An overloading of the gel with a soluble protein creates a semicircular band of this protein (e. g. in the marker lane of the image at 66 KDa), allowing other proteins with similar molecular weights to be covered.
Like arrowroot, tapioca also comes from the root of a plant, however, in this case it is the root of the Cassava plant. It is ground into powdered form and is often referred to as tapioca flour.
I disagree with the above answer. The biggest difference between the two is that bread flour is a white flour made only of the endosperm and whole wheat includes the germ and bran. The closest flour to bread flour would be regular unbleached white flour.