Xylem and Phloem - Transport in Plants Transport in Plants Every cell in our body needs many different substances to function properly. For example, glucose and oxygen. But the cells cannot obtain the substances directly from outside. Therefore, they rely on the circulatory system to carry these substances from the body part that provides them, like lungs and small intestine, to all the body cells in need. In plants, vital substances like water and minerals are provided by the soil and are absorbed via the root, while the glucose is produced in the leaf during photosynthesis. The vascular tissue allows the substances to move from certain parts of the plant to the others. The two main vascular tissues in plants are the xylem and phloem. If you've ever seen a fallen tree and take a closer look inside, almost all of its radial contents, consisting of heartwood and sapwood, are actually xylem tissues and the inner part of its bark is the phloem. Xylem Xylem is responsible for distributing water and minerals taken by the roots. An interesting fact about xylem is that some parts of it do not have protoplasms or cell walls, allowing water and minerals to pass easily. Xylem consists of tracheids or conducting cells, vessels, fiber, and parenchyma. The water in tracheids does not flow continuously, the roots and leaves are connected through a series of tracheid cells with pitted walls. In contrast, the xylem vessels are long, wider, hollow tubes continuously stretching from the roots to the leaves. The fiber cells function mainly as supporting structures, and the parenchyma, the only living cells of the xylem, help with the food storage. The xylem cells are strengthened by a substance called lignin. The pattern of lignin will vary depending on the location. It can be a ring pattern, spiral, reticulate, or pitted. Phloem The phloem transports manufactured food like sucrose and amino acids from the green parts of the plant like leaves, to other parts of the plant. The process is called translocation. Phloem consists of sieve tubes, companion cells, fiber, and parenchyma. A sieve tube consists of a single row of elongated, thin-walled cells. Just like the name suggests, it has walls perforated by minute pores like a sieve. A mature sieve cell has a thin layer of cytoplasm which conducts manufactured food from one cell to another. The sieve tube cell has a degenerated protoplasm which means that it needs another to carry out its vital processes. This is why a sieve tube cell has a companion cell. The companion cell has everything that the sieve tube doesn’t, such as abundant cytoplasm and nucleus. It has an extremely thin but flexible cell wall so that there’s no hassle in keeping the sieve tube cell alive. Just like in the xylem, the fiber cell helps to give structural support, and the parenchyma stores the food and other substances. In phloem, the fiber cells are the only type of cell that is dead. Arrangement of Vascular Tissue The vascular tissue has different arrangements in various parts of the plants. In the root of herbaceous dicot plants, the xylem forms an x-like shape in the middle, while phloem fills around the xylem. The xylem and phloem in the stem are clustered into circular shapes. These clusters are located near the edge of the stem. While in leaf, the xylem and phloem are located in the vascular bundle with the xylem positioned above the phloem.