USA Biology Olympiad (USABO) Practice Exam

Which of the following is NOT a characteristic of synovial joints?

1. Bones held together by ligaments

2. Bones held together by cartilage

3. Bones lined with synovial membrane

4. Bones being able to move freely

The correct answer is: Bones held together by cartilage

Synovial joints are defined by several key characteristics that facilitate movement while providing support and stability. One of these defining features is the presence of a synovial membrane, which lines the joint cavity and secretes synovial fluid, aiding in lubrication and reducing friction between the bones during movement. Additionally, bones in synovial joints are connected by ligaments, which are tough bands of connective tissue that stabilize the joint while allowing for a range of motion. The correct answer emphasizes that bones in synovial joints are not held together by cartilage. Instead, cartilage serves as a cushion on the surfaces of the bones at the joint, providing shock absorption and facilitating smooth movements. This distinction is critical; while cartilage is involved in joint function, it does not bind the bones together in the way that ligaments do. Therefore, the characteristic that describes bones being held together by cartilage does not accurately reflect how synovial joints function, reinforcing this option as the correct choice regarding what is NOT a characteristic of synovial joints.