Chapter 4: Understanding the biosphere and the living systems, which inhabit, requires a basic understanding of chemistry. Chapter Three covers this by discussing the structure of the atom, singling out the 30 elements that are important in living systems, related the structure and properties of these essential elements to the periodic table, discussing the difference between atoms and ions. This product uses the interactive capabilities of a computer. The chapter has embedded an end of chapter quiz, uses graphics, animations or user interactivity on almost all pages. This product is designed to provide bite-sized pieces of information in an effort to enhance the scientific literacy of our next generation, not to overwhelm them with sheer quantity of information. Chapter 4 sections: The Atom • Elements in Living Systems Names and Symbols Quiz • Atomic Structure and the Periodic Table • Ions • Checking Your Understanding. This product works both on a Macintosh or PC computer.