Gas Exchange CONNECTIONS: Life Challenges and Solutions in Plants and Animals Absorption Transport Gas Exchange The villi (projections) that line the intestines of animals Plants transport water, Animals pump circulatory in The root hairs of increase the surface area minerals, and sugars fluid through vessels. plants increase the available for absorption. through vessels. surface area available Animals for absorption. Gas Exchange In plants, highly In animals, highly convoluted surfaces, convoluted surfaces, such as the spongy such as the alveoli of mesophyll of leaves. lungs. Figure 40.22 Organismal Respiration WHY RESPIRE? vs. Cellular Respiration • External gas exchange: • Mitochondria need Ø environmental gases / tissues O2 to make ATP. • Internal gas exchange C6H12O6 + O2 è CO2 + H2O + Energy Ø tissues / tissues ATP ¿ q Cell membranes are permeable to simple diffusion of dissolved O2 and CO2 • CO2 by-product • Cellular Respiration: using the oxygen to drive must be removed ATP production – The more cells (more body mass), the more O2 needed (oxygen demand) SIZE MATTERS How do animals get enough O2? • Small organisms have high s/v ratios & use v Size matters! cutaneous exchange (protozoans, sponges, cnidarians, flatworms) v So does activity level. • Ciliated epidermal & gastrodermal tissues keep fresh water flowing over surface v Larger, faster animals need tricks to speed up exchange of gases between environment & tissues. • Surfaces must be moist for exchange to occur! Heyer 1 Gas Exchange FICKS LAW Adolf Fick, 1858 Diffusion of Dissolved Gases Ficks law of diffusion of a gas across a fluid membrane: Rate of diffusion = KA(P2–P1)/D • FICKS LAW Wherein: • GILLS vs. LUNGS § K = a temperature-dependent diffusion constant. • AQUATIC RESPIRATION § A = the surface area available for diffusion. • TERRESTRIAL RESPIRATION § (P –P ) = The difference in concentration (partial • RESPIRATORY PIGMENTS 2 1 pressure) of the gas across the membrane. § D = the distance over which diffusion must take place. FICKS LAW FICKS LAW Ficks law of diffusion of a gas across a fluid membrane: Ficks law of diffusion of a gas across a fluid membrane: Rate of diffusion = KA(P2–P1)/D Rate of diffusion = KA(P2–P1)/D Therefore, since: Therefore, since: § The diffusion is of dissolved gases across a fluid § K = a temperature-dependent diffusion constant. membrane ØTemperature is important! ØThe respiratory surface must stay wet! FICKS LAW FICKS LAW Ficks law of diffusion of a gas across a fluid membrane: Rate of diffusion = KA(P2–P1)/D KA(P –P ) Therefore, since: Rate of diffusion = 2 1 /D § (P2-P1) = The difference in concentration (partial pressure) of the gas across the membrane. Therefore, since: ØButContinually since the result replenish of diffusion the respiratory is to eliminate fluid the § A = the surface area available for diffusion. concentration(ventilation difference,system) and how body can fluid the rate (circulatory be § D = the distance over which diffusion must take place. sustained?system) to maintain disequilibrium across the membrane! ØHow can gas exchange rate be increased? outside ØIncrease surface area and decrease thickness membrane inside of respiratory surfaces as much as possible! equilibrium Rate of of Rate diffusion Time Heyer 2 Gas Exchange Gas Concentrations Dissolved Gas Concentrations Concentration of a gas in a mixture measured as partial pressure Still measured as partial pressure = % of total gas x total gas pressure = amount of that gas dissolved in water at equilibrium with a gas having that partial pressure (at STP) Air: composition & partial pressures v cylinder contains Dry air at 1 atm total pressure (sea level) PO =0.2 atm 1 liter water and 2 1 liter air v N2: 78%; PN2= 0.78 atm (total 1 atm at 25C) v O : 21%; P = 0.21 atm 2 O2 v Oxygen diffuses v CO : 0.03%; P = 0.0003 atm between air & 2 CO2 water. v Other gases bring total up to 1 atmosphere Dissolved Gas Concentrations Still measured as partial pressure = amount of that gas dissolved in water at equilibrium with a gas RESPIRATION having that partial pressure (at STP) v The air & water are • FICKS LAW at equilibrium • GILLS vs. LUNGS PO =0.2 atm 2 \ they have the • AQUATIC RESPIRATION = 210 ml O2 same P • TERRESTRIAL RESPIRATION O2 • RESPIRATORY PIGMENTS v The amount of a gas PO =0.2 atm 2 dissolved in water depends on its = 5.8 ml O2 solubility. § ­ temp ® ¯ gas solubility Respiratory Surfaces GILLS vs. LUNGS Maximizing the respiratory surfaces: – Evaginations (gills) – Invaginations (lungs) ésurface area / êdistance between environment and tissues Heyer 3 Gas Exchange Terrestrial vs. Aquatic Respiration Terrestrial vs. Aquatic Respiration — the Trade-offs % metabolism •Hence, in low-oxygen environments (i.e., in water), for ventilation 5C 35C need