Which of the following organisms show external fertilization? I. Pigeon II. Frog III. Fish IV. Lizard Select the answer using the code given below:

The correct answer is B, II and III only. Frogs and most fishes release their eggs and sperm into water, where fertilisation takes place outside the female's body. In external fertilisation, a large number of eggs and sperm are shed together, because many are lost to currents and predators. In frogs, the male clasps the female in the water and fertilises the eggs as she lays them, and the fertilised eggs float in clumps called spawn. Most bony fishes, such as rohu and catla, also spawn in water. Birds and reptiles, which lay eggs with shells on land, must have internal fertilisation, because a shell would block the sperm. Option A is wrong because it includes the lizard, a reptile with internal fertilisation. Option C is wrong because both the pigeon and the lizard fertilise internally, and it leaves out the frog and the fish. Option D is wrong because it includes the pigeon, a bird whose eggs are fertilised inside the female before the shell forms. Exam tip: external fertilisation = most fishes and amphibians, in water; internal = reptiles, birds and mammals.