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BSCI207 EXAM 3 STUDY GUIDEGas Exchange: Lecture 22 (CH. 44 pages 999-1011)I. Composition of Air- What gases make up the atmosphere?- Nitrogen 21%, Oxygen 78%, Carbon Dioxide .03%, Argon .93 %II. Partial Pressure of A Gas- Pgas=pressure- Concentration of that gas in a mixture of gases- To calculate the pressure of O2 in air :- 02 is 21% of air, and total pressure of air at sea level is 760 mm Hg- So…P02 is calculated as 0.21x760 mm Hg=160 mm Hg- Partial pressure of oxygen falls with increasing elevationIII. What are the Gas exchange issues living organisms face?- Diffusion considerations: surface/volume, diffusion distance, atmospheric pressures in different environments, etc.- Solubility in water: other way of carrying gases in body fluids?- Adapting to Different environments: gas concentrations (partial pressures), temp, salinity- Organisms metabolic demandsIV. Diffusion: Entropy in Action- O2 and CO2 get into and out of organisms by diffusion - Negative change in G, so spontaneous- Flux (J or dS/dT) is diffusion rate, molecules moving from one point toanother per unit of time- Rate of Diffusion= k (constant depends on solubility of gas and temp) x Area x (P2-P1 diff in partial pressures on either side of barrier)/D (distance)- J=-DAT∆P/∆X- Diffusion Coefficient determined by physical characteristics of solution and solute, inversely proportional to solute’s molecular weight, units are cm^2/sec, D of CO2 > D of O2V. Problem: Diffusion- Thus Organisms: - 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 ∆PVI. Problem: Diffusion Distances- T=x^2/2D- T=elapsed time since diffusion began- X is mean distance traveled by solute in time T- D=diffusion coefficient of solute in free solutionVII. Problem: Surface to Volume- As cell radius increases, the surface area increases by radius squared- However th volume increases by radius cubed- Thus the surface area available to support the increased volume is notadequate- S.A=4 r^2π- V=4 r^3/3π- Question: In nature, what types of cells are the smallest and have the most surface area/volume? What are their characteristics that requirethem to be small?VIII. To Overcome surface/volume and diffusion distance problems, place cells in thin layers very near to circulating fluid (water currents, open fluid sinuses, or capillaries)IX. Thinking About Respiration- What gases concern aerobic organisms?- O2 and CO2- Why? 1. Ventilation, 2. Gas exchange, 3. Circulation, 4. Cellular respirationX. O2 and CO2- O2 is not very soluble in water, but organisms can carry lots of dissolved CO2- CO2 30 times more soluble in water than O2XI. Carbonic Anhydrase- Present in many organisms including diatoms, plants, methane producing bacteria, marine cyanobacteria, and some chemolithotrophs- CO2+H2O  (CA)  H2CO3  H+ = HCO3-- Key Point: Role of CA in carrying CO2 in body fluids and in regulating pH- Increase CO2 and decrease pH- Decrease CO2 and increase pH- Increase H+ and increase CO2- Decrease H+ and decrease CO2XII. As temp increases, Pgas dissolved decreasesXIII. As solute increases, Pgas dissolved decreasesXIV. Oxygen in Sea water/ Fresh- solubility decreases as temp decreases and as pressure decreases- Oxygen levels drop significantly at depths of oceanXV. Diffusion and Single Celled organisms- Small- Membrane foldings- Move through water- Sessile cells move water over surface (cilia) or live in currentsXVI. Small Animals- Like sponges, cnidarians, flatworms- Small, specialized body plans: channeled, septate, flattened- Low metabolic rates- No specialized respiratory structures-diffusion adequate for both gas exchange and distribution- Gills: external gills are in direct contact with waterXVII. Large Animals- Huge scaling problems- Specialized respiratory surfaces-produce fractal respiratory surfaces: gills, lungs- Diffusion+ passive bulk flow in inadequate: requires mechanisms for active bulk flow- 2 active bulk flow systems requird- each with its own pumping system: ventilation (respiratory) and circulation (blood)XVIII. Large Aquatic Animals- Like mollusks- Mussels and clams : sessile filter-feeders- Squid-active carnivoresXIX. Mollusks- Mussels and clams- Large gills used to 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 and fastest aquatic invertebrates- water is forced out through siphon, propelling animal forwardGas Exchange 2 (Ch 44 3rd edition)I. Gills and Lungs- Moist surface-terrestrial problem: water loss with each breath- Move fluid or air over large surface area- Air or water flow related to metabolic activity of organism-matched by blood flow to pick up O2 and unload CO2- Fish use counter currant mechanism II. 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 inflationIII. 2 ways to inflate a balloon- 1. Negative pressure lung: when diaphragm is pulled down, the balloon inflates and when it is released the balloon deflates- 2. Alveoli: see slide 44.11bIV. Air Moves due to ∆P- Make lung and alveoli bigger, intra alveolar pressure drops and lung fills with fresh atmospheric air- Make lung and alveoli smaller and intra alveolar pressure increases and lung expels stale air- Works like blacksmiths bellowsV. Breathe by changing lung volume- Lungs expand and contract in response to changes in pressure inside the chest cavityVI. Respiration in Birds- High O2 demand- Posterior and anterior air sacs- Inhales and fills sacs with air, exhales, filling lungs with that air and emptying sacs- 3 adaptations of bird lungs: little dead space, exchange gases during both inhalation and exhalation, lung capillaries cross the parabronchi perpendicularlyVII. How do animals solve prob of low solubility of gases in body fluids- Carbonic anhydrase converts much of the CO2 to H+ and HCO3- (70% of CO2 in your blood is carried this way)- Oxygen carried by a blood protein-respiratory pigment, hemoglobin in animalsVIII. Hemoglobin (Hb)- Each molecule can bind up to four molecules of oxygen- 98.5% O2 unloaded onto hemoglobin in red blood cells, 1.5% onto


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UMD BSCI 207 - EXAM 3 STUDY GUIDE

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