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Respiration

Respiration. Acquisition of O 2 Elimination of CO 2. Need to understand about gases and diffusion. Gas N 2 O 2 A CO 2. Mol Fraction (%) 0.7809 78 0.2095 21 0.0093 0.93 0.0003 0.03. Dry atmospheric air:. The pressure of these gases

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Respiration

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  1. Respiration • Acquisition of O2 • Elimination of CO2 Need to understand about gases and diffusion

  2. Gas N2 O2 A CO2 Mol Fraction (%) 0.7809 78 0.2095 21 0.0093 0.93 0.0003 0.03 Dry atmospheric air:

  3. The pressure of these gases plus that of water vapor is: Barometric press. = PB At sea level, PBis approximately: [1 atm = 760 mmHg] = 760 torr = 14.7 psi = 101.3 kPa

  4. The pressure of a particular gas in a mixture is called its partial pressure, PG PG = PB (mol fraction of G) In dry air at sea level, PB = 760 mmHg. What is the partial pressure of O2 or PO2?

  5. PO2 = PB (mol fraction of O2) PO2 = 760 mmHg (0.2095) = 159 mmHg or PO2 = 1 atm (0.2095) = 0.2095 atm

  6. Temp (°C) 20 37 100 PH2O at 100% RH (atm) 0.023 0.062 1.000 If water vapor is present, it displaces the other gases.The water vapor pressure, PH2O, depends ontemperature and relative humidity:

  7. Problem: PB = 1 atm, T = 20°C, RH = 100% What is PO2? P air = PB - PH2O = 1 atm- 0.023 atm = 0.977 atm PO2 = Pdry air (0.2095) = 0.205 atm

  8. Problem: You breathe in air at sea level. What is the PO2 of the air in your lungs? The temperature in your lungs is 37°C The air in your lungs is saturated with water RH = 100%, so PH2O = 0.062 atm In your lungs,Pair = PB - PH2O = 1 atm - 0.062 atm PO2 = Pdry air (0.2095) = 0.938(0.2095) = 0.197 atm

  9. Problem: Temperature notwithstanding, could you live over a free surface of water at 100°C? At 100°C, 100% RH: PH2O = 1 atm P air = PB - PH2O = 1 atm - 1 atm = 0 atm There’s NO oxygen!

  10. Gases are soluble in water. • Concentration depends on: • 1) solubility of the gas • 2) partial pressure of the gas • Henry’s Law: • VG/VH2O = a (PG) VG/VH2O = conc. of gas a = solubility coefficient PG = partial pressure of gas

  11. Gas O2 N2 CO2 a (ml·l-1 H2O·atm-1 PG) 34.1 16.9 1019.0 Solubility Coefficient

  12. a depends on temperature and salinity ml O2·l-1 Temp. (°C) FW SW 10 8.0 6.4 30 5.6 4.5

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