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Discovered by Robert Hook
in 1665
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It is the outermost
boundary of plant cells.
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Secreted by protoplasm of
the cell.
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Thickness varies in
different cells of the plant.
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Each cell whether isolated
or in tissue form has its own cell wall.
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Neighbouring cells are
cemented together by an intercellular substance called middle lamilla.
Ø
Cell walls has three
fundamental parts.
(1)
Middle lamilla
(2)
Primary wall
(3)
Secondary wall
Middle Lamilla
ü
Cements together the walls
of the neighbouring cells.
ü
About 1µm
in thickness.
ü
Commenly lignified in woody
tissues.
Primary wall
ü
The first wall forming in
developing cells.
ü
1-3 µm in thickness.
ü
Elastic , extendable ,
crystalline and optically active.
ü
Composed of cellulose,
pectic compounds, mostly polysaccharide and hemicellulose.
Secondary Wall
ü
Laid down inside the
primary wall.
ü
5 – 10 µm
in thickness.
ü
Rigid, crystalline and
strongly optically active.
ü
Composed of cellulose, non
cellulosic polysaccharides
hemicelluloses and mineral salts of Ca, Mg, K and some Silica.
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