The circulatory system — common mistakes

When drawing or interpreting diagrams of the heart, pay close attention to the relative thicknesses of the ventricular walls – the left ventricle is always depicted thicker. For blood vessels, differentiate carefully between the lumen size, wall thickness, and the presence or absence of valves. Always connect these visual cues to their functional significance. Be prepared for calculations involving cardiac output.

To ace the circulatory system, focus on understanding the why behind each structure's design. Use diagrams to trace blood flow, learn valve functions, and practice explaining the cardiac cycle's pressure changes. Our free Cambridge 9700 Biology course offers detailed lessons, and tackling past papers is crucial for applying your knowledge to exam-style questions.

Cambridge expects you to compare and contrast these vessels based on their structure-function relationship. Arteries have thick, muscular, elastic walls for high-pressure transport; capillaries have one-cell thick walls for efficient exchange; and veins have thinner walls, larger lumens, and valves for low-pressure blood return, preventing backflow. Focus on these adaptations!

The left ventricle pumps oxygenated blood to the entire body (systemic circulation) at very high pressure, requiring a powerful contraction. In contrast, the right ventricle only pumps deoxygenated blood to the lungs (pulmonary circulation) at much lower pressure. Therefore, the left ventricle's thicker, more muscular wall is an adaptation to generate the greater force needed for systemic circulation.

Cardiac output is calculated using the formula: Cardiac Output = Heart Rate × Stroke Volume. Heart rate is the number of beats per minute, and stroke volume is the volume of blood pumped by a ventricle in one beat. Ensure your final units are correct, as you may need to convert cm³ to dm³ (1000 cm³ = 1 dm³).