Metabolic network and elementary flux modes. Species are represented as circles and reactions as rectangles. Reaction stoichiometries are ones. The network has four elementary flux modes that are illustrated using small numbered squares with different colors. For example, mode 3 uses reactions R6, R4, and R1.
Aho et al. BMC Systems Biology 2007 1:22 doi:10.1186/1752-0509-1-22