Q.) In which of the following groups of
organisms, blood flows through the heart
only once during one cycle of passage
through the body?
(a) Rabbit, Parrot, Turtle
(b) Frog, crocodile, Pigeon
(c) Whale, Labeo, Penguin
(d) Shark, dog fish, sting ray
Ans. (d) Shark, dog fish, sting ray
Explanation: The blood goes through the heart of fishes only once during one cycle of passage through the body, whereas in other vertebrates it goes twice through the heart during each cycle.
