Answer
a. Hormones
Work Step by Step
Gland cells secrete hormones that travel through the bloodstream. Hormones can affect cells that are far from the site where the hormones are initially secreted.
Neurotransmitters are signaling chemicals that act on other cells close to the site of secretion. Pheromones are signaling chemicals that are secreted outside of the body and act on other organisms of the same species.
