Effects of close association on respiration. A) The number of protons that need to pumped across the membrane to achieve a -200 mV Δp decrease as inter-cell spacing (gap) decreases. B) When normalized to the number of protons needed to achieve a -200 mV Δp with an infinite gap, the effects of cell shape essentially disappear and the effects of cell size are diminished (that is, the six curves now nearly overlap). This overlap shows that each cell type derives approximately the same relative energetic benefit from decreases in gap. These benefits are substantial, a 30% reduction in number of protons needed to be pumped (relative to the infinite case) at a 7 x 10-8 M gap and a 50% reduction at 3.5 x 10-8 M gap. C) Decreasing gap decreases the cytoplasmic alkalization necessary to achieve the Δp. D) Decreasing gap increases the acidification of the extracellular medium, but even with small gap this acidification is not extreme. E) Decreasing gap strongly increases the percentage of the Δp arising from the concentration term (and hence decreases the percentage arising from the electrical term) of the proton motor force equation. Key applies to all panels.