement. Sense environment and respond to it: product of four billion years of evolution, v. well adapted to environment. If something changes in env, can change transcription and proteins accordingly to do better in that environment: living cells that can communicate with each other and environment and can evolve (viruses can also evolve) Life style starts at a fruiting body.