1. 1
   A blood donation centre spins a donated blood sample in a centrifuge, separating it into layers: a pale yellow liquid layer at the top, a thin white-ish layer in the middle, and a dense red layer at the bottom of the tube.

   (a)

   Which layer is made up mainly of plasma?

   [1 mark]

   • AThe pale yellow liquid layer at the top
   • BThe thin white-ish middle layer
   • CThe dense red layer at the bottom
   • DNone of the layers

   (b)

   Which type of blood cell is most likely responsible for the dense red layer at the bottom of the tube?

   [1 mark]

   • AWhite blood cells
   • BPlatelets
   • CRed blood cells
   • DPlasma proteins

   (c)

   Explain how the structure of red blood cells is adapted to their function of transporting oxygen.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A brewer adds yeast to a sugar solution in a sealed fermentation vessel with no air present. Over several days, the sugar solution produces bubbles of gas and begins to smell of alcohol, while the temperature of the vessel rises slightly.

   (a)

   Which type of respiration is occurring in the yeast in the sealed, air-free vessel?

   [1 mark]

   • AAerobic respiration
   • BAnaerobic respiration
   • CPhotosynthesis
   • DOsmosis

   (b)

   What are the products of this type of respiration in yeast?

   [1 mark]

   • ACarbon dioxide and lactic acid
   • BCarbon dioxide and ethanol
   • COxygen and glucose
   • DWater and oxygen

   (c)

   Explain why much less energy is released per glucose molecule during this type of respiration in yeast compared with aerobic respiration.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   During a hospital stress test, a patient's heart rate and stroke volume are monitored on a treadmill. At rest, her heart rate is 72 beats per minute and her stroke volume is 65 cm³. After five minutes of exercise, her heart rate rises to 150 beats per minute and her stroke volume rises to 90 cm³.

   (a)

   Calculate the patient's cardiac output at rest and during exercise, using cardiac output = stroke volume × heart rate, giving your answers in cm³ per minute.

   [3 marks]

   (b)

   Calculate the percentage increase in the patient's cardiac output from rest to exercise, and explain why both her heart rate and stroke volume increase during exercise.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A patient diagnosed with anaemia has a lower than normal concentration of red blood cells in her blood. She reports feeling unusually breathless and fatigued even during light exercise, such as climbing a single flight of stairs, and sometimes needs to stop and rest.

   (a)

   Explain how having a lower than normal concentration of red blood cells would reduce the amount of oxygen the patient's blood can transport to her muscles, and explain why this would make her feel breathless and fatigued even during light exercise.

   [6 marks]

   (b)

   Explain the difference between aerobic and anaerobic respiration in muscle cells, and evaluate why relying more on anaerobic respiration during light exercise is disadvantageous for this patient compared with a person with a normal red blood cell count.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   A baby born prematurely has underdeveloped lungs, with fewer and larger alveoli than a full-term baby, giving a much smaller total surface area for gas exchange for their body size. Medical staff give the baby extra oxygen through a face mask to help maintain his blood oxygen levels while his lungs continue to develop.

   (a)

   Which feature of the alveoli mainly helps to increase the rate of gas exchange in a healthy, full-term baby's lungs?

   [1 mark]

   • AA large total surface area from many small alveoli
   • BA thick alveolar wall
   • CA low blood supply to the alveoli
   • DA wide diffusion distance

   (b)

   Why would having fewer, larger alveoli reduce the rate of oxygen diffusion into the premature baby's blood, for a given lung volume?

   [1 mark]

   • AIt removes the concentration gradient entirely
   • BIt increases the concentration of oxygen in the blood
   • CIt reduces the total surface area available for diffusion
   • DIt increases the total surface area available for diffusion

   (c)

   Explain why giving the baby extra oxygen through a face mask would help increase the rate of oxygen diffusion into his blood, despite his reduced total alveolar surface area.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   An insect has no blood-based circulatory system to transport oxygen; instead it has a network of branching air tubes (tracheae) that carry air directly to its tissues. A mammal of similar total body volume instead relies on a circulatory system to transport oxygen from its lungs to its tissues in the blood.

   (a)

   Why does a mammal need a circulatory system to transport oxygen, while a small insect can rely on direct air tubes instead?

   [1 mark]

   • AA mammal produces more carbon dioxide than an insect
   • BA mammal does not have a gas exchange surface
   • CA mammal's tissues do not require oxygen
   • DA mammal's greater size and lower surface area to volume ratio means diffusion alone is too slow to supply its tissues

   (b)

   Which of these substances must a mammal's circulatory system transport that an insect's tracheal system does not need to transport in the same way?

   [1 mark]

   • AOxygen to tissues
   • BCarbon dioxide from tissues
   • CNitrogen from the air
   • DDissolved food molecules and hormones between organs

   (c)

   Explain why a larger, more complex organism such as a mammal generally has a lower surface area to volume ratio than a small organism such as an insect, and why this creates the need for a transport system.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A transplant surgeon inspects a donor heart before surgery. She notes that the wall of the left ventricle is considerably thicker and more muscular than the wall of the right ventricle, and that thick flap-like valves are present between the atria and ventricles on both sides of the heart.

   (a)

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

   [3 marks]

   (b)

   Explain the function of the flap-like valves between the atria and ventricles, and evaluate what might happen to blood flow through the heart if one of these valves failed to close properly.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   A professional cyclist trains for six weeks inside a specialised chamber that simulates high-altitude conditions by reducing the concentration of oxygen in the air she breathes, while keeping temperature and pressure controlled. Doctors monitor how her lungs and heart adapt to the lower oxygen concentration over the six weeks.

   (a)

   Using Fick's law (rate of diffusion is proportional to surface area × concentration difference, divided by membrane thickness), explain why the lower oxygen concentration in the chamber would initially reduce the rate of oxygen diffusion into the cyclist's blood, and suggest one way her body might adapt over the six weeks to help compensate for the lower oxygen concentration.

   [6 marks]

   (b)

   Explain how you would expect the cyclist's heart rate to change during a training session in the low-oxygen chamber compared with an identical session at normal oxygen concentration, and evaluate how an increased red blood cell count, built up over the six weeks, could benefit her cardiac output and performance once she returns to race at normal, sea-level oxygen concentrations.

   [6 marks]

   Total for question 8: 12 marks

End of questions