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How much fluorine is too much fluorine?

Credit: James Hanly For most of us, our closest encounter with the element fluorine is likely to be our toothpaste or a municipal water supply with added fluoride. But excess fluorine can be a problem. For example, high levels of

The colorful history of plastids

Credit: S Sibbald and J Archibald A billion years ago, a single-celled eukaryote engulfed a cyanobacterium--an organism capable of converting the sun's energy into food in the form of carbohydrates. In one of the single most