The overall layout of the terpenoid biosynthetic pathway model. All metabolites are represented using continous places whereas the regulatory components such as the on/off switches and parameter modulators are represented using generic places. Each transition entity represents a process such as phosphorylation, synthesis and degradation. Each substrate or intermediate is connected to the transition entity by a normal arc whereas an enzyme is connected to its transition entity using a test arc. The MEV subnetwork is on the left and the MEP subnetwork is secluded in a different compartment to depict that the pathway is operative in plastids of eubacterias or chloroplasts or plants.