Tissues Blog 3

Hello Learners,

In the previous blog, we have discussed about the growth of plants. We are aware that the growth of plants occurs only in certain specific regions. This is because the dividing tissue known as Meristematic tissue is located at these points. We have also discussed about different types of Meristematic tissues and its location.

Today, we will discuss more about Permanent Tissue of PLANT TISSUES.

At the end of today's topic, learners will be able to 
(i) define permanent tissue.
(ii) explain the importance of permanent tissue in the plant body.
(iii) tell the location of permanent tissue in the plant body.
(iv) draw the location of permanent tissue in the plant body.
(v) explain the diversity in epidermis layer.


So, let us start our topic for today............

Permanent Tissues

The cells which are differentiated to perform a specific function and have lost the ability to divide are called permanent tissues. This process of taking up a permanent shape, size and a function is called differentiation. Cells of meristematic tissue differentiate to form different types of permanent tissue.

(Refer Fig 6.3 Pg 70 of your text book. Diagram need to be drawn)

Characteristic Features of Permanent Tissues

(i)          The cells may be thin or thick walled.

(ii)         The cells have undergone differentiation and assumed definite size and function.

(iii)        Nucleus is small in relation to cell size.

(iv)       Cytoplasm is peripheral with a big central vacuole.

The major difference between meristematic and permanent tissues are-

Features	Permanent Tissue	Meristematic Tissue
1.   Cell size      2.   Cell wall      3.   Cytoplasm      4.   Nucleus      5.   Vacuoles      6.   Intercellular spaces      7.   Living/Dead      8.   Power of cell division	Large Thick As a layer along cell wall Small Large and central Present Living or dead Absent	Small Thin Rich Prominent Small or absent Absent Always living Present

Types of Permanent Tissues- Depending on the type of cells composing a tissue, permanent tissues are of two types:

   

    1.   Simple Tissues- Composed of single type of cells like parenchyma, collenchyma and sclerenchyma.

    2.   Complex Tissues- Composed of different types of cells like xylem and phloem.

Simple Permanent Tissues- Plant tissue which is made up of only one type of cells is called simple permanent tissue. It is of three basic types.

    1.   Parenchyma

Structure of Parenchyma

(i)          Parenchymatous cells are living and isodiametric (almost equal in length and width).

(ii)         They are usually loosely packed as they have intercellular spaces are present.

(iii)        Each cell possesses a large central vacuole with a prominent nucleus and thin cell wall.

(iv)       These cells are present in the soft areas of the stems, leaves, roots, flower, fruits etc. 

                                                      

Function of Parenchyma

(i)          Storage of food

(ii)         Photosynthesis (parenchyma with chlorophyll is called chlorenchyma).

(iii)        Buoyancy so that the aquatic plants can float (parenchyma with large air cavities is called aerenchyma).

    2.   Collenchyma

Structure of Collenchyma

(i)          Collenchymatous cells are also living and isodiametric or some what elongated.

(ii)         Intercellular spaces are very less.

(iii)        Each cell possesses a large central vacuole and a peripheral cytoplasm with a prominent nucleus.

(iv)       Thickenings are present at corners.

(v)         The cells are present below the epidermis- in petiole and stems of herbaceous dicots.

Function of Collenchyma

(i)          Mechanical strength

(ii)         Prevent tearing of leaves

(iii)        Storage

(iv)       Photosynthesis

https://www.youtube.com/watch?v=euyvrLhmfJU

3.   Sclerenchyma

Structure of Sclerenchyma

(i)          Sclerenchymatous cells are thick walled with little or no protoplasm.

(ii)         Cells are dead at maturity.

(iii)        These cells are generally divided into two types, fibre and sclereids.

(iv)       The cells are long and narrow as the walls are thickened due to lignin a chemical substance which acts as cement and hardens them.

Function of Sclerenchyma

(i)          They provide stiffness to the part of in which they occur. The husk of coconut is made up of sclerenchymatous cells.

(ii)         This tissue is present in stems around vascular bundles in the veins of leaves and in the hard covering of seeds and nuts. It provides strength to the plant parts.

https://www.youtube.com/watch?v=E1PkOuJDDkk

Diversity in Epidermis

      Epidermis is a protective tissue present in the outermost layer of the plant        body such as leaves, flowers, stem and roots. Some of its characteristic             features are as follows:

(i)          Leaves of some plants in very dry habitat may have multilayered epidermis for protection against water loss. The epidermis has a thick waxy coating of cutin which is chemical substance with water proof quality on its outer surface.

(ii)         Aerial parts (trunk and branches) of plants generally secrete a waxy, water resistant layer on their outer surface. It helps in protection against loss of water, mechanical injury and invasion by parasitic fungi.

(iii)        Since epidermal cells of the aerial parts are connected with protection, these cells are continuous layer without intercellular spaces and are relatively flat with outer side walls are thicker than the inner walls.

(iv)       Small pores are seen on the lower surface of leaves. These pores are stomata. Stomata are enclosed by two kidney shaped cells called guard cells. They are necessary for exchanging gases with the atmosphere. The process of transpiration also take place through stomata.

(v)    Epidermal cells of the roots, whose function is water absorption commonly bear long hair-like parts that greatly increase the total absorptive surface area.

(vi)   When plants grow older, the outer protective tissue undergoes certain changes. A strip of secondary meristem located in the cortex forms layers of cells which constitute the cork. Cells of cork are dead and compactly arranged without intercellular spaces having a chemical called suberin in the walls.

https://www.youtube.com/watch?v=9NCvTNcS2lU

Home Assignment:

1. Complete the notes.
2. Why is the epidermis present as a thick waxy coating of cutin in desert plants?
3. Describe the structure and function of stomata.
4. Give reason:
(i) meristamatic cells have a prominent nucleus and dense cytoplasm but they lack vacuole.
(ii) intercellular spaces are absent in sclerechymatous tissues.
(iii) we get crunchy and granular feeling when we chew pear fruit.
(iv) branches of tree move and bend freely in wind velocity
(e) it is difficult to pull out the husk of a coconut tree.
5. Write the difference between parenchyma, collenchyma and sclerenchyma tissues.