Answer:
Epithelial tissue is the protective
tissue of animal body. (1)
Depending
upon the shape and function of the cells, they are of following types
(i)
Squamous epithelium Simple squamous epithelium consists of extremely
thin and flatcells forming delicate lining, e.g., the oesophagus and lining of
mouth. (1)
(ii)
Cuboidal epitheliumIt consists of cube-likecells with rounded nuclei and
forms the lining of kidney tubules and duct of salivary glands, where it
provides mechanical support. (1)
(iii)
Columnar epitheliumIt consists of pillar-like cells having elongated
nuclei. It is found in inner lining of intestine where absorption and secretion
occur. (1)
(iv)
Ciliated epithelium The columnar epithelium tissue also has cilia, which
are hair-like projections on the outer surface of epithelial
cells. (1/2)
(v)
Glandular epithelium The columnar epithelium is often modified to form
glands, which secrete chemicals. (2)
Or
(i)
It is the outer protective tissue of older stem and roots.
(1)
(ii)
It is formed by secondary lateral meristem called cork cambium.
(1)
(iii)
The mature cork become dead and filled with tannin, resin and air.
(1)
(iv)
The cells are arranged compactly without intercellular spaces. (1/2)
(v)
The cells become several layers thick, which are impermeable due to deposition
of suberin in their wall.
(1/2)
Formation
of Cork
As
plant grow older, the outer protective tissue undergoes certain changes. A
strip of secondary meristem replaces the epidermis of stem. Cells on the
outside are cut-off from this layer. This form several layers thick cork or
bark of theno overlap. (1)
Role
of Cork
(i)
It prevents loss of water by evaporation.
(ii)
It protects plant from the invasion of parasites and other harmful
microorganisms.
(iii)
It is used for manufacture of insulation boards, sport goods, shock absorber, etc.
(2)
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