If networks of chemical reactions are the circuits of biology then catalysts are the transistors, or perhaps switches. But which species should be called catalysts? Come to the talk and find out. In the real world, transistors have leakage currents which make the circuit designer's life harder. In contrast, it turns out that leakage currents make analysis simpler. Some elementary algebraic geometry shows that leakage currents rule out relevant siphons, and make the dynamics particularly well-behaved. This will be a chalk talk. All are welcome but the talks are aimed at those comfortable with theorems and proofs.