Cambridge A Level Biology AS Partial Pressures Oxygen Loading Questions

[Maximum number: 3]

The high blood pressure at the arterial end of a capillary network results in some components of blood leaving the capillaries and forming tissue fluid. At the venous end, the presence of plasma proteins allows movement of water by osmosis back into the capillaries.

Fig. 2.1 is a diagram showing a capillary network. The lymph vessels and the blood vessels at the arterial and venous ends of the network are also shown.

Fig. 2.1

When a person moves from sea level and stays at high altitude for a few months, there is an increase in the number of red blood cells per $\mathrm{mm}^{3}$ of blood.

Explain why this increase occurs.

Marking guidance:

accept Hb / hb for haemoglobin

any three from:

1 (at altitude) lower, partial pressure of oxygen / $p \mathrm{O}_{2}$ (in, atmosphere/inhaled air/inspired air/alveolar air) ;

I low $\mathrm{pO}_{2}$ in blood

R if stated as high $\mathrm{ppCO}_{2}$ and low $\mathrm{pp} \mathrm{O}_{2}$

R low, volume / saturation, of oxygen

2 percentage saturation of haemoglobin (with oxygen), lower / decreased ;

A haemoglobin is less saturated

A fewer molecules of / less, oxygen, combine / associate, with haemoglobin I absorbed / taken up by

R if in context of Bohr effect but then allow ecf for overall max 2

3 (as) haemoglobin has lower affinity for oxygen (than at sea level) ;

4 more haemoglobin (synthesised / required / provided) ;

5 compensation / described ;

e.g. helps to transport the same quantity of oxygen as at sea level

6 AVP ;
e.g.

idea of more rbc through pulmonary capillaries per unit time

ref. to EPO / erythropoietin (secreted to increase red blood cell production)

CAIE A-Level Biology AS 8.2.5 Partial Pressures and Oxygen Loading Questions

Exam points

CAIE A-Level Biology AS 8.2.5 Partial Pressures and Oxygen Loading Questions question 1