Here's why:

* Vacuoles are membrane-bound organelles that can take up a large portion of a plant cell's volume. They can store water, nutrients, and waste products.

* Other large structures like the nucleus, chloroplasts (in plant cells), and mitochondria are also significant, but typically occupy less space than a large vacuole.

* Animal cells generally have smaller vacuoles compared to plant cells, but they still contribute to the overall cell structure.

Therefore, while the specific size of a vacuole varies depending on the cell type, it is generally considered the largest cell structure.