Biological Systems MCAT Practice Exam

What type of bone structure is characterized by a compact shell surrounding a spongy core with red marrow?

1. Long bone

2. Flat bone

3. Compact bone

4. Spongy bone

The correct answer is: Flat bone

The correct answer is flat bone. Flat bones are characterized by their structure, which consists of two layers of compact bone surrounding a spongy core that contains red marrow. This structure provides both strength and the ability to produce blood cells due to the presence of red marrow, making flat bones integral to the hematopoietic system. Common examples of flat bones include the bones of the skull, sternum, and rib cage. Long bones, on the other hand, typically have an elongated shape and are designed to bear weight; they also contain a medullary cavity filled with yellow marrow rather than a spongy core like flat bones. Compact and spongy bone represent types of bone tissue rather than categories of bone structure, with compact bone providing strength and spongy bone, or cancellous bone, typically found in the interior of bones for shock absorption and housing marrow.