The external intercostal muscles and the diaphragm contract:
1. during inhalation
2. during exhalation
3. during both inhalation and exhalation
4. during neither inhalation nor exhalation.

All terrestrial vertebrates, except amphibians, breathe by expanding their lungs due to
1. negative pressure within the lungs
2. positive pressure within the lungs
3. neutral pressure within the lungs
4. countercurrent pressure within the lungs
 

The gills in the fishes are the most efficient of all respiratory systems because:
1. the countercurrent flow of water over the gills
2. the blood within the gills
3. increasing the temperature of the blood to the gills
4. the countercurrent flow of water over the gills and the blood within the gills

Carbon dioxide is transported in blood by all the following mechanisms except:
1. bound to the protein portion of hemoglobin
2. bound to the iron atoms of hemoglobin
3. dissolved in plasma
4. as bicarbonate

Humans are not able to survive for long periods at very high altitudes primarily because:
1. The oxygen content is very low with respect of that found at sea level.
2. The carbon dioxide is much more than that found at sea level.
3. The partial pressure of oxygen is very low than that found at sea level.
4. The atmospheric pressure is much higher than that found at sea level, which makes the amount of oxygen available one-fourth that found at sea level.

All the following statements regarding hemoglobin are true except:
1. Hemoglobin loads up with oxygen in the alveolar capillaries.
2. Approximately 97% of hemoglobin in red blood cells is in the form of oxyhemoglobin.
3. Hemoglobin has a lower affinity for oxygen at higher temperatures.
4. Each molecule of hemoglobin can carry one molecule of oxygen.

When you hold your breath the urge to inhale first results from
1. rising PCO₂
2. falling PCO₂
3. rising PO₂
4. falling PO₂

The conversion of carbon dioxide into carbonic acid in the red blood cells is catalyzed by the enzyme:

The efficiency of a respiratory system is enhanced by all the following except:

The most efficient respiratory system amongst the following would be:
1. mammal lungs
2. reptile lungs
3. bird lungs
4. fish gills