Role of Mb and CK in offsetting diffusion constraints for O20 = 35.1 μM, εmito = 0.25, L = 5 – 50 μm, and Vmax,ATPase = 1 – 120 mM/min; Surfaces are the ratio of (A) η with Mb vs. without Mb and CK, (B) η with CK vs. without Mb and CK, (C) η with Mb and CK vs. without Mb and CK, vs. L and <Rmax,ATPase> for higher mitochondrial volume fraction, smaller size cells and larger ATPase rates.