Here's why:

* Plant cells can be quite large, with some reaching up to 100 micrometers in diameter. They have a rigid cell wall made of cellulose, which provides structural support and allows them to grow to significant sizes.

* Animal cells are generally smaller than plant cells, ranging from 10 to 30 micrometers in diameter. They lack a cell wall, so their size is limited by the flexibility of their cell membrane.

* Bacterial cells are the smallest of the three, typically ranging from 0.5 to 10 micrometers in diameter. They are single-celled organisms and have a simple structure compared to plant and animal cells.

So, in terms of size, the order is:

1. Plant cells (largest)

2. Animal cells

3. Bacterial cells (smallest)