cellular organisation in plant
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CELLULAR ORGANISATION
PLANT
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Least specialized plant
cells
Thin and somewhat
flexible cell walls
Living at maturity
Carry on most of the
plant's metabolic
functions
Generally have a largecentral vacuole
Most parenchyma cells
have the ability to
differentiate into other
cell types under specialconditions
During repair and
replacement of organs
after injury
PARENCHYMA CELLS
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The cells of parenchyma are large, thin-walled,
and usually have a large central vacuole. They
are often partially separated from each otherand are usually stuffed with plastids.
In areas not exposed to light, colorless plastids
predominate and food storage is the main
function. The cells of the white potato are
parenchyma cells.
Where light is present, e.g., in
leaves, chloroplasts predominate
and photosynthesis is the main function.
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/Chloroplasts.htmlhttp://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/P.htmlhttp://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/P.htmlhttp://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/Chloroplasts.html -
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COLLENCHYMA CELLS
Thicker primary cells walls (usually with uneven thickness)
Living at maturity
Role in support of herbaceous plants
Example - the "strings" of celery
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Collenchyma cells have thick walls that
are especially thick at their corners.
These cells provide mechanical support
for the plant.
They are most often found in areas that
are growing rapidly and need to be
strengthened.
The petiole ("stalk") of leaves is usually
reinforced with collenchyma
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SCLERENCHYMA CELLS
Thick secondary cell walls
Dead at functional maturity
Cannot increase in length - occur in
parts of the plant which have quit
growing in length
Two types - fibers and schlerids
Fibers - long, slender cells with a
more or less regular secondary cell
wall
Example - hemp fibers for
making ropeSchlerids - shorter cells with an
irregular shape
Example - stone cells in pears
and hard nut and seed shells
http://www.uic.edu/classes/bios/bios100/labs/schlerenchyma.jpghttp://www.uic.edu/classes/bios/bios100/labs/schlerids.jpghttp://www.uic.edu/classes/bios/bios100/labs/schlerids.jpghttp://www.uic.edu/classes/bios/bios100/labs/schlerenchyma.jpg -
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The walls of these cells are very thick and built up in
a uniform layer around the entire margin of the cell.
Often, the cell dies after its cell wall is fully formed.
Sclerenchyma cells are usually found associated with
other cells types and give them mechanical support.
Sclerenchyma is found in stems and also in leaf
veins.
Sclerenchyma also makes up the hard outer
covering of seeds and nuts.
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EPIDERMAL CELLS
Protective tissue covers
the surface of leaves and
the living cells of roots
and stems.Its cells are flattened with
their top and bottom
surfaces parallel.
The upper and
lower epidermis of the
leafare examples of
protective tissue
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TISSUES
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EPIDERMAL TISSUES
Generally a single layer of cellsThe "skin" of the plant
Primarily parenchyma cells
Main role is protection of the plant
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MERISTEM TISSUES
The main function of meristematic tissue is mitosis. The cellsare small, thin-walled, with no central vacuole and no
specialised features.
Meristematic tissue is located in
-the apical meristems at the growing points of roots and
stems.
-the secondary meristems (lateral buds) at the nodes of stems
(where branching occurs), and in some plants,
-a ring of meristematic tissue, called the cambium, that isfound within the mature stem.
The cells produced in the meristems soon become
differentiated into one or another of several types.
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Apical meristems
located at the tips of roots and shoots
supply cells for the plant to increase in length (grow up for
shoots and down for roots)
growth in this direction is known as primary growth
primary growth found in herbaceous and woody plants
primary growth found in monocots and dicots
Lateral meristemslocated near the periphery of the plant,
usually in a cylinder
supply cells for the plant to increase in girth
growth in this direction is known as secondary growth
found in all woody and some herbaceous plants
lateral meristems and secondary growth found only in
dicots
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GROUND TISSUES
Makes up the bulk of the plant
Predominately parenchyma,
but collenchyma and
schlerenchyma cells are found
Diverse functions including
photosynthesis, storage,
and support
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VASCULAR TISSUES
Involved in thetransport of water,
ions, minerals, and
food
Also has a secondary
role in support
Composed of xylem,
phloem, parenchyma,
schlerenchyma
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VASCULAR TISSUES
XYLEM
Thick secondary cell walls, oftendeposited unevenly in a coil-likepattern so that they may stretch
Dead at functionally maturity. Involved in conduct of water and
ions in the plant
Two types - tracheids and vessels
Tracheids - long, slender cellsconnected to each other bypits. Found in all vascular plants
Vessels - shorter, larger diametercells with completely perforatedcell wall ends. Found only inAngiosperms
PHOLOEM
Involved in transport of sucrose,other organic compounds, and someions
Living at functional maturity
Protoplast may lack organelles andnucleus, though
Endwalls connect to each other viasieve-plates
Two types of cells in the phloem -sieve-tube members and companioncells
Sieve-tube members - actual conduitfor sucrose transport
Companion cells - has a nucleus thatmay also control the sieve-tubeelement and may aid in sucroseloading
http://www.uic.edu/classes/bios/bios100/labs/trachei1.gifhttp://www.uic.edu/classes/bios/bios100/labs/vessel3.gifhttp://www.uic.edu/classes/bios/bios100/labs/vessel3.gifhttp://www.uic.edu/classes/bios/bios100/labs/trachei1.gif -
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ORGAN
LEAF
FLOWER
STEM
ROOT
FRUIT
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SYSTEM
Root System
Underground (usually)
Anchor the plant in the soil
Absorb water and nutrients
Conduct water andnutrients
Food Storage
Shoot System
Above ground (usually)
Elevates the plant above thesoil
Many functions including: photosynthesis
reproduction & dispersal
food and water conduction
Note: the shoot system
includes the leaves and thereproductive organs,although these will becovered in more detailseparately
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The shoot system includes organs such
asleaves, buds, stems, flowers,
and fruits and usually it develops above
ground.The functions of the shoot
system includePhotosynthesis,
Reproduction,
Storage,
Transport,
Hormone production.
The root system includes roots as well
as modified stem structures such
as tubers andrhizomes and usually it
developsunderground.The functions of
the root system include
Anchorage,Absorption,
Storage,
Transport,
Production of certain hormones
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