Suppose the (1) ____ oocyte is on its way down an oviduct when a female and male are engaged in sexual intercourse, or (2) _____. The male sex act requires (3) _____________ and ejaculation. During coitus, pelvic thrusts stimulate the penis, the female's (4) ____________, and the vaginal wall. The mechanical stimulation induces involuntary contractions in the male reproductive tract. It forces sperm from the (5) _____ and contents of seminal vesicles and the (6) ________ gland into the urethra. The substances mix and form (7) _____, which is ejaculated into the vagina. During male (8) ________, the end of the sex act, strong sensations of physical release, warmth, and relaxation dominate. Similar sensations typify female orgasm.
Following sexual intercourse, (9) _____ are in the vagina. Fertilization most often takes place in the upper portion of the (10) _____. When living sperm contact an oocyte, they relase (11) ______ that clear a path through the zona pellucida. Usually only one sperm fuses with the secondary oocyte; only its nucleus and centrioles do not degenerate in the oocyte's cytoplasm. Sperm penetration induces the secondary oocyte and the first polar body to finish meiosis (12) _______. There are now three polar bodies and a mature egg, or (13) ______. As the sperm and egg nuclei fuse, their chromosomes restore the (14) ____ number for a brand new zygote.