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Chapter 22 Gas Exchange PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey © 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko Gas Exchange - Function of the Respiratory System Gas exchange (respiration), the interchange of – O2 and CO2 – O2 is substrate for cellular respiration (ATP generation). – CO2 waste product from cell respiration C6H12O6 + O2 -----> CO2 + H2O + ATP © 2012 Pearson Education, Inc. O2 3 Stages of Gas Exchange CO2 1 Lung Heart 1. breathing, Blood vessels 2. transport of oxygen and carbon dioxide in blood, and 2 3. exchange of gases with body cells. – Body tissues take up oxygen and – release carbon dioxide. © 2012 Pearson Education, Inc. Breathing Transport of gases by the circulatory system Capillary 3 Exchange of gases with body cells Circulatory System Mitochondria O2 CO2 Cell Universal Rules of Gas Exchange Gas exchange is occurs by simple diffusion of gases across cell membranes Respiratory surfaces must be moist Respiratory surfaces must be thin – Optimize SA:volume © 2012 Pearson Education, Inc. Gas Exchange in Air vs. Water Aquatic: – Disadvantage: – Water holds only about 3% of the oxygen in air. – Cold water holds more oxygen than warm water. – Water move difficult to move across respiratory surfaces. – Advantage: – Respiratory surfaces remain moist - can be directly exposed to water environment © 2012 Pearson Education, Inc. Gas Exchange in Air vs. Water Land: – Advantage: – Concentration of O2 much higher in air – Air requires less energy to move over respiratory surfaces. – Disadvantage: – Respiratory surfaces more likely to dry out Land organisms use internal respiratory systems (lungs, trachea, etc.) Plants regulate stomata opening using guard cells to prevent water loss by transpiration. © 2012 Pearson Education, Inc. Small organisms have sufficient SA:volume ratio that they do not require a specialized respiratory system. Diffusion Mouth Gastrovascular cavity Diffusion Diffusion Single cell Two cell layers Gas Exchange Structures in Various Organisms Organisms have specialized body parts for gas exchange: – Skin in earthworms – gills in fish – Lungs and skin in amphibians, – tracheal systems in arthropods – Plants use stomata – lungs in tetrapods that live on land, such as – amphibians, reptiles, birds, mammals © 2012 Pearson Education, Inc. Cross section of the respiratory surface (the outer skin) CO2 O2 Capillaries Body surface Respiratory surface (gills) CO2 O2 Capillary Figure 22.3 Oxygen-poor blood Oxygen-rich blood Water flow Lamella Blood vessels Operculum (gill cover) Gill arch Water flow between lamellae Blood flow through capillaries in a lamella Countercurrent exchange Water flow, showing % O2 Gill filaments Diffusion of O2 from water to blood 100 70 40 15 80 60 30 5 Blood flow in simplified capillary, showing % O2 Body surface Tracheae Air sacs O2 CO2 Tracheoles Opening for air Body cell Tracheole Air sac Trachea Body wall O2 CO2 Respiratory surface (tips of tracheae Body cells (no capillaries) Figure 22.2D Body surface CO2 CO2 Respiratory surface (within lung) O2 O2 Capillary CO2 O2 Light H2O Sugar O2 H2O and minerals CO2 Plants Gas exchange thru leaves Eudicot leaf Vein Cuticle Upper epidermis Xylem Phloem Mesophyll Guard cells Lower epidermis Stoma Sheath Key Stoma = site of CO2 / O2 exchange Dermal tissue system Ground tissue system Vascular tissue system Guard cells of stomates CLOSE when too much water is lost. When water is plentiful, guard cells actively transport K+ INTO cell, water follows, and stoma open. Guard cells H2O H2O H2O H2O H2O K Vacuole H2O H2O H2O H2O Stoma H2O Stoma opening