8.1. The circulatory system
A subsection of Biology, 9700, through 8. Transport in mammals
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Red blood cells are suspended in plasma which has a concentration equivalent to that of 0.9% sodium chloride (NaCl ) solution. A student investigated what happens to red blood cells when placed into sodium chloride solutions of different concentration. A small drop of blood was added to 10 cm3 of each sodium chloride solution. Samples were taken from each mixture and observed under the microscope. The number of red blood cells remaining in each sample was calculated as a percentage of the number in the 0.9% solution. The results are shown in . 0.0 0.5 1.0 concentration of NaCl / % percentage of cells remaining 1.5 With reference to , describe the student’s results. The student also measured the cell volumes of the red blood cells in three of the sodium chloride solutions. The results are shown in Table 3.1. Table 3.1 concentration of sodium chloride / % mean red cell volume / µm3 0.7 0.9 1.5 shows the appearance of some red blood cells removed from the 1.5% sodium chloride solution. Explain the results shown in , Table 3.1 and , in terms of water potential. 0% NaCl solution 0.7% NaCl solution 1.5% NaCl solution Red blood cells each contain about 240 million molecules of haemoglobin that transport oxygen and carbon dioxide. Describe the role of haemoglobin in the transport of oxygen and carbon dioxide. oxygen carbon dioxide The haematocrit is the proportion of the blood that is composed of red blood cells. Samples of blood were taken from an athlete who lived at sea level since birth and moved to live and train at an altitude of 5000 m for three weeks. The haematocrit and the number of red blood cells per mm3 were determined before moving to high altitude and after three weeks at that altitude. The results are shown in Table 3.2. Table 3.2 altitude haematocrit number of red blood cells × 106 per mm3 sea level 0.45 6.1 5000 m (after three weeks) 0.53 7.3 Calculate the percentage increase in the number of red blood cells per mm3 after three weeks at 5000 m. Show your working. Answer = % Explain why the haematocrit increases at altitude.
9700_w10_qp_21
THEORY
2010
Paper 2, Variant 1
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