1. 1
   A biologist compared the circulatory systems of a fish and a mammal. In the fish, blood passes through the heart once for each complete circuit of the body. In the mammal, blood passes through the heart twice for each complete circuit, once to the lungs and once to the rest of the body.

   (a)

   What term describes the mammal's circulatory system?

   [1 mark]

   • ADouble circulation
   • BSingle circulation
   • COpen circulation
   • DLymphatic circulation

   (b)

   Which structures make up the circulatory system in both the fish and the mammal, according to the biologist's comparison?

   [1 mark]

   • AA network of air-filled tubes with no pump
   • BA system of blood vessels with a pump and valves ensuring one-way flow
   • CA single tube with no valves and no pump
   • DA system of nerves carrying electrical impulses

   (c)

   Explain one advantage of the mammal's double circulation compared with the fish's single circulation.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student dissected a mammalian heart and traced the direction of blood flow through the major vessels attached to it, noting one-way valves present in some vessels but not others.

   (a)

   In which type of vessel does blood flow away from the heart?

   [1 mark]

   • ACapillaries only
   • BVeins
   • CArteries
   • DLymph vessels

   (b)

   The student noticed that one-way valves were present in the walls of veins but not in arteries. What is the main function of these valves in veins?

   [1 mark]

   • AProducing hormones that regulate heart rate
   • BIncreasing the pressure of blood flowing towards the heart
   • CFiltering waste products out of the blood
   • DPreventing the backflow of blood, since blood in veins is at low pressure

   (c)

   Explain why valves are necessary in veins but are not needed in the same way in arteries.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A patient was diagnosed with a heart defect in which a hole existed between the two ventricles, allowing oxygenated and deoxygenated blood to mix before being pumped around the body. Doctors explained the health consequences of this defect in terms of the normal double circulation.

   (a)

   A patient with a heart defect had a hole between the two ventricles, allowing oxygenated and deoxygenated blood to mix before being pumped around the body. Explain why this mixing is harmful, referring to the double circulation.

   [3 marks]

   (b)

   Explain the normal pathway of blood through the double circulation of a healthy person, starting from the right atrium, and describe how this pathway would be disrupted by the hole between the ventricles described above.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A cardiology lecturer used a working model of a four-chambered heart to explain to students why mammals rely on a double circulation, rather than the single circulation seen in fish, to supply their tissues with oxygen efficiently.

   (a)

   Explain why mammals have evolved a double circulation with a heart divided into four chambers, describing the roles of the septum, valves and the relative thickness of the chamber walls in maintaining this system's efficiency.

   [6 marks]

   (b)

   Discuss the likely consequences for an athlete's performance if their heart valves became damaged and leaky, allowing some blood to flow backwards within the heart during contraction, and explain how the body might attempt to compensate for this over time.

   [6 marks]

   Total for question 4: 12 marks

End of questions