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of Phylogeny Fishes Subphylum Vertebrata Class Agnatha Hagfish Lamprey Armored jawless fishes Placoderms Armored Chronichthyians Acanthodians the most primitve of the Teleostomi The swim bladder or lung is another feature of all Teleostomi typical Teleost Actinopteryniian knifefish Banjo catfish Diversity of ray-finned fishes: Actinopterygii Piranha Lookdown Bone Tetra tongue Two groups of lobe-finned fishes: Sarcopterygii Coelocanth Respiratory Systems - become necessary when organisms are too large for gas exchange to occur by simple diffusion - a gas will follow a diffusion gradient from an area of higher concentration to an area of lower concentration Direct diffusion ENVIRONMENT CELLS Respiratory system BLOOD Circulatory system Vertebrate Respiratory Systems - depend on the environment in which gas exchange must occur - in water vertebrates generally use aquatic respiration with gills - on land vertebrates generally use terrestrial respiration with lungs - aquatic respiration can be supplemented with cutaneous, tracheal and / or cloacal respiration - aerial respiration can be supplemented with or replaced by cutaneous respiration (lungless salamanders) The pharynx is the major respiratory structure in early vertebrates. This water is forced across gills and out external gill slits What mechanism makes gases move from water to blood or blood to water? Deoxygenated blood from heart meets oxygenated water in a counter - current exchange mechanism that results in highly oxygenated blood leaving gills and entering dorsal aorta Highly oxygentated water enters gills from pharynx 150 140 Counter - current exchange mechanism 120 110 100 60 50 30 30 20 140 - all numbers represent 2 20 partial pressure (PO ) of oxygen - the counter current mechanism allows the maintenance of a strong diffusion gradient for a maximum amount of time. deoxygentated blood gills enters from heart Understanding partial pressures How do we measure concentrations of gases in air and water so we know what diffusion gradients exist? We measure the partial pressure made up by each contributing gas. Air pressure or barometric pressure (reported by the weatherman) is the total weight of the air on a pan of mercury of a given size. Total air pressure and is usually just under 30 Hg or 760 mm Hg The gases that make up the atmosphere contribute differently to the total air pressure They contribute their partial pressure. PERCENT OF PARTIAL GAS ATMOSPHERE PRESSURE N2 O2 CO2 80% 20% 0.3% 610 mm Hg 150 mm Hg 3 mm Hg What about partial pressure of gases in water? - the partial pressure of a gas dissolved in a liquid is the partial pressure of that gas in the atmosphere above the liquid, assuming that the liquid is saturated. PO2 = 150 mm Hg - so the water that our shark is swimming in has a PO2 = 150 mm Hg - but since the oxygen is dissolved in the water, the water is on 0.7% O2 by volume PO2 = 150 mm Hg The evolution of aerial breathing Oxygen is about 30 time more abundant in air than in water. Air is much lighter than water. Aquiring needed oxygen from air rather than water could save lots of energy. Some fish supplement aquatic respiration by gulping air into swim bladder normally used for bouancy control. They do this especially when O2 in water gets depleted. Exaptation of the swim bladder as a respiratory organ appears to be a characteristic of the Choanata. Choanata include lungfishes and tetrapods. Members of the Choanata include lungfishes and tetrapods. All have lungs for gas exchange All have a breathing nose not just a smelling nose. Lungs are filled with air by expansion of the pleural cavity Gas exchange takes place in alveoli Inside cells In alveoli CO2 poor CO2 rich Cellular respiration C6 H12 O6+ 6O2 6CO2 + 6H2 O + E O2 rich O2 poor

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