Table 1. Contributions of membranes to total cellular growth costs.

Ot denotes the green alga Ostreococcus tauri, Sc the yeast Saccharomyces cerevisiae, Ds the green alga Dunaliella salina, and Ss the pig (Sus scrofa) pancreas cell; references given in Supplementary material. Cell volumes and total membrane areas are in units of μm³ and μm², respectively, with the latter excluding membranes associated with the plastids in the algal species. The fraction of the total cell growth budget allocated to membranes is obtained by the ratio of Equations (1b) and (4), using the species-specific reduced costs in Table 1 where available, and otherwise applying the averages for eukaryotic species; this total cost is then apportioned into five different fractional contributions in the following lines.

	Ot	Sc	Ds	Ss
Cell volume	1	44	591	1060
Total membranes	15	204	2299	12952
Fraction of absolute cell growth budget	0.324	0.096	0.094	0.302
Plasma membrane	0.556	0.328	0.134	0.044
Mitochondria	0.243	0.359	0.197	0.223
Nucleus	0.113	0.085	0.034	0.008
Endoplasmic reticulum + Golgi	0.034	0.111	0.318	0.706
Vesicles/vacuoles	0.055	0.114	0.316	0.019