Class 9 Tissue Notes

Class – IX                                CSCE TUTORIAL                                       Biology

Tissues

 

Tissues

Tissues are the cluster of structurally and functionally similar cells arranged to give the highest possible efficiency of the function they perform. All cells of a tissue have a common origin.

Characteristics of Tissues

1. There is division of labour in multicellular organisms, as different group of cells perform different functions.
2. Tissues become organized to form organs and organs thereby develop into systems.
3. Due to improved organisation and higher efficiency, multicellular organisms have higher rate of survival than unicellular organisms.

 

Plant Tissue

On the basis of dividing capacity, plant tissues can be classified into two fundamental types as:-

1). Meristematic Tissue

The tissue whose called divide actively throughout life is known as meristematic tissue. It is also called as growth tissue and is found in the growing regions of plant like root and shoot tip. The process of cell division in meristematic tissue is prominent to get new cells. Cell forming in this tissue are active and have dense cytoplasm, thin cellulose walls and prominent nuclei. These are classified on the basis of  the regions where they are present as growth of plants occurs only in certain specific regions.

1. Apical Meristem – These are present at growing tips of stems and roots. Thus, are helpful in increasing the length of the stems and the roots. It acts as pro-meristem having actively dividing cells, giving rise to other meristems.
2. Intercalary Meristem – These are present at the base of the leaves or internodes on twigs. It helps in longitudinal growth of plants by adding primary tissues.
3. Lateral Meristem – These are present on the lateral sides of stem and roots. It helps in increasing the girth of the stem or root.

 

2). Permanent Tissue

This tissue is formed from the cells of meristematic tissue when they loose their ability to divide and have attained a permanent shape, size and function by the process called differentiation.

1. Simple permanent tissue
   It is made up of only one type of cells, the cell forming these tissues are similar in structure and function.
2. Parenchyma
   They are present in cortex and pith of stem and roots and also in mesophyll of leaves.

Characteristics of Parenchyma are:-

1. The cells are isodiametric, i.e. all sides equal with thin cell walls made up of cellulose.
2. Cells are loosely packed with large spaces between cells (i.e. intercellular spaces).
3. Each cell encloses a large vacuole and a peripheral cytoplasm containing nucleus.

Functions of Parenchyma are :-

1. It stores and assimilates food and serves as food storage tissue.
2. It provides support to plant due to its turgidity property.
3. When the parenchyma cell contains chlorophyll in some situations, it performs photosynthesis. Such Parenchyma tissues are called Chlorenchyma.
4. In aquatic plants, large air cavities are present in parenchyma cells in order to give buoyancy to plants which help them to float. Such type of parenchyma tissue is called Aerenchyma. 

   Aerenchyma

1. The presence of intracellular spaces between the cells allows the exchange of gases.
2. It serves as a packing tissue to fill the spaces between other tissues and maintains the shape and firmness of the plants.
3. Collenchyma

These are the tissues which are found in leaf stalks below the epidermis, leaf mid-ribs and herbaceous dicot stems.

Characteristics of Collenchyma are:-

1. Cells are living, elongated and irregularly thickened at the corners.
2. Cell wall has extra deposition of cellulose and pectin and possesses simple pits.
3. They have very little intercellular spaces.
4. They contain chloroplast.

Functions of Collenchyma are:-

1. It provides mechanical support and elasticity or flexibility to plants.
2. It allows easy bending in various parts of a plant without breaking.
3. They manufacture sugar and starch when possess chloroplasts.
4. Sclerenchyma
   It is present in stems, around vascular bundles, in the veins of leaves and in the hard covering of seeds and nuts.

Characteristics of Sclerenchyma are:-

1. The cells of sclerenchyma tissue are dead and do not contain protoplasm.
2. The cells are long and narrow in appearance.
3. Cells are of two types : fibres and sclereids (grit cells or stone cells).
4. Cell wall are thickened due to lignin deposition which acts as cement and hardens them.
5. A prominent middle lamella exists between two cells.
6. Due to the presence of thick walls, there is no internal space inside the cell.

Functions of Sclerenchyma are:-

1. It is known to be chief mechanical tissue which makes plant hard and stiff.
2. It provides strength and enables the plant to bear various stresses.
3. It forms protective covering around seeds and nuts.
4. It gives rigidity, flexibility and elasticity to the plant body.

