Scheme of Work Cambridge International as & a level

Extension activity: Construct an oxygen dissociation curve for a variety of organisms other than humans.

8.3 The heart KC6

8.3.1 Describe the external and internal structure of the mammalian heart. 8.3.2 Explain the differences in the thickness of the walls of the: atria and ventricles left ventricle and right ventricle. 8.3.3 Describe the cardiac cycle, with reference to the relationship between blood pressure changes during systole and diastole and the opening and closing of valves. 8.3.4 Explain the roles of the sinoatrial node, the atrioventricular node and the Purkyne tissue in the cardiac cycle (knowledge of nervous and hormonal control is not expected).

Review learners’ prior knowledge of the structure and function of the heart by asking them to construct a dichotomous key to differentiate between the different chambers/valves of the heart. For example, the first branch could read ‘chamber’ or ‘vessel.’ The second branches leading from these could read ‘carry oxygenated blood’ or ‘carry deoxygenated blood,’ and so on. (F) Being mindful of cultural sensitivities, host a dissection for learners to explore the anatomical features of the heart. Arrange the heart with the blood vessels facing away from them (towards the head of the animal) and to find the coronary vessels, which travel diagonally from top right to bottom left across the ventricles. They trace the pathway as it leaves the chambers by putting a finger into a chamber and finding out which vessel(s) this leads into. Drawings, or possibly photographs, could be taken when key structures are exposed. Challenge learners to draw valves and connected tendons, and measure thicknesses of the walls of the chambers. Resource Plus Carry out the Heart dissection experiment (in Resource Plus for Cambridge IGCSE/O Level Biology 0610/5090) referring to the Teaching Pack for lesson plans and resources. Learners construct a graph on the wall or floor of the classroom that shows the pressure and volume changes on one side of the heart. Hand out sections of the graph to learners, who discuss what is happening in their small section. Hold a discussion in which learners contribute ideas and produce a fully annotated version of the graph by joining the sections together. To reinforce their learning, show an animation to help learners visualise the circulation of blood and the electrical control of the heartbeat: www.abpischools.org.uk/topic/heartandcirculation/1/1 www.nhlbi.nih.gov/health-topics/how-heart-works