Which of the following helps in the clotting of blood?

1. Analyze the question You are asked which blood component helps in clotting (coagulation), the process that stops bleeding after an injury.

2. Explain the concept Blood has four main components, each with its own job:

• Red blood cells (erythrocytes): carry oxygen using haemoglobin.
• White blood cells (leucocytes): defend the body against infection (phagocytosis and antibody production).
• Plasma: the liquid part that transports dissolved food, hormones, CO₂ and waste. It does contain clotting proteins like fibrinogen, but it is mainly a transport medium.
• Platelets (thrombocytes): small cell fragments that gather at a wound and start the clotting process.

3. Step-by-step solution When a blood vessel is cut:

1. Platelets stick to the damaged site and release thromboplastin (clotting factor).
2. Thromboplastin, with calcium ions and vitamin K-dependent factors, converts prothrombin → thrombin.
3. Thrombin converts soluble fibrinogen → insoluble fibrin.
4. Fibrin forms a mesh of threads that traps blood cells, forming a clot (scab) that seals the wound.

4. Identify the answer Plasma supplies the fibrinogen, but the component that actually initiates and helps the clotting is the platelets.

5. Exam tip Remember: Platelets = Plug. Red cells carry oxygen, white cells fight germs, platelets plug wounds. Also note that "thrombocyte" means "clotting cell" (thrombo- means clot).