The simplest life-forms on Earth have just one cell. An example of a one-celled life-form is a bacterium. These species of bacteria all cause diseases in humans. But many bacteria are not harmful, or even helpful.
I hate the questioning format for a hook, but I can redesign this handout for my students, because I like the use a hook or walk the plank idea. I think I would use these 3 ways though: big idea, outside quotation, or metaphor