A-LevelBiologyImmunity9700/22 · Feb/Mar 2021 · Q411 Marks

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.

(a)(i)Fig. 4.1 is a key to identify different types of blood cell in prepared slides of mammalian blood. In Fig. 4.1, letters C, D, E and F represent four different types of blood cell. Identify the cell types C, D, E and F in Fig. 4.1. [Figure 4.1][3]
(a)(ii)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.[2]
(b)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 1530m above sea level to 5700m above sea level, over a period of 14 days. 5700m above sea level is an extremely high altitude. Table 4.1 is a summary of some of their results. Compare the results for day 1 with the results for day 14 in Table 4.1 and explain the results shown for day 14. [Table 4.1][4]
(c)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.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Feb/Mar 2021). The mark or mark type is shown in brackets.

[3] 4(a)(i) C = red blood cell / erythrocytea red blood corpuscle D = lymphocyte A plasma cell R if also stated as granulocyte A B- or T-Cell I white blood cell / leucocyte / agranulocyte E = monocyte R if also stated as granulocyte I white blood cell / leucocyte / agranulocyte A macrophage F = neutrophil A eosinophil A basophil R if also stated as agranulocyte I white blood cell / leucocyte / granulocyte C correct = one mark D correct = one mark E and F correct = one mark
[2] 4(a)(ii) any two from: more white blood cells because result of immune response ; clonal expansion / described, of, B- / T-, lymphocytes / cells ; idea of producing (large quantity of specific) antibody in context of immune response increased, production of macrophages / phagocytes ; if written in context of HIV/AIDS as the infectious disease fewer white blood cells ; further detail; e.g. T-helper lymphocytes destroyed
[4] 4(b) 1 decreased / 13% less, percentage oxygen saturation / percentage saturation haemoglobin with oxygen and similar (quantity) / same (quantity) / 0.1 cm³ per 100 cm³ blood less, oxygen delivered by haemoglobin to tissues; plus any three from: 2 at high altitude lower partial pressure of oxygen, in atmosphere / in inhaled air / in alveolus / into pulmonary capillaries / AW ; 3 in lungs / in pulmonary capillaries / at the alveolus, less oxygen, binds to / taken up by / AW, haemoglobin; 4 haemoglobin has lower affinity for oxygen (in lungs); 5 increased production of haemoglobin ; 6 increased, production / number / density, of red blood cells ; A increased haematocrit 7 (so) more haemoglobin available to bind oxygen / same quantity of oxygen can be taken up as at sea level ; 8 AVP; e.g. ref. to decreased plasma volume increase in erythropoietin (EPO) concentration other described physiological change
[2] 4(c) absence of, good health / well-being / lack of physical well-being / AW ; A disorder / illness further detail; e.g. having an adverse effect reduced / impaired, function A described e.g. less oxygen, taken up / transported produces, (specific) signs / symptoms ; A described symptoms