Lecture 1 Gas Exchange 1 Ch 44 pgs 999 1011 Composition of Air o Nitrogen 78 o Argon 93 o Carbon dioxide 03 Partial pressure of a gas PGAS pressure of that gas in a mixture of gases e g air o Calculate the pressure of O2 in air o O2 is 21 of air o Total pressure of air at sea level 760 mm Hg or 1 Atm o Thus PO2 is calculated 0 21 x 760 mm Hg 160 mm Hg The partial pressure of oxygen falls with increasing elevation o Ex Top of mount Everest PO2 53 mm Hg o Lake Titicaca PO2 95 mm Hg Sea level PO2 160 mm Hg o o As altitude increases Pressure of gases O2 N2 atmosphere drops Gases of concern for most multicellular organisms O2 CO2 o Why Because of gas exchange We breathe in oxygen and breath out produce carbon dioxide Oxygen and carbon dioxide circulate in our blood and are used in cellular respiration Solubility of O2 CO2 in Water o Only 0 003 ml of O2 dissolves in water for every mm Hg pressure of O2 e g at 160 mm Hg P of O2 only 3 ml of the gas dissolves in 100 mls of your blood o In contrast CO2 is 30 times more soluble Consequences for organisms Carbonic Anhydrase o CO2 H2O H2CO3 H HCO3 o Present in many organisms including plants diatoms and methane producing bacteria marine cyanobacteria and some chemolithothrophs What does the enzyme CA do for an organism Role of CA in carrying CO2 in body fluids in regulation of pH o o Key Point Carbonic Anhydrase pH Increase CO2 and decrease pH o o Decrease CO2 and increase pH Increase H and increase CO2 o o Decrease H and decrease CO2 o CO2 H2O H2CO3 H HCO3 What do we know about CO2 and O2 o O2 is not very soluble in water Only about 0 003 ml O2 in 100 ml water for every 1 mm Hg PO2 o As temperature increases the amount of dissolved gases decreases PGAS dissolved is inversely proportional to water temperature degrees celcius 1 As Solute increases PGAS dissolved decreases o o So what are issues facing organisms as they maximize the rates at which they unload CO2 and take up O2 Diffusion Entropy in Action pgs 108 123 O2 and CO2 get into and out of cells and organisms by diffusion Diffusion increases Entropy Diffusion o Negative G so it is spontaneous Notice increase in S entropy o Organisms rely on diffusion to move obtain and remove essential molecules Diffusion is a rate o Often referred to as FLUX o Molecules moving from one point to another per unit time e g mmoles sec o Abbreviated as J or dS dT Diffusion across a membrane of area A and thickness x J or dS dT D A T P x o o D Diffusion coefficient o A area for diffusion o T Temp in oK o P concentration or pressure gradient o x thickness of membranes Problem Diffusion 2 o Thus organisms to maximize diffusion are have small cells with max surface area to volume ratios have thin respiratory gas exchange surfaces with large surface areas have moist respiratory gas exchange surfaces therefore a large D move air or fluid to maximize P D Diffusion Coefficient o Determined by physical characteristics of solution and solute Inversely proportional to solute s molecular weight o o Units are cm2 sec o D of CO2 is than D of O2 Problem Diffusion Distances t o X2 2D t elapsed time since diffusion began o o X is mean distance traveled by solute in time t o D diffusion coefficient of solute in free solution Problem Surface Volume o As cell radius increases the surface increases by radius2 o However the volume increases by radius3 o Thus the surface area available to support the increased volume is not adequate Surface Area to Volume Ratios Surface Area to Volume Ratios o o 3 Problem Surface Volume o QUESTION In Nature what types of cells are the smallest and have the most surface area volume What are their characteristics that require them to be small To overcome surface volume and diffusion distance problems place cells in thin layers very near to circulating fluid water currents open fluid filled sinuses or capillaries Diffusion and single celled organisms Small o o Membrane foldings o Move through water o Small Animals e g sponges cnidarians flatworms o Small specialized body plans Channeled Septate Flattened o Gills Sessile cells move water over surface cilia or live in currents o Low metabolic rates o No specialized respiratory structures diffusion adequate for both gas exchange distribution o Large Animals o Huge scaling problems metabolic rate mass Specialized respiratory surfaces produce fractal respiratory surfaces o Gills Lungs o Diffusion passive bulk flow is inadequate Requires mechanisms for active bulk flow 2 active bulk flow systems required each with its own pumping system Fig 44 1 4 Ventilation bulk flow of respiratory medium Circulation bulk flow of blood Large Aquatic Animals e g mollusks o Mollusks o Mussels clams Mussels clams sessile filter feeders Squid active carnivores Large gills used for both gas exchange and feeding Ventilation produced by cilia on surface of gills Circulation via low pressure open circulatory system Ventilation and circulation represent ancestral condition in mollusks Squid largest fastest aquatic invertebrates o Squid o o Gills only used for gas exchange Ventilation by muscles of mantle Circulation via high pressure closed circulatory system Ventilation circulation highly derived adaptations for active highspeed lifestyle Squid ventilation has 2 phases Fig 32 11d Inhalation due to negative pressure contraction of longitudinal muscles Exhalation due to positive pressure contraction of circular muscles o Ventilation current is intermittent unidirectional 5 o o o o Lecture 2 Gas Exchange 2 Ch 44 Gills and Lungs o Moist surface Terrestrial Problem water loss with each breath o Move fluid or air over large surface area o Air or water flow related to metabolic activity of organism Matched by blood flow to pick up O2 and unload CO2 Fish use counter current mechanism Increase thickness of diffusion membrane ex by putting a layer of gunk on it Lungs Reptiles amphibians mammals Principles Large surface area Close connection to capillaries Airflow matches blood flow Moist surface for diffusion of O2 into tissue Negative pressure inflation o When you get pneumonia you get inflammation layer of gunk on inside of air sac big problems with Why if a bullet hits someone they actually wouldn t be able to talk or gasp Because there lungs would be diffusion punctured Negative pressure lung 6 o o o Fill lung up by making pressure more negative o o What is pressure pressure is a concentration of a gas o When decrease concentration of air then the pressure goes down o When you
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