Mark the odd one in each series.
prothrombin, heparin, fibrinogen, thromboplastin

Explanation

To solve the question of identifying the odd one out from the series: prothrombin, heparin, fibrinogen, and thromboplastin, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Function of Each Substance**:
- **Prothrombin**: It is a protein that is converted into thrombin during the blood coagulation process. It plays a crucial role in blood clotting.
- **Heparin**: This is a natural anticoagulant that prevents blood from clotting. It is released during allergic reactions and helps to maintain blood flow.
- **Fibrinogen**: This is another protein that is converted into fibrin, which forms the mesh that constitutes the bulk of a blood clot.
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