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Lecture 9

Lecture 9 - Gaseous Exchange

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Biology 2601A/B
Graeme Taylor

LECTURE 9 – GASEOUS EXCHANGE Gaseous Exchange  Trillions of cells out in metazoan bodies connected to the environment  They need a certain temperature, need to be fed, want food and water, but mostly oxygen  Gaseous exchange – the means by which animals acquire oxygen and rid themselves of carbon dioxide  Therefore respiratory gases are oxygen and carbon dioxide  The process: o Exchange of gases with the respiratory medium o Transport of gases in the circulatory system o Exchange at the tissues to supply mitochondria with O and remove CO 2 2  The transportation of the gases is controlled by basic physical laws  As CO2builds up in the system, problems of acidity arise, which must be mitigated  The respiratory system supplies the body with 2 and disposes of C2  Four processes are needed: o Ventilation of respiratory structure o External respiration o Transport of respiratory gases o Internal respiration  Diffusion plays a large role and can be described by Fick’s law o Q = DA x (P1– P2) / L o Q = rate of simple diffusion o D = coefficient of diffusion o A = area over which diffusion takes place o (P1– P2) = the concentration gradient o L = path length, distance over which diffusion occurs Area (A) o Huge difference in size between the blue whale and rotifer snail o Ability for oxygen to diffuse into the inner tissue is next to impossible for bigger animals o The blue whale has a smaller surface area relative to its mass/volume o The rotifer snail has a large surface area relative to its mass/volume  Time required for diffusion through water to halve a concentration difference for small solutes suc2 as O o 10 micrometers = 100 milliseconds o 1 millimeter = 17 minutes o 1 meter = 32 years  There has been no active transporters of2O in the cell, has to occur by diffusion or convection (passive processes that do not require energy)  O2always has to move to a state of equilibrium  Flatworm – has no circulatory system, relies primarily on diffusion o Also has gas vascular system – in addition, acts as an animal epidermis which allows respiration to take place – makes diffusion length smaller
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