"A biology class" joke

In a biology class, the professor was discussing the
high glucose levels found in semen. A young female
freshman raised her hand and asked "If I understand,
you're saying there is a lot of glucose in male semen?"
"That's correct," responded the professor, going on to
add statistical info.
Raising her hand again, the girl asked, "Then why doesn't
it taste sweet?" After a stunned silence, the whole class
burst out laughing.
The poor girl's face turned bright red; she picked up her
books without a word and walked out of class never to return.
As she was going out the door, the totally straight-faced
professor answered her question:
"It doesn't taste sweet because the taste-buds
for sweetness are on the TIP of your tongue!"