Fish respiratory systems exchange gas and receive oxygen at the gills. This oxygen then enters the blood stream and is pumped through the heart and back through the gills without first returning to the heart. This order of events best describes which type of circulation system?

a) double loop

b) single loop

c) open

d) recycling

the answer is single loop

b) single loop

Explanation:

In fishes, deoxygenated blood is carried to the heart which in turn pumps it to the gills for exchange of gases. Oxygenated blood is delivered from gills to the body parts.

As per given information, fishes exhibit a single loop circulatory system. If the blood passed through the heart only once during one loop of circulation, the system is said to be single loop circulation.