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Gas exchange and respiration

Haemoglobin is strongly attracted to change significantly at different altitudes,
carbon dioxide molecules. Carbon dioxide but the atmospheric pressure falls with
is removed to reduce its concentration in increasing altitudes. The oxygen tension
the cell and is transported to the lungs (partial pressure of oxygen molecules
where its concentration is low. This process dissolved in blood plasma) varies with
is continuous since oxygen concentration altitudes (Table 6.1). Organisms living in
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in the lungs, is always higher than that of a particular altitude have to develop adaptive
carbon dioxide, while in the respiring cells features that can enable them to sustain their
carbon dioxide concentration is always lives in their particular environment. Among
higher than that of oxygen. the organisms that live in the environments
that need them to develop some adaptive
6.1.3 Adaptation of organisms to features aimed at facilitating oxygen uptake
oxygen uptake include mountain dwellers, divers, and
The percentage of oxygen in the air does not mammalian foetus.

Table 6.1: The effects of altitude on the atmospheric pressure and oxygen tension
Altitude(m) above Atmospheric Oxygen Oxygen tension(kPa)
sea level pressure(kPa) content(%)
0 101.3 20.9 21.2
2500 74.7 20.9 15.7
5000 54.0 20.9 11.3
7000 38.5 20.9 8.1
10000 26.4 20.9 5.5

Adaptations to oxygen uptake for (b) They possess a form of haemoglobin with
mountain climbers and dwellers higher affinity to oxygen. This allows
In mountain climbers and high altitude loading of oxygen by haemoglobin even
dwelling mammals, the rate of metabolism at low oxygen tension.
is high in order to ensure constant (c) They secrete more alkaline urine that
generation of enough energy to cope with normalises blood pH. The chemoreceptors
climbing activities, hence the supply of become sensitive to carbon dioxide
oxygen should be assured. However, the concentration and normal ventilation
partial pressure of oxygen in high altitude rates are maintained.
is low which makes the climbers difficult (d) Their tissues are tolerant to high levels
to pick up oxygen. For these reasons, of lactic acid due to oxygen deficiency.
mountain climbers and mammals living (e) They have large lungs, with increased
in high altitudes develop the following lung volumes and total lung capacity, and
adaptive features: therefore large amount of haemoglobin
(a) Their bone marrow produces more red loaded with oxygen.
blood cells in order to raise the oxygen- (f) They have deep and slow breathing rate
carrying capacity of the blood. that improves ventilation efficiency

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