Addison Wesley, 1995. Cell size and geometry . Indeed, if you were to average the diameter of all the cells on the planet, the average would certainly be far less than that because most of the cells on this planet are bacteria and the average bacterial cell is 3-5 micrometers in diameter. There are three different basic forms of bacteria. Their role is normally related to diseases.
Bacteria are both useful and harmful to humans.
Some are used for soil enrichment with plants, in alcohol and cheese fermentation, to decompose organic wastes and clean up toxic waste sites, and in genetic engineering. Others, called pathogens, cause a number of plant and animal diseases including cholera, syphilis, typhoid fever and tetanus. Bacteria are so tiny that hundreds of thousands of them are able to fit into a space the size of the period at the end of a sentence.