Which plant organ transports substances up and down the plant?

Final answer: The xylem and phloem are the plant organs that transport substances within a plant. Xylem moves water and minerals from roots to leaves, while phloem carries organic molecules like sugars throughout the plant. Explanation: The plant organs responsible for transporting substances up and down the plant are the xylem and phloem. These two types of tissue are part of the plant's vascular system and play crucial roles in transport. The xylem primarily carries water and dissolved minerals absorbed from the soil by the roots up to the leaves. On the contrary, the phloem moves sugars, proteins, and other organic molecules produced through photosynthesis from the leaves to the rest of the plant. This movement can be in any direction, catering to the plant's needs, and is made possible by the structure of the phloem's sieve tube members, which are composed of elongated cells with pores at their ends.