Flight requires greater efficiency of oxygen delivery. Therefore, birds have a unique respiratory system that allows them to filter oxygen. During the initial inhalation, the air passes through the trachea and into the . During the second inhalation, the oxygen-depleted gas moves to the , and is then exhaled.
A. posterior air sacs; anterior air sacs
B. lamellae of the gills; anterior air sacs
C. anterior air sacs; posterior air sacs
D. lamellae of the gills; bronchioles
E. bronchioles; capillaries
A. posterior air sacs; anterior air sacs
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A high proportion of the food that cattle eat cannot be digested by cattle
a. True, cattle have large saclike pouches that house plant-digesting microbes. b. False, cattle are herbivores and thus produce the necessary enzyme to digest plant material. c. True, this is why cattle have to eat large amounts of food, because most passes undigested through their gut. d. False, cattle eat highly nutritious plants that are readily digested
The SA node
a. generates excitatory signals for muscle contraction. b. is under voluntary control. c. receives electrical signals from the AV node. d. is located in the right atrium. e. is all of these
A pine tree is called a sporophyte because it
a. develops from a germinated spore. b. produces spores by meiosis. c. is haploid. d. undergoes fertilization. e. reproduces by both sexual and asexual means.
The location and/or metabolism of a substance such as a hormone or drug can be followed in the body by labeling the
substance with a(n): a. acid b. isotope c. element d. radioisotope e. DNA molecule