. Biophysical science. Biophysics. 23 : 4/ Diffusion, Permeability, and Active Transport 429 plotted as a function of oxygen pressure fail to fit these theoretical predictions. The steady-state, spherical model can be brought closer to the experimental data by including several steps in the utilization of 02; these alter the values for q. Mathematically, if one is willing to include enough arbitrary constants, one can fit any experimental curve. The model in Figure 5 is supported by some biochemical evidence and can fit any measured curve merely by juggling LA = Lactic Acid G- Glu
. Biophysical science. Biophysics. 23 : 4/ Diffusion, Permeability, and Active Transport 429 plotted as a function of oxygen pressure fail to fit these theoretical predictions. The steady-state, spherical model can be brought closer to the experimental data by including several steps in the utilization of 02; these alter the values for q. Mathematically, if one is willing to include enough arbitrary constants, one can fit any experimental curve. The model in Figure 5 is supported by some biochemical evidence and can fit any measured curve merely by juggling LA = Lactic Acid G- Glucose Figure 5. Spherical-cell model. This model with its numerous constants can account for 02 diffusion into living cells. The model is also supported by metabolic studies of other types. The spherical-cell model shows that a simple assumption such as the constancy of the rate of oxygen utilization cannot be maintained. More complex chemical reactions and equilibria must be included to fit the 02-uptake data. Although diffusion and permeability play an import- ant role, they are not the only rate-limiting steps in the intracellular use of On. 4. Permeability of Red Blood Cells The mathematical problems of analyzing diffusion into biological cells can be greatly simplified if the rate at which a substance penetrates the cell membrane is slow compared to its rate of diffusion on cither side of this membrane. Mammalian red blood cells haw proved very useful for studies of this nature. They are especially convenient because the cells act as "osmometers," swelling or shrinking accordingly as their internal osmotic pressure varies. In spite of very large variations in the volume, the surface area of the erythrocytes remains almost Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Ackerman, Euge
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