The only vertebrates in which blood flows directly from respiratory organs to body tissues without first returning to the heart are the
A) amphibians.
B) birds.
C) fishes.
D) mammals.
E) reptiles.

Question

Quizplus · Accepted Answer

Fish have a single circulation system where blood flows from the gills to the body tissues without first returning to the heart. This is called a single-loop circulatory system. The other choices (amphibians, birds, mammals, and reptiles) all have a double-loop circulatory system where blood goes from the heart to the lungs or respiratory organs before being pumped to the rest of the body.

The Only Vertebrates in Which Blood Flows Directly from Respiratory