 

Protective Tissue

The protective tissue is meant to provide protection to the plants from undue loss of water and retain adequate water in them. The two types of protective tissues present in plants are:-

(i) Epidermis                                                         (ii) Cork (or Phellum)

• Epidermis

Epidermis is the outer covering of the plant. It is meant to provide protection to all the parts of the plant. On the aerial parts of the plant, Epidermal cells often secrete a waxy, water-resistant layer on their outer surface which provides protection against loss of water, mechanical injury and invasion of parasitic fungi. Cells of epidermis tissue form a continuous layer and no intercellular spaces due to protective role.

Epidermal cells of leaf bear small pores known as stomata. These are enclosed by two kidney shaped cells called guard cells. Stomata are responsible for the exchange of gases with the atmosphere and for the process of transpiration. The epidermal cells of roots whose main function is water absorption bear long hair like outgrowths called root hair that greatly increase the total absorptive surface area and helps the roots to absorb water and nutrients from the soil. In desert plants, epidermis has a thick waxy coating of cutin on its surface to prevent water loss. Cutin is a chemical substance with waterproof quality.

 

• Cork

It is the strip of secondary meristem which replaces the epidermis of older stems. Cells of cork are dead, compactly arranged and have no intercellular spaces. It forms bark of the tree. A chemical called suberin is present in their walls which make them impervious to gases and water. It prevents desiccation, infection and mechanical injury.

 

Complex Permanent Tissue

It is made of more than one type of cells having a common origin. The cells look different from each other. Regardless of different appearances, all the cells co-ordinate to perform a common function.

Types of Complex Permanent Tissue are:-

• Xylem

It is a vascular and mechanical conducting tissue, also known as wood. The cells of xylem have thick walls and many of them are dead. It transport water and minerals from roots to other parts of the plant. It provides mechanical strength to the plant. Xylem consist of various types of elements which are :-

1. Tracheids
   These are long, tubular, elongated, dead cells with lignified walls and tapering ends. They transport water and minerals vertically. They possess pits for transport of water from cell to cell.
2. Vessels
   These are long, tube like structures, formed by a row of cells, placed end to end. These  are dead cells with lignified walls. These are shorter and wider than tracheids due to their thick walls and broad lumen.
3. Xylem Parenchyma
   These are the only living cells of xylem with thin cell walls. It stores food and help in the sideways conduction of water.
4. Xylem Fibres
   They have elongated dead cells with tapering ends and thick cell walls. They are sclerenchyma fibres associated with Xylem.

• Phloem

It is another kind of living conducting tissue, also known as bast. It transport food from leaves to other parts of the plant. Materials can move in both direction in it. All phloem cells are living except phloem fibres.

1. Sieve tubes
   These are tubular cells with walls perforated by numerous pores and are called sieve plates. Nucleus is absent, but present in young cells. They have thin layer of cytoplasm.
2. Companion cells
   These are small elongated cells having thin walls. They have dense cytoplasm and prominent nucleus. They are connected to sieve tubes with numerous plasmodesmata. They help in maintain pressure gradient in sieve tube.
3. Phloem parenchyma
   These are thin-walled living parenchymatous cells. They help in storage and slow lateral conduction of food by plasmodesmatal connections.
4. Phloem fibre
   These are thick-walled, elongated, dead sclerenchymatous cells having narrow lumen. They provide mechanical strength to the tissue. Bast fibers obtained from plants like jute, hemp, flex etc. have commercial value.

 

Animal Tissue

1. Epithelial Tissue
   It is the simplest protective tissue of the animal body, which covers most organs and cavities of the body. Cells of epithelial tissues are tightly packed and form a continuous sheet. They have a very small amount of cementing material between them. It forms a barrier to keep different body systems separated from each other. It is separated from underlying tissue by an extracellular fibrous basement membrane containing collagen.

On the basis of shape and arrangement, epithelial tissues further classified as:-

1. Squamous Epithelium

   ‘Squama’ means scales. It has scale like appearance, it is also known as tessellated or pavement epithelium.
   It is further categorized as :-
   1. Simple Squamous Epithelium
   The cells are very thin and flat and appear as tiles over a floor. It is single layered and closely fitted. It forms a delicate lining of blood vessels and lung alveoli, where substance transport occurs through a selectively permeable membrane.
   2. Stratified Squamous Epithelium

    

2. Cuboidal Epithelium
3. Column Epithelium
4. Ciliated Columnar Epithelium