A ____ is an Extracellular Signaling Molecule That Exerts Its

Question

A ____ is an extracellular signaling molecule that exerts its effect at very low concentrations.  
A) statolith
B) protein receptor
C) plant hormone
D) cytochrome
E) phytochrome

Accepted Answer

The description given matches that of a plant hormone. Plant hormones are extracellular signaling molecules that exert their effects in very low concentrations, sometimes in parts per million or parts per billion.