How very Mr. Wizard! We did not excel at science in school, but every so often came across some little scientific tidbit that was useful in daily life.
Ethylene is a gas that causes ripening, aging, and eventually spoilage of produce. Many fruits and vegetables release it and these same fruits and vegetable also have the ability, through receptors, to absorb other ethylene molecules in the air. This can come in handy when one has a pear that's as hard as a rock. You see where we're going with this?
Maybe you already knew that you could put an avocado or banana in a paper bag (with the top loosely closed) to hasten ripening. And it works. Isn't it nice to know why? Those increased levels of ethylene inside the bag, released by the produce itself, serve as a stimulant after re-absorption to initiate the production of more ethylene.
Poof! Within days, and sometimes hours, that hard-as-a-rock piece of fruit is ready to eat.
Not sure which fruits and vegetables release and re-absorb best? Don't risk it. Put an apple in the bag, and this guaranteed-ethylene producer will work wonders. For this same reason, apples should not be stored in a fruit bowl with other fruits, potatoes, onions, or garlic (anything you keep out of the refrigerator) unless you want everything to rot in no time.
Ah, science. If you cook, you simply cannot ignore it. Luckily, no one is grading you this time.