Blood clotting (Edexcel International A-level Biology)

This fully-resourced lesson describes the key steps in the blood clotting process, including the roles of thromboplastin, thrombin and fibrin. The engaging PowerPoint and accompanying worksheets have been primarily designed to cover the content detailed in point 1.11 of the Edexcel A-level International specification but time has been taken to look at haemophilia as a sex-linked disease so that students are prepared for when this is covered in greater detail in topic 3.

The lesson begins with the introduction of clotting factors as integral parts of the blood clotting process and explains that factor III, thromboplastin, needs to recalled as well as the events that immediately precede and follows its release. Students will learn how damage to the lining and the exposure of collagen triggers the release of this factor and how a cascade of events then results. Quick quiz rounds and tasks are used to introduce the names of the other substances involved which are prothrombin, thrombin, fibrinogen and fibrin. In a link to the upcoming topic of proteins, students will understand how the insolubility of fibrin enables this mesh of fibres to trap platelets and red blood cells and to form the permanent clot. In the previous lessons, students described the events in atherosclerosis and a link is made to the role of blood clotting in CVD.
The final part of the lesson introduces haemophilia as a sex-linked disease and students are challenged to apply their knowledge to an unfamiliar situation as they have to write genotypes and determine phenotypes before explaining why men are more likely to suffer from this disease than women.