Mass transport and the mammalian heartEdexcel A-Level Biology A: Subtopic test

1. 1
   A flatworm is a flat animal about 1 mm thick with no heart or blood. It obtains oxygen and nutrients directly from the surrounding water. A mouse is a small mammal with a very high metabolic rate, a heart and a circulatory system.

   (a)

   Which statement best explains why the flatworm does not need a heart?

   [1 mark]

   • AIt is thin with a large surface area to volume ratio, so oxygen and nutrients reach all its cells quickly by diffusion
   • BIt has a very high metabolic rate so needs little oxygen
   • CIt is large so the diffusion distance to its cells is short
   • DIt has a small surface area to volume ratio, so gases diffuse in slowly

   (b)

   What happens to the surface area to volume ratio as an animal's body increases in size?

   [1 mark]

   • AIt increases
   • BIt decreases
   • CIt stays the same
   • DIt first increases then stays constant

   (c)

   Explain why the mouse needs a heart and circulatory system.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In a practical lesson a student dissects a sheep's heart. She cuts across both ventricles to compare the walls and then opens the atria and ventricles to look at the valves.

   (a)

   Which blood vessel carries oxygenated blood into the left atrium?

   [1 mark]

   • AThe pulmonary artery
   • BThe vena cava
   • CThe aorta
   • DThe pulmonary vein

   (b)

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

   [1 mark]

   • AThe bicuspid (atrioventricular) valve
   • BThe tricuspid valve
   • CThe pulmonary semilunar valve
   • DThe aortic semilunar valve

   (c)

   Explain why the wall of the left ventricle is thicker than the wall of the right ventricle.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   In a healthy adult at rest one cardiac cycle lasts 0.8 s. Atrial systole lasts 0.1 s, ventricular systole lasts 0.3 s and cardiac diastole lasts 0.4 s. During ventricular systole the pressure in the left ventricle rises from about 0.5 kPa to about 16 kPa, while the pressure in the aorta is about 11 kPa.

   (a)

   Explain how the pressure changes in the left ventricle control the opening and closing of valves during ventricular systole.

   [3 marks]

   (b)

   Calculate the heart rate in beats per minute and the percentage of the cardiac cycle spent in cardiac diastole, and state what happens in the heart during cardiac diastole.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A group of students dissects a pig's heart to investigate how its structure relates to its function. They notice that the wall of the left ventricle is much thicker than the right, that thin cords (tendons) attach to the flaps of the valves between the atria and ventricles, and that blood vessels run across the surface of the heart.

   (a)

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

   [6 marks]

   (b)

   Describe how a heart dissection can be carried out to investigate the relationship between the heart's structure and its function, and discuss the limitations of the investigation.

   [6 marks]

   Total for question 4: 12 marks

End of questions