8.2. Transport of oxygen and carbon dioxide
A subsection of Biology, 9700, through 8. Transport in mammals
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is a photomicrograph of human blood cells from a healthy individual who lives at sea level. The cells labelled C, D and E are white blood cells. C D E red blood cell Name cells C, D and E. C D E In humans, an increase in the white blood cell count can be associated with leukaemias and with infectious diseases, such as measles. Chronic lymphocytic leukaemia (CLL) is a type of cancer that starts in the bone marrow. In the early stages, many people with CLL feel well. The disease is sometimes diagnosed by chance during a routine blood analysis, when a high white blood cell count is noticed. Many of these white blood cells are only partially mature. Suggest why CLL starts in the bone marrow and not in any other location in the body. Explain why a high white blood cell count is a feature of measles and of CLL. measles CLL Most of the oxygen that enters the mammalian circulatory system is transported by red blood cells. Describe and explain the passage of oxygen across the cell surface membrane of the red blood cell. At a high altitude, the partial pressure of oxygen in the atmosphere is lower than at sea level. If a person travels from low altitude to high altitude and remains there for a few weeks, the red blood cell count increases. Explain why the body needs to respond to high altitude by increasing the number of red blood cells. Polypeptide synthesis occurs before a red blood cell is released into the circulation. The HBB gene codes for the β-globin polypeptide of haemoglobin. There are two alleles of HBB, known as HbA and HbS. Describe the difference between the HbA allele and the HbS allele and state how this difference affects: • the β-globin polypeptide • the haemoglobin molecule.
9700_s19_qp_22
THEORY
2019
Paper 2, Variant 2
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is a photomicrograph of human blood cells that have been placed in a solution of sodium chloride. Y crenated red blood cell State the function of the cell labelled Y. The red blood cell labelled in is described as crenated because it has an abnormal, shrivelled appearance. Explain how this red blood cell has become crenated. Researchers studied the effect of altitude on the red blood cell count of humans. They recorded the red blood cell count of healthy adults from populations living at four different altitudes in a mountainous region. The results are shown in Table 5.1. Table 5.1 population altitude of population / m above sea level mean red blood cell count / number of cells ×106 mm−3 A 4.50 B 5.14 C 5.04 D 5.11 Calculate the percentage increase in mean red blood cell count between population A and population D. % Describe and suggest explanations for the data shown in Table 5.1. Carbonic anhydrase is an enzyme found in red blood cells which has an important role in the transport of respiratory gases. Explain why a non-competitive inhibitor of carbonic anhydrase will reduce the supply of oxygen to actively respiring tissues.
9700_s19_qp_23
THEORY
2019
Paper 2, Variant 3
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Questions Discovered
241