**Core Concept**
The joint between the epiphysis and diaphysis of a long bone is a type of synovial joint that allows for limited movement and is characterized by a hyaline cartilage covering the ends of the bones. This joint is responsible for facilitating the growth and development of long bones by allowing for the accommodation of increasing bone length.

**Why the Correct Answer is Right**
The correct answer is a growth plate, also known as an epiphyseal plate. The growth plate is a type of hyaline cartilage that separates the epiphysis from the diaphysis in long bones. It is composed of chondrocytes and is responsible for producing new bone tissue, allowing for the elongation of the bone. The growth plate is also richly supplied with blood vessels, which provide the necessary nutrients and oxygen for growth. As the bone grows, the growth plate gradually ossifies and eventually closes, marking the end of bone growth.

**Why Each Wrong Option is Incorrect**
**Option A:** A synovial joint is a type of joint that is characterized by a space between the articulating bones that is filled with synovial fluid. While the joint between the epiphysis and diaphysis is a type of synovial joint, it is not the correct answer because it is more specifically a growth plate.

**Option B:** A fibrous joint is a type of joint that is characterized by a fibrous connective tissue that holds the bones together. The joint between the epiphysis and diaphysis is not a fibrous joint because it is a synovial joint with a hyaline cartilage covering the ends of the bones.

**Option C:** An interosseous membrane is a type of fibrous tissue that connects two bones. While interosseous membranes do play a role in the joints of the body, they are not the correct answer because the joint between the epiphysis and diaphysis is a synovial joint with a growth plate.

**Clinical Pearl / High-Yield Fact**
The growth plate is a critical component of long bone growth and development, and its closure can be influenced by various factors, including genetics, nutrition, and hormones. Understanding the growth plate is essential for diagnosing and managing conditions such as growth hormone deficiency, hypothyroidism, and certain genetic disorders.

**Correct Answer: D. Growth plate**