my team study tubers (potatoes, onions, yams, and others like that) and tried to a potato clock. a tuber is a eatable root. Most tubers have many acids in them. they produce energy because they have all those acids in them it creates a chemical reaction between copper and zinc or magnesium. in our project we tried to make a potato clock. We couldn't get the clock to work with potatoes or with yams but we did create 4.0 volts. i was in-charge of studding why tuber produce energy. this is the website i used.
Senn, Rob. "How Do Potatoes Produce Electricity?" EHow. Demand Media, 17 June 2010. Web. 18 Apr. 2012. <http://www.ehow.com/about_6640109_do-potatoes-produce-electricity_.html