STUDY OF TISSUE

INTRODUCTION:  

A tissue is a group of cells which have a common origin, similar shape, size and structure and perform the same function. Cells in a tissue are usually held together by a cementing substance and form a tissue system. ( what is tissue)

Different types of tissues are : Tissue present in plant( Plant tissue) and Tissue present in animal  (Animal tissue).

Plant tissues are divided into two main categories based on the ability of their cells to divide: Meristematic tissue and Permanent tissue.

 

                             CLASSIFICATION OF PLANT TISSUE

Meristematic tissue : These tissues are formed of young , undifferentiated living cells that keep dividing and adding new cells throughout the life of a plant. They cause all types of  plant growth.

CHARACTERISTICS OF MERISTEMATIC TISSUE:

• They are living cells, compactly packed without intercellular The vacuoles are almost absent.
• The cells are small, thin-walled and cuboidal in shape.
• They have granular cytoplasm.
• The nucleus is large, prominent and centrally located.
• The cells are immature and undifferentiated.
• They continue to divide indefinitely adding new cells to plant.
• They don’t store reserve food material.
• They are usually found at the tip of root and shoot.
• After maturation new cells produced are transformed into permanent tissue.

LOCATION OF MERISTEMATIC TISSUE:

These tissues are present in the growing regions of the plant, such as tips of root, shoot and branches. They also occur as leaf primordial and as cambium.

TYPES OF MERISTEMATIC TISSUES:

Based on their location, in the plant three types of meristems are APICAL MERISTEM, LATERAL MERISTEM AND INTERCALARY MERISTEM.

APICAL MERISTEM: It is found at the growing tips of stem, roots their branches and growing young leaves and on the tip of axillary buds. It consists of a group of cells which give rise to primary permanent tissue. Due to the growth of apical meristem, there is increase in the length of stems and roots.

LATERAL MERISTEM (CAMBIUM): It occurs on the sides of roots and stems and is responsible for the increase in the diameter (girth) of the plant roots and stems. These tissues help in increasing thickness by the help of secondary tissues and this phenomenon is called secondary growth. Some plants grow in thickness by producing new tissues laterally from root tip to shoot tip with the help of vascular cambium. Cork cambium are found in the bark of roots and stems of woody plants. The cambium of the vascular bundles and the cork cambium are example of lateral meristem.

INTERCALARY MERISTEM:- These are another part of meristem which are separated from apical part by permanent tissue development. Intercalary meristems help in elongation of the organs and are present mostly at the base of nodes, internodes and internodes.

                                           PERMANENT TISSUES

The cells which lost their ability to divide are forming Permanent tissues . Through derived from meristematic tissues These tissues  have definite permanent shapes and are specialised to carry out different functions though these are originated from undifferentiated meristematic tissue.

                                 CHARACTERISTICS OF PERMANENT TISSUE

• The cells are differentiated and have definite shape and size, related to the function they perform.
• The cells may have a thin or thick
• Between the cells intercellular spaces may be present or absent.
• It contains living or dead cells.
• The vacuoles may be present or absent .
• Cells are not having capability to divide.

A permanent tissue is made up of cells which have lost their ability to multiply and in which growth has either stopped completely or for the time being. It contains dead or living cells. On the basis of functions performed, the permanent tissues can be

• Supporting Tissues
• Conducting tissues
• Protective tissues.

On the basis of composition, permanent tissues can be Simple or Complex tissues.(WHAT IS TISSUE)

 

