Distinguish between Xylem and Phloem :
Xylem and phloem are two different types of vascular plant tissues and both are completely different from each other. In this article we explain all their difference between xylem and phloem so that you can distinguish them perfectly in your preparation. Before starting lets know about concepts and similarities of xylem and phloem.
Xylem is part of the vascular wall. On the other hand, the phloem is the second part of the vascular tissue and is soft-walled. In addition, the xylem transports water and minerals, and the phloem transports food and nutrients. We can think of this as the key difference between xylem and phloem. In addition, xylem movement is one-way, and phloem movement is two-way. However, both xylem and phloem are complex tissues composed of several cell types.
Defination of Xylem :
Xylem is a tubular plant tissue that transports water and dissolved minerals from the roots to other parts of the plant body. The xylem runs next to the phloem in the vascular bundle and also runs longitudinally from the root to the stem and leaves. Structurally, the xylem is a collection of several different cell types. In addition, after in-depth analysis, we can see that the xylem is composed of the following cells: blood vessels, trachea, xylem fibers and parenchyma.
Definition of Phloem :
Phloem is a tubular plant tissue that conducts food from the photosynthetic part of the plant to other parts of the plant. It is conducive to the two-way movement of food. Structurally, it includes three main types of cells, namely sieve cells, companion cells and phloem parenchyma. Unlike the xylem, the phloem does not have a lignified cell wall. Instead, all cells have a soft cell wall. In addition, the cells are surviving. In the vascular bundle, the phloem occurs outside the vascular bundle.
What are the similarities between xylem and phloem?
- Phloem and xylem are closely connected, usually adjacent to each other.
- Moreover, they together form a vascular bundle.
- Both are tubular structures.
- In addition, they are complex organizations
- Both are made up of different types of cells.
- The xylem and phloem are responsible for transporting substances throughout the plant.
- They carry nutrients for plants.
- Both Found in plants and play role in photosynthesis.
- Both have conductive tubes that help transport nutrients, sugars etc.
Differentiate between Xylem and Phloem :
|Xylem is the complex tissue of plants, responsible for transporting water and other nutrients to the plants.||Phloem is living tissue, responsible for transporting food and other organic materials.|
|It helps to carry water from roots to leaves.||It helps to carry food from the leaves to growing organs and also to the storage organs.|
|Xylem is located in the centre of the vascular bundle, deep in the plant.||Phloem is located on the outer side of the vascular bundle.|
|The cell wall of xylem is thick and made up of lignin.||The cell wall of phloem is thin. made up of cellulose.|
|It is usually made up of dead cells.||It is usually made up of living cells.|
|Their movement is unidirectional.||Their movement is bidirectional.|
|It helps in the passive transport of water.||It helps in the active transport of sugar and food.|
|Xylem transports only minerals and waters from the roots||Phloem transports food materials that are prepared by the green parts of the plants to other parts of the plant.|
|Provide mechanical support||Does not provide mechanical support.|
|Xylem fibres are smaller.||Phloem fibres are larger.|
|They are present in roots, stems and leaves.||They are present in stems and leaves, which later transports and grow in roots, fruits and seeds.|
|The total amount of xylem tissue is more.||The total amount of phloem tissue is less.|
|Forms vascular bundles with phloem.||Forms vascular bundles with xylem.|
|It consists of tracheids, vessel elements, xylem parenchyma, xylem sclerenchyma and xylem fibres.||It consists of four elements: companion cells, sieve tubes, bast fibres, phloem fibres, intermediary cells and the phloem parenchyma.|
|Xylem constitutes mostly the bulk of the body of the plant||Phloem constitutes a small part of the body of the plant|
|It is responsible for replacing the total amount of lost water molecules through transpiration and photosynthesis.||It is responsible for transporting proteins and mRNAs throughout the plant.|
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What is Xylem ?
- Xylem is the transport system of vascular plants. It is responsible for transporting the water absorbed by the roots and the ions dissolved in the water upwards for use by other organs and tissues, and it also supports the plant body.
- Xylem distributed in root and stem. In Root xylem has Radial (cross-shaped) arrangement, which can enhance the pulling force of the root.
- In Stem xylem can resist wind pressure. Monocotyledonous plants are scattered on the stem along with vascular bundles. Dicotyledonous plants are arranged in a ring with vascular bundles in the stem.
- During the primary growth and differentiation of vascular plants, the xylem differentiated from the protocambium is called primary xylem which contains fibers and parenchyma cells but no rays so it does not constitute an axial system or a radial system.
- In stems, leaves, flowers and other parts, the primary xylem and primary phloem are combined into bundles which are called vascular bundles.
- There is parenchyma between the vascular bundles of the stem, which is called the medullary ray.
- In the root the primary xylem forms a core in the center, which is pithed or not pithed.
