BlogNCERTImportant Topic Of Biology: Phloem Transport

Important Topic Of Biology: Phloem Transport

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    The sugar produced from sources, such as leaves, needs to be delivered to the growing parts of the plant through the phloem by a process called translocation, or the flow of the sugar. Photosynthates from the source is usually transported to a nearby sink using phloem filter tube elements.


    Groups of cells are found to have the same structure and work together to perform a specific function called tissue. The word tissue is derived from a verb meaning “weave” which is a form of the old French language. In animals, there are four distinct types of tissues such as connective tissue, muscle tissue, nerve tissue, and epithelial tissue.

    What is Phloem Tissue?

    Complex tissue acting as a transport system found in vascular plants transporting soluble organic compounds, mentioned above, the definition of phloem.

    Plant-derived nutrients in plants are made from living tissues that use turgor pressure and energy in the form of ATP to transport sugar to plant organs such as fruits, flowers, shoots, and roots. Another element that makes up the system of transporting arterial plants, the xylem, carries water and minerals from the root to the various parts of the plant.

    Components of Phloem Tissue

    Phloem tissue is made up of several different components. Each of these components performs functions in a cooperative manner, these functions include facilitating the processing of sugars and amino acids, from source tissues to sink tissues where they are consumed or stored. The elements of phloem are as follows;

    Sieve Elements

    The filter elements are expanded and small cells are connected together to form the phloem filter tube structure. They are considered to be the most specialised types of cells found in plants. These elements have no nucleus in maturation and are deficient in organelles such as ribosomes, cytosol, and Golgi apparatus, in order to increase the available space for transfer.

    There are two main types of filter elements: both are found in the normal mother cell form.

    1. Sieve Member: Found in angiosperms.
    2. Sieve Cells: These are associated with gymnosperms.

    Sieve Plates

    The filter plates are located between the cells of the filter members, which is a modified plasmodesma. Larger and smaller in structure, these are areas of pores that help facilitate the exchange of substances between the cells of the element.

    If the phloem is cut or damaged then in preventing loss of fluid the filter plates also act as a barrier, usually by an insect or herbivorous animal. After injury, a unique protein called “Phloem-protein or P-protein”, built into the sieve element is removed from its anchor site and collected to form a ‘breakdown’. These particles are located in the holes of the sieve plate which helps to prevent the loss of milk in the area of ​​damage.

    In gymnosperms, filter elements have much older features compared to angiosperms. They have many holes in the sharp end of the cell walls instead of the filter plates so that the material passes through it directly.

    Companion Cells

    Each sieve element cell is closely related to the ‘partner cell’ in angiosperms and the ‘Strasburger cell’ or albuminous cell in gymnosperms. Friendly cells contain the nucleus, which is packed with dense cytoplasm. The cytoplasm is made up of many ribosomes and mitochondria. For this reason, parallel cells are responsible for triggering metabolic reactions and other cellular functions. A feature of the filter is the lack of proper organelles as a result of which these elements cannot participate in the metabolic reaction process as they do not contain the proper organelles. With function and life, the features of the filter depend on or require compatible cells.

    The filter tube and companion cells are connected by a plasmodesma, a small channel that connects the cytoplasm of cells, allowing the transfer of sucrose, proteins, and other molecules to the filters. The transport of material around the plant and immersion tissue is carried out by parallel cells, and it helps to load the filter tubes with photosynthesis products, and the loaded products are dumped into the sink tissues.

    Phloem Parenchyma

    Parenchyma is a group of cells, which form the ‘filling’ of plant tissues. They have small, flexible walls made of cellulose. The main function of the existing parenchyma in the phloem is to store starch, fats, and proteins, and in the case of other plants, which help retain tannins and resins as well.

    Phloem Sclerenchyma

    The sclerenchyma is the main phloem tissue that provides support, firmness, and strength to the plant. Sclerenchyma comes in two forms: fibers and sclereids; both usually die as they reach maturity and are reflected in the second layer of the cell wall.

    Bast fibers provide strong strength support while allowing phloem flexibility. Small, long cells where the walls contain thick cellulose, hemicellulose, lignin, and a small lumen.

    Sclereids are short, irregular cells that help increase the pressure on the phloem but limit flexibility. Sclereids act as herbivory protection measures by creating a gritty texture when chewed.

