The heart and mammalian circulationEdexcel A-Level Biology B: Subtopic test

1. 1
   A bony fish has a heart with one atrium and one ventricle. Blood leaves the heart, passes through the narrow capillaries of the gills, and then flows on to the capillaries of the body tissues before returning to the heart. A mammal has a heart with four chambers, and its blood returns to the heart after the lungs before it is sent to the body.

   (a)

   How many times does blood pass through the heart during one complete circuit of the body in the fish?

   [1 mark]

   • ATwice
   • BThree times
   • CNone, because the gills pump the blood
   • DOnce

   (b)

   Which is an advantage of the mammalian double circulation over the single circulation of the fish?

   [1 mark]

   • AOxygenated and deoxygenated blood mix, giving the tissues a more stable supply
   • BOxygenated blood from the lungs returns to the heart and is pumped to the body at higher pressure
   • CBlood does not need to pass through capillaries
   • DThe heart needs only one ventricle, so less muscle is required

   (c)

   Explain why blood reaches the body tissues of the fish at a lower pressure than blood reaches the body tissues of the mammal.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In a resting adult the heart beats 75 times per minute, and the left ventricle ejects 70 cm³ of blood with each beat. During each cardiac cycle the pressure in the left ventricle first rises above the pressure in the left atrium, and a little later rises above the pressure in the aorta.

   (a)

   Which valve closes when the pressure in the left ventricle first rises above the pressure in the left atrium?

   [1 mark]

   • AThe atrioventricular (bicuspid) valve
   • BThe semilunar valve at the base of the aorta
   • CThe tricuspid valve
   • DThe pocket valves in the veins

   (b)

   What happens when the pressure in the left ventricle rises above the pressure in the aorta?

   [1 mark]

   • AThe semilunar valve closes and blood stays in the ventricle
   • BThe semilunar valve opens and blood is ejected into the aorta
   • CThe atrioventricular valve opens and blood flows into the atrium
   • DThe atria contract to fill the ventricle

   (c)

   Calculate (i) the duration of one cardiac cycle and (ii) the cardiac output of the adult, in cm³ per minute.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A cardiologist examines the electrocardiogram (ECG) of a patient. The trace shows regular P waves, but some P waves are not followed by a QRS complex, and when the QRS complex does occur the delay after the P wave is longer than normal.

   (a)

   Explain how the delay between the P wave and the QRS complex is produced in a healthy heart and why the delay is important.

   [3 marks]

   (b)

   Explain why some P waves are not followed by a QRS complex in this patient, and describe how a wave of excitation normally spreads from the atrioventricular node to cause ventricular systole.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student is revising the circulatory system of a mammal. She compares the wall of the aorta, a vein and a capillary seen in section, and she traces the events that occur in the left side of the heart during one cardiac cycle.

   (a)

   Explain how the structure of the aorta, a vein and a capillary is related to the function of each vessel.

   [6 marks]

   (b)

   Describe and explain the sequence of events that occurs in the left side of the heart during one cardiac cycle.

   [6 marks]

   Total for question 4: 12 marks

End of questions