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.
For every 1 Tbsp. of Cornstarch, substitute approximately 2 1/2 tsp. of Arrowroot. For every 2 Tbsp. of All-Purpose Flour, substitute approximately 2 1/2 tsp. of Arrowroot. Note on Experimenting with arrowroot: You can adjust the amount of arrowroot to get the desired amount of thickness in the dish you are using it in.