plant tissues tissue – group of vegetative cells with one or more specific functions. two kinds...
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Plant TissuesTissue – group of vegetative cells with one or
more specific functions.Two kinds based on state of development:
Meristematic tissues or Meristems Actively engaged in cell division (production of new
cells) Enlarge and differentiate to become permanent
tissues Remain meristematic or repeatedly divide (initials)
Permanent tissues Attained mature form and perform their specific
functions No longer divide and give rise to new cells All are derived from meristematic tissues
Kinds of Meristems
Based on position or location within the plant body:Apical meristems (promeristems)
Found at the tips or apices of stems and roots Responsible for the increase in length of stems and roots 3 meristematic zones:
Protoderm, Ground meristem, Procambium
Lateral meristems (or cambia) Found along the sides of certain roots and stems Responsible for the increase in width or diameter Dicots have cambia whereas monocots have no cambia Types: vascular cambium and cork cambium (phellogen)
Intercalary meristems Found at the bases of young leaves and internodes Considered temporary (short-lived) meristems
Kinds of MeristemsBased on origin, meristems may be
classified as:Primary meristems
Originate in the embryo and persist throughout the lifetime
Apical meristems or their meristematic zones Intercalary and the vascular cambium
Secondary meristems Derived from permanent tissues Cork cambium Living permanent tissues lining injured or wounded
portions of plants become meristematic to heal the injured portions resulting in formation of “callus” or scar tissue.
Kinds of Permanent TissuesBased on the number of cell types/kinds
of cells:Simple permanent tissues
for the most part consist of only one kind of cell Composed of similar in structure and function
Complex permanent tissues Consist of several kinds of cells working together as
a unit in carrying out one or more specific functions
Different Kinds of Simple Permanent Tissues
EpidermisExternal tissue consists of single layer of
living cellsServes as outermost tissue of leaves, young
roots and young stems; also in old roots and old stems of monocot plants and herbaceous dicot plants
Appear cubical or rectangular in shapeIn terms of function, a protective tissueIn leaves and stems:
2 kinds of cells: Ordinary epidermal cells Guard cells (kidney-shaped) which occur in pairs and
bound by tiny openings or pores called stomata
epidermis
cortex
pith
vascular bundle
Different Kinds of Simple Permanent Tissues
EpidermisIn leaves and stems:
2 kinds of cells: Ordinary epidermal cells Guard cells (kidney-shaped) which occur in pairs
and bound by tiny openings or pores called stomata. Outer wall is coated with a heavy waxy substance
(cutin or cuticle) that prevents excessive transpiration or evaporation of water from the leaves and stems; roots not cutinized
Epidermal hairs (trichomes) for protective function
Different Kinds of Simple Permanent Tissues
ParenchymaInternal tissueConsists of living cells with uniformly thin cell
wallsLarge intercellular spacesIn cross section, appear rounded Chlorenchyma – parenchyma with
chloroplastidsInvolved in food manufacturing and in food
storage
Parenchyma Cells
- Parenchyma cells are living cells with uniformly thin walls. They comprise the photosynthetic tissue of a leaf, the soft flesh of fruits, and the storage tissue of roots and seeds.
- A widely distributed tissue located beneath the collenchyma between the vascular bundles (consisting of vascular tissues and at the center of the section.
epidermiscollenchyma
parenchyma
Different Kinds of Simple Permanent Tissues
CollenchymaAlso an internal tissueConsists of living cells with unevenly thickened
walls– thin on the sides but thickened at the angles where two or more cells meet
Appear cubical or slightly rectangular and are more or less compactly arranged
A strengthening or support tissue; storage of food
Collenchyma CellsCollenchyma cells have unevenly thickened cell walls, which are their distinguishing characteristic. They form strands along veins in leaves and beneath the epidermis in stems to provide support and strength against the onslaught of strong winds and rains.
Different Kinds of Simple Permanent Tissues
SclerenchymaAlso an internal tissueConsists of dead cells when mature, with
heavily thickened cell walls mainly due to the deposition of lignin
It may appear in the form of fibers or sclerids Fibers –elongated cells with tapering ends occurring
in groups; appear as cells with tiny empty cell cavities or cell lumina with heavy and uniformly thickened cell walls in cross section
Sclerids –irregularly-shaped cells and typically not elongated; various forms but the most common are stone cells (isodiametric and like sand particles occur singly or in groups) Found in fruits: coconut shell is sclerids, coconut husk is
fibersgritty texture of sugar apple (atis) and chico due
to stone cellsStrengthening or supportive tissue
Sclerenchyma Cells
- Sclerenchyma cells have thick and rigid cell walls. They serve as strengthening elements to support mature plant parts.