Stoma closing THE HUMAN RESPIRATORY SYSTEM © 2012 Pearson Education, Inc. To the heart Nasal cavity Left lung Pharynx (Esophagus) Oxygen-rich blood From the heart Oxygen-poor blood Bronchiole Larynx Trachea CO2 O2 Right lung Bronchus Bronchiole Alveoli Blood capillaries Diaphragm (Heart) Alveoli are well adapted for gas exchange with high surface areas of capillaries. – O2 diffuses into the blood and – CO2 diffuses out of the blood. Alveoli are site of gas exchange in lungs! Animation: CO2 from Blood to Lungs Animation: CO2 from Tissues to Blood Animation: O2 from Blood to Tissues Animation: O2 from Lungs to Blood © 2012 Pearson Education, Inc. Gas Exchange occurs by passive diffusion!!! Gasses diffuse towards regions of lowest partial pressure. (Partial pressure = measure of concentration of gas dissolved in liquid) CO2 in exhaled air O2 in inhaled air Alveolar epithelial cells Air spaces CO2 O2 Alveolar capillaries of lung CO2-rich, O2-poor blood O2-rich, CO2-poor blood Tissue capillaries CO2 Interstitial fluid Heart O2 Tissue cells throughout the body Figure 22.10_1 [CO2] LOWEST in alveoli and tissue capillaries Alveolar capillaries of lung CO2-rich, O2-poor blood [CO2] HIGHEST in tissues and blood arriving to lung from tissues [O2] LOWEST in blood at tissues and in blood arriving at O2-rich, lung CO2-poor blood Tissue capillaries Heart [O2] HIGHEST in alveoli and blood arriving TO tissues Blood transports respiratory gases Gases move from areas of higher concentration to areas of lower concentration. – Gases in the alveoli of the lungs have more O2 and less CO2 than gases in the blood. – O2 moves from the alveoli of the lungs into the blood. – CO2 moves from the blood into the alveoli of the lungs. – The tissues have more CO2 and less O2 than gases in the blood. – CO2 moves from the tissues into the blood. – O2 moves from the blood into the tissues. © 2012 Pearson Education, Inc. Hemoglobin carries O2 in the blood Iron atom O2 loaded in lungs O2 O2 unloaded in tissues Heme group Polypeptide chain Hemoglobin: 4 subunits: 2 , 2 2o structure: all -helical protein Contains heme coenzyme with iron cofactor at center Fe cofactor directly binds to O2 © 2012 Pearson Education, Inc. O2 Hemoglobin carries O2 in the blood Hemoglobin: 4 subunits: 2 , 2 2o structure: all helical protein Contains heme coenzyme with Fe cofactor at center Fe cofactor directly binds to O2 © 2012 Pearson Education, Inc. Hemoglobin binding to O2 is reversible!! Iron atom O2 loaded in lungs O2 unloaded in tissues Heme group Polypeptide chain © 2012 Pearson Education, Inc. O2 O2 Hb binding to O2 is affected by pH and CO2 Bohr Effect: Decreased pH Increases O2 unloading!! © 2012 Pearson Education, Inc. CO2 is transported as bicarbonate ion in blood!! CO2 forms carbonic acid in water Carbonic acid dissociates by a reversible reaction Ratio of acid/base regulated by mass action and breathing rates. © 2012 Pearson Education, Inc. Brain Cerebrospinal fluid 2 1 Nerve signals trigger contraction of the rib muscles and diaphragm. Medulla Breathing control center responds to the pH of blood and cerebrospinal fluid. Breathing is automatically controlled Breathing control centers in the brain sense and respond to CO2 levels in the blood. A drop in blood pH increases the rate and depth of breathing. Diaphragm Rib muscles Additional sensors in aorta may monitor O2 levels Brain Cerebrospinal fluid 2 1 Nerve signals trigger contraction of the rib muscles and diaphragm. Medulla Breathing control center responds to the pH of blood and cerebrospinal fluid. 3 Nerve signals indicate CO2 and O2 levels. CO2 and O2 sensors in the aorta Heart Diaphragm Rib muscles