Does this kind of circuit work? I am going to see if having electric voltage through fruit will slow the decay.
So I have my treatment set up here:

and I am going to wrap this so that:

However, my teacher told me that this might not work because in order for the circuit to work, I need to have two types of metals. Also he told me that I need some sort of way to "ground" this. I do not understand why this wouldn't work.
Also, how should I change this so that the fruit will have electric voltage going through, or at least have a contact with electric voltage?
 A: If you wrap the whole thing in aluminum foil (that is the intention, right?), then the current will only travel through that aluminum. Simply because it is much more conducting than the banana, and the contact to the banana is not so good. 
A sidenote: You should not do this, because that would be a short circuit. It is the same as attaching a wired directly form end to end of a battery. A very high current will flow in a short circuit, where it isn't braked, and this will produce extreme heat. And melt / burn something. But well, if you work with a battery and a large foil sheet, the effect will be limited... 
If you wish to actually have current running through the banana, then stick the electrodes through the surface into the creamy banana bulk at each end. Be sure they have good contact, so don't wiggle too much. Avoid air bubbles etc. 
I can't say anything about how or if this will work, since I have no clue about the conductivity or ease of such experiment on a banana, but if the banana has some conductivity and can let electrons move around (just like they can do through your own body of you touch an electric fence), this might give a result. 
About the grounding, this really depends on the equipment - specifically  on the voltage source. If it is a battery, I don't see any need with such low voltage, but let someone more experienced with electronics answer that. 
