Lecture 2: Circulation and Gas Exchange I (Chapter 42)
Keywords
Themes that weíll often come across:
Cellular respiration
Organismal respiration -- a simple view
The simple view is true for animals, but there are differences
Major causes for these differences:
Why does size matter in respiration?
How fast is diffusion of oxygen?
How does diffusion work? Consider a point source of a diffusing substance
Each molecule will travel randomly (brownian motion)
Over time particles will become separated
But particles donít just move away from the original point source
They are travelling randomly
Thus...
ìSpeedî of oxygen diffusion in liquid
Examples where oxygen diffuses only short distances
Vertebrate Lung
Very Small Organisms
Rate of oxygen entry is influenced by external concentration
How small does an organism have to be to rely on diffusion alone?
How about a spherical sea creature 1 cm wide?
Relationship between surface area and volume changes as a function of size
Example of organism relying solely on surface: the Protist Paramecium
What do you do if you want to be bigger than 1 mm? Adaptations to enhance gas exchange:
Example of increased surface area: Green Hydra (several mm long)
The jelly fish Aurelia
Gas exchange structures
Gills (definition)
Gills vs. Lungs
Fish Gill
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