Figure 2.

Conceptual representations of physical systems. (a) A bond graph for the illustrated simple electric circuit with two capacitors and a resistor in series. (b) A bond graph analogous to the electric circuit in (a) can also represent the chemical reaction $A\rightleftharpoons B$. (c) Bond graphs can also model interaction of components in both the chemical and physical domains, such as the transport of an ion across a membrane. (d) Transport of an ion across a membrane through an ion channel involves gating which modulates the rate of reaction. Thus the ion channel is analogous to a potentiometer. (Online version in color.)