Bacteria do not have a circulatory system like animals do. They are single-celled organisms and rely on diffusion to transport nutrients and waste products.

Here's why:

* Small size: Bacteria are incredibly small, meaning the distance for substances to travel within the cell is very short. This makes diffusion an efficient way to move materials.

* High surface area to volume ratio: The small size of bacteria means they have a large surface area relative to their volume. This allows for efficient exchange of materials across their cell membrane.

* No specialized cells: Bacteria lack specialized cells for transport, such as blood cells or vessels, that are found in animals.

Therefore, bacteria rely on the simple process of diffusion to move nutrients and waste products throughout their single cell.