The best answer to fill in the blank would be B) Small intestine or the second option.
B. Photosynthesis/Cellular respiration releases energy stored in food and produces carbon dioxide and water
The hormone calcitonin is controlled by a negative feedback mechanism because it's release leads to the decrease of calcium blood levels.
<h3>What is negative feedback mechanism?</h3>
A negative feedback mechanism is the defined as a type of regulatory mechanism in the body where by the increased output of a system leads to a decrease of another system.
Therefore, the release of the hormone calcitonin (increased level of calcitonin in the blood) will lead to decrease in blood levels of calcium.
Learn more about hormones here:
brainly.com/question/8162998
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Answer:
C. A concentration gradient must exist.
