Most bacteria range from 1 to 5 microns in size. The electron microscope, which can magnify more than 300,000 times, has greatly increased man's knowledge of bacteria. The compound microscope, the only one available for many years, was limited to a magnification of about 1,000. How Bacteria Live Bacteria absorb their food and secrete their wastes through the cell wall. They secrete enzymes that break down the food into soluble form so that it can pass through the wall.
Some bacteria can live on simple mineral compounds.
Others have very complex food requirements. At the other extreme are the disease bacteria, which are parasitic. They rely on their host to supply their food in a predigested form. The saprophytes live on decaying remains of plants or animals. The anaerobes can grow without air because they obtain their oxygen from their food.