plant tissues - wordpress.compermanent tissues •mature tissues of the plant •derived from...
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Non Permanent Tissues -
Meristematic Tissue
• Undifferentiated plant cells that
are continually dividing by mitosis
• Large thin walled cells
• No vacuole
• Dense cytoplasm
• Large nucleus
• Found at growing tips of roots and stems to increase length of these structures – apical meristem
• Also as cambium which causes increase in width of stems and roots
• Function: to produce new cells for growth, repair and replacement of damaged or lost parts or organs
Meristems
• Apical meristems