We’ve talked about one major class of infectious agents: bacteria. Let’s look at the other major class: viruses.

What is a virus?
A virus is a piece of genetic material wrapped in a protein coat: essentially an instruction sheet inside a box. We’re not really sure if viruses are alive. They reproduce and evolve like life, but they don’t have cells, metabolism, and don’t react to being poked, as all other lifeforms do. They also can’t reproduce without the help of a living cell. Have a handful of scientists debate this idea at your next dinner party – it’ll be fun.