- Found in groups of cluster among the parenchyma cells around the vascular tissues
Different Kinds of Simple Permanent TissuesCork
External tissue serving as outermost tissue or covering of old stems/roots of woody dicot plants
Consists of several layers of dead cells when mature
Cell walls are impregnated with waxy substance (suberin) – impermeable to substances, resulting to the death of cells upon reaching maturity
Rectangular in shape and arranged in layers in cross-section
Protective tissue
epidermisphellem (cork)
cortical parenchyma
phellogen (cork cambium)
phelloderm
phellem
phellogen
phelloderm
BARKp
eri
derm
Plant Cell TypesPLANT CELL
TYPEPROTOPLASM
+/-, CELL LIVING OR DEAD
CELL WALL CHARACTERS FUNCTION
CELL THICKNESS CHEMICAL COMPOSITION
Parenchyma +, living Uniformly thin Cellulose, hemicellulosemay have cutin
Food storage, food manufacture
Collenchyma +, living Irregularly thick Cellulose, hemicellulose
Food storage, strengthening
Sclerenchyma 1. sclereid 2. fiber
-, dead Uniformly thick Cellulose, hemicellulose added suberin or lignin
Strengthening and support
CELL SHAPEPolyhedral to much branched sclerenchyma cellsLong and slender sclerenchyma cells
Kinds of Complex Permanent Tissues
PhloemFunction: mainly conductive or vascular tissueConducts dissolved organic food materialsConsists of the following cell types:
Phloem fibers Phloem parenchyma Sieve tube elements Companion cells
Kinds of Complex Permanent Tissues
Phloem: cell typesPhloem fibers
appear like ordinary schlerenchyma fibersPhloem parenchyma
appear like ordinary parenchyma cells
Kinds of Complex Permanent TissuesPhloem: cell types
Sieve tube elements conducting cells of the phloem living, non-nucleated cell when mature elongated in form and uniformly thin-walled with
the end walls perforated to form sieve plates that are attached end-to-end forming long conducting tubes (sieve tubes)
consists of protoplasmic connections between adjacent cells - plasmodesmata
Kinds of Complex Permanent TissuesPhloem: cell types
Companion cells parenchymatous cells which are always found
beside the sieve tubes small, elongated and nucleated living cells when
mature plasmodesmata have also been observed to occur
between the companion cells and the sieve tubes
Kinds of Complex Permanent Tissues
Xylem or WoodFunction: mainly conductive or vascular tissueConducts water and mineral salts The main strengthening tissue of the plantConsists of the following cell types:
Xylem fibers Xylem parenchyma Vessel elements Tracheids
Kinds of Complex Permanent Tissues
Xylem: cell typesXylem fibers
appear like ordinary schlerenchyma fibersXylem parenchyma
structurally similar but much smaller than the ordinary parenchyma cells
Kinds of Complex Permanent TissuesXylem: cell types
Vessel elements main conducting cells of the xylem Elongated in shape and dead when mature Heavily thickened cell walls Have relatively large cavities or lumina which
generally appear rounded in cross section Vessel elements are attached end-to-end with their
end walls perforated to form long conducting tubes (xylem vessels)
Perforation plate – perforated wall having one or more openings
Kinds of Complex Permanent TissuesXylem: cell types
Tracheids simplest conducting cells of the xylem dead cell when mature elongated in shape and square-like in cross section
with heavily thickened cell walls Tracheary elements – consists of the vessel
elements and the traceheids; have different types depending on how lignin is deposited on their cell walls
xylem
phloem
vessel
vessel
air space
companion cell
sieve tube
bundle sheath
Cross section of a monocot stem
vascular bundle
phloem fiber
sieve tubecompanion cell
xylem parenchyma
xylem fiber
phloem parenchyma
vascular cambium
vessel
Tracheid (schlerenchyma)
Kinds of Complex Permanent TissuesMain types of tracheary elements:
Annular type – thickening of the cell wall is in the form of rings
Spiral type – the thickening is in the form of a spiralling or helical structure
Scalariform – the thickening is ladder-likeReticulate – the thickening is net-likePitted type – the uniformly thickened cell walls
show the presence of more or less rounded depressions or pore-like structure (pitts) representing the non-lignifed portions of a wall
reticulate
Plant TrichomesTrichomes or epidermal hairs
appendages of the epidermal cellsmay be unicellular or multicellularglandular and non-glandular structuresGlandular trichomes – consist of living cells
and produce secretions Types: glandular and stinging trichomes
Non-glandular trichomes – consist of dead cells and non-secretory Kinds: bristles, scales, stellate, and branched
(dendroid)
Plant Trichomes
Glandular TrichomesGlandular trichomes
produce secretions in enlarged terminal portions Examples: ratilis, oregano and malvarosa
Stinging trichomes Consist of enlarged base containing secretion from
which projects a stiff, slender structure that ends in a sharp point
Example: lipang kalabaw
Plant Trichomes
Non-glandular TrichomesBristles - stiff, sharp pointed hairs which may
be barb-like protuberances along the sides as in lipa
Scales - flattened structure as in alingaroStellate trichomes – star-like structure as in
ratilis and MallotusBranched trichomes (dendroid) – as in the
velvet dock
Glandular trichomes
Glandular trichomes - Enlarge terminal portions
Glandular trichomes - Enlarge terminal portions