NDA (I) 2025 General Ability Test · Question 111 of 150

Correct — B, Fibrinogen. Fibrinogen is a soluble plasma protein (clotting Factor I). When a blood vessel is injured, the enzyme thrombin converts fibrinogen into insoluble threads of fibrin, and this fibrin mesh traps blood cells to form the clot. Fibrinogen is therefore the clotting protein among the options.

• (a)Pathogen — A pathogen is a disease-causing organism such as a bacterium or virus. It is not a blood protein and has no role in forming a clot.
• (c)Macrophage — A macrophage is a type of white blood cell that engulfs microbes and debris (part of immune defence). It is a cell, not a clotting protein.
• (d)Phagocytes — Phagocytes are white blood cells that ingest and destroy pathogens. Like macrophages they belong to the immune system, not to the blood-clotting protein machinery.

Blood clotting (coagulation) seals an injured vessel. A cascade of clotting factors ends with the enzyme thrombin converting the plasma protein fibrinogen into fibrin. The fibrin threads form a mesh that, together with platelets and trapped blood cells, makes the clot that stops bleeding.

The question asks specifically for a clotting protein. Three of the options — pathogen, macrophage, phagocyte — are either an organism or immune cells, none of which are clotting proteins. Only fibrinogen is a plasma protein directly involved in clot formation, so it is the answer.

• Fibrinogen (Factor I) is a soluble plasma protein converted to insoluble fibrin during clotting.
• The enzyme thrombin catalyses the fibrinogen-to-fibrin step.
• Platelets and the fibrin mesh together form the blood clot.
• Vitamin K and calcium ions are needed for normal clotting.

• Confusing clotting proteins with immune cells (macrophages, phagocytes).
• Mixing up fibrinogen (the soluble protein) with fibrin (the insoluble clot threads).

Blood questions ask for the clotting protein or the cell involved — separate the coagulation proteins (fibrinogen) from the immune cells.

No directly related past PYQ was found.

• practice — not a real PYQ

  During blood clotting, fibrinogen is converted into fibrin by the enzyme

  • (a)Amylase
  • (b)Thrombin
  • (c)Pepsin
  • (d)Lipase

  Answer(b) Thrombin — it catalyses the fibrinogen-to-fibrin conversion.

• practice — not a real PYQ

  Which vitamin is essential for the normal clotting of blood?

  • (a)Vitamin A
  • (b)Vitamin C
  • (c)Vitamin D
  • (d)Vitamin K

  Answer(d) Vitamin K — required for the synthesis of several clotting factors.