Page 304 - Biology_F5

Gas exchange and respiration

the respiratory surfaces. Thus, an efficient a variety of respiratory surfaces, ranging
respiratory surface must be moist for rapid from gills in fish and tadpoles to lungs in
exchange and transportation of respiratory adult amphibians, reptiles, and mammals.
gases.
Oxygen transport in vertebrates
(g) Membrane permeability In vertebrates oxygen is transported in
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Since the membrane form the boundary two ways: as dissolved oxygen in blood
between organism and its extracellular plasma and by means of red blood cells.
environment, it permeability affects The oxygen transported in solution form in
the rate of gas exchange. Therefore, a the blood plasma accounts for only about
respiratory surface must be permeable to two percent (2%), and the remaining ninty
allow gases to pass through. eight percent (98%) is transported by the
red blood cells. The red blood cells have
6.1.2 Oxygen and carbon dioxide a red pigment called haemoglobin which
transport in vertebrates is responsible for transport of oxygen and
Oxygen and carbon dioxide are the carbon dioxide in the blood. Structurally,
respiratory gases that have to be transported the haemoglobin molecule consists of
from one part of the body to another. four Iron-containing parts and four protein
Oxygen is transported from the respiratory chains. Each haemoglobin molecule binds
surfaces to the respiring body tissues and to four oxygen molecules, forming the
carbon dioxide has to be transported from oxyhaemoglobin molecule. This is carried
the respiring body tissues to the respiratory to individual cells in the body tissue where
surfaces. Vertebrates, such as mammals, it is released. The binding or combination
of oxygen and haemoglobin is a reversible
birds, reptiles, amphibians and fish, have
process as shown in the equation below:

According to the above equation, at high the haemoglobin becomes. Usually the graph

oxygen concentration, oxyhaemoglobin is S-shaped or sigmoid.

is formed, whereas at low oxygen The curve shows the following:

concentration, oxyhaemoglobin dissociates (a) At relatively low oxygen concentration,

into haemoglobin and oxygen. there is uncombined haemoglobin in the
This dissociation releases oxygen from blood and little or no oxyhaemoglobin
haemoglobin. The balance can be shown exists. This is most likely to occur
by an oxygen dissociation curve of in the body tissues, where oxygen

oxyhaemoglobin (Figure 6.4). In the concentration is likely to be low.

oxygen dissociation curve, the greater (b) At relatively high oxygen concentration,

the concentration or partial pressure of haemoglobin combines with oxygen

oxygen, the more saturated with oxygen
in the blood to form oxyhaemoglobin.
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