Double circulatory system of a mammal (WJEC A-level Biology)

This lesson describes the vascular system of mammals as a double circulatory system to allow comparisons with those in earthworms, insects and fish. The PowerPoint and accompanying resources have been designed to cover the final content of specification point (a) in topic 3 (Adaptations for transport) of AS unit 2 in the WJEC A-level Biology specification and there is a primary focus on the differences in pressure between the pulmonary and systemic circulation.

The lesson begins with a focus on the meaning of a double circulatory system and checks that students are clear in the understanding that the blood passes through the heart twice per cycle of the body. Beginning with the pulmonary circulation, students will recall that the pulmonary artery carries the blood from the right ventricle to the lungs. An opportunity is taken at this point to check on their knowledge of inhalation and the respiratory system as well as the gas exchange between the alveoli and the capillary bed. A quick quiz is used to introduce arterioles and students will learn that these blood vessels play a crucial role in the changes in blood pressure that prevent the capillaries from damage. When looking at the systemic circulation, time is taken to look at the coronary arteries and renal artery as students have to be aware of these vessels in addition to the ones associated with the heart. In the final part of the lesson, students are challenged to explain how the structure of the heart generates a higher pressure in the systemic circulation and then to explain why the differing pressures are necessary.