Yeast is a fungus that feeds on organic matter, breaking it down in a visible way. When you sprinkle dry yeast on a banana slice and seal it in a bag, the yeast consumes the sugars and releases carbon dioxide gas. A plain slice sealed in a separate bag stays as the control. Over three to four days, the yeast-covered slice breaks down noticeably faster.

Bananas contain sugars that yeast — a fungus that feeds on organic matter — can break down for energy. When you sprinkle dry yeast on a banana slice and seal it in a bag, the yeast uses the fruit's carbohydrates as fuel. As a result, the yeast-covered slice breaks down noticeably faster than the plain control slice.