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) fishes
C) mammals
D) reptiles

Question

Quizplus · Accepted Answer

Fishes have a single circulatory system where blood flows directly from the gills to body tissues without first returning to the heart. In contrast, mammals, amphibians and reptiles have a double circulatory system where blood is pumped to the lungs or respiratory organs and then back to the heart before being pumped to the rest of the body.

The Only Vertebrates in Which Blood Flows Directly from Respiratory