The latest issue of the Hexagon (newsletter for Alpha Chi Sigma) included some actual answers to quizzes/exams from science students (junior high through college). The best of these were

"When you smell an odorless gas, it is probably carbon monoxide."

"Three kinds of blood vessels are arteries, vanes, and caterpillars."

"Blood flows down one leg and up the other."

"A super saturated solution is one that holds more than it can hold."

and then my favorite

"To collect fumes of sulphur, hold a deacon over a flame in a test tube."