Which of the following best summarizes how hormone levels are controlled?

Group of answer choices

Hormones are controlled by a feedback loop; information about a system is sent back to the controller of the system to improve its function.

Hormones are controlled by oxygen levels; the internal environment maintains all systems, including endocrine functions.

Hormones are controlled by muscles; hormones are released when muscles contract and stopped when muscles relax.

Hormones are controlled by the nervous system; the spinal cord sends messages about hormone levels to the brain.

Option A, Hormones are controlled by a feedback loop; information about a system is sent back to the controller of the system to improve its function.

Explanation:

Negative feedback loop controls the hormone production and release. This is done by eliciting the release of substances till a certain level after which the stop signal is activated thereby preventing further release. By this method,  concentration of hormones in blood is maintained within the narrow range.  

For example – Thyroid hormones is released when the anterior pituitary signals the thyroid. This continues till the hormones in the blood reach the threshold level. Once the threshold level is reached, hypothalamus receives a feedback and then signals anterior pituitary to inhibit further signaling to the thyroid

Hence, option A is correct

b. the carbon cycle ensures living things have a source of hydrogen

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