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:
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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