Fruits and vegetables contain an additional class of nutrients called phytochemicals. Phytochemicals simply means "plant chemicals." Some phytochemicals, including certain vitamins, are antioxidants. As you already know, oxidizing agents (free radicals) are molecules hungry for electrons that snatch them away from any molecule they can find. These oxidizing bad boys snatch electrons from molecules in the cell membrane; they grab electrons from organelles within the cell; they even steal electrons from the cell's sacred DNA.
When a molecule loses electrons, it can become altered in a way that makes it dysfunctional. Good-guy antioxidants work by selflessly sacrificing their own electrons to the bad-guy oxidizing agents so that the vital cell structures won't be robbed of their electrons. Oxidizing agents come from the ultraviolet radiation of the sun, cigarette smoke, and pollution. Each one of your cells actually gets thousands of oxidative hits each day, so it is critical that you get an adequate supply of antioxidants. The health consequences of oxidation include cancer, heart disease, blindness from macular degeneration, and cataracts.