Control of the heartbeat and cardiac outputEdexcel A-Level Biology A: Subtopic test

1. 1
   A researcher removes the heart from an anaesthetised frog and places it in oxygenated saline solution at room temperature. All nerves to the heart have been cut. The isolated heart continues to beat rhythmically for several hours.

   (a)

   In which region of a normal heart is the pacemaker that sets the rhythm of the beat found?

   [1 mark]

   • AThe wall of the right atrium
   • BThe wall of the left ventricle
   • CThe septum between the ventricles
   • DThe wall of the left atrium

   (b)

   Which tissue prevents the wave of depolarisation from spreading directly from the atria to the ventricles?

   [1 mark]

   • AThe bundle of His
   • BA layer of non-conducting fibrous tissue between the atria and ventricles
   • CThe Purkyne fibres
   • DThe sinoatrial node

   (c)

   Explain why the isolated heart continues to beat after its nerves have been cut, naming the structure that sets its rhythm.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A 55-year-old man attends a cardiology clinic complaining of a fluttering sensation in his chest. A technician attaches electrodes to his chest and records an electrocardiogram (ECG) while he rests. The trace shows a normal sequence of P wave, QRS complex and T wave, with a constant interval of 0.50 s between the R peaks of successive heartbeats.

   (a)

   What is the heart rate of this patient, in beats per minute?

   [1 mark]

   • A50
   • B80
   • C100
   • D120

   (b)

   Which term best describes this patient's resting heart rate, given a normal sequence of waves on his ECG?

   [1 mark]

   • ABradycardia
   • BEctopic beat
   • CTachycardia
   • DAtrial fibrillation

   (c)

   Another patient's ECG shows no regular P waves, QRS complexes or T waves, only rapid, irregular, disorganised electrical activity. Deduce what this indicates about the ventricles and explain why this is a medical emergency.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student volunteers for a spirometer investigation. She breathes from a closed spirometer chamber containing soda lime, which absorbs carbon dioxide, and a pen recorder traces the volume of gas in the chamber. At rest her tidal volume is 0.50 dm³ and her breathing rate is 14 breaths per minute. After five minutes of cycling these values are 2.0 dm³ and 28 breaths per minute. The trace shows her oxygen consumption rising from 0.30 dm³ min⁻¹ at rest to 2.4 dm³ min⁻¹ during cycling.

   (a)

   Calculate the student's minute ventilation at rest and during cycling, and state how many times greater it was during cycling.

   [3 marks]

   (b)

   Explain how oxygen consumption is determined from the spirometer trace and why it rises during cycling.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A 58-year-old man has complete atrioventricular block, in which electrical impulses can no longer pass from his atria to his ventricles. His cardiologist is explaining how a healthy heart is normally coordinated and how heart rate and breathing adjust when a person begins to cycle.

   (a)

   Explain how the normal electrical activity of a healthy heart coordinates the heartbeat, and why complete atrioventricular block disrupts it.

   [6 marks]

   (b)

   Explain how heart rate and ventilation rate are controlled when he begins to cycle, and why both need to increase.

   [6 marks]

   Total for question 4: 12 marks

End of questions