- According to the time of differentiation, the primary xylem can be divided into two parts: the primary xylem and the epigenetic xylem. Xylem is composed of vessels, tracheids, wood fibers, and parenchyma cells.
Vessels : It exists in most angiosperms, gymnosperms, and some ferns the upper and lower cell walls are perforated and connected to each other, so the liquid flows faster in them than in tracheids. Each vessel cell is called a vessel molecule. The ductal cells in the early stage of growth are living cells, but when they mature, the cytoplasm is dissociated, the cells die and the cell walls are lignified. In the process of lignification, pits appear in the cell wall. Through the pits water can flow laterally. From an evolutionary point of view the ducts are developed from primitive tracheids. But it doesn’t have the support function like tracheids. The supporting function is assumed by another structure developed from primitive tracheids, namely wood fiber.
Tracheids : In few angiosperms, gymnosperms and ferns only tracheids are present while in most angiosperms they contain both vessel and tracheids. Tracheid cells are in fusiform structure it means ends are tapered and the middle is enlarged. Its life history is similar to that of a duct. At first it was a living cell and then the cytoplasm was dissociated and the cell died. The cell wall will also thicken with wood and pits appear and the pit membrane is highly permeable. Gymnosperms have typical contiguous pits. The flow of water can be adjusted by the movement of the pit plug. In more primitive plants, tracheids have transport and support functions.
Wood fiber : The fiber cells in the xylem mainly perform supporting functions and usually appear in bundles which are called xylary fibers. The source of its evolution also comes from tracheids. Wood fibers are long, thick-walled tissue cells withtapering ends, generally with lignified secondary walls, which are often thicker than tracheal walls. It mainly plays a supporting role in plants. Wood fibers can be divided into two types: fiber tracheids and tough fibers. The former are fibrous tracheids, generally with thickened secondary walls, with lenticular pores with biconvex or crack-like openings on the wall. The latter is longer and thicker than the former with single pits on the wall. Both fibers can be separated. Separating wood fibers are widely present in dicotyledonous plants, and in mature sapwood, protoplasts remain, which play a role in storing nutrients.
Parenchyma cells : In the xylem parenchyma cells are of two types Axial and Radial. Longitudinal parenchyma cells are mixed between fibroblasts and tube cells, and the size of a single cell is about equal to or smaller than tracheids. The horizontal parenchyma cells are called ray parenchyma (ray parenchyma) in the xylem. They contain starch granules and crystals and can be used for storage.
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What is Phloem?
- Phloem and xylem transport water together form the vascular system. The phloem is composed of sieve tubes, sieve cells, companion cells, phloem fibers and parenchyma cells.
- The sieve tube is formed by connecting the tops of a series of sieve tube molecules. The young sieve tube molecules have cytoplasm, nucleus and various organelles; after maturation, the nucleus disintegrates, the vacuole membrane disappears, and the cytoplasm merges with the cell fluid.
- There are many small holes on the transverse wall connecting the molecules of the sieve tube, called sieve holes; the end wall with sieve holes is called the sieve plate. The sieve holes are often distributed in groups to form a sieve domain, and adjacent sieve tube molecules communicate through protoplasmic filaments, which is beneficial to the transportation of materials.
- On one side of the sieve tube molecule, there are one or several cells associated with each other, called companion cells. Companion cells are also living cells, with thick cytoplasm and obvious nuclei.
- The sieve tube molecule and its neighboring companion cells are connected by many plasmodesmata.
- Sieve cells are the cells in ferns and gymnosperms that are mainly responsible for transporting nutrients. The cell structure is similar to the sieve tube molecule, but the sieve cell is a single cell, and the sieve cells are connected by the sieve domain on the side wall without the formation of a sieve plate.
- Phloem fiber is the mechanical tissue in the phloem. A single fiber is long and prismatic, with sharp ends. The cell wall is strongly thickened, and most of it is lignified, and the cells die after maturation.
- The parenchyma cells of the phloem often contain starch, alkaloids, tannins, crystals, etc., and have multiple functions such as storage, synthesis, and secretion.
- The phloem parenchyma cells of some plants differentiate into secretory structures such as secretory cells, secretory tracts or milk organs, such as the eucommia capsule in the phloem of eucommia ulmoides and the milk organ in the hevea.
- According to different sources, phloem can be divided into primary phloem and secondary phloem.
- The primordial phloem is the primary phloem which is differentiated from the meristem at the top of the root or stem. The roots and stems of gymnosperms and most dicotyledonous plants are produced by dividing the vascular cambium outwards during the secondary growth process and are a part of the bark.
- The main function of the phloem is to transport organic matter, that is, to transport the photosynthetic products formed in the leaves to various parts of the plant.
- The material transported in the sieve molecules is mainly sugar, which accounts for about 90 % of the dry mattermainly sucrose. In addition, there are proteins, amino acids, vitamins, inorganic salts and plant hormones.