Prothrombin that helps in clotting of blood, is present in

Options

A. Blood plasma
B. Blood corpuscles
C. Blood platelets
D. Serum

Answer

To determine where prothrombin, a crucial factor in blood clotting, is present, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Prothrombin**:
- Prothrombin is a glycoprotein that plays a significant role in the blood coagulation process. It is essential for the formation of blood clots.

2. **Vitamin K Dependency**:
- Prothrombin is known to be a vitamin K-dependent coagulation factor. This means that its synthesis requires vitamin K.

3. **Location of Prothrombin**:
- Prothrombin is primarily found in the blood plasma. Plasma is the liquid component of blood that carries cells and proteins throughout the body.

4. **Function of Prothrombin**:
- When a blood vessel is injured, prothrombin is converted into thrombin through the action of prothrombinase. Thrombin then catalyzes the conversion of fibrinogen (another plasma protein) into fibrin, which forms the mesh that constitutes a blood clot.

5. **Evaluating the Options**:
- **Blood Plasma**: This is the correct answer as prothrombin is present in this component of blood.
- **Blood Carcass Cells**: This option is incorrect as it refers to the cellular components of blood (RBCs, WBCs, and platelets) which do not contain prothrombin.
- **Blood Platelets**: This is also incorrect since platelets are involved in clotting but do not contain prothrombin.
- **Serum**: This is incorrect as serum is the liquid that remains after blood has clotted and does not contain clotting factors like prothrombin.

6. **Conclusion**:
- Based on the information, the correct answer is that prothrombin is present in **blood plasma**.

### Final Answer:
Prothrombin that helps in the clotting of blood is present in **blood plasma**.