Part 1: Marvelous Molecules
http://www.ducksters.com/science/molecules.php
Part 2: Our Digestive System
https://www.niddk.nih.gov/health-information/health-topics/Anatomy/your-digestive-system/Pages/anatomy.aspx
Part 3: Science Museum
http://www.sciencemuseum.org.uk/whoami/findoutmore/yourbody/whatdoyourcellsdo/whatisacellmadeof