To create spark and to create fire you can use lemon. How? Check out this video which shows the procedure to generate electricity, using lemon. Lemon is convenient, because it provides both the electrolyte and a simple way to support the electrodes. The acid involved in lemon is citric acid.
A piece of zinc metal (such as a galvanized nail) and a piece of copper (such as a penny) are inserted into a lemon and connected by wires. That results in generation of power by reaction of the metals. The zinc and copper are called the electrodes, and the juice inside the lemon is called the electrolyte.