|MadSci Network: Botany|
Fruits conduct electricity because they contain ions, which are positively or negatively charged atoms or molecules. Fruits often contain a large amount of positively charged potassium ions. Pure water will be a very poor conductor of electricity as will solutions of uncharged molecules, such as sugar. A solution of table salt will conduct electricity strongly.
You can purchase pocket-size, battery-operated electrical conductivity meters from science supply companies or build a crude one from a 9-volt battery and paperclips. Maybe your school's chemistry teacher can help you.
Try a search on the MadSci Website for potato clock to find out how fruits can be used to generate electricity.
Hershey, D.R. and Sand, S. 1993. Electrical conductivity. Science Activities. 30 (1):32-35.
Try the links in the MadSci Library for more information on Botany.