International units are the Standardized units used in Scientific literature across the world. They are different than the US Units. (For Example; The US unit for length is Mile/Feet/Inches; Whereas...
scientists use SI units so they can make sure they don't have any misunderstanding like say one person said they had the biggest fish ever it was 70cm long then the other person said the probably...
Semen is a lot more fun to produce ;) But seriously, there are chemical differences. Semen, when mixed with a woman's egg, will most likely result in the conception of a child. Pee, on the other...