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Why are Xylem and Phloem called Complex Tissues?

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  • Last Updated : 22 Aug, 2022
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The anatomy of flowering plants includes the organisation of cells and tissues within the bodies of flowering plants. Tissues are formed by a group of cells to perform a function., Plant tissues are classified into two types based on their ability to divide. They are Merismatic and permanent tissue.

Merismatic tissue

This is the simple tissue that has the ability to continuous cell division. In this type of tissue, growth occurs in the roots and shoot tips of the plant. Based on the region of meristematic tissue in the plant body, we can group the meristems into three types. They are:

  • Apical Meristems – These meristems are situated at the tips of roots and shoots.
  • Intercalary Meristems – The intercalary meristems are situated at the internodes or the foundation of the leaves.
  • Lateral Meristems – These are available on the lateral side of the stem and foundation of a plant.

Permanent tissue

These tissues are derived from the merismatic tissues and have lost their capacity to divide. This type of tissue can be found in mature plants. They are classified into two types- Simple and complex tissue

Simple tissue: This is also called homogeneous tissue which consists of a single type of cells. Simple tissues are of three types which are parenchyma, collenchyma and sclerenchyma.

  • Parenchyma: These tissues are found in the delicate pieces of a plant like the roots, stems, leaves, and blossoms. The cells of this tissue contain huge intercellular spaces between them. Every cell has a vacuole in the middle. The functions of parenchyma tissues are photosynthesis, storage and assisting the plant with drifting on the water.
  • Collenchyma: Collenchyma is like parenchyma cells that contain oval, round, or polygonal cells with thick walls. The thickness of the walls is due to pectin, cellulose and hemicellulose. They are intended to offer mechanical help to the plant structure in parts like the petiole of the leaf.
  • Sclerenchyma-The cells of this tissue are dead. This type of cell lacks a nucleus and cytoplasm. Their cell walls are thickened by lignin and cellulose. Their principal capability is to give mechanical strength to parts of the mature plant.

Complex Tissue

 

This type of tissue is also known as heterogeneous tissue which consists of different kinds of cells and these differentiated types of cells are coordinated to perform a function. Complex tissues are of two types which are xylem and phloem.

Xylem (water-conducting tissue) 

Xylem is framed by tracheary components like tracheids and vessels transcendently. Essential xylem begins from the procambium during essential development while optional xylem has its starting point in the vascular cambium during auxiliary development. It is found in a deep layer of plants which is made up of trachea, xylem fibres, tracheids and xylem parenchyma. Tracheids and vessels are cylindrical designs. This permits them to in an upward direction (vertically) transport water and minerals. The essential capability of the xylem is to move water from roots to stems and leaves, however, it additionally ships supplements. It also provides mechanical strength to plants. Xylem tissues are tubular-shaped structures, with the absence of cross walls. This tissue resembles the shape of a star. Xylem fibres are smaller and are located in the centre of vascular bundles. Xylem fibres are present in roots, stems and leaves. It is responsible for replacing the total amount of lost water molecules through transpiration and photosynthesis.

Phloem (Food conducting tissue)

Phloem begins from meristematic cells in vascular cambium-essential phloem from the apical meristem and optional phloem from vascular cambium. It is found in the outer layers of the plant, which is made up of companion cells, phloem parenchyma, phloem fibres, sieve cells and sieve tubes. Unlike the xylem, the phloem moves in both directions. It is responsible for transporting food from the leaves to the other parts of the plant. It does not provide mechanical strength to plants. Phloem fibres are larger and are located on the outer side of vascular bundles. They are present in stems and leaves, which later transport and grow in roots, fruits and seeds. It is responsible for transporting proteins and mRNAs throughout the plant.

Characteristics of Xylem and Phloem

Xylem and Phloem

 

Phloem and xylem are complex tissues that perform the transportation of food and water to the parts of plants. They are vascular tissues of the plant. 

Characteristics

Xylem

Phloem

Structure Tubular shape with no cross walls which allows a continuous column of water and facilitates rapid transport within the xylem vessels. There are two types, protoxylem and metaxylem depending on the pattern of lignin. Elongated, tubular shape with thin-walled sieve tubes. The sieve tubes have pores at each end in the cross walls and microtubules that extend between sieve elements allowing the longitudinal flow of material.
Elements Xylem comprises xylem vessels, fibre and tracheids. Xylem comprises xylem phloem fibres, sieve tubes, sieve cells, phloem parenchyma and companion cells.
Shape Xylem is star-shaped. Phloem is not star-shaped.
Location It is located in the centre of the vascular bundle, deep in the plant. It is located on the outer side of the vascular bundle.
Movement Movement is unidirectional. Movement is bidirectional.
Functions It provides mechanical strength and responsible for transporting water and other nutrients to the plants. It does not provide mechanical strength and Phloem is living tissue, responsible for transporting food and other organic materials.
Nature of tissue Xylem consists of dead cells (parenchyma is the only living cells present in the xylem). Xylem constitutes the bulk of the plant body. Phloem contains living cells (fibres are the only dead cells in the phloem). It forms a small part of the plant body.

Frequently Asked Questions

Question 1: Why is xylem known as water-conducting tissue?

Answer:

Xylem is called water conduction tissue since it transports water molecules from the roots to the parts of the plants.

Question 2: Why is phloem known as food conducting tissue?

Answer:

Phloem is called food conducting tissue since it transports food and nutrients from leaves to other parts of the plant.

Question 3: What are the complex tissues and types of complex tissue?

Answer:

Complex tissue is a heterogeneous tissue which involves more than one type of cells and these various types of cells are combined to work for a specific function. Hence they are called vascular tissues. They transport water and food to the parts of plants. Complex tissue is classified as xylem and phloem.

Question 4: What are the characteristics of xylem and phloem?

Answer:

  • Xylem: The essential capability of the xylem is to move water from roots to stems and leaves, however, it additionally ships supplements. It also provides mechanical strength to plants. Xylem tissues are tubular-shaped structures, with the absence of cross walls. This tissue resembles the shape of a star. Xylem fibres are smaller and are located in the centre of vascular bundles. Xylem fibres are present in roots, stems and leaves. It is responsible for replacing the total amount of lost water molecules through transpiration and photosynthesis.
  • Phloem: It is responsible for transporting food from the leaves to the other parts of the plant. It does not provide mechanical strength to plants. Phloem fibres are larger which are located on the outer side of vascular bundles. They are present in stems and leaves, which later transport and grow in roots, fruits and seeds. It is responsible for transporting proteins and mRNAs throughout the plant.

Question 5: What are the functions of xylem and phloem?

Answer:

Xylem and phloem work with the transportation of water, minerals and food all through the plant. Xylem transports water and minerals from the roots to the leaves. Though, phloem conveys the food arranged by the passes on to various pieces of the plant.


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