Serum is

Options

A. Blood-Blood cells
B. Plasma -Fibrinogen
C. Blood-Plasma
D. Blood-RBC

Answer

**Step-by-Step Solution:**

1. **Understanding Blood Composition**: Blood is composed of two main components - formed elements and plasma. The formed elements include red blood cells (RBCs), white blood cells (WBCs), and platelets. Plasma is the liquid component of blood that carries these formed elements.

2. **Defining Plasma**: Plasma itself is made up of water, electrolytes, proteins (including clotting factors), hormones, and waste products. The key protein in plasma that is involved in blood clotting is fibrinogen.

3. **Defining Serum**: Serum is the component of blood that remains after the blood has clotted. It is essentially plasma without the clotting factors, particularly fibrinogen. Therefore, serum contains proteins such as antibodies and hormones but does not contain any clotting factors.

4. **Analyzing the Options**:
- **Blood minus blood cells**: This would leave you with plasma, not serum.
- **Plasma minus fibrinogen**: This is the correct definition of serum, as it removes the clotting factor from plasma.
- **Blood minus plasma**: This would leave the formed elements (RBCs, WBCs, and platelets), not serum.
- **Blood minus RBCs**: This would still leave plasma with WBCs and platelets, not serum.

5. **Conclusion**: The correct answer is that serum is obtained from plasma when fibrinogen (the clotting factor) is removed. Therefore, the correct option is "Plasma minus fibrinogen".