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External Gas Transport

External Gas Transport. Chapters 20 & 21. Respiration. The process of acquiring oxygen and releasing carbon dioxide. Why do animals require oxygen?. Aerobic respiration C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O Enough Energy for 30 ATP Anaerobic respiration C 6 H 12 O 6  2C 3 H 6 O 3

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External Gas Transport

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  1. External Gas Transport Chapters 20 & 21

  2. Respiration The process of acquiring oxygen and releasing carbon dioxide

  3. Why do animals require oxygen? • Aerobic respiration • C6H12O6 + 6O2 6CO2 + 6H2O • Enough Energy for 30 ATP • Anaerobic respiration • C6H12O6 2C3H6O3 • Enough Energy for 2 ATP • All known metazoans require oxygen

  4. Why do animals need to release carbon dioxide? • CO2 tends to react with water CO2 + H2O  H2CO3  H+ + HCO3-  2H+ + CO3- •  [H+],  pH • Low pH’s can disrupt physiological function (e.g., enzyme activity)

  5. Composition (Dry Air): May vary in some environments (burrows, soil) Water vapor can also alter this composition Air

  6. Principles of Gas Diffusion in Air • Gases Exert Pressures • Atmospheric Pressure (760 mmHg (1 atm) at sea level) • The relationship between the concentration of a gas and pressure is described in the Ideal Gas Law PV = nRT • P = pressure • V = volume • n = moles of gas • R = universal gas constant (8.314 J/mol*°K) • T = temperature (°K)

  7. Principles of Gas Diffusion • Dalton’s Law of Partial Pressures • the total pressure exerted by a gas mixture is the sum of individual pressures exerted by each gas • e.g. PO2 = 20.95% * 760 mmHg = 159 mmHg • Diffusion (for Gases) • movement of a gas from an area of high partial pressure to one of low partial pressure • Movement of a gas can occur against a concentration gradient as long it flows along the partial pressure gradient

  8. Factors Influencing Gas Diffusion in Air • J = net rate of diffusion between point 1 and point 2 • K = Krogh’s diffusion coefficient (depends on medium permeability, temperature, and the specific gas being transported) • P1and P2 = particle concentration at points 1 and 2 • X = distance between points 1 and 2

  9. Diffusion rate increases with… • Bigger differences in concentration • Shorter diffusion differences • Greater medium permeability • Higher temperatures

  10. Water • Gases are soluble in water • Amount of a gas in water depends on: • solubility of the gas • the pressure of the gas in the gas phase • temperature • presence of other solutes

  11. Solubility • Measured as the solubility coefficient () • volume of gas dissolved in 1 L when the pressure of the gas = 1 atm • Different gases have different solubilities:

  12. Pressure • Amount of gas dissolved is proportional to the pressure (tension) of the gas • Henry’s Law: • Vg = (Pg/760)*VH2O • Vg = volume of gas dissolved (ml) • Pg = pressure of the gas (mmHg) • VH2O = volume of water (L) •  = solubility coefficient

  13. Temperature and Other Solutes • Temperature •  temperature,  solubility of gases • Opposite of solid solutes • Other Solutes •  [solid solutes],  solubility of gases • [other gases] does not affect solubility

  14. Temperature and Other Solutes

  15. Partial Pressures in Water • Amt of gas in water corresponds to a specific gas pressure in the gas phase • Gas Tension • pressure of a gas in an atmosphere with which the solution is in equilibrium

  16. Air vs. Water • Air contains more O2 than water (30x) • Air is less dense than water (1/800th) • easier to move over respiratory surfaces • less energy expenditure • Respiratory gases diffuse much more quickly in air than in water (~10,000x greater for O2) • Use of air can lead to water loss through evaporation

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