Blood contains red blood cells, white blood cells, plasma and platelets. When you get a cut, platelets (cell fragments that play an important role in forming blood clots) collect and stick to the edge of the cut in the blood vessel. Then the platelets release chemicals. The chemicals begin to produce some thread-like substances called "fibrin". Fibrin begins to form a net like substance across the opening of the cut in the blood vessel. This net traps and collects platelets and blood cells. This forms the blood clot that stops the bleeding. As the part of the clot that is on the surface dries out, it forms a scab.
In life science text books there is often a magnified picture showing fibrin and blood cells. This activity creates a hands-on model of that picture and illustrates the concept involved.
It is helpful if the student has studied the circulatory system, the kinds of blood vessels, and the parts of the blood before carrying out this activity. It may be difficult for some students to imagine that the cup represents a part of a blood vessel.
- Small paper cups
- A variety of beads, buttons or other small objects to represent platelets and blood cells
- Elastic bands
The student will:
1. Place the parts of the blood (beads and buttons etc.) into the cup. These parts of the blood are inside a blood vessel represented by the cup.
2. Imagine that the opening on the top of the cup is now a cut in the blood vessel.
3. Tip the cup over- all the parts of the blood come out of the blood vessel.
4. Place the small items back into the cup. Cover the top of the cup with gauze representing the net of fibrin that forms. Fasten the gauze in place with an elastic band.
5. Now tip the cup over. The net of “fibrin” now captures the parts of the blood preventing the blood from leaving the vessel.