Which Statement is True Regarding Calcium in Bone Matrix

Question

Which statement is true regarding calcium in bone matrix?
A) Calcium is found in crystals called hydroxyapatite.
B) Calcium is secreted by osteoblasts into the matrix.
C) Once deposited, calcium cannot be removed from bone.
D) Calcium provides flexibility to the bone matrix.
E) Calcium is the organic part of the matrix.

Accepted Answer

Calcium is found in crystals called hydroxyapatite, which makes up about 70% of the weight of bone. This mineral provides bone with its hardness and strength. B is incorrect because osteoblasts are responsible for depositing the calcium into the matrix, not secreting it. C is incorrect because bone is constantly undergoing remodeling, which involves both deposition and resorption of calcium. D is incorrect because flexibility is provided by collagen fibers, not calcium. E is incorrect because calcium is an inorganic mineral, not an organic component of the matrix.