Figure 9.

The simplified PN model of the initiation, synthesis, and degradation of starch adapted from Nöthen (2014). The PN is not pure, because the place Starch is a pre-place as well a post-place of the transition Starch synthesis. The starch initiation (dashed lines) was required to avoid a deadlock. In the presence of glucose, the metabolite starch is able to auto-catalyze the production of more starch until no starch is present in the system, e.g., all starch has been degraded. Without the starch initiation, the production of starch would be blocked, producing a deadlock.