A Spool Of Thread
Students describe a spool of light colored thread that the teacher holds in his/her hands. They are asked what substances (cotton and wood) are present and what structures (thread and spool) are present. The teacher conclude that the thread of cotton is wound around the spool of wood. Equate the substance DNA ( one molecular per one spool) to thread and the substance wood to the protein (his tone) it's wound around.