Sperm and semen are often used interchangeably, but they are actually two different things. Semen is the fluid that contains sperm and is produced by the seminal vesicles, prostate gland, and Cowper's gland. Sperm is just one of the many things found in semen and is produced by the testes. In addition to sperm, semen also contains sugar, electrolytes, enzymes, and zinc. All of these substances help to protect and nourish the sperm so that they can survive their journey through the reproductive tract. While sperm make up a small percentage of semen by volume, they are essential for fertilization to occur. Without sperm, there would be no way to fertilize an egg and no way to produce offspring.