I found this website, The Elements of Life, and wanted to point out a cool part for my 8th grade Life Science students:
"The most common elements in a cell are:
Hydrogen (H) 59%
Oxygen (O) 24%
Carbon (C) 11%
Nitrogen (N) 4%
Others such as phosphorus (P) and sulphur (S) 2% combined
But these are not the only elements that have important roles for living things! Plants and animals need a variety of elements to survive and grow.
Some elements that are important for animals (including people) are calcium (Ca), for bones and muscles, chlorine (Cl) for digesting food, fluorine (F) for tooth enamel and iron (Fe) to help blood carry oxygen around the body."
This is cool info!