(A) Numerical solution (diamonds and circles) and analytic solutions (carbonic anhydrase unsaturated, solid lines, and saturated, dashed lines) correspond well. On all plots CO2 (red circle) (blue diamond). Concentration in the cell along the radius, r, with carboxysome permeability kc = 10−5 cm/s (B), kc = 10−3 cm/s (C), kc = 1 cm/s (D). Grey dotted lines in (B), (C), (D) indicate location of the carboxysome shell boundary. The transition from low CO2 at high permeability (D) to maximum CO2 concentration at optimal permeability (C) occurs at . At low carboxysome permeability (B) diffusion into the carboxysome is slower than consumption. For all subplots the rate of CO2 to conversion at the cell membrane, α = 0 cm/s and uptake, jc = 0.6 cm/s. Qualitative results remain the same with varying jc, increasing α will increase the gradient of CO2 across the cell as CO2 is converted to at the cell membrane.