what would the variables and controls in this experiment be?

 

What makes apples and bananas go brown?

That isn't an experiment, it's a question. You need to provide an outline of the experiment you would use to try to answer that question.

ummm it is for a science project. im going to cut pieces of apple and banana and observe what happens

Well that will only confirm what you suspect--that they go brown. You need to test WHY they go brown. Let's say you suspect that an exposure to oxygen (not necessarily true, I just threw that out) would turn them brown. Then you might want to design an experiment which exposed pieces to high flow O2, some pieces that were not exposed to any O2, and some that were just left in the air.

Here's another idea for your project: adding lemon juice keeps apple pieces from browning, so you could test what it is about the lemon juice that prevents the browning. For instance, you could hypothesize that the acidity of the juice is responsible. You could then coat some apple slices with lemon juice, some with another acid (like vinegar), and some with water, which has a neutral pH.

Ethene gas is also responsible for "over ripening", it may be worth looking into that as well as most all fruits and some veg give off this gas naturaly, and more so when damaged

but suppose you did the lemon juice one. your independent variable would be the amount of lemon juice(coz you can control that), though your dependent is the amount of browning, b/c it relies on the amou8nt of lemon juice. I think

In the experiment outlined by Ms DNA (which is a good one; I would go with it), your independent variable would what substance you coated the fruit with, and will have three levels: Lemon Juice, vinegar, water (water being the control).

 

That would be easier than having amount of lemon juice as an IV, because I think coating a piece of fruit in a liquid would take a fixed amount (depending on the viscosity of the liquid), so to manipulate the amount of lemon juice, you would have to work out several different concentrations of lemon juice and things could begin to get complicated then.

 

Your dependent variable would be rate of browning. This is probably the easiest measure as you can simply record the amount of time until the fruit starts going brown rather than trying to measure how brown a piece of fruit is or how much 'browner' any piece of fruit is than any other, which may be a bit subjective.