Question

7 a bone lengthens
a as a result of increased activity within the epiphyseal plate
b as a compact bone is deposited beneath the periosteum of the diaph
c as a result of cell division in the medullary cavity
d due to increase production of bone matrix by osteoclasts

Explanation:

• Option A: The epiphyseal plate (growth plate) has chondrocytes (cartilage - forming cells). Chondrocytes divide, and new cartilage is formed. Then, osteoblasts replace the cartilage with bone tissue, leading to bone elongation.
• Option B: Deposition of compact bone beneath the periosteum (periosteal bone deposition) is mainly responsible for bone thickening (appositional growth), not bone lengthening.
• Option C: The medullary cavity contains bone marrow. Cell division in the medullary cavity is not related to bone lengthening. The medullary cavity expands as bone grows, but this is not the cause of bone length increase.
• Option D: Osteoclasts are responsible for bone resorption (breaking down bone matrix), not for producing bone matrix. Osteoblasts produce bone matrix.

Answer:

A. as a result of increased activity within the epiphyseal plate