**Core Concept**
Collagen biosynthesis is a fundamental process in extracellular matrix formation, primarily occurring in cells that produce fibrous connective tissue. This process involves the synthesis of type I collagen, the most abundant collagen in the body, which is essential for structural integrity of skin, tendons, and other connective tissues.

**Why the Correct Answer is Right**
Fibroblasts are the primary cells responsible for collagen production in connective tissues. They synthesize procollagen in the cytoplasm, which is then processed and secreted into the extracellular space. This process involves enzymes like prolyl hydroxylase and lysyl oxidase, and occurs in the endoplasmic reticulum and Golgi apparatus. While osteoblasts and chondroblasts produce matrix components, they do not synthesize collagen as their primary function—osteoblasts form bone matrix, and chondroblasts produce cartilage matrix. Odontoblasts form dentin, not collagen-rich connective tissue.

**Why Each Wrong Option is Incorrect**
Option A: Chondroblasts produce cartilage matrix, including type II collagen, but not the primary site of collagen biosynthesis in general connective tissue.
Option B: Odontoblasts lay down dentin and produce dentin matrix proteins, not collagen in the broad sense.
Option C: Osteoblasts form bone and secrete osteoid, which contains type I collagen, but their main role is mineralization, not collagen biosynthesis.

**Clinical Pearl / High-Yield Fact**
Fibroblasts are the key cells in collagen production throughout the body—understanding this is vital in dermatology, orthopedics, and dentistry, especially in conditions like scleroderma or scarring.

✓ Correct Answer: D. Fibroblasts