large, wet respiratory surface exposed to the respiratory medium. % O2 in •Gills! air 21% 21% 1% •But, in dry environments (i.e., in air), large, wet respiratory surface would dry out and result in % O2 in excessive water loss. 0.9% 0.5% 20% * •No gills! water •In dry, high-oxygen environments (i.e., in air), contact of the wet respiratory surface with the respiratory O2 in medium can be restricted to protect from drying out. air/water 25x 40x •Lungs! •But, in viscous, low-oxygen environments (i.e., in water), restricted contact provides inadequate gas * Water is ~800x more dense & 50x more viscous than air! exchange. •No lungs! Aquatic Respiration Structures Fish usually need Animal Gill type Ventillation more oxygen than Fish Pharyngeal gills Buccal pumping invertebrates; Polychaete worm Parapodia Gill movement they have more Aquatic mollusk Ctenidia Cilia gill area than Echinoderm Dermal branchia Cilia most Crustacean Gills Gill bailer invertebrates. Horseshoe crab Book gills Gill movement Buccal pumping Fish ventilation 1-way flow of water across gills v Fish use energy to pump water across gills (ventilation). v At low speed, buccal pumping is used. v At higher speed, ram ventilation (swimming with mouth & operculum open) is more efficient (but still costs energy). Heyer 4 Gas Exchange O2 diffuses from high concentration to low concentration. Fig. 42.22 If fish used Concurrent Exchange: So fish use Countercurrent Exchange. Equilibrium reached: Equilibrium prevented: No further exchange Exchange continues c.f., Campbell Fig. 42.22 More active fish have bigger gills. index of relative gill surface area/body mass Aquatic Respiration Structures Animal Gill type Ventillation Fish Pharyngeal gills Buccal pumping Mackerel: 2551 Polychaete worm Parapodia Gill movement Aquatic mollusk Ctenidia Cilia Echinoderm Dermal branchia Cilia Toadfish: 137 Crustacean Gills Gill bailer Horseshoe crab Book gills Gill movement Heyer 5 Gas Exchange Counter-current exchange in mollusc ctenidia • Flattened filaments attached on alternate sides to a longitudinal axis • Water flow through chamber generated by cilia counter to blood flow direction of gills Water flow Fig. 42.21 Cross-section view ARACHNIDS & BOOK LUNGS • . • Page-like structure. • In larger species its supplemented by a tracheal system. Tracheal Systems of Terrestrial Arthropods Terrestrial Arthropod Tracheal System – Insects, millipedes, onycophorans, and big arachnids. silkworm spiracle & tracheae Spiracle (w/ filters) • Ventilated by air sacs in larger or Trachea more active species. (lined w/ taenidia) Tracheole Tracheole Tracheole Tracheole cockroach trachea Fig. 42.23 Heyer 6 Gas Exchange Flight muscles have very high aerobic demand —Tracheoles end near mitochondria in each cell. Insect gas exchange: vSpiracles can close to limit water loss. spiracles silkworm spiracle Fig. 42.23c & tracheae dung beetle spiracle Vertebrate Lungs Terrestrial snails & slugs have: • Amphibians & Reptiles: – Septate sac Lung w/ Septa • lost their ctenidia from mantle cavity • vascularized mantle cavity acting as lung • Mammals: – Complex, w/alveoli • Birds: – Elaborate flow- through system w/ parabronchi Lungless salamanders Amphibians with lungs vGas exchange through vFrogs and larger skin; blood gets salamanders do gas oxygenated when if exchange through flows near skin. skin and lungs. vSmall, slender bodies. vUsually most O2 is absorbed in the lungs, vThey dry out easily. but most CO2 is vCold bodies; dont use eliminated through much O2. the skin. Heyer 7 Gas Exchange Frogs: positive-pressure breathing Reptiles forces air into lungs v Reptiles have impermeable skin; gas exchange happens in lungs. v Most have fairly low oxygen requirements. Breathing is not continuous. v Body temperature is usually near ambient; this keeps water loss low compared to warm-bodied animals. Mammalian Lung — 300 Million Alveoli Negative pressure breathing Fig. 42.24 Human lung: • Surface area = 100 m2 • Only 0.2 µm between air/blood Fig. 42.27 Negative pressure breathing O2 & CO2 diffuse from high concentration to low concentration. § Dead space: 150 ml § Tidal volume (resting): 500 ml § Tidal volume (exercise): 3000 ml Fig. 42.29 Heyer 8 Gas Exchange Both Positive- & Negative-Pressure Breathing Air Capillary Lung of Birds expand & contract rib cage (no diaphragm) • Parabronchi: continuous, one- way, flow-through exchange Constant air flow through rigid lungs • Negative pressure ventilation during inhalation • Positive pressure ventilation during exhalation • Two ventilation cycles needed for inhaled air to be exhaled Fig. 42.26 http://people.eku.edu/ritchisong/avian_biology.htm Counter-current exchange between air capillaries and blood capillaries http://tabletopwhale.com/2014/10/24/3-different-ways-to-breathe.html