Fig. 3 Nutrient supply and demand depends on the type of organism, and the density of exoenzymes. C E , N E , and P E denote the density of the relevant nutrients in the environment (yellow), and we assume that cylindrical cells and hyphae obtain resource over a distance κ times greater than the cell radius ( a ). The metabolic core of all organisms requires C T , N I , and P I for each unit volume of growth (grey). The total mass of C and N required for exoenzymes (blue dots) is equal to x C T + x N I for each unit volume of organism, where in each case the relative density x is chosen to maximise growth rates. Motile cells ( b ) and fungi ( c ) require additional resource for each unit volume (red shapes), to enable motility and internal transport, respectively. These additional costs are represented by the parameters α ¼ 0 : 02 48 and β ¼ 0 : 1,