PHYSICS

due to extensive skin folds, and high hematocrit and erythrocyte
concentrations. Thus the capacity of the frog for transporting
oxygen is substantially increased.
Mules are used at Aucanquilcha, a base camp for the International
High Altitude Expedition, as a transport means in the
5250 - 6000 m altitude range. The animals demonstrate the ability
to accurately assess their capacity for work and refuse to be
pushed beyond a safe limit. Other animals at high altitudes are the
vicuna (5000 - 6000 m), domestic sheep (up to 5250 m), and
horses (up to 4600 m). Birds, however, hold the high altitude records:
condors (7600 m), geese (8534 rn), chough (9000 m) and
griffon vulture (11278 m).
6.1.8. Effects of Altitude on the Plants
6.1. Typical values for diffusion coefficients of small molecules
in aqueous solutions and air (Nobel, 1983)
Substance
Diffusion coefficient,
m 2.s -t
Substance
Diffusion coefficient,
m 2·s-1
Glucose 0.67. 10 9 CO 2 (solution) 1.7 . 10- 9
Ca-+ (with Cl ) 1.2 . 10- 9 CO 2 (gas) 1.5 . 10- 5
K+(with Cl ) 1.9. 10- 9 H 2O 2.4 . 10- 5
Na+ (with Cl ) 1.5 . 10- 9 O 2 1.9 . 10- 5
solution at the right is higher than at the left. It would be
necessary to apply additional pressure by way of a piston (fig. 6.3)
to compensate the pressure difference. The pressure required to
ap -+
Altitudinal variation of climate induces morphological and
physiological changes in plants and their canopy architecture.
Often the plants maintain a compact or dwarf form with small,
narrow or densely pubescent leaves. The ecological zone between
3230 and 3660 m is called an alpine area. Here it is possible to
find considerable changes in quantitative and qualitative characteristics
of the fauna. In addition, there are certain changes in climatic
conditions that are related to the effects of pressure, wind,
humidity and preci pitation, temperature, radiation and gas exchange,
which in turn, also modify the fauna.
6.1.9. Osmotic Pressure
abc
Fig. 6.3. An ideally semipermeable membrane, which separates
two solutions of different concentrations
balance the osmotic flow of water is called the osmotic pressure.
For dilute solutions, osmotic pressure (Posm) obeys the Van't Hoff
relation:
Posm = RTC A
(6.5)
where R is the gas constant (R = 8,31 J·mo)-'·K-I), T the absolute
temperature, and C A
the molar concentration.
6.1.10. Osmotic Phenomena in Plants
The process of osmosis can be considered as a special case of
membrane diffusion in which only the solvent (water) moves
across the membrane (via water channels), while the solute molecules
are restrained by the membrane, which is therefore described
as semipermeable. Typical values for diffusion coefficients
are presented in Table 6.1.
If two solutions with different concentrations are separated by
a membrane (M), the concentration of solution II exceeds that
concentration of solution I, and they are separated by a semi per­
meable membrane that allows the passage of water but not the
Most animals are characterized with constant osmotic pressure
which is maintained by the blood. Plant cells, in contrast, exist in
a dilute aqueous environment. Osmosis in plant cells result the
solute, there is a flow of water from left to right and the level of
transfer of solvent molecules from regions of high concentration
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