Mechanism of blood clotting is given below :
An injury or a trauma stimulates the platelets in the blood to release certain factors which activate the mechanism of coagulation . An enzyme complex,
…………P……… is formed by a series of linked enzyme reactions
(...........Q.........Process) involving a number of factors present in the plasma in an inactive state. This enzyme complex is required for formation of ...............R............
..........S........... ions play a very important role in clotting .
Identify the correct option that represents P, Q, R , and S .

Options

A. `{:(P,Q,R,S),("thrombokinase","inhibitory","prothrombin","magnesium"):}`
B. `{:(P,Q,R,S),("prothrombin","cascade","thrombin","magnesium"):}`
C. `{:(P,Q,R,S),("thrombin","cascade","thrombokinase","calcium"):}`
D. `{:(P,Q,R,S),("thrombin","cascade","thrombin","calcium"):}`

Answer

To solve the question regarding the mechanism of blood clotting, we need to identify the correct terms for the blanks P, Q, R, and S based on the information provided in the question and the video transcript.

### Step-by-Step Solution:

1. **Identifying P:**
- The enzyme complex formed during blood clotting is known as **thrombin**. This is the enzyme that converts fibrinogen into fibrin, which is essential for clot formation.
- **So, P = thrombin.**

2. **Identifying Q:**
- The process that describes the series of linked enzyme reactions leading to blood clotting is known as the **cascade process**. This refers to the sequential activation of clotting factors.
- **So, Q = cascade.**

3. **Identifying R:**
- The enzyme complex that is required for the formation of the clot is **thrombokinase** (also known as prothrombin activator). This complex is essential for converting prothrombin into thrombin.
- **So, R = thrombokinase.**

4. **Identifying S:**
- Calcium ions (Ca²⁺) play a crucial role in the blood clotting process, as they are necessary for several steps in the cascade of reactions.
- **So, S = calcium.**

### Final Answers:
- P = thrombin
- Q = cascade
- R = thrombokinase
- S = calcium