The kidney cells referenced in the previous question present functionally different cell-surface areas to the two bodily fluids that they are mediating substance transfer between. This would be best classified as an example of which general membrane property? membrane fluidity as dictated by molecular packing interactions between membrane lipids uniform permeability to substances across the entire surface of a single membrane heterogeneity of lipid and/or protein content within a single membrane biochemical asymmetry of the two opposing faces of a single membrane heterogeneity of lipid and/or protein content between two different membranes.