See if the cup on the windowsill grows mold more slowly, more quickly or at the same rate as the one in the refrigerator. Look around your home for other molds. We can find molds in all sorts of unexpected places. Unlike green plants, they can't make their own food from sunlight. Instead, they live directly off of what they are growing on.
Molds can be a nuisance when they settle on our food or possessions.
But molds are also useful. The green spots on old oranges are penicillin mold. This is what the medicine is made from.