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 Form 2 Biology transport in animals questions and answers

Describe the process of blood clotting in human beings.

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Answer Text:
- When blood vessels are damaged, blood comes out and platelets are exposed to air and they rupture on the damaged tissue. On rupturing, they
release an enzyme called thrombokinase or thromboplastin. Thrombokinase is an enzyme that initiates the process of blood clotting by neutralizing anticlotting or anti-coagulant factor called heparin.
- It also catalyses conversion of inactive prothrombin to active thrombin in presence of calcium ions. Vitamin K is needed for formation of prothrombin in the liver. Thrombin activates conversion of soluble plasma protein fibrinogen to insoluble fibrin fibres. Fibrin forms a meshwork of fibres on the cut surface to trap red blood cells to form a clot. When the clot dries up, it forms a scab that stops excessive bleeding and also protects the damaged tissues from entry of pathogens or infections.


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