    Phloem, also known as bast, is a plant tissue that transports nutrients from leaves to another plant. Phloem tubes, friendly cells, phloem fibers, and phloem parenchyma cells are all special types of cells found in the phloem.

    Apical meristems (areas of new cell production) of roots and germination tips form the main phloem, which may be a protophloem or metaphloem, depending on whether the cells mature before or after the extension (growth) of the source. Protophloem tube tubes cannot stretch and stretch tissues, and as the plant ages, they are torn apart and destroyed. Different types of phloem cells may be converted into fibers. In cambium-containing plants, the later matured metaphloem is not destroyed and can function for the entire plant life, but is replaced by the second phloem.

    The food supplies flow through a filter tube, which is a line of filter cells with a filter-like section with holes in the sidewalls or ends walls.

    Metastatic and marginal parenchymal cells, also called phloem parenchyma, are found in the small branches and at the ends of the arteries, which also play a role in supplying food.

    Phloem fibers are long, flexible cells that make up soft fibers used commercially (such as flax and hemp).

    Phloem is a biological tissue of plants with arteries that carry photosynthesis, a soluble organism produced during photosynthesis, to various plant parts. Translocation is the name of this type of transport. Since the phloem is the deepest layer of bark, the name comes from the ancient Greek word o (phloiós), meaning “bark”. Carl Nägeli first coined the term 1858.

    Definition of translocation in plants

    Translocation is a biological process that involves the transfer of water and other soluble nutrients from one part of a plant to another by xylem and phloem, which are found in all plants.

    • The transport of the product of soluble photosynthesis or food from the leaves to other parts of plants is called translocation.
    • Feeding cells reach the phloem component called the filter tubes, for transplantation, when they have transported up or down all parts of the plant, such as the roots.
    • Transport is done using ATP energy which provides the osmotic pressure needed for food to move up and down.

    Also read: Important Topic Of Biology: Plant Growth Rate


    Q. Describe the phloem. What are the characteristics of phloem?

    Ans: Phloem is a complex tissue that acts as a transport system, which is often found in vascular plants to transport soluble organic compounds.

    The components of phloem tissue are:

    • Sieve the elements
    • Sieve plates
    • Friendly cells
    • Phloem parenchyma
    • Phloem sclerenchyma

    Q. What is phloem?

    Ans: The phloem of the vascular plant is responsible for transporting and distributing the sugar produced by photosynthesis. Phloem can be found in the outer part of the root cylinders, the stem of the vascular bundles, and the abaxial region of each leaf outlet because the plant is continuous. Although the most common arrangement is for the phloem to be free of xylem at the roots and stems and abaxial in the leaves, there are significant tax-specific variations. Internal or intraxylary phloem is the phloem present within.

    Q. What is the difference between xylem and phloem, and how do you distinguish them?

    Ans: Xylem and Phloem are two types of vascular tissue that play a key role in the transport process. These tissues form a mass circulatory system that works as a whole. Xylem movement is not straightforward, but phloem movement is double-directed.

    Sr. No. Xylem Sr. No. Phloem
    1 The tubular structure of the xylem tissue does not have cross walls. This tissue has the appearance of a star. 1 Phloem tissue is an expanded structure with a small filter tube on the wall.
    2 It is located in the center of the vascular bundle. 2 It is located on the outer edge of a number of arteries.
    3 Xylem fibers are smaller than ectoderm fibers. 3 Fibers in larger phloem.
    4 It can be found in the roots, stems, and leaves of plants. 4 They are found in stems and leaves and then go to the roots, fruits, and seeds, where they grow.
    5 It provides the plant with mechanical strength and resources to strengthen the stem. 5 It is responsible for transporting proteins and mRNAs throughout the plant.


    Q. What are the components of phloem?

    Ans: The filter tubes, the corresponding cells, the phloem fibers, and the phloem parenchyma are the four main components that make up the phloem.

    (i) Filter tubes: These are tubular cells with perforated holes. Diet and nutrient transfer are the responsibility of these cells.

    (ii) Companion cells: These cells are located near the filter tubes and connected to them through holes. The walls of these cells are long, thin, and thin. These are living cells.

    (iii) Phloem fibers: These fibers have thick cell walls, and mechanically support the plant.

    (iv) Phloem parenchyma: These living cells are usually cylindrical.

    Transport refers to the movement of food from the leaves to other regions of the plant.

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