Answer: The correct answer for fill in the blank is Gametes.
Gametes are also called sex cell that are haploid cells ( like sperms in males and ovum in females) and produced by the process of gametogenesis.
The formation of male gamete ( that is spermatozoa or sperm) is called spermatogenesis. It begins with the onset of puberty in males when the secretion of GnRH ( gonadotropin releasing hormone) is triggered by hypothalamus.
Male reproductive system is present from birth. It possesses organs like testes ( with coiled structure that is seminiferous tubule), vas deferens, epididymis etc.