Some people use the terms sperm and semen interchangeably. But sperm cells are only one component. Semen also contains substances from the prostate and a pair of rabbit ear-shaped organs inside the pelvis called the seminal vesicles.
Sperm cells - which are made in the testicles - need lots of high-octane fuel to whip their tails. Lucky for them (and us), sperm get the fuel they need in the form of sugar fructose, which is supplied by the seminal vesicles.
Fluid from the prostate contains chemicals that cause semen to liquefy once it's inside the female. Without it, sperm would be locked in place and unable to swim.
