The word "stem" can refer to several things, so it's important to be specific about which stem you're asking about. Here are a few possibilities:

1. Plant Stem:

The stem of a plant transports water and nutrients throughout the plant. This happens through two main systems:

* Xylem: This system carries water and dissolved minerals upwards from the roots to the leaves and other parts of the plant.

* Phloem: This system carries sugars (produced through photosynthesis in the leaves) downwards to the roots and other parts of the plant for storage or use.

2. Human/Animal Stem Cells:

Stem cells are unspecialized cells that have the potential to differentiate into various types of cells. They are not specifically responsible for transporting anything. However, their role in development and repair means they are essential for the transportation of nutrients and other substances within tissues and organs.

3. Stem of a Pipe or Tube:

This refers to the central part of a pipe or tube. It doesn't transport anything directly, but its shape and structure are essential for the flow of whatever substance is being transported through the pipe or tube.

Please clarify which "stem" you're referring to so I can give you a more specific and accurate answer.