Blood coagulation
- ICSE Class 10, Unit 3 Human Anatomy and Physiology
Blood coagulation is the clotting of blood at a wound, where a mesh of fibrin threads traps blood cells and stops the bleeding.
Blood stays liquid inside the vessels. At a cut, it must turn solid fast, or too much is lost. Platelets and the hurt tissue start a short chain of steps:
- The injured cells and platelets release thromboplastin.
- With calcium ions, thromboplastin turns prothrombin into thrombin.
- Thrombin turns fibrinogen, a protein in plasma, into threads of fibrin.
- The fibrin threads form a net. Blood cells get caught in it, and the clot forms.
Vitamin K is needed too, but earlier: the liver needs it to make prothrombin.
A small example
You scrape your knee. Within a few minutes the bleeding stops and a soft red plug forms. That plug is fibrin with red cells stuck in it. Later it dries into a scab.
Where marks go
The 2024 ICSE Biology paper asked for the mineral needed for clotting. CISCE's 2024 Biology report records "vitamin K" written instead of "calcium". Both help, so read which one the question asks for: a mineral is calcium.
Odd-one-out questions test this chain too. In the same paper, albumin was the odd one, and the category was "clotting of blood". The report notes answers that said the others were "present in blood platelets". The 2027 specimen paper repeats the idea with haemoglobin as the odd one. A category must name the shared job. More on how answers are checked against value points.
Sources
Facts last checked against these sources on 30 September 2026.
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