A-LevelBiologyTransport in mammals9700/23 · May/June 2019 · Q510 Marks

Fig. 5.1 is a photomicrograph of human blood cells that have been placed in a solution of sodium chloride. [Figure 5.1]

(a)(i)State the function of the cell labelled Y.[1]
(a)(ii)The red blood cell labelled in Fig. 5.1 is described as crenated because it has an abnormal, shrivelled appearance. Explain how this red blood cell has become crenated.[2]
(b)(i)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] Calculate the percentage increase in mean red blood cell count between population A and population D. ....................................................................% [1][1]
(b)(ii)Describe and suggest explanations for the data shown in Table 5.1.[4]
(c)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.[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 (May/June 2019). The mark or mark type is shown in brackets.

[1] phagocytosis (of, dead cells / pathogens / AW) ; A endocytosis of pathogens
[2] (sodium chloride) solution has lower water potential (than cytoplasm); ora
A Y for water potential
water, leaves / AW, cell by osmosis ;
[1] 13.56; A 13.6 / 14
[4] allow (red) blood cell count for mean red blood cell count
allow ora
any four from:
1 description of data; e.g.
lowest mean red blood cell count for, (population) A / lowest altitude
(populations) B, C and D / all other altitudes, have a higher mean red blood cell count than A / 695m altitude
(population) B has highest mean red blood cell count
(population) B has higher mean red blood cell count than C and D
physiological explanation population A compared to B/C/D
2 decrease in partial pressure of oxygen in the atmosphere with increase in altitude / AW
or
lower partial pressure of / less, oxygen in, inhaled air / lungs / alveoli AW
3 ref. to haemoglobin;
e.g. lower saturation of haemoglobin with oxygen (in lungs)
lower affinity of haemoglobin for oxygen (in lungs)
more haemoglobin required to carry sufficient oxygen to tissues
4 suggestion of increase in count at 1676 m and above;
e.g. rate of production of red blood cells increases
higher erythropoietin (EPO) levels
ref. to changed proportion of plasma to red blood cells / plasma volume decreases
5 little difference between B, C and D / AW ;
6 differences in altitude are not great / AW ; in context of B, C, D
7 ref. to genetic differences / adaptation to environment ;
allow if general statement includes population A
8 AVP; e.g. ref. to differences in demographics
[2] less haemoglobinic acid is formed / fewer hydrogen ions to bind to haemoglobin (to cause dissociation of oxygen) ;
any one from:
binds to allosteric site / site other than active site (of enzyme), qualified ;
e.g. causes change in shape of active site
substrate cannot bind to active site
fewer / no, enzyme-substrate / ES, complex formation
prevents / reduces / AW, carbonic acid / H2CO3, formation / AW ; A fewer hydrogen ions produced from carbonic acid
dissociation