How does organic fruit differ from ordinary fruit? Will just washing it be enough?

There is so much fruit in the stores right now, but when I see things like strawberries, blueberries, etc, and some are organic and some are not, I wonder what exactly is the difference in what I am eating. I know that pesticides can be used on traditional fruit and they can't be used on organic fruit but does washing the traditional fruit, is that enough? Or does the pesticide get inside the fruit?