Q.Differentiate between external and internal fertilizations.

External fertilization occurs outside the body in an aquatic medium; internal fertilization occurs inside the female's reproductive tract.

In external fertilization, sperm and ova are released by the male and female (usually simultaneously) into the surrounding water, where fusion occurs by chance; this demands the release of very large numbers of gametes to compensate for losses (to predation, dispersal, or failed contact) and is largely restricted to aquatic organisms such as most bony fishes, frogs, and many aquatic invertebrates like starfish, since the gametes and resulting zygote would desiccate on land. In internal fertilization, the male introduces sperm directly into the female's reproductive tract (by copulation), where fusion with the ovum takes place inside the body; this requires far fewer gametes, gives better protection to the zygote from predation and desiccation, and is the mode seen in reptiles, birds, most mammals, and many terrestrial invertebrates such as insects. Internal fertilization is thus …