Advanced Placement (AP) Biology Practice Exam

What is a chemical that carries messages affecting cells in other parts of the body called?

1. Enzyme

2. Amino acid

3. Hormone

4. Neurotransmitter

The correct answer is: Hormone

A chemical that carries messages affecting cells in other parts of the body is known as a hormone. Hormones are signaling molecules produced by glands in the endocrine system and are released into the bloodstream, allowing them to travel to various tissues and organs, where they exert their effects on growth, metabolism, reproduction, and mood, among other physiological processes. In contrast, enzymes are biological catalysts that speed up chemical reactions but do not primarily serve as signaling molecules. Amino acids are the building blocks of proteins and can serve various roles in the body, including as precursors to hormones, but they do not act as messengers themselves. Neurotransmitters are chemicals that transmit signals across synapses between nerve cells, primarily affecting communication within the nervous system rather than throughout the body as hormones do. Hence, the role of hormones in the communication and regulation of physiological processes makes them the correct answer.