The document discusses human reproduction. It describes the primary and secondary sex characteristics that develop during puberty to distinguish males and females. It explains that sperm and ova are the reproductive cells, and describes the basic structures of the male and female reproductive systems. Fertilization occurs when an ovum and sperm join to form a zygote. Pregnancy lasts about 9 months, during which an embryo develops protected structures like the placenta and umbilical cord, before birth.