Question

how sex is important for human reproduction

Answer 1

Sex is important as it helps in the continuation of a generation.If no new offspring will be reproduced then the generation of that family will not continue.It is also a nature rule.It is also important for the ecological balance.If correct population is maintained then no harm will be there to the environment.

Answer 2

Sex results in the entry of sperm cells of male into the vagina of female.
Sperm cells travel into the uterus and one of them fuses with the female gamete, ovum, resulting in the formation of a zygote, in the fallopian tube. This process is called as Fertilization.
Fertilization is one of the major events of sexual reproduction.
The zygote, thus formed, develops gradually and gives rise to a baby.

Hence, coapulation (sex) is important for human reproduction.