Gaseous exchange systems

Biology 2: Form and Function

Gaseous exchange in animals• Respiratory surfaces must be kept moist

and maximize surface area• Small, aquatic animals may use direct

diffusion• Medium aquatic animals use gills

– All exchange systems (gases, heat, wastes) use counter-current mechanism

– Larger aquatic animals use ventilation

• Terrestrial animals internalized respiratory surface (lungs)

Lower blood pH and higher blood temperatures facilitate oxygen unloading

Gaseous exchange in plants• Plants must:

– Receive CO2 to fix carbon (photosynthesis)

– Remove O2 as a byproduct of photosynthesis, and receive O2 for respiration

• So that plants can control gaseous exchange, it only occurs at particular pores called stomata that regulate flow

• Stomata also play a key role in controlling transpiration

Stomata - the movie

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