Most medications that affect mood and behavior change the strength of the chemical signal passing through the synapses.

Both types of synapses rely on neurotransmitters to transduce the electrical signal into a chemical signal and back.

This leads to the opening of the channel converting the chemical signal to an electrical impulse.

When a conditioned seed receives a chemical signal from a host plant, it germinates, forming a germ tube which grows toward the host.

Growth cycles are controlled by a chemical signal like epidermal growth factor.