Final answer:
The epididymis ensures sperm survive during intercourse by maturing and storing them before they are transported out of the body via the vas deferens.
Step-by-step explanation:
The internal structure of the male reproductive system that ensures sperm survive during intercourse is the epididymis. The epididymis is a coiled tube located on top of each testis that serves to mature and store sperm. It provides a favorable environment for sperm to gain the ability to swim and fertilize an egg. During ejaculation, sperm are released from the epididymis into the vas deferens for transport out of the body.