Final answer:
Spongy bone, or cancellous bone, is a less-dense, open structure found in the inner layers of bones, containing trabeculae and red bone marrow, and is essential for the bone's strength and hematopoiesis.
Step-by-step explanation:
The student is referring to spongy bone, also known as cancellous bone, which is found in the inner layer of bones. Unlike compact bone, spongy bone has a less-dense, more open structure. It contains trabeculae, which are rod-like or plate-like structures providing strength while being lightweight. These trabeculae form along the lines of stress within the bone, optimizing the bone's structural integrity. The porosity of the spongy bone also allows for the presence of red bone marrow, which is crucial for hematopoiesis, the process of blood cell formation. Spongy bone makes up about 20 percent of the total bone mass, with the rest being composed of denser compact bone, which provides greater structural strength.