The correct answer is option 4, the stem. The stem is the part of a plant that conducts water. It acts as a pipeline, transporting water and nutrients from the roots to the other parts of the plant, such as the leaves, flowers, and fruits. The stem contains vascular tissues called xylem and phloem, which are responsible for the transport of water and nutrients. The xylem carries water and minerals from the roots upward to the leaves, while the phloem transports sugars and other organic compounds from the leaves to other parts of the plant. The stem also provides support and structure to the plant, allowing it to stand upright and reach towards the sunlight for photosynthesis.