Download Why do we need oxygen?

Respiratory System
Why do we need oxygen?
All animals need to obtain
Oxygen molecules and eliminate carbon dioxide
 Gas exchange
These gases move by diffusion
Implication:
Oxygen must be dissolved in water before
animals can take it up.
Implication:
Water bodies have less dissolved oxygen (5%)
than the atmosphere
Implication:
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Different respiratory surfaces
Moist skin as the only respiratory organ
Animals with no respiratory system or circulatory system:
Sponges and Cnidarians
Flatworms
Animals with no respiratory system but circulatory:
Earthworms
All of these are
restricted in which way?
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Larger animals need specialized respiratory surfaces
and circulatory system
Gills are outfoldings of the body
surrounded by water
Water is dense and O2 concentration is low  need to create water flow
Amphibians move their external gills
Mollusks pump water into mantel cavity
Some crustaceans have gills on their legs
Sea stars: scattered projections
Marine worms (annelida): parapodia (also for walking)
Fish: gills behind the body wall
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Fish gills remove 80% of the oxygen from
water by a countercurrent exchange
Flow of blood is in the opposite direction than the flow of water,
Fish extract more oxygen than if blood moved in the same direction
Why can’t gills work on land?
Internal respiratory surfaces
for land animals
Land slugs and snails:
mantle cavity works as a lung
Insects, centipedes and some spiders:
Tracheae  system of tubes that bring
oxygen directly to tissues
Spiracles are openings on the side of the body
What about the circulatory system?
Vertebrates: lungs
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Evolution of Lungs in Vertebrates
Lungs in Vertebrates
Amphibian lungs is a simple sac, most O2 is obtain across ____________
Reptiles: skin is _________, lungs posses alveoli
In birds and mammals
there are more alveoli
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Lungs in Vertebrates
Birds: more branched alveoli (air sacs)
Air flow is one-way:
during inspiration the air sacs fill
during expiration they empty
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