Countercurrent exchange is evident in
A) the flow of water across the gills of a fish and that of blood within those gills.
B) the flow of blood in the dorsal vessel of an insect and that of air within its tracheae.
C) the flow of air within the primary bronchi of a human and that of blood within the pulmonary veins.
D) the flow of water across the skin of a frog and that of blood within the ventricle of its heart.
E) the flow of fluid out of the arterial end of a capillary and that of fluid back into the venous end of the same capillary.

Question

Quizplus · Accepted Answer

Countercurrent exchange refers to the exchange of two substances, such as water and blood, flowing in opposite directions. This is evident in the flow of water across the gills of a fish and that of blood within those gills, where oxygen is efficiently extracted from the water due to the countercurrent exchange of oxygen-poor blood with oxygen-rich water.

Countercurrent Exchange Is Evident in