What would be the consequences if we were to reverse the direction of water flow over the gills of a fish, moving water inward past the operculum, past the gills, the out the mouth? this reversal of water flow would ?

B. reduce efficiency of gas exchange

Explanation:

The consequence of a reversal in the direction of water movement during a fish's gaseous exchange process would be a reduced efficiency in gas exchange.

Normally during exchange of gases in fishes, oxygen-rich water enters through the mouth and pumps over the gill during which the operculum remains closed. The gill filaments enable them to have the surface area necessary for the exchange of oxygen in the water for carbon dioxide in the blood of the fishes. The oxygen-deficient, carbon dioxide-rich water is then pushed out through the operculum.

If the process becomes reversed, the efficiency of gas exchange will greatly reduced due to the directional structure of the filaments of the gills that serve as the surface for gaseous exchange.