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T Nora Nomal No No SpHedingHeading Spac.. Heading 1 Heading 2 2 Styles Paragraplh 100% 75% 509% 20 40 680100 Partial pressure of oxygen (mm Hg) Figure 21-30 part 1 Whot hs Life A Guide To Biology, Second Edition 2012 WH Freeman and Company At an oxygen partial pressure of 25 mm Hg, how many o, molecules would you expect to bind to hemoglobin? Would you expect an organism that lives at a very high elevation to have hemoglobin with a higher or lower affinity for 02 (higher = stickier hemoglobin)? why?Explanation / Answer
The binding of a molecule of hemoglobin to oxygen is directly proportional to the partial pressure of oxygen. A molecule of hemoglobin can bind to four molecules of oxygen at the maximum level. From the given graph, we look at the x-axis to locate 25 mm Hg partial pressure of oxygen. We next determine the corresponding value of oxygen saturation on the y-axis. A careful observation, or even extrapolation of the graph shows the oxygen saturation to be 25%. 25% of oxygen saturation means that hemoglobin can bind only 25% oxygen molecules of its maximum capability. 25% * 4 molecules gives us the answer as one molecule. This means that a hemoglobin molecule can be expected to bind to only one molecule of oxygen at partial pressure of 25 mm Hg.
At a higher altitude, the bodies of organisms have evolved over the generations to adapt to the changes in environmental conditions. The organisms become adapted to the low oxygen availability at the higher altitudes. Even the RBCs in the blood have modified themselves to carry sufficient oxygen with the help of hemoglobin. Athigher altitudes, the hemoglobin level in the blood increases. The affinity of hemoglobin to bind to oxygen molecules is directly proportional to the partial pressure of oxygen in the atmosphere. At higher altitudes, this partial pressure is very low. The affinity of hemoglobin reduces at higher altitudes due to this low partial pressure of oxygen. This is compensated in the human body by increasing the amounot of hemoglobin in the blood. The breathing rate also becomes high to take in more oxygen. More the hemoglobin, more is the number of oxygen molecules that it can hold. Also, the accumulation of hemoglobin in the blood causes the blood to become sticky and increases its oxygen holding capacity. This all acts as a compensatory mechanism to even out the low exygen binding affinity of hemoglobin at high altitudes.
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