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Correct Answer: C. Calcium and phosphorus
The bone matrix is rich in calcium and phosphorus, which play a vital role in giving bones their characteristic hardness and strength. This is a key concept in Class 11 Biology, especially when studying the skeletal system and the composition of connective tissues.
Why Calcium and Phosphorus?
Calcium and phosphorus exist in the form of hydroxyapatite crystals Ca10(PO4)6(OH)2, which are deposited in the extracellular matrix of bones. These crystals are embedded within a collagen framework, and together, they give bone its rigidity and resistance to compression.
- Calcium (Ca²⁺) is essential not only for bone strength but also for muscle contraction, blood clotting, and nerve transmission.
- Phosphorus (PO₄³⁻) complements calcium by contributing to bone mineralisation and cellular energy metabolism (as a component of ATP).
Structure of the Bone Matrix
The bone matrix is a part of connective tissue and consists of:
- Organic components – Mainly collagen fibers (type I), which provide tensile strength and flexibility.
- Inorganic components – Dominated by calcium and phosphorus salts, especially hydroxyapatite, which provide hardness.
The ratio of organic to inorganic components is finely balanced. If bones had only minerals, they’d be brittle. If they had only collagen, they’d be soft and bend easily.
Let’s look at why the other options are incorrect:
- Calcium and potassium (A) – Potassium is important for nerve impulses but is not a structural component of bone.
- Phosphorus and potassium (B) – Lacks calcium, which is the primary mineral in bone.
- Calcium and sodium (D) – Sodium plays roles in fluid balance and nerve function, but not in the bone matrix.
Understanding the composition of bone helps in grasping broader concepts like the function of connective tissues, mechanisms of bone development (ossification), importance of minerals in homeostasis, and clinical conditions like osteoporosis (low bone density due to reduced calcium)
Common Doubts in Biology