NAME OF THE TISSUES	STRUCTURE	OCCURRENCE / DISTRIBUTION	FUNCTION	DIAGRAM
Parenchyma para(beside)   enkhuma( in fusion)	·         Cells are thin-walled and oval rounded or polygonal in shape.   ·         Cells are loosely packed. ·         There are inter cellular spaces present  between the cells. ·         Each cell encloses a single large central vacuole, cytoplasm and a prominent nucleus.	Found in softer parts of all plants like epidermis, cortex (outer region) pith (central region) of roots, stem ad leaf mesophyll.   It is also found in xylem and phloem.	·         It stores food material in potato, sweet potato.   ·         In the leaves of green plants parenchyma tissues contain chloroplast and is called chloren chyma which helps in photosynthesis. ·         In most of the  aquatic plants,there are well developed air spaces in parenchyma cells  and areknown as aerenchyma which helps in floatation. ·         It forms the basic packing tissues and protect the internal tissue.
Collenchyma koll (glue)   enkhuma (infusion)	·         The cells are living, elongated with cellulose thickening at the corners.   ·         Each cell contains a  central vacuole which is large in size and a nucleus at centre surrounded by dense cytoplasm.	It found beneath the epidermis in the stem. Also, found in the petiole or leaf stalk of dicot plants. It is usually absent in monocot plant.	·         It supports parts of the plant by providing tensil strength and rigidity to the plants due to thickening of the wall.   ·         It helps to maintain elasticity plant parts.
Sclerenchyma skleros (hard)   enkhuma (infusion)	·         These are found in stems and veins of the leaves.   ·         On maturity, they don’t have protoplasm and hence dead. ·         Cell wall is very thick due to deposition of lignin which acts as a cement and hardness it. ·         Central cavity of the cell is highly reduced due to formation of secondary thickening.	Function is to give mechanical strength and rigidity to the plant parts.	·         It protects the plant from environmental forces like strong winds.   ·         It makes plant hard and stiff. (WHAT IS TISSUE)

                          PROTECTIVE PLANT TISSUES

EPIDERMIS	CORK
§  It is the outermost protective tissues of plant.   §  It consists of thick walled cells . §  The  outer epidermal outer walls are  thick and having cutinized cover. §  This thick wall prevents loss of water by transpiration. §  Wax is also present on the upper surface of floating leaves. §  It protects them from melting.	§  As roots and stems grow older with time, protective tissues at the periphery undergo changes and become cork cells.   §  Cork in maturity becomes woody made up of dead thick-walled  and highly suberized cells which protect the inner tissue. §  It provides insulation from freezing temperature.

 

                                               CONDUCTING TISSUE

Complex tissues are more than one type of cells which work in close coordination to perform a common function. These tissues, also called vascular tissues, provide a channel for movement of water and dissolved minerals up and down the plant. The components of vascular bundle are XYLEM and PHLOEM.

                                   XYLEM

VARIOUS COMPONENT	GENERAL STRUCTURE and FUNCTION	DIAGRAM
Xylem vessels and Traceid:   ·         These are long tube like structure with hard and thick cell walls. ·         Their transverse walls got dissolved and make a continuous tube to transport water. ·         They keep in the upward movement of water and minerals from roots to aerial parts of the plant. Xylem fibres: ·         These are found in woody dicotyledonous plant.   Xylem parenchyma: ·         Out of all components, xylem parenchyma is living performing storage of food.	§  It helps to conduct water from soil through root.   §  It provides  mechanical rigidity and strengthness to the plant. §  Xylem cells are thick-walled. §  As a conducting strand, xylem holds a long uninterrupted tube through all aerial parts. §  Old  xylem tissues form the wood and forms woody stem.

                                                     PHLOEM

 

VARIOUS COMPONENTS	GENERAL STRUCTURE and FUNCTION	DIAGRAM
Sieve tube :   §  These are elongated tubular conducting channels. §  These are arranged end to end. §  Sieve plates connect the protoplasts to the adjacent sieve tube elements. Companion cells: §  It lies on the side of the sieve tubes and are closely associated with them.   §  They help sieve tube in conduction. Phloem parenchyma: §  These are ordinary living parenchyma cells associated with phloem. §  They store food. Phloem fibres: §  These are dead sclerenchyma fibres. §  They provide mechanical strength. §  The textile fibres of flax,jute and hemp are phloem fibres.	·         It is chief food conducting tissues of plants.   ·         Substances can move in both direction in phloem. ·         It is responsible for downward and upward movement of food prepared in leaves to other parts of the plant. ·         Except phloem fibres which are dead, all other members of the phloem tissues are living.

Xylem and Phloem together form vascular bundle.For example, veins, which are in continuity with conductiong tissue of xylem and phloem.

                                       SPECIAL PERMANENT TISSUE

Special tissues are formed of cells that are associated with secretion or excretion of material.  Three types of tissues are:-

LATICIFEROUS TISSUE	GLANDULAR TISSUE	HYDATHODE TISSUE
ü  Its cells are tubular and are filled with fluid called LATEX.   ü  The latex is a sticky fluid composed of starch grains proteins, tannins, mucilage and rubber.	ü  It secretes gum, resin, mucilage, oil or digestive enzymes.   ü  These cells are organised to form glands in different parts of the plant body.	ü  The tissue is modified to exude water (guttation) as in Nasturtium and colocasia also in Tomato leaf.