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Tissues and its types

Introduction:

  • Tissues are made up of a group of cells that work together performing a specific function and have originated from the same source.
  • Tissues play a vital role in controlling various physiological activities.
  • In plants, these tissues are generally divided into certain groups on the basis of cell division. These groups are meristematic tissues and permanent tissues.
  • Tissues can also be classified on the basis of constituting cells, i.e. xylem, phloem.

Topics covered:

  • Tissues and its types on basis of cell division
  • Tissues on basis of constituting cells

Tissues and its types on basis of cell division
 

Detailed explanation:

A. Meristematic tissues

  • Meristematic tissues comprise special kinds of cells called meristematic cells that have the ability to divide endlessly.
  • These cells are found on the meristems or meristematic zones on the plant, these are the regions from which a plant grows.
  • Meristematic zones can be found in shoots known as the shoot apex(shoot apical meristem) or in roots called the root apex (root apical meristem).
  • Vascular cambium is also made up of meristematic cells but these are much later formed meristems.
  • These are found in between the xylem and phloem layers.
  • These are responsible for the secondary growth in higher plants.


    meristematic-tissues
     

B. Permanent tissue

  • Permanent tissues are made up of cells that have lost the ability to divide further.
  • Permanent tissues can be grouped into two on the basis of constituting cells:
    i) Simple permanent tissues-The constituting cells are similar and perform a common function, e.g., Parenchyma, collenchyma, sclerenchyma.
    ii) Complex permanent tissues: They are formed by the aggregation of dissimilar cells that performs a common function, e.g., Xylem and Phloem.


    permanent-tissue
     

Tissues on basis of constituting cells


Introduction:

  • Permanent tissues can be differentiated based on their constituting cells.
  • There are two basic kinds of tissues under permanent type tissues on the basis of their constituting cells, i.e., Simple Permanent tissues and Complex permanent tissues.
  • These two types of tissues perform different functions and are present in different regions of the plant body.
  • This differentiation is necessary for area-specific functions and properties of cells these tissues are made of.

Detailed explanation:

A. Simple permanent tissues

  • Simple permanent tissues are such types of tissues that are composed of just a single type of cell that is homogeneous.
  • This type of tissue is majorly found in the construction of organs, epidermal layer, and mechanical support.
  • This tissue forms the basis of a plant body.
  • Simple permanent tissue is differentiated into three further categories based on its function and cellular structure.

i) Parenchyma-

  • Parenchyma tissue is made of cells that are generally spherical, oval, round or elongated in shape.
  • These cells are alive with a living protoplasm and hence carry out functions like photosynthesis, storage and secretion.


    primary-cell-wall
     

ii) Collenchyma(Living mechanical tissue)-

  • Collenchyma tissue is made up of cells that are oval, spherical or polygonal and often with chlorophyll within them.
  • These cells are much thickened at the corners because of cellulose, pectin and hemicellulose deposition.
  • They provide mechanical support and flexibility to the growing parts of the plant like leaf petiole and young stem.
  • There are no intercellular spaces between these cells.
     

collenchyma
 

iii) Sclerenchyma(Dead mechanical tissue)-

  • Sclerenchyma tissue is made up of cells that are usually dead and without protoplasts.
  • These cells are narrow, with thick walls due to lignin deposition.
  • These tissues provide mechanical support to the organs.


    sclerenchyma
     

B. Complex permanent tissues

  • Complex permanent tissues are made up of more than one type of cell, i.e. heterogeneous.
  • These tissues function as conducting tissues and all different types of cells work together as a unit.
  • There are two main types of complex permanent tissues, i.e. Xylem and Phloem.

i) Xylem-

  • Xylem is the conducting tissue responsible for water transport throughout the plant body.
  • This type of tissue is made up of 4 different kinds of cells, i.e. Tracheids, vessels, xylem fibres and xylem parenchyma.
  • All these separate cells have individual functions. And they work together to conduct water from the soil via roots to the stem and the leaves.


    xylem
     

ii) Phloem-

  • Phloem is the conducting tissue that transports food that is synthesized in leaves to other plant parts.
  • This tissue is composed of 4 different kinds of cells, i.e. Sieve tube elements, companion cells, phloem parenchyma and phloem fibres.
  • These cells have to work together to make sure food reaches every part of the plant for the continuation of all physiological processes properly.


    phloem
     

Frequently Asked Questions (FAQs)

Q1. Define permanent tissue.
Ans:
The tissue whose cells have lost the power of division and get differentiated to perform specific functions are called permanent tissues.

Q2. Meristems are responsible for?
Ans:
The cells of the meristematic tissues present in the meristems at certain locations in the plant body show rapid and active cell division which helps in increasing the length and girth of the plant. Due to the presence of meristems, plants show an open type of growth as new cells are continuously added to the plant body.

Q3.Which tissue shows the aggregation of dissimilar cells working together as a unit?
Ans:
Complex permanent tissues are made of dissimilar cells working together in sync to perform a specific function. Xylem being a complex permanent tissue carries water through the plant body from roots to leaves consists of dissimilar cells such as tracheids, vessels, xylem parenchyma and xylem fibres.

Q4. Describe the functions of sclerenchyma?
Ans:
Sclerenchyma is a type of simple permanent tissue. These tissues are responsible for providing mechanical support to the organs of the plants. Sclerenchyma has thick lignified walls that add to the strength and support the organs.

Q5. Which type of tissue cells can perform photosynthesis?
Ans:
Parenchyma cells (mesophyll of leaves) and often collenchyma cells can perform photosynthesis due to the presence of chloroplasts within them.

Q6. What is the main function of permanent tissue in plants?
Ans:
Permanent tissues main functions include protection of the plant body from environmental stress and microbial attack, conduction of water, minerals and food, photosynthesis and storage of food materials.

Q7. Differentiate between simple and complex tissue.
Ans: Simple tissues-

  • Simple permanent tissues are such types of tissues that are composed of just a single type of cell that is homogeneous.
  • This type of tissue is majorly found in the construction of organs, epidermal layer and mechanical support.
  • Example: parenchyma, collenchyma and sclerenchyma

Complex tissues-

  • Complex permanent tissues are made up of more than one type of cell, i.e. heterogeneous.
  • These tissues function as conducting tissues for the translocation of food and water. All different types of cells work together as a unit.
  • Example: Xylem and phloem

Q8. What are the main characteristics of meristematic tissues?
Ans:

  • Meristematic tissues are made up of cells that are immature and have the capacity to divide and give rise to new cells.
  • These cells have the ability to divide infinitely without undergoing differentiation.
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