What effect on the body is associated with the endocrine system?

The correct answer focuses on hormone balance, which is a central function of the endocrine system. The endocrine system is comprised of various glands that produce hormones—chemical messengers that regulate a multitude of bodily functions. This balance of hormones is crucial as it affects various physiological processes such as growth, metabolism, and mood. Maintaining optimal hormone levels is essential for homeostasis, ensuring that the body's internal environment remains stable, despite external changes.

While other choices like metabolism rate, muscle growth, and body temperature regulation can indeed be influenced by the hormones secreted by the endocrine system, they are more specific functions rather than the primary effect associated with the endocrine system as a whole. The endocrine system's primary role is to maintain hormonal balance, which subsequently impacts other bodily functions.