8. Transport in mammals
A section of Biology, 9700
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Using a light microscope at a magnification of ×400, it is possible to identify different types of blood cell in prepared slides of mammalian blood. is a key to identify different types of blood cell in prepared slides of mammalian blood. In , letters C, D, E and F represent four different types of blood cell. key 1a nucleus present go to 2 1b nucleus absent C 2a large rounded nucleus D 2b nucleus not rounded go to 3 3a nucleus is kidney shaped E 3b nucleus is lobed F Identify the cell types C, D, E and F in . C D E F Explain why blood taken from a person with an infectious disease may have a different number of white blood cells compared with blood taken from a healthy person. As part of a research project, a team of doctors and scientists carried out tests to investigate the effect of altitude on the ability of blood to carry oxygen. They assessed the changes in the oxygen-carrying ability of their own blood as they walked from 1530 m above sea level to 5700 m above sea level, over a period of 14 days. 5700 m above sea level is an extremely high altitude. Table 4.1 is a summary of some of their results. Table 4.1 day 1 at 1530 m day 14 at 5700 m percentage saturation of haemoglobin with oxygen in blood leaving the lungs volume of oxygen delivered to tissues by 100 cm3 of blood / cm3 19.3 19.2 Compare the results for day 1 with the results for day 14 in Table 4.1 and explain the results shown for day 14. The results of the research project have led to an improved understanding of diseases such as sickle cell anaemia. Explain why sickle cell anaemia is an example of a disease.
9700_m21_qp_22
THEORY
2021
Paper 2, Variant 2
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Control of heartbeat is myogenic. This means the electrical activity controlling the rhythm of a regular heartbeat begins in the heart muscle itself. Atrial fibrillation (AF) is an abnormal heart rhythm that causes rapid and irregular contractions of the atria. Untreated cases of AF can lead to a stroke. A stroke is caused when a small blood clot, often forming in the left atrium, is carried by the blood to the brain where it blocks a small artery and leads to brain damage. List all of the structures through which a blood clot in the left atrium must travel to reach the blood vessels supplying the brain. The structures must be listed in the correct sequence. Explain why blocking a small artery in the brain leads to brain damage. A common cause of AF is when a small group of muscle cells in the wall of the left atrium starts to send out electrical impulses to the surrounding heart muscle cells. Explain how the control of heartbeat by the sinoatrial node can be disrupted by AF, resulting in rapid and irregular atrial contractions. Red blood cells are involved in the transport of oxygen and carbon dioxide in the blood. is a diagram representing the exchange of oxygen and carbon dioxide between a red blood cell in a capillary and a respiring cell. Some of the reactions that take place in the red blood cell are also shown. The diagram is not drawn to scale. capillary wall respiring cell CO2 4O2 Z Z endothelial cells CO2 + H2O 4O2 + Y red blood cell enzyme X H2CO3 carbonic acid HCO3 – hydrogencarbonate ion HbO8 + H+ oxyhaemoglobin H+ + basement membrane Identify enzyme X and molecule Y in . X Y The hydrogencarbonate ions shown in leave the red blood cell and are replaced by chloride ions. State why it is necessary for chloride ions to enter the red blood cell as hydrogencarbonate ions leave. Identify the aqueous environment, labelled Z in , that surrounds the respiring cell. Oxygen and carbon dioxide are also exchanged between blood capillaries and alveoli in the lungs. The gas exchange system has specialised cells to prevent harmful microscopic particles that are present in inhaled air from reaching the alveoli. These particles are associated with many respiratory diseases. Explain how specialised cells in the gas exchange system prevent harmful microscopic particles from reaching the alveoli.
9700_m22_qp_22
THEORY
2022
Paper 2, Variant 2
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The red blood cells of people with sickle cell anaemia have reduced oxygen-carrying capacity. Explain the relationship between the gene mutation that causes sickle cell anaemia and the reduced oxygen-carrying capacity of red blood cells. People with sickle cell anaemia may need a blood transfusion. One risk associated with a blood transfusion is a condition known as transfusion-associated circulatory overload (TACO). TACO is caused by a large increase in blood volume over a short period of time. This increase in blood volume can be harmful. Predict the effect of an increase in blood volume on ADH secretion and state one consequence for kidney function of this change in ADH secretion. One feature of TACO is an increase in fluid entering the alveoli, which makes it difficult to breathe. This increase in fluid can be caused by an increase in blood pressure in the pulmonary capillaries that surround the alveoli. Suggest how an increase in blood pressure in the pulmonary capillaries can cause fluid to enter the alveoli. People with kidney disease may be at a higher risk of TACO following a blood transfusion. A study carried out in 2019 investigated whether there is a link between kidney disease and TACO. This study included data from: • 200 people who developed TACO after a blood transfusion • 405 people who did not develop TACO after a blood transfusion. The people in the study were put into one of four categories: • people with acute (short-term) kidney injury (AK• people with chronic (long-term) kidney disease (CKD) who do not require dialysis • people with severe chronic kidney disease who do require dialysis (CKD + D) • people who do not have kidney disease. In dialysis, a machine is used to carry out the function of the kidneys. The results of this study are shown in . AKI CKD category percentage of people CKD + D no kidney disease key percentage of the 200 people who developed TACO percentage of the 405 people who did not develop TACO With reference to , describe the effect of having kidney disease on the risk of developing TACO. Suggest reasons for this effect. Patients who are at high risk of developing TACO following a blood transfusion can be given a type of drug called a loop diuretic. In normal urine production, 99% of sodium ions in the glomerular filtrate are reabsorbed and 1% are excreted. In urine production of people who take loop diuretics, 80% of sodium ions in the glomerular filtrate are reabsorbed and 20% are excreted. Explain how loop diuretics affect water reabsorption in the kidneys and suggest why this reduces the risk of developing TACO following a blood transfusion.
9700_m22_qp_42
THEORY
2022
Paper 4, Variant 2
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Table 2.1 shows descriptions of three types of white blood cell. Complete Table 2.1 by stating the names of these three types of white blood cell. Table 2.1 description name of white blood cell A large cell that has a bean-shaped (kidney-shaped) nucleus. It can develop into a macrophage. A cell that has a large spherical nucleus and little cytoplasm. It responds to non-self antigens. A cell that has a lobed nucleus. It is phagocytic. Dromedary camels are classified in the family Camelidae and live in desert habitats of North Africa and Asia. In these hot, dry environments, dromedary camels can lose up to 30% of their body mass from dehydration, causing their blood to become more viscous . shows a drawing of red blood cells of a dromedary camel. is a drawing of human red blood cells. ×2000 ×2000 The llama is also classified in the family Camelidae. Llamas live in mountainous areas of South America, often at altitudes of 3500 m or higher. As the altitude above sea level increases, the air pressure decreases. The partial pressure of oxygen in the lungs of mammals at 3500 m is 6.4 kPa. shows the oxygen dissociation curve of adult human haemoglobin and adult llama haemoglobin. 0.0 2.0 4.0 6.0 8.0 partial pressure of oxygen / kPa 10.0 12.0 14.0 percentage saturation of haemoglobin with oxygen key adult llama haemoglobin adult human haemoglobin With reference to , explain how the differences between the oxygen dissociation curves for humans and llamas show that llamas are better adapted for living at high altitudes than humans. Sketch a curve on to show the effect of an increased carbon dioxide concentration on the percentage saturation of adult human haemoglobin with oxygen. Explain the importance of the Bohr shift in metabolically active organs, such as the liver.
9700_m24_qp_22
THEORY
2024
Paper 2, Variant 2
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