1. Aquatic Respiration The gas exchange mechanisms in aquatic environments

2. Characteristics of Water Dipolar molecule Dipolar molecule Strong cohesive and adhesion properties Strong cohesive and adhesion properties Dissolves a large number of chemical compounds Dissolves a large number of chemical compounds Lower O 2 solubility Lower O 2 solubility Gas Solubility decreases as water temperature increase Hydrogen Oxygen

3. The Composition of Air 78.08% N 2 20.95% O 2 0.03% CO 2 Other inert gases (argon, krypton, neon, etc) Percent Composition

4. Partial Pressure STP – standard temperature and Pressure used to compare amounts of gas (in moles) even volume is measured at different pressures. STP – standard temperature and Pressure used to compare amounts of gas (in moles) even volume is measured at different pressures. 101 kPa=1 atm 101 kPa=1 atm kPa (kiloPascals) increases under water kPa (kiloPascals) increases under water Partial pressures of gases change but the % composition does not. Partial pressures of gases change but the % composition does not. Relationship between altitude and pressure is exponential Relationship between altitude and pressure is exponential 10meters H2O = 101kPa 10meters H2O = 101kPa Dalton’s Law Partial Pressures : Pressure Total =Pressure 1 +Pressure 2...

5. Gases dissolved in Water Gases have Different molar concentrations in water Gases have Different molar concentrations in water [A] is the molar concentration of A in moles per liter., [A] is the molar concentration of A in moles per liter., pA is the partial pressure for A in mole per liter kPa. pA is the partial pressure for A in mole per liter kPa. Value of solubility constant depends on the gas in question (e.g., O 2, N 2 ), the nature of the solvent (e.g., water, lipids), temperature, and ionic concentration Value of solubility constant depends on the gas in question (e.g., O 2, N 2 ), the nature of the solvent (e.g., water, lipids), temperature, and ionic concentration O 2 and N 2 have lower molar concentrations in water compared to air O 2 and N 2 have lower molar concentrations in water compared to air CO 2 remains the same CO 2 remains the same Henry’s Law: [A]=pA α A

6. Diffusion Movement of molecules from one region to another do the random thermal motion Movement of molecules from one region to another do the random thermal motion Flicks Law describes the net diffusional flux of respiratory gas Flicks Law describes the net diffusional flux of respiratory gas generally adequate for oxygen exchange only in very small animals (<1mm diameter) generally adequate for oxygen exchange only in very small animals (<1mm diameter) Metabolic consumption depletes O 2 layer around animal, and the pO 2 gradient is established Metabolic consumption depletes O 2 layer around animal, and the pO 2 gradient is established Flicks Law of Diffusion: 1 st law gives rise to equation Flux=-P*A*(C 2 -C 1 ) P - is the permeability, an experimentally determined membrane “conductance” for a given gas at a given temperature. A - is the surface area over which diffusion is taking place. (C2-C) is the difference in concentration of the gas across the membrane for the direction of flow (from c1 to c2) O 2 and CO 2

7. Exchange and Diffusion of Gases O 2 moves from high concentration in the water to where there is a lower concentration in the blood of the capillaries. O 2 moves from high concentration in the water to where there is a lower concentration in the blood of the capillaries. CO 2 moves from high concentration in the capillary blood to where there is a low concentration in the water. CO 2 moves from high concentration in the capillary blood to where there is a low concentration in the water. Membrane Flow Net Flow= 0

8. Boundary Layer When steady-state exchange is established layer will be infinitely thick. When steady-state exchange is established layer will be infinitely thick. thickness of the boundary layer can be reduced by movements of the animals through the medium or of the water passing over the animal thickness of the boundary layer can be reduced by movements of the animals through the medium or of the water passing over the animal boundary layer can go from infinity to 10 x that of the animals radius or even 0.1 x greatly increasing the size that animal can achieve boundary layer can go from infinity to 10 x that of the animals radius or even 0.1 x greatly increasing the size that animal can achieve

9. Bulk flow The transport of O2 by physical movement of water or blood The transport of O2 by physical movement of water or blood The transport caused by movement of the medium, called convection transport: Q (e.g., ml O 2 min -1 ) From a area of high concentration to low concentration dependent on the mass flow of water V w (e.g., ml H 2 0 min -1 ) and the differences between the two regions The transport caused by movement of the medium, called convection transport: Q (e.g., ml O 2 min -1 ) From a area of high concentration to low concentration dependent on the mass flow of water V w (e.g., ml H 2 0 min -1 ) and the differences between the two regions The rate of convection transport is greater than diffusional transport The rate of convection transport is greater than diffusional transport Bulk Flow equation: Q=V w (C 2 -C 1 )

10. General aquatic respiratory system

11. Gills