The mammalian heart and cardiac cycleEdexcel International A Level Biology: Subtopic test

1. 1
   A student dissects a sheep's heart. She identifies the four chambers and the major blood vessels attached to the heart, and notes the difference in thickness between the walls of the two ventricles.

   (a)

   Which vessel carries oxygenated blood from the heart to the body?

   [1 mark]

   • AAorta
   • BPulmonary artery
   • CPulmonary vein
   • DVena cava

   (b)

   Why is the wall of the left ventricle thicker than the wall of the right ventricle?

   [1 mark]

   • AThe left ventricle holds a larger volume of blood than the right ventricle
   • BThe lungs are much further from the heart than the body tissues are
   • CIt must generate a higher pressure to pump blood around the whole body
   • DThe right ventricle has no muscle in its wall

   (c)

   Describe two features the student could use to identify the left ventricle in the dissected heart.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Valves in the heart make sure that blood flows in one direction only. A doctor listening to the heart of a patient with a stethoscope hears two sounds in every cardiac cycle, which are made by valves closing.

   (a)

   When are the atrioventricular valves forced shut?

   [1 mark]

   • ADuring atrial systole
   • BAt the start of ventricular systole, when the ventricular pressure becomes greater than the atrial pressure
   • CDuring cardiac diastole, when the ventricles are filling
   • DThey stay open throughout the cardiac cycle

   (b)

   Which valve prevents blood flowing back from the aorta into the left ventricle?

   [1 mark]

   • AThe bicuspid valve
   • BThe tricuspid valve
   • CThe pulmonary valve
   • DThe aortic valve

   (c)

   The atrioventricular valves are attached to the ventricle walls by tendons (valve tendons). Explain the function of these tendons.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A resting person has a heart rate of 75 beats per minute. In each cardiac cycle, atrial systole lasts 0.1 s and ventricular systole lasts 0.3 s. As the left ventricle contracts, the pressure in it rises from about 0.5 kPa to about 16 kPa. At the start of this contraction, the pressure in the left atrium is about 1 kPa and the pressure in the aorta is about 10 kPa.

   (a)

   Calculate the length of the cardiac diastole in each cycle, in seconds. Show your working.

   [3 marks]

   (b)

   Using the pressures given, explain the changes in the atrioventricular valve and the aortic valve as the left ventricle contracts and then relaxes.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student has dissected a sheep's heart and now needs to revise the structure of the mammalian heart and the events of the cardiac cycle. The heart has four chambers and is supplied with blood by the coronary arteries.

   (a)

   Describe the events of the cardiac cycle, starting with atrial systole and ending with cardiac diastole.

   [6 marks]

   (b)

   Explain how the structure of the mammalian heart is related to its function.

   [6 marks]

   Total for question 4: 12 marks

End of questions