Xylem & Phloem

What Is The Xylem and Phloem!

Similar to humans, plants also have their own circulatory system that facilitates their growth. The main parts of this circulatory system are called Xylem and Phloem. Plants (and trees) have a top and a bottom portion. The top portion consists of trunk, branch and leaves, and the bottom portion is a system of roots. The top portion conducts photosynthesis and helps the plant reproduce, whereas, the lower portion keeps the plant steady and consumes moisture and nutrients from the soil. Both the portions are dependent on each other for survival, and need to be connected. Xylem and Phloem are responsible for making this connection.

What Does The Xylem and Phloem Do?

Xylem and Phloem are two types of vascular tissues which are considered as the transport system in plants. They are responsible for moving materials such as food, water, nutrients and other minerals around the plant body (between the roots, stems and leaves). Xylem and Phloem are found in groups called vascular bundles and work together as a unit. The vascular bundles connect tissues in the roots, stems and leaves, and also provides structural support to the plant. Xylem vessels are tough and are made of complex, dead and permanent tissues, whereas Phloem vessels are soft and are made up of living cells. Xylem vessels are composed of dead tissue at maturity which makes the vessels hollow with no cell contents. Phloem vessels are composed of living tissue, but sieve tube elements lack nuclei and have few organelles. Xylem’s movement is unidirectional. They only move upwards. The movement of Phloem is bidirectional. They move both upwards and downwards. While the basic function of Xylem is to transport water from roots to stems and leaves, it also transports nutrients. On the other hand, Phloem transports photosynthates (soluble organic compounds made during photosynthesis) and amino acids to those parts of the plant where it is needed.

Apart from these, there are some other evident differences between Xylem and Phloem. The structure of Xylem tissues is similar to that of a star. They are tubular shaped and has no cross walls. Phloem tissues are also tubular shaped but are elongated. They also have thin sieve tubes with walls. The vessel wall of Xylem consists of fused cells that build a continuous tube for uninterrupted flow of materials. The vessel wall of Phloem has cells that are connected at the transverse ends to create porous sieve plates, which functions as cross walls. The fibers in Xylem are smaller, and larger in Phloem. Xylem consists of xylem parenchyma, xylem sclerenchyma, xylem fibers, tracheids, and vessel elements. Phloem consists of sieve tubes, phloem fibers, bastfibers, phloem parenchyma, companion cells, and intermediary cells. Xylem occupies the center (or inner portion) of the vascular bundles, and Phloem is located on the outer side of the vascular bundles. Xylem moves materials through the process of transpiration, and Phloem moves materials around the plant through the process of translocation. Xylem gives mechanical strength to plant and helps in making the stem strong. Phloem transfers the synthesized sugars, especially sucrose, made through photosynthesis, to storage organs such as roots, bulbs and tubes. Xylem lives with hollow dead cells, and Phloem lives with cytoplasm within the nucleus. The total amount of Xylem tissue is more in comparison to Phloem. Xylem replaces the total amount of lost water molecules through transpiration and photosynthesis, and Phloem transports proteins and mRNAs all over the plant.