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Lecture 14: Big Ideas I: Physical Considerations (Fick's Law of…
Lecture 14: Big Ideas I: Physical Considerations
Surface Area:Volume Ratio
As size increases, surface area:volume decreases
Reasons why this ratio is important
Gas exchange
Regulation of body temperature
Water balance
Water balance
Absorption of nutrients and disposal of wastes
Fick's Law of Diffusion: Q=DA(P1-P2)/L
A=Cross-sectional area on which diffusion occurs
P1 & P2: Partial Pressures of the gas at two locations
D=Diffusion Coefficient- depends on diffusing substance, medium, temperature
L=Path Length between locations
Q=Rate of diffusion
Partial Pressure Gradient: (P1-P2)/L
In order to facilitate gas exchange, a large surface area, large partial pressure difference, and small L is optimal.
Surface Area:
Gills, Lungs, Tracheae (Insects)
Partial Pressure Difference:
Ventilation & Perfusion (P's)
Ventilation: Active movement of respiratory medium over gas exchange surfaces
Perfusion: Active circulation of blood over gas exchange surfaces
Reducing L
: respiratory/circulatory systems
Countercurrent Flow & unidirectional flow: Used by bony fish to maximize gas exchange
Gills made of gill filaments covered by lamellae, thin folds & site of gas exchange
Countercurrent flow allows there to be a gradient across the entire region of gas exchange
Birds use unidirectional air flow to maintain partial pressure gradient.
Anterior & Posterior air sacs
Temperature
Big organisms must remove heat from metabolism; small organisms must conserve heat
Rate of biochemical reactions doubles with 10 degree Celsius increase in temperature
Organisms either regulate body temperature so environment doesn't affect them, or live under more narrow conditions & accept environmental influence