Kentucky Medication Aide (KMA) State Practice Exam

What substance is primarily responsible for the hardness of bones?

1. Phosphorus

2. Calcium

3. Magnesium

4. Iron

The correct answer is: Calcium

The substance primarily responsible for the hardness of bones is calcium. Calcium is a vital mineral that contributes significantly to the structure and strength of bone tissue. Approximately 99% of the body's calcium is stored in the bones, where it forms a crystalline structure known as hydroxyapatite. This mineral composition gives bones their rigidity and resilience, enabling them to support the body's weight and withstand physical stress. While phosphorus is important for bone health and works in conjunction with calcium, it is calcium that plays a pivotal role in providing the hardness and structural integrity of bone. Magnesium and iron are essential for various bodily functions; however, they do not directly contribute to the hardness of bones as calcium does. Therefore, calcium's primary function in bone density and strength makes it the correct answer to this question.