The mudpuppy (Necturus maculosus) is a fully aquatic salamander native to North America. Like all amphibians, it has a double circulatory system, but its heart contains only a single ventricle, as shown in the simplified diagram below.
a.[1]
Define the term double circulatory system.
b.[2]
With reference to the diagram, explain why having only one ventricle makes the transport of oxygen to the mudpuppy's body tissues less efficient than in organisms with a four-chambered heart (such as mammals).
c.[4]
The mudpuppy obtains dissolved oxygen from the water via its external gills. Explain why the mudpuppy may die if the concentration of dissolved oxygen in its aquatic habitat becomes very low.