Biological Systems MCAT Practice Exam

Which component of bone structure provides strength by forming calcium phosphate crystals?

1. Osteocytes

2. Hydroxyapatite

3. Collagen

4. Lamellae

The correct answer is: Hydroxyapatite

The correct answer is hydroxyapatite, which is a naturally occurring mineral form of calcium apatite. Hydroxyapatite is composed primarily of calcium phosphate crystals that provide bones with their strength and rigidity. These crystals are deposited in a structured manner within the bone matrix, contributing to the overall hardness and mechanical properties of bone tissue. In the context of bone structure, hydroxyapatite crystals form an integral part of the mineralized matrix, allowing bones to withstand compressive forces that they encounter throughout various activities, such as walking or lifting. This mineral component is vital for maintaining the structural integrity of bones. While osteocytes are mature bone cells involved in maintaining the bone matrix and signaling between bone and the rest of the body, they do not directly provide strength through crystal formation. Collagen, on the other hand, is a protein that forms a fibrous network within bones, offering flexibility and tensile strength but does not consist of calcium phosphate crystals. Lamellae refer to the concentric layers of bone matrix that contain both collagen fibers and mineral deposits, but it is specifically the hydroxyapatite within these layers that provides the essential strength through the formation of calcium phosphate crystals.