He uses porn to demonstrate insemination!

"So Aimee, I need to tell you that my field is Chemistry, but Professor Smith has very kindly given me some notes with which to prepare some lessons for you. The first lesson in Biology that we'll be studying is reproduction."

Aimee's eyebrows shot up as she squeezed her legs together as her pussy creamed itself once more. They shot up again when she saw Professor Lex connect his laptop to a screen in his office, she whimpered when she saw the first clip of a male pornstar cumming (just) inside the female pornstars pussy.

"Now then Aimee, can you tell me why that will not get the female pregnant?"

"U-Um, b-because h-he d-didn't g-g d-deep i-inside?"

"Yes, very good. If the male pornstar in this clip had wanted to inseminate the female, he would have made sure that he had gotten as deep as he could before ejaculation occurred. Another thing that would be necessary of course is for the woman to be fertile, do you know your cycle Aimee?"

Aimee was blushing hard while nodding, picturing herself as the female pornstar and wishing she was the one being cream-pied. "M-My cycle isn't due for a week, that's when I'll be at my most fertile." Professor Lex noticed this and without Aimee knowing sent a message to Melissa to get her to bring it up with Aimee next time she saw her. After showing Aimee a couple more clips, he gave her some homework, to write an essay about reproduction and the male and female genital organs.