Biology - Plant Tissues Notes

PLANT  TISSUES                                                                                                          CLASS : IX                                      

CHARACTERISTICS OF MERISTEMATIC TISSUE

1.       They are living cells, and are very active. They have thin cellulose walls.

2.       They have dense granular cytoplasm.

3.       The nucleus is large and prominent.

4.       They have compactly arranged cells without intercellular spaces.

5.       They are capable of dividing indefinitely.

 

TYPES OF MERISTEMS ACCORDING TO THEIR POSITIONS IN THE PLANT BODY

APICAL MERISTEM

1.They are found at the apices of stem , root  and their branches.

2. They give rise to primary permanent tissues that constitute the primary body of the plant.

3. Due to the growth of apical meristems, the stem and roots increase in length.

 

LATERAL MERISTEM

1.They occur on the sides of the plant body.

2.They are responsible for increase in the diameter of the plant roots and stem ( GIRTH ).

3.Also responsible for growth in thickness by the addition of secondary tissues ( SECONDARY GROWTH )

4. They are found in the CAMBIUM OF THE VASCULAR BUNDLES & CORK CAMBIUM.

 

INTERCALARY MERISTEM

1.       It is the part of apical meristem which gets separated from the apex due to the development of permanent tissues in between.

2.       It helps in elongation of the organs and present mostly at the base of nodes, internodes and leaves.

SIMPLE PERMANENT TISSUES ( supportive tissues )

PARENCHYMA

FUNCTIONS:

1. It stores food material in the form of proteins, starch , oil and fats.

2. It stores nutrients and water.

3. Provide support and rigidity to the plants by keeping the cells rigid.

4. Form the basic packing tissue and protect the internal tissues.

5. In the leaves of green plants, parenchyma tissue  contain chlorophyll, and is called CHLORENCHYMA.

6. In many aquatic plants, they have well –developed air spaces and are known as AERENCHYMA.

COLLENCHYMA

FUNCTIONS:

1.       It provides tensile strength and rigidity to the plants due to thickenings.

2.       It provides elasticity to the plant organs. It provides bending of leaves and stems without breaking them.

3.       It also store food.

SCLERENCHYMA

FUNCTIONS:-

1.       It provides mechanical strength to the plant and its parts.

2.       They protect from environmental forces like strong winds.

3.       They make the plant hard and stiff.

 

PROTECTIVE PLANT TISSUE

Epidermis is the outermost protective layer of plant organs. It is usually single layered . The cells of epidermis are flat. Outer and side walls of most epidermal cells are thicker than the inner walls.

 

Epidermal cells of aerial parts of the plant secrete a waxy, water resistant layer on their outer surface. It protects them against loss of water, mechanical injury and any attack by pathogenic fungi.

 

In desert plants, outer walls of the epidermis are usually thick and covered with CUTIN. Cutin is a chemical substance that is waterproof and reduces loss of water by transpiration.

 

The epidermal cells of roots contain long hair- like structures called root hairs which helps to increase surface area for absorption of water and nutrients from soil.

 

FUNCTIONS OF CORK

1.       Cork cells are highly suberized  ( SUBERIN IS  A CHEMICAL SUBSTANCE WHICH IS IMPERVIOUS TO WATER AND GASES ) and thick walled protect the inner tissues.

2.       It provides insulation from freezing temperatures.

3.       It protects the inner tissues from the attacks of microorganisms and prevent water loss.

XYLEM :-    It consist of four types of cells -  XYLEM VESSELS, TRACHEIDS, FIBRES & PARENCHYMA.

XYLEM VESSELS & TRACHEIDS are tubular structures. They help in conduction of water & minerals from roots to aerial parts of the plant body.

XYLEM FIBRES are supportive in nature and provides mechanical strength to the plant body.

XYLEM PARENCHYMA ( only living component ) are concerned with the storage of food and sideways conduction of water.

PHLOEM :--        It is the chief food- conducting tissues of plants. There are four types of elements of phloem- SIEVE TUBES, COMPANION CELLS , PHLOEM PARENCHYMA & PHLOEM FIBRES ( DEAD CELL ).

SIEVE TUBES are elongated tubular conducting channels, which are placed end to end. They have perforated walls.

COMPANION CELLS  lie on the sides of sieve tubes and are closely associated with them.

PHLOEM PARENCHYMA store food.

PHLOEM FIBRES are sclerenchyma fibers. They provide mechanical strength. EXAMPLES :- FLAX , HEMP AND JUTE ARE PHLOEM FIBRES.