If you want to prove that living things can produce electricity, you can make a lemon battery.

Gently squeeze the lemon in your hands to release juice from the cells inside the lemon. Make sure you don't break the peel. Now push a straightened paperclip or steel nail so that it goes through the peel. Push a stiff piece of copper wire through the peel next to the paperclip. Moisten your tongue and let it touch the clip and wire. You should feel a tingle. That is electricity flowing through your tongue.