Syllabus Edition

First teaching 2023

First exams 2025

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Blood Clotting (HL IB Biology)

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The Process of Blood Clotting

Platelets

  • When the skin is cut, microorganisms have an entry point to get into the body
    • The first line of defence is compromised
  • In order to minimise the risk of substantial blood loss and entry of unwanted microorganisms, the blood starts to clot and seal the wound
  • In response to blood vessel damage, platelets form a temporary plug to stem bleeding
    • Platelets are cellular fragments that make up one component of the blood
  • They release chemicals called clotting factors that trigger a chemical cascade which results in blood clotting

Components of Blood DiagramThe components of the blood

The blood is made up of 4 key components; plasma, red blood cells, white blood cells and platelets

Blood clotting process

  • The chemical cascade, triggered by the clotting factors, involves a large number of steps and several plasma proteins
    • First of all, the clotting factors stimulate the release of the enzyme thrombin
    • Thrombin catalyses the conversion of the soluble protein fibrinogen into fibrin, which is insoluble
    • Fibrin forms a mesh that traps more platelets and blood cells to prevent entry through the wound
      • A small initial stimulus is amplified to produce a large amount of fibrin so that the wound is quickly sealed
    • Exposure to air results in the hardening of the mesh to create a scab

Blood Clot Formation Diagram

Clotting factors and blood clot formationClotting factors and blood clot formation 2Clotting factors and blood clot formation 3

Blood clotting involves a chemical cascade process

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Ruth

Author: Ruth

Expertise: Biology

Ruth graduated from Sheffield University with a degree in Biology and went on to teach Science in London whilst also completing an MA in innovation in Education. She gained 10 years of teaching experience across the 3 key science disciplines and physical education. Ruth decided to set up a tutoring business to support students in her local area. Ruth has worked with several exam boards and loves to use her experience to produce educational materials which make the mark schemes accessible to all students.