As a teen, what is the difference between bacterial infections and viruses?

The way many people distinguish between bacteria and viruses is that bacteria respond to antibiotics, while viruses don't. (Some viruses respond to antiviral medications such as oseltamivir--Tamiflu--to combat influenza and certain antiviral medications for AIDS, for example, but most viruses simply run their course without treatment.) But their main differences lie in their structure, size, and function. Bacteria are complex cells that have the ability to replicate themselves, while viruses are about one hundred times smaller, much simpler on a cellular level, and don't have the tools to replicate themselves. They need your cells to make babies, and, boy, do they use your cells! Viruses, which can be transmitted from hand-to-hand or mouth to- mouth contact (the common cold) as well as sexually (HIV, HPV), need to spread in order to survive. When a virus attacks one of your cells, it essentially hijacks it, booting out your DNA and substituting its own, then commanding your cellular machinery to make millions of virus clones to send all throughout your bloodstream. (It's similar to how email viruses commandeer your address book and send messages to all of your friends.) The most common virus is the common cold, which is actually caused by several different families of viruses. Even though some bacterial infections do cause upper-respiratory symptoms, most cases of the common cold are not caused by bacteria--thus making antibiotics useless against the fight. In fact, taking them unnecessarily only weakens your immune system.