The membrane-bound sacs that contain hydrolytic enzymes which digest complex organelle molecules are called lysosomes.

Here's a breakdown:

* Membrane-bound sacs: Lysosomes are enclosed by a single membrane, keeping their powerful enzymes separate from the rest of the cell.

* Hydrolytic enzymes: These are enzymes that break down molecules by adding water. Lysosomes contain a variety of hydrolytic enzymes, such as proteases (break down proteins), nucleases (break down nucleic acids), lipases (break down fats), and glycosidases (break down carbohydrates).

* Digest complex organelle molecules: When organelles become old or damaged, they are engulfed by lysosomes. The hydrolytic enzymes break down the complex molecules within these organelles into simpler molecules that can be reused by the cell.

In essence, lysosomes are like the cell's recycling center and garbage disposal, breaking down waste products and old organelles to maintain cellular health.