Home · A-Level Biology 9700 · Transport in mammals · The heart and the cardiac cycle · Practice
AS · Practice questions · The heart and the cardiac cycle

Read the pressures, then place the valves.

Six original Cambridge-style questions on the heart, from explaining wall thickness to reading valve events off a pressure graph and explaining the AVN delay.

Original questions All questions on this page are original work, written in the Cambridge AS & A Level style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Keep these straight

Pressure first, then valve.

01
Recall
[4 marks]

Describe the internal structure of the mammalian heart.

  • Four chambers: two thin-walled atria above two thick-walled ventricles. ✓
  • A muscular septum separates the left side (oxygenated blood) from the right side (deoxygenated blood). ✓
  • Atrioventricular valves (tricuspid on the right, bicuspid on the left) lie between atria and ventricles, attached to tendons. ✓
  • Semilunar valves lie at the bases of the aorta (from the left ventricle) and pulmonary artery (from the right ventricle). ✓
02
Explain
[4 marks]

Explain the differences in the thickness of the walls of the atria and ventricles, and of the left and right ventricles.

  • Atria have thin walls because they pump blood only a short distance, into the ventricles, needing little pressure. ✓
  • Ventricles have thicker walls because they pump blood out of the heart into the arteries, against much greater resistance. ✓
  • The left ventricle wall is thicker than the right because it pumps blood at high pressure all round the body (systemic circulation). ✓
  • The right ventricle pumps only to the nearby lungs at lower pressure, which also avoids damaging the delicate lung capillaries. ✓
03
Explain
[4 marks]

Explain the roles of the sinoatrial node, the atrioventricular node and the Purkyne tissue in the cardiac cycle.

  • The SAN (pacemaker) sends out a wave of excitation across both atria, which contract (atrial systole). ✓
  • Non-conducting tissue stops the wave reaching the ventricles directly; the AVN picks it up and delays it (about 0.1 s). ✓
  • The delay lets the atria finish emptying blood into the ventricles before the ventricles contract. ✓
  • The Purkyne tissue carries the wave down the septum to the apex and up the ventricle walls, so the ventricles contract from the base upwards, pushing blood into the arteries. ✓
04
Analysis
[5 marks]

Describe the cardiac cycle, relating the pressure changes during systole and diastole to the opening and closing of the valves.

  • Atrial systole: atria contract; atrial pressure slightly above ventricular, so blood passes through the open AV valves into the ventricles. ✓
  • Ventricular systole: ventricular pressure rises above atrial pressure, so the AV valves close. ✓
  • When ventricular pressure exceeds pressure in the aorta and pulmonary artery, the semilunar valves open and blood is ejected. ✓
  • Diastole: ventricles relax; when their pressure falls below arterial pressure the semilunar valves close. ✓
  • When ventricular pressure falls below atrial pressure the AV valves open and the ventricles fill with blood returning from the veins. ✓
05
Data
[3 marks]

Use Fig. 1. State the time at which the semilunar valve opens and the time at which it closes, and calculate the percentage of the 0.8 s cycle during which blood is ejected into the aorta.

  • The semilunar valve opens at about 0.15 s, when left ventricular pressure rises above aortic pressure. ✓
  • It closes at about 0.40 s, when left ventricular pressure falls below aortic pressure. ✓
  • Ejection lasts about 0.25 s; 0.25 ÷ 0.8 × 100 = about 31% of the cycle. ✓
06
Calculation
[3 marks]

A person's heart rate rises from 70 to 120 beats per minute during exercise while each ventricle pumps 75 cm3 per beat. Calculate the cardiac output (volume pumped per minute by one ventricle) at each rate in dm3 min-1, and the percentage increase.

  • At rest: 70 × 75 = 5250 cm3 min-1 = 5.25 dm3 min-1. ✓
  • Exercise: 120 × 75 = 9000 cm3 min-1 = 9.00 dm3 min-1. ✓
  • Increase = 3.75 ÷ 5.25 × 100 = 71% (to 2 significant figures). ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.