Once enzymes were selected and lumped metabolic pathways were finalized, yield coefficients were determined in a similar manner to the original PPM (Table ). Briefly, the 15 reaction equations (R1-R15) were assembled to describe microalgal metabolism and growth. Multiple sets of linear equations were then solved using Mathematica (Wolfram Research) based on the active reaction equations for a given set of conditions (nutrient availability and carbon source used). Each set of linear equations also included a reduction balance and assumed no net accumulation of acetyl-CoA, G6P, G3P, biomass precursor, NADH, and ATP.