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Lecture 13 Objectives Explain why Echinoderms and Chordates are grouped together evolutionarily, even though they are so different. List the distinctive characters of all Chordates, and explain why many Chordates seem to lack those characters as adults. Evaluate the costs and benefits of terrestrial vs. aquatic living, especially for the capture and transport of oxygen in the body. Compare the efficiency of gills and lungs in each environment. Describe the role of hemoglobin in animal respiration. Explain why hemoglobin is able to pick up oxygen in the lungs and release it in the tissues. Deuterostomes Embryonic development differs from other animals Two types of development of triploblastic bilaterians Fate of Embryonic Cells Cleavage Determinate development Spiralian Protostomes Four-cell embryo Axis Side view Fate of Blastopore Cell excised Formation of Coelom Solid masses of mesoderm split and form coelom. Blastopore becomes mouth Archenteron Example: molluscs, arthropods, etc. Mouth Top view Mesoderm Development arrested Spiral cleavage Indeterminate development Four-cell embryo Mesoderm Anus Deuterostomes Cell excised Axis Blastopore becomes anus Side view Top view Radial cleavage Coelom Normal embryos Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Example: chordates & Archenteron echinoderms Folds of archenteron form coelom. Eumetazoa Metazoa Bilateria Chordata Echinodermata Chaetognatha Onychophora Arthropoda Tardigrada Nematoda Kinorhyncha Loricifera Nemertea Mollusca Annelida Platyzoa Bryozoa (Ectoprocta) Brachiopoda Platyhelminthes Cycliophora Parazoa Protista Acoelomorpha Rotifera Micrognathozoa Acoela Ctenophora Cnidaria Porifera Choanoflagellates Phylum Chordata Approximately 56K species Segmented coelomates with closed circulatory systems 4 Characteristics define the Chordates Modern Phylogeny Eumetazoa Spiralia Deuterostomes Lophotrochozoa Ecdysozoa Here be weirdos Psychrolutes Amphisbaena Phylum Chordata Distinguishing traits Notochord Dorsal nerve cord Pharyngeal Post-anal slits tail Phylum Chordata Where is your tail? Where are your pharyngeal slits? Big Steps of Life Vertebrate adaptations Red blood cells Specialized gas exchange Specialized circulation Efficient ventilation Respiration: Why bother? Aerobic respiration = ATP source Red blood cells • Hemoglobin transports O2 • Drops O2 in areas with low pH and high temperatures Hemoglobin • This chart shows dissociation curves from two people. How do they differ? • Which would do better in a low-O2 environment? Respiratory Surfaces Animals require large, moist respiratory surfaces for exchange of gases between their cells and the respiratory medium Animals can use air or water as a source of O2 In a given volume, water has < 3% as much O2 as air Single Cell Organisms Amphibians O2 CO2 CO2 O2 Echinoderms Epidermis Epidermis O2 Papula CO2 Blood vessel a. b. Insects Spiracle c. Fish Trachea O2 Mammals CO2 CO2 O2 Alveoli Blood vessel CO2 O2 CO2 O2 Gill lamellae d. e. f. Gas exchange in water • Countercurrent exchange system maximizes gas exchange Fluid flow through gill filament Oxygen-poor blood Anatomy of gills Oxygen-rich blood Gill arch Lamella Gill arch Gill filament organization Blood vessels Water flow Operculum Water flow between lamellae Blood flow through capillaries in lamella Countercurrent exchange PO2 (mm Hg) in water 150 120 90 60 30 Gill filaments Net diffusion of O2 from water to blood 140 110 80 50 20 PO2 (mm Hg) in blood
