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Respiration I.

Respiration I. Introduction Oxygen and Carbon Dioxide. Cells use O 2 and Produce CO 2 . In order to produce energy most cells must obtain O 2 from the external environment. As a result of O 2 utilization and energy production CO 2 is produced. The cells must get rid of this CO 2 .

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Respiration I.

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  1. Respiration I. Introduction Oxygen and Carbon Dioxide

  2. Cells use O2 and Produce CO2. • In order to produce energy most cells mustobtain O2 from the external environment. • As a result of O2 utilization and energy production CO2 is produced. • The cells must get rid of this CO2. • Q: How do they do it? • A: By diffusion and convection.

  3. Diffusion. • Unicellular organism can exchange O2 and CO2 by simple diffusion.

  4. Remember Diffusion? • Movement of molecules from one location to another solely as a result of their random motion. • Fick diffusion equation • (dQs/dt) = DsA (dCs/dx) • dQs/dt is the rate of diffusion or flux (J). • Ds is the diffusion coefficient. • A is the cross sectional area. • dCs/dx is the concentration gradient.

  5. Flux is flow of materials through a pathway • Factors that affect flux • Concentration gradient. • Temperature. • Mass of molecule. • Surface area.

  6. Small multicellular organisms face a challenge in supplying the cells at their center with O2.

  7. Multicellular Organisms Use Diffusion Plus Convection. • Convection is movement in bulk. • O2 and CO2 are moved in masse. • The force is provided by pumps.

  8. In air breathing animals(mammals) • Two convection and two diffusion mechanisms at play. • Alveolar ventilation. • Alveolar gas exchange. • Circulation. • Tissue gas exchange.

  9. In water breathing animals(fish) • Gill perfusion replaces alveolar ventilation. The gills are perfused by the water in which the animals lives. Usually a pump forces water through the gills.

  10. O2 and CO2 in Air. • Normal dry atmospheric air. • O2 = 20.95% (21%). • CO2 = 0.03% (0.0 %). • N2 = 78.08% (79 %). • H2O = 0.0%. • Inert gases; pollutants = the rest.

  11. Pressures • Gas molecules have mass and acceleration. • Therefore, they exert a force that is made evident when they hit a surface. • This results in pressure. • Gases in the atmosphere exert the so called barometric pressure. • At sea level PB = 760 torr (mm Hg).

  12. PB=PO2+PCO2+PN2 • In dry air barometric pressure is equal to the sum of the partial pressures of O2, CO2 and N2. • PB = 760 torr. • PO2= 0.21 (760) = 159 torr. • PCO2= 0.00 (760) = 0 torr • PN2= 0.79 (760)= 600 torr.

  13. Pressures Change With Altitude.

  14. Pressures Change With Altitude. • Molar fraction of O2 is 0.21 at sea level or at any elevation. • PO2 at sea level is 160 torr. • PO2 in Denver is 132 torr. • Why? • Because PB in Denver is 630 torr.

  15. Why does PB change? • Because the concentration of the gases changes. Gravity pulls molecules lower • Concentration of a gas in air is related to its pressure.

  16. O2 and CO2 in solution. • Gases in solution do not exert atmospheric pressure. • When we say the pressure of O2 in a solution is 100 torr, what we are saying is: • The concentration of O2 in the liquid is such that it is in equilibrium with a gaseous phase in which the pressure IS 100 torr.

  17. O2 and CO2 in solution.

  18. O2 and CO2 in solution. • The concentration of a gas in solution is • [G] = PGas x SGas • [G] is the molar concentration. • PGas is the pressure of the gas. • SGas is the solubility coefficient. • This is Henry’s Law

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