The following are needed for blood -clotting in mammals

Options

A. `Ca^(++)` and vitamin E
B. `Ca^(++)` and vitamin K
C. `Ca^(++)` and vitamin A
D. `K^+` and vitamin K

Answer

**Step-by-Step Solution:**

1. **Understanding Blood Clotting**: Blood clotting is a complex process that involves various proteins and factors to prevent excessive bleeding when a blood vessel is injured.

2. **Key Proteins Involved**: The two main proteins required for blood clotting in mammals are:
- **Prothrombin**: This is an inactive form of a protein that is converted into thrombin during the clotting process.
- **Fibrin**: This is the protein that forms the mesh-like structure of the clot.

3. **Role of Vitamin K**: Prothrombin is synthesized in the liver and its formation requires Vitamin K. This vitamin is essential for the production of prothrombin, which is crucial for the clotting process.

4. **Activation of Prothrombin**: The conversion of prothrombin into thrombin (the active form) is facilitated by calcium ions. Calcium ions play a vital role in the clotting cascade, activating various factors that lead to the formation of the clot.

5. **Formation of Fibrin Clot**: Once thrombin is formed, it catalyzes the conversion of fibrinogen (soluble) into fibrin (insoluble), which then forms a mesh that traps blood cells and forms a stable clot.

6. **Identifying the Correct Factors**: Based on the above information, we can conclude that:
- Vitamin K is necessary for the synthesis of prothrombin.
- Calcium ions are essential for the activation of prothrombin to thrombin and for the formation of the fibrin clot.

7. **Final Answer**: Therefore, the correct factors needed for blood clotting in mammals include Vitamin K and Calcium ions.