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What is phloem and its function

In this article we want to talk to you about another of the important plant tissues for the correct development of plants. As with the xylem, the phloem is a conductive tissue responsible for transporting beneficial substances for the plant organism. The origin of the word phloem, as well as its meaning comes from the Greek word “phloios”, which translates as “bark”. From this word the famous botanist Karl Wilhem von Nageli coined the term phloem to define one of the main conductive tissues of vascular plants in 1873.

Thus, in this AgroCorrn text we are going to teach you everything you need to know about this plant tissue, since it is formed, what the phloem transports and what is its main function within the vegetative system.

You may also be interested in: What is the xylem and its function

What is phloem

The phloem is in charge of achieving the transfer of nutrients produced in the aerial part of the plant or photosynthetic sector until it reaches the root of the individual. Hence, its main function is to transport and distribute the sap produced throughout the plant for its management, absorption and storage. Phloem, also called bast or sieve tissue , is made up of plant cells without nuclei capable of forming walls through which nutrients can be conducted.

  • Parenchymal cells: these types of cells, although not very specialized, are found in voluble amounts in the primary and secondary phloem. Its main function is to ensure the translation of the sieving compounds that transport the sugar, in addition to storing other substances such as oils and tannins.
  • Sieve tubes: they are individual cells with a flattened appearance and that have longitudinal rows that communicate with the sieve plates located on the terminal walls. They are typical of plants belonging to the group of angiosperms. The sieve plates have pores that go through the wall completely and thus facilitate communication with the sieve tubes as well as with the parenchymal cells, very specialized cells.

In the same way, as we have already mentioned above, we can distinguish two types of phloem :

Primary phloem

It is the one that begins in the procambium or primary meristem. This is divided into two sections: the protofloem and the metaphloem. The protofloem appears in certain areas of the plants that are in the growth stage while the metaphloem appears after the maturation process.

Secondary phloem

This is formed in the cambium. This is located just at the end of the stem or root of the plant and is made up of cells arranged in two routes, both axial and radial, of 90 degrees. The axial ones are upright and parallel in the central area and are made up of cribrotic units and parenchymal cells. Radials are grouped in rays perpendicular to the axis and are also made up of parenchymal cells, although they lack secretory ducts.

Phloem function

Phloem is the vascular tissue responsible for transporting the resulting sugars and nutrients after photosynthesis . Once the raw sap has been converted into processed sap , the phloem transports it through all the organs of the plant, starting from the leaves to the root, so that these are consumed or stored according to the needs of the plant. We recommend you to know better what sap is, its types and functions with this other post.

This process carried out by the phloem is also known as translocation. This occurs when the sugars that have accumulated during the development of the plant are transported to the so-called meristems, which are another type of plant tissue in charge of developing new cells to increase and improve the development of the plant. This process usually occurs especially during spring, which is the time of year when the plants are most active.

Difference between xylem and phloem

We have created a list of the main differences between xylem and phloem . The main idea is that after having a good understanding of the function of this type of plant tissue, you will be able to learn to differentiate them by following this small list:

  • The phloem is the order to transport the processed sap, which is the result after the photosynthesis process carried out by the plant, while the xylem is the conductive tissue that transports the raw sap for its transformation into processed sap.
  • The phloem’s main function is to transport the nutrients necessary for the optimal development of the plant, while the xylem is mainly responsible for transporting water and mineral salts.
  • The phloem transport system works bi-directionally, transporting nutrients throughout the plant. In the case of xylem, this is unidirectional.
  • The phloem transports the nutrients from the leaves to the roots, to later carry the necessary substances back to the whole plant. However, the xylem only transports from the roots to the leaves.
  • Finally, the phloem is made up of a series of cells that make up a soft cell wall, while the xylem is made up of lignified cell walls.

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