Question

what is a copulation? when did the pregnancy will occur in female? What is the role of plecenta?

Answer 1

copulation is insertion of erect penis into vagina for reproduction.
pregnancy will occur the fusion of male and female gamete(fertilisation).
placenta help to nourish developing embryo in the mother's womb by exchange of gases, receiving excretory waste from embryo etc...

Answer 2

Copulation is the time period or the we can say time of intercourse during when sperm enters Vagina

Secondly., Pregnancies occurs when mature egg (ova) is fertilised by a sperm and forms a two celled zygote

And at last , placenta is disk like tissue present between embryo and mother's uterine wall which helps to provides necessary nourishment to the embryo and it also help to excrete out the waste material through mother's body