Online Notes on Chapter = 6 ( TISSUE) Part 1

This is Biology Online Notes on Chapter = 6 ( TISSUE) Part 1 of 9th class of NCERT Book for preparation of examinations like CBSE Board, Biology Olympiad, NTSE, CSIR NET etc.

CHAPTER AT A GLANCE:

PLANT TISSUE – Meristematic & Permanent

Meristematic Tissue:

These are simple living tissues having thin walled compactly arranged immature cells which are capable of division and formation of new cells.

Main features of Meristematic tissues are :

• Thin primary cell wall (cellulosic).

• Intercellular spaces are absent (compact tissue).

• Generally vacuols are absent, dense cytoplasm & prominent             nuclei are present.

• Large numbers of cell organelles are present.

• Active metabolic state, stored food is absent.

• Actively dividing cells are present in growing regions of plants         e.g., root & shoot tips.

Classification on the Basis of Origin:

(A) Primary (Promeristem):

• Derived directly from the meristems of embryo.

• They consist of cells derived from primary meristem.

• They add to primary growth of plants

(B) Secondary:

• Formed by permanent tissues.

• These are having cells derived from primary permanent tissue.

• They usually add to the diameter of plants.

Permanent tissue differentiation Secondary Meristem:

Classification on the Basis of Location:

(A) Apical Meristem

• It is present at the growing tips of stems and roots.

• Cell division in this tissue leads to the elongation of stem & root,     thus it is involved in primary growth of the plant.

(B) Intercalary Meristem

• It is present behind the apex.

• It is the part of apical meristem which is left behind during growth

    period.

• These are present at the base of leaf & internode region.

• These lead to the increase in the length of leaf (Primary) e.g., in        grass stem, bamboo stem, mint stem etc.

(C) Lateral Meristem

• It is also called as secondary meristem.

• It occurs along the sides of longitudinal axis of the plant.

• It gives rise to the vascular tissues.

• Causes growth in girth of stem & root.

• They are responsible for secondary growth.

PERMANENT TISSUE:

• The permanent tissues are composed of those cells which have          lost their capability to divide.

• They have definite shape, size and thickness. The permanent              tissue may be dead or living.

• The division & differentiation of the cells of meristematic tissues      give rise x

• The cells of permanent tissue loose the capacity to divide and            attain a permanent shape, size and function.

Depending upon the Structure and Composition, the Permanent tissues are classified into two types :

(A) Simple Permanent Tissues

• These are made up of same type of cells which are similar                  structurally and functionally.

• They include two types of tissue :

(a) Protective Tissues : These tissues are primarily protective in

function. 

They consist of :

(i) Epidermis

• Epidermis forms one cell thick outermost layer of various body

  organs of plants such as leaves, flowers, stems and roots.

• Epidermis is covered outside by cuticle. Cuticle is a waterproof

  layer of waxy substance called as cutin which is secreted by the      epidermal cells.

• Cuticle is very thick in xerophytes.

• Cells of epidermis of leaves are not continuous at some places

   due to the presence of small pores called as stomata.

• Each stomata is guarded by a pair of bean-shaped cells called

   as guard cells. These are the only epidermal cells which possess

   chloroplasts, the rest being colourless.

Functions of Epidermis:

• The main function of epidermis is to protect the plant from

   desiccation and infection.

• Cuticle of epidermis cuts the rate of transpiration and

   evaporation of water and prevents wilting.

• Stomata in epidermis allow gaseous exchange to occur during

   photosynthesis respiration.

• Stomata also helps in transpiration.

(ii) Cork or Phellem:

• In older roots and stems, tissues at the periphery become cork 

   cells or phellem cells.

• Cork is made up to dead cells with thick walls and do not have

   any intercellular spaces.

• The cell walls in cork deposit waxy substance called as suberin.

• The cells of cork become impermeable to water and gases due

   to the deposition of suberin.

• The cork cells are without any protoplasm but are filled with

   resins or tannins.

Functions of Cork :

• Cork is protective in function. Cork cells prevent desiccation,

   infection and mechanical injury.

• Imperviousness, lightness, toughness, compressibility and

   elasticity make the cork commercially valuable.

• Cork is used for insulation, as shock absorber in linoleum.

• Cork is used in the making of a variety of sport goods such as

   cricket balls, table tennis, shuttle cocks, wooden paddles etc.

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