Due to its system of nine air sacs connected to the lungs, the respiratory system of birds is arguably the most effective respiratory system of all air-breathers. Upon inhalation, air first flows into posterior air sacs, then into the lungs, and then into anterior air sacs on the way to being exhaled. Thus, there is one-way flow of air through the lungs, along thousands of tubules called parabronchi.
If the inner lining of the air sacs is neither thin nor highly vascularized, then what can be inferred about the air sacs?
A) They must not belong to the respiratory system.B) They cannot be derived from endoderm.
C) They cannot be sites of gas exchange between air and blood.
D) They must obtain nutrition from some source other than the bloodstream.
E) They cannot effectively moisturize the air before it reaches the lungs.
Answer: C
Some bird bones are hollow rather than honeycombed. The hollow bones mostly contain air sacs. The replacement of bone marrow with air sacs is properly understood as an adaptation to
A) reduce the weight of the bird.B) facilitate flight.
C) eliminate the functions that marrow performs.
D) All three of the options listed are correct.
E) Only two of the options listed are correct.
Answer: E
Birds generate a lot of heat, especially during flight. Yet the adipose tissue under their skin and the feathers atop their skin make it difficult to eliminate excess heat across the skin. Which of the following alternatives can absorb body heat and eliminate it from the bird most effectively?
A) air in the air sacsB) lymph in the lymphatic vessels
C) blood in the vessels
D) blood in the heart
E) urine in the bladder
Answer: A
If Archaeopteryx had air sacs, then which of its features would have had the opposite effect on enabling Archaeopteryx to fly long distances from that provided by air sacs?
1. teeth
2. contour feathers
3. wing claws
4. long tail with many vertebrae
A) 1 and 2
B) 1 and 4
C) 2 and 3
D) 1, 2, and 4
E) 1, 3, and 4
Answer: E
Which feature of some carinates has the same effect on weight as the presence of air sacs?
A) presence of a large, heavily keratinized beakB) absence of a urinary bladder
C) presence of a carina (keel)
D) number of chambers in the heart
E) presence of large pectoral muscles
Answer: B
The movement of air along parabronchi is most similar to the movement of
A) air in the lungs of other amniotes.B) food/waste in a gastrovascular cavity.
C) food/waste in a digestive system with separate mouth and anus.
D) the frog tongue during feeding.
E) air in lungs of terrestrial amphibians.
Answer: C
Which type of bird is most likely to need air sacs to reduce its weight?
A) birds that migrate long distancesB) waterfowl that float on water, but do not dive
C) birds that spend much of their time underwater
D) ratites
Answer: A
The one-way flow of air along parabronchi makes what type of exchange mechanism possible, at least theoretically?
A) the same as that occurring in fish gillsB) the same as that occurring in insect tracheae
C) the same as that occurring in mammalian lungs
D) the same as that occurring in echinoderm skin gills
Answer: A
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