Midterm 1 notes - Lecture 2 Gaseous Exchange 58-67 69-71...

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Lecture 2: Gaseous Exchange 2016-02-07 58-67, 69-71 & 72-81 (Chapter 11) Energy obtained by oxidation of food Plenty of oxygen in air and it is dissolved in water ° Huge differences in the availability of oxygen between air and water and across different temperatures. Body size, shape and metabolic rate also have an effect how you access the oxygen, how much of it you need and how much CO2 you rid of ° ° Water vs Air Table There are low diffusion rate in water Less oxygen is available in given volume of fluid o This means that more energy is required to “pump” the oxygen o Breathing is much more expensive in water since the rate of diffusion is less effective ° ° Simple Diffusion Fick’s law is used to describe the rate of diffusion Q= DA*(P1 –P2) ° L Q= rate of simple diffusion D= the coefficient of diffusion (temperature and solubility of gas) A= the area over which diffusion/gas exchange takes place (P1-P2)= the concentration gradient ( difference in partial P of gas on either side of barrier to diffusion)
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L= distance/thickness of the barrier to diffusion (the path length over which diffusion occurs ° Fick’s law focuses on how animals use: Ventilation: o Gas exchange with the environment o Active movement of respiratory medium Perfusion: o Gas deliver within the body ° ° D increase/decrease ° ° P1 P2 ° ° ° L ° ° A ° ° ° ° °
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° ° ° ° Respiration The size and mass of an organism is usual proportional to its volume o If an organism is small in volume it will have a large surface area (A) This large surface allows for simple diffusion to supply enough oxygen and remove CO2 o Some large animals also rely on this for example flatworms Flat shape is a larger SA relative to their V There is a short path length (L) from the external environment to the internal o A round or spherical animal has a much greater volume in comparison to its SA Needs specialized structures to acquire oxygen and excrete CO2 The path length (L) puts most of the animal’s cells out of the range for which simple diffusion can be effective for this gas exchange As animals breath they remove oxygen from their environment (from air or water) that is next to their respiratory surface This in turn lowers the concentration of oxygen in the animals immediate environment and raises it on the other side of the respiratory surface. The concentration of CO2 on either side of the surface changes in the opposite of direction (in comparison to oxygen) as it is produced by metabolism and excreted into the environment Regardless of what gas we are talking about the concentration gradient (P1-P2) maximizes the diffusion. o Molecules move from a high concentration to a lower concentration Through ventilation animals move air/water past their respiratory surface, INCREASING P1 Through perfusion animals move body fluids on the other side of the surface (more obviously seen in animals that transport gases through blood) LOWERS P2 °
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