Have you thanked your free radicals today?

We hear so much about the havoc that can be wreaked in our bodies by free radicals running amok that it's easy to forget why they're there in the first place. They're actually pretty useful in protecting us from foreign invaaders like bacteria, and maybe even cancer cells that crop up within us. This animation is about how oxygen can trigger the generation of a whole host of reactive oxygen and nitrogen species that our immune cells, like the macrophage shown in this video, can use to destroy pathogens.