Option D Human Physiology Notes
IB Biology
D.6 Transport of Respiratory Gases
Nature of Science: Scientists have a role in informing the public: scientific research has led to a
change in public perception of smoking. (p. 704)
UNDERSTANDING STATEMENTS
 Oxygen dissociation curves show the affinity of hemoglobin for oxygen.
o Hemoglobin is the protein found in red blood cells that transports oxygen.
o The degree to which oxygen binds to hemoglobin is determined by the partial pressure
of oxygen (pO2) in the blood.
o Note the significant change in saturation over a narrow range of oxygen partial
pressure – typifies oxygen pressures surrounding cells under normal metabolism. At low
pO2 , such as might occur in the muscles, oxygen will dissociate from hemoglobin. At
high pO2 such as might occur in the lungs, the hemoglobin will become saturated.
Draw Graph here: Oxygen dissociation of hemoglobin fig 1 – pg 700

Carbon dioxide is carried in solution and bound to hemoglobin in the blood.
o Carbon dioxide is carried in three forms in blood plasma;
o Dissolved as carbon dioxide
o Reversibly converted to bicarbonate (hydrogen carbonate) ions (HCO3-) that
are dissolved in the plasma
o Bound to plasma proteins
o Fill in the table from page 700 showing the amounts of each form of carbon dioxide in
arterial blood and venous blood at rest and during exercise.
Form of transport
Arteriole
mmol-1 blood
Venous
mmol-1 blood
Rest
Exercise

Carbon dioxide is transformed in red blood cells into hydrogencarbonate ions.
o The majority of carbon dioxide produced by the body during cellular respiration is
converted to the more soluble and less toxic bicarbonate (hydrogen carbonate) ion.
The reaction occurs in red blood cells and is catalyzed by the enzyme carbonic
anhydrase. Show the equation (pg 701) and tell when it proceeds from left to right and
right to left.

The Bohr shift explains the increased release of oxygen by hemoglobin in respiring tissues.
o Increased metabolism results in greater release of CO2 into the blood, which lowers the
pH of the blood. This increased acidity shifts the oxygen dissociation curve to the right,
which results in a decreased affinity of the hemoglobin for oxygen; that is, a greater
release of oxygen from hemoglobin at the same partial pressure of oxygen (known as
the Bohr shift). Why is this important??
Draw the graph showing the Bohr Shift on page 701 (fig 2)

During exercise the rate of ventilation changes in response to the amount of CO2 in the blood.
o Increase in exercise causes an increase in metabolism and lead to an increase in the
production of CO2 as a waste product of cell respiration. Increased CO2 causes blood
pH to decrease because CO2 dissolves in water to form carbonic acid.
o Chemoreceptors in the medulla, the aorta and the carotid artery are able to detect a
change in blood carbon dioxide.
o High levels of carbon dioxide in the blood trigger an increase in the ventilation rate.
WHY???

The rate of ventilation is controlled by the respiratory control center in the medulla oblongata.
o Medulla oblongata is in the brainstem. Two sets of nerves travel to the lungs from this
center: the intercostal nerves stimulate the intercostal muscles of the thorax and the
phrenic nerves stimulate the diaphragm.
o Explain how it works!


Chemoreceptors are sensitive to changes in blood pH.
Fetal hemoglobin is different from adult hemoglobin allowing the transfer of oxygen in the
placenta onto the fetal hemoglobin.
o Fetal hemoglobin has a higher affinity for O2 at all partial pressures. This ensures that O2
is transferred to the fetus from the maternal blood across the placenta.
Draw figure 5 graph that compares fetal and adult oxygen dissociation curves. (p 703)
APPLICATIONS
1.
2.
3.
SKILLS
Analysis of dissociation curves of hemoglobin and myoglobin. Read the purple box on pg 703 and
draw the graph as you see it.
Identification of pneumocytes, capillary endothelium cells and blood cells in light micrographs and
electron micrographs of lung tissue. Read the purple box on pg 705 and draw the diagram as you
see it.