A-LevelBiologyImmunity9700/22 · Feb/Mar 2024 · Q213 Marks

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]

(a)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][3]
(b)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 (thicker). Fig. 2.1 shows a drawing of red blood cells of a dromedary camel. Fig. 2.2 is a drawing of human red blood cells. [Figure 2.1] [Figure 2.2] Suggest how these differences adapt dromedary camels for living in hot, dry environments.[3]
(c)(i)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 6.4kPa. Fig. 2.3 shows the oxygen dissociation curve of adult human haemoglobin and adult llama haemoglobin. [Figure 2.3] With reference to Fig. 2.3, 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.[3]
(c)(ii)Sketch a curve on Fig. 2.3 to show the effect of an increased carbon dioxide concentration on the percentage saturation of adult human haemoglobin with oxygen.[1]
(c)(iii)Explain the importance of the Bohr shift in metabolically active organs, such as the liver.[3]

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Mark scheme

Marking points from the official mark scheme (Feb/Mar 2024). The mark or mark type is shown in brackets.

[3] 2(a)
description: A large cell that has a bean-shaped (kidney-shaped) nucleus. It can develop into a macrophage. name of white blood cell: monocyte;
description: A cell that has a large spherical nucleus and little cytoplasm. It responds to non-self antigens. name of white blood cell: lymphocyte; I B- / T-
description: A cell that has a lobed nucleus. It is phagocytic. name of white blood cell: neutrophil;
[3] 2(b) allows, easier / quicker, flow / movement, of blood (compared to human red blood cells);
plus any two explanations from :
lozenge / torpedo / elliptical / AW, shape of camel red blood cells (vs, biconcave disc of human red blood cells) ;
camel red blood cells are smaller (than human red blood cells) ; ora
larger number of camel red blood cells (per unit volume) ;
[3] 2(c)(i) any three from:
in context of better adapted for uptake in lungs
(at high altitude) haemoglobin of llama more highly saturated with oxygen (than haemoglobin of human);
I ref. to higher saturation in partial pressures found in tissues
at 6.4 kPa / 3500 m, oxygen saturation is, 86% for llama and 79/80% for human /6 /7% higher oxygen saturation for llama ;
llama haemoglobin has a higher affinity for oxygen than human haemoglobin ;
more oxygen, transported / delivered to tissues ;
(so) sufficient oxygen unloaded in tissues to satisfy demand ;
[1] 2(c)(ii) curve drawn to the right of the human dissociation curve ;
[3] 2(c)(iii) any three from:
(metabolically active organs) release more carbon dioxide / partial pressure of carbon dioxide is higher ;
ref. to decreased affinity of haemoglobin for oxygen / explained ; e.g. ref to haemoglobinic acid
more oxygen released ;
for more aerobic respiration / more ATP production ; look for 'more' once