Imagine that a researcher discovers a new type of chemical signal. This signal can only produce an effect over very short distances (only about 10 nm), and is found in close association with synaptic clefts. This signal is MOST likely a:

Question

Quizplus · Accepted Answer

The fact that this signal can only produce an effect over short distances and is found in close association with synaptic clefts points towards it being a neurotransmitter, which is a chemical signal that is released by neurons to transmit information to neighboring neurons or other target cells in the body.  Growth factors and hormones can have effects over longer distances, while bone morphogenetic proteins and histamine are not typically found in close association with synaptic clefts.

Imagine That a Researcher Discovers a New Type of Chemical