Question

Give details of two different ways in which a zygote develops in case of animals where fertilization is internal

Answer 1

In humans, the male gametes, sperms are formed in the male gonads (testes in humans), while the female gamete, ovum (egg) is formed in the female gonads (ovary in humans). During copulation, the sperms mixed with the semen, through the vas deferens, urethra and the penis enters the female, through the vagina and through the cervix and the uterus enters the Fallopian tube. 
After the Ovulation takes place, the ovum comes out of the ovary reaches the ampulla part of the Fallopian tube. Where, the sperm comes and fuses with the ovum and form the first cell, Zygote (n + n -> 2n). then, as the  days go, the cells divide and then ,a day comes when, there is a ball of 32 cells, called embryo is formed. This embryo further divides to from a foetus (baby).

Answer 2

(i) Internal fertilization in earthworm: An earthworm , though a hermaphrodite, does not fertilize itself. Two earthworms come in contact with each other and exchange sperms. The eggs are fertilized internally with the sperms

received from the partners. Thus, a zygote is developed.

(ii) Internal fertilization in human: In human fertilization takes place on meeting of male and female gamete inside body. Fertilization is internal, and the development of the zygote into a fully formed individual also occurs inside the body of the female.