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A Handbook of Biology
ato
Longitudinal
Longitudinal
Cross section
Cross section
racellular
irspace
Thin primary
cell wall
Thin primary
cell wall
Thick secondary
cell wall
Thick primary
cell wall
Nucleus
Cytoplasm
Starch grain
Vacuole
Lumen
Celery
Pear
b. Collenchyma
It occurs in layers below the epidermis (as
hypodermis) in dicot plants.
It is found as a homogeneous layer or in
patches. - It consists of cells with much
thickened corners due to deposition of
cellulose, hemicellulose and pectin.
Intercellular spaces are absent.
Cells are oval, spherical or polygonal and often contain chloroplasts.
Functions: They provide mechanical support to the growing parts such
as young stem and petiole of a leaf. The cells that contain chloroplasts
assimilate food.
c. Sclerenchyma
It consists of long, narrow cells
with thick and lignified cell walls
having a few or numerous pits.
They are usually dead without
protoplasts.
Based on the form, structure,
origin and development.
Potato
Cross section
Longitudinal
Longitudinal
Longitudinal
Cross section
Cross section
Intracellular
airspace
Thin primary
cell wall
Thin primary
cell wall
Thick secondary
cell wall
Thick primary
cell wall
Nucleus
Cytoplasm
Starch grain
Vacuole
Lumen
Celery
Pear
Sclerenchyma is of 2 types:
fibres & sclereids.
Fibres: These are thick-walled, elongated and pointed cells, generally
occurring in groups.
Sclereids: These are spherical, oval or cylindrical, highly thickened
dead cells with very narrow cavities (lumen). These are found in the
fruit walls of nuts; pulp of fruits like guava, pear and sapota; seed
coats of legumes and leaves of tea.
Function: It provides mechanical support to organs.
2. ÇØMPLËX PËRMÅÑËÑT TÏSSÜËS
These are made of more than one type of cells and they work together as
a unit.
2 types: Xylem and Phloem.