As hard as it is to believe, bacteria (also known to scientists as Bacillus, thuringensis) are everywhere; on your hands, on door handles, there's even thousands bacteria on the period at the end of this sentence (That's how small they are). Bacteria have been around for about 3.5 billion years. They were the first life forms on earth and more numerous then any other species we know of. Yet, while they are extremely common, they are also very small. Bacteria can only be seen with microscopes and are usually less then one micron (0.00002 inches) in length. Before I can explain how bacteria affect our world, you need to know more about them. Basically, bacteria are numerous, unicellular organisms that don't contain a nucleus and consist of a capsule and a cell membrane made of peptidoglycan (that's a protein-sugar molecule). Like all cells, bacteria contain DNA, but the DNA in bacteria is different then other organisms, see it's arranged in a single circular chromosome while most cells have several rod shaped chromosomes. Some bacteria also have flagella. This assists the bacteria in moving by beating in a propeller-like motion.
             Bacteria can be classified in many different ways. Because of their simple cells structure they fit into the Moneran kingdom. Within that everything is a prokaryote (single celled organism that does not contain a nucleus) so the Moneran kingdom is sometimes called the Prokaryotae kingdom. (Confusing system right?) Bacteria are also sometimes classified as gram negative or gram positive depending on the composition of their cell walls. There are also bacteria that need oxygen called aerobic bacteria and bacteria that don't need oxygen called anaerobic bacteria. Since there are so many different types of bacteria it's hard to figure out how exactly how to group them and which characteristics are most important when putting them into categories. Of course different bacteria co...