Correct option is B
Explanation of Each Statement:
A. Bone marrow stem cells are not the source of osteoclast and mast cells.
This statement is incorrect. Bone marrow stem cells, specifically hematopoietic stem cells (HSCs), are the source of osteoclasts and mast cells.
Osteoclasts are derived from the monocyte/macrophage lineage of HSCs and play a critical role in bone resorption.
Mast cells, involved in immune responses and allergy, also originate from HSCs.
Hence, HSCs are multipotent progenitors for various blood and immune cells, including these.
B. Normally, three fourths of the cells in the marrow cavities mature to white blood cells and one fourth to red blood cells.
This is a correct statement.
The bone marrow is highly active in producing blood cells. Approximately 75% (three-fourths) of developing cells in marrow are committed to the white blood cell (leukocyte) lineage, which includes granulocytes, monocytes, lymphocytes, etc.
About 25% (one-fourth) of the cells are committed to the red blood cell (erythrocyte) lineage.
This proportion reflects the body’s continuous need for immune defense and oxygen transport.
C. In adults, blood cells are not actively produced in the marrow cavities of all the bones.
This is correct.
In adults, active hematopoiesis is mostly restricted to the axial skeleton, including the vertebrae, ribs, sternum, pelvis, and proximal ends of long bones like the femur and humerus.
The marrow in many other bones becomes fatty and inactive, a process called marrow involution.
This limits the sites of active blood cell production in adults.
D. Hematopoietic stem cells are derived from committed cells.
This statement is incorrect.
Hematopoietic stem cells (HSCs) are primitive, multipotent stem cells capable of giving rise to all blood cell types.
They precede committed progenitor cells in the differentiation hierarchy.
Committed progenitor cells have limited differentiation potential, deriving from HSCs, not the other way around.
