**Question:** The ratio of fat cells and blood cells in bone marrow is-

A. Fat cells
B. Blood cells
C. Equal number of fat cells and blood cells
D. Greater number of blood cells

**Core Concept:** Bone marrow is a soft, spongy tissue found within the cavities of bones. It plays a crucial role in hematopoiesis, the production of blood cells. In adult humans, bone marrow comprises approximately 50% fat cells and 50% hematopoietic cells (blood cells).

**Why the Correct Answer is Right:** The correct answer, D, states that there are "Greater number of blood cells." This is accurate because hematopoietic cells, which produce blood cells, outnumber fat cells in bone marrow.

**Why Each Wrong Option is Incorrect:**

A. Fat cells: Although bone marrow contains fat cells, they only make up about 50% of its volume. The focus on fat cells makes this option incorrect.
B. Blood cells: This option is partially correct, but since the correct answer is "Greater number of blood cells," focusing solely on blood cells is not accurate.
C. Equal number of fat cells and blood cells: This option is incorrect because, as explained above, there are more blood cells in bone marrow.

**Correct Answer: D. Greater number of blood cells**

**Clinical Pearl:** The understanding of bone marrow composition is essential in clinical scenarios, such as interpreting bone marrow biopsies and assessing hematopoietic disorders like leukemia, where an abnormal increase or decrease in blood cell production can be observed.