Gas Exchange

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University of Toronto Scarborough
Biological Sciences
Mary Olaveson

Chapter 48 Gas Exchanges in Animals 48.1 What Physical Factors Govern Respiratory Gas Exchange? (1025) - CO 2nd O are2the respiratory gases that animals must exchange. - Diffusion (random movement of molecules or other particles, resulting in even distribution of the particles when no barriers are present) is the only means of gas exchange between the internal body fluids of an animal and the outside medium (water or air). Diffusion is a physical process. Diffusion is faster in higher temperatures and faster in air than water. Diffusion is Driven by Concentration Differences (1025) - Net movement of molecules via diffusion is always down its concentration gradient. - Partial pressure of the gases is one way biologists express the concentrations of different gases in a mixture. - Solubility of a gas in liquid is a factor that makes it more difficult to describe of respiratory gases in a liquid such as water. - Actual amount of a gas in a liquid depends on the partial pressure of that gas in the gas phase in contact with the liquid as well as on the solubility of that gas in that liquid. Ficks Law Applies to All Systems of Gas Exchange (1026) - Ficks law of diffusion describes diffusion quantitatively with an equation (all environmental variables that limit respiratory gas exchange and all adaptations that maximize respiratory has exchange are included): Q = DA- - Q is the rate at which a gas such as O di2fuses between two locations. - D is the diffusion coefficient (i.e. perfume has a higher D than motor oil vapour). - A is the cross-sectional area through which the gas is diffusion. - P1and P a2e the partial pressures of the gas at the two locations. - L is the path length, or distance, between the two locations. - (P -P )L is a partial pressure gradient. 1 2 Air is a Better Respiratory Medium than Water (1026) - Oxygen can be obtained easier from air than from water because: - O2content of air is much higher than in water. - O2diffuses about 8000 times more rapidly in air than in water. - More energy is done to move water than to move air, because water is 800x more dense. - Eukaryotic cells carry out cellular respiration in the mitochondrion which is in the cytoplasm an aqueous medium as well as they are bathed in extracellular fluids which is also an aqueous medium. - Animals in liquid mediums (i.e. fish) have gills which are very efficient in gas exchange provide large surface area for gas exchange). High Temperatures Create Respiratory Problems for Aquatic Animals (1026) - Because most water breathers are ectotherms, their body temperature and metabolic rate increases as the environments temperature increases; they need more O as th2 water gets warmer and warm water hold less dissolved gas than cold water. O Availability Decreases with Altitude (1026) 2 - Rise in altitude reduces O a2ailability. The P (p02tial pressure of oxygen) decreases as well, and since diffusion (gas exchange) relies on this, gas exchange is less efficient and O upt2ke is constrained. C O i2 Lost by Diffusion (1027) - CO 2 diffuses out of the body as O d2ffuses in. Direction and rate of diffusion across the respiratory exchange surfaces depend on the partial pressure gradients of the gases. - Partial pressure of CO d2es not change with altitude.
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