Respiration I. Introduction Oxygen and Carbon Dioxide.
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Transcript of Respiration I. Introduction Oxygen and Carbon Dioxide.
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Respiration I.
Introduction
Oxygen and Carbon Dioxide
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Cells use O2 and Produce CO2.
• In order to produce energy most cells must obtain 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.
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Diffusion.
• Unicellular organism can exchange O2 and CO2 by simple diffusion.
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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.
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Flux is flow of materials through a pathway
• Factors that affect flux– Concentration gradient.– Temperature.– Mass of molecule.– Surface area.
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• Small multicellular organisms face a challenge in supplying the cells at their center with O2.
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Multicellular Organisms Use Diffusion Plus Convection.
• Convection is movement in bulk.
• O2 and CO2 are moved in masse.
• The force is provided by pumps.
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In air breathing animals(mammals)
• Two convection and two diffusion mechanisms at play.
• Alveolar ventilation.• Alveolar gas exchange.• Circulation.• Tissue gas exchange.
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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.
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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.
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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).
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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.
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Pressures Change With Altitude.
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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.
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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.
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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.
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O2 and CO2 in solution.
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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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