Human blood does not contain

Options

A. prothrombin
B. fibrinogen
C. calcium ions
D. collagen

Answer

To solve the question "Human blood does not contain," we need to analyze the options provided and determine which one is not found in human blood.

### Step-by-Step Solution:

1. **Identify the Options**: The options provided are:
- Prothrombin
- Fibrinogen
- Calcium ions
- Collagen

2. **Evaluate Each Option**:
- **Prothrombin**: This is a protein that is essential for blood clotting and is present in human blood. It is a vitamin K-dependent coagulation factor.
- **Fibrinogen**: This is another protein that plays a crucial role in blood clotting. It is synthesized in the liver and is present in human blood.
- **Calcium Ions**: Calcium ions are vital for various physiological processes, including blood clotting. They are indeed present in human blood.
- **Collagen**: Collagen is a structural protein found in connective tissues, but it is not present in the blood itself.

3. **Conclusion**: After evaluating all the options, we find that **Collagen** is the only substance that is not found in human blood. Therefore, the correct answer is option 4.

### Final Answer:
Human blood does not contain **Collagen**.

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