(a) Internal fertilization is a type of sexual fertilization. It is the union of an egg cell with a sperm during sexual reproduction inside the body of a female. For this process, male sperms are required to enter into the female reproductive system. (b) Metamorphosis is a biological process of physical change in an animal after its growth.  (c) A zygote is a fertilized egg formed after the union of male and female gamete. It has two nuclei contributed each by male and female gamete.