Similarities between economic markets and biological markets.

<p><b>(a)</b> Market trade between countries where labor is used to produce goods. A unit of labor can produce 1 wine or 3 cloth in <i>Country 1</i> and 3 wine or 1 cloth in <i>Country 2</i>. Both countries benefit through trade by having <i>Country 1</i> trade cloth to <i>Country 2</i> for wine. Demand drives production and consumers purchase goods to maximize their utility. <b>(b)</b> Metabolic exchange between microbial cells. Microbes convert an input resource (grey symbol) into metabolites needed for growth (colored squares/triangles). For each unit of input, <i>Cell 1</i> can produce either 2 square metabolites or 1 triangle metabolite, while <i>Cell 2</i> can produce either 1 square metabolite or 2 triangle metabolites. <i>Cell 1</i> exports its squares and <i>Cell 2</i> exports its triangles into the environment, where metabolites mix and are imported back into cells. Metabolites are then used for growth as cells tune their production levels to maximize individual growth rates.