Question 20

Hormones are the chemical messengers that control growth, differentiation, and metabolism of specific target cells.

Hormones act as regulators in the body, facilitating communication between various organs and tissues to maintain homeostasis and support cellular functions.

A) Hormones

This option is correct as hormones are defined as chemical messengers that are secreted into the bloodstream and influence the activity of target cells by binding to specific receptors, thus regulating processes such as growth, differentiation, and metabolism.

B) Neurons

Neurons are the fundamental units of the nervous system responsible for transmitting signals throughout the body. While they play a crucial role in communication, they do not function as chemical messengers in the same way that hormones do, focusing instead on electrical impulses and neurotransmitter release.

C) Glands

Glands are organs that produce and secrete hormones, but they are not the chemical messengers themselves. Rather, they serve as the source of hormones that are then released into the bloodstream to affect target cells.

D) Second messengers

Second messengers are molecules that relay signals received from receptors on the cell surface to target molecules inside the cell. They play a role in the action of hormones but are not themselves the primary chemical messengers that control growth and metabolism.

Conclusion

Hormones are essential for regulating various biological processes, including growth and metabolism, by acting directly on target cells. Other options, while related to the system of communication in the body, do not fulfill the specific role of chemical messengers as effectively as hormones do, making A the definitive correct choice.