Product vs. biomass yield for every EM in the ( a ) ethanol and ( b ) lycopene model. The number of EMs was 33,220 and 42,659 for the ethanol and lycopene models, respectively (more information on these models can be found in Table 1). Yields are expressed as fractions of the theoretical yield of product or biomass. The theoretical yields of product or biomass on substrate were determined by searching the EMs of the template-genome (the parent strain) and finding the maximal yields for product or biomass on substrate, respectively. Each point in the scatter plot corresponds to an EM (or number of EMs) with a pair of product and biomass yield values. Several EMs were associated with the same pair of product and biomass yield values, which are represented by a single point.