What is a hormone in biological terms?

A hormone is defined as a chemical messenger produced by glands in the endocrine system, which is capable of modifying or regulating the activity of specific cells and organs within the body. Hormones are secreted directly into the bloodstream, allowing them to travel to different parts of the body, where they bind to specific receptors on target cells and instigate a response. This regulatory function is crucial for various physiological processes, including growth, metabolism, and reproduction.

Understanding that hormones operate on a very specific level is key. They do not merely provide energy or structural support like proteins or vitamins, nor are they minerals found in plants. Instead, they play a pivotal role in communication between different parts of the body, making option B the accurate definition of hormones in biological terms.