1.8.1 The Mechanism of Blood Clotting (Structured Question 1 & 2)

Question 1:
(a)(i) Diagram below shows an electron micrograph of cellular components of human blood.

Based on Diagram I, explain how platelets help to stop bleeding when a wound occurs. [4 marks]

A blood test shows that a man’s erythrocytes count is below normal.
Explain the possible consequences of this condition on his health.
What type of food should be included in his diet to improve this condition? [8 marks]

Diagram II shows the blood circulatory system in organism P and organism Q.

Based on Diagram II:
(i) Give one example of organism P and organism Q. [2 marks]

Describe the similarities and differences between the blood circulatory system in organism P and organism Q. [6 marks]



  • Platelets clump together and produce thrombokinase.
  • Thrombokinase converts prothrombin to thrombin.
  • Thrombin converts fibrinogen (a type of soluble protein plasma) to fibrin (vitamin K is needed in the formation of prothrombin).
  • Fibrin forms a network to trap the erythrocytes
  • To form a clot


  • Less red blood cells to combine with oxygen
  • Less oxygen is transported to the body cells.
  • Less energy is produced
  • Resulting in tiredness/ pale looking appearance/ anaemia
  • Need food which is rich in iron
  • Examples: Cockles, liver, spinach


P: Fish
Q: Human being



  • Both have a closed circulation
  • Blood flows in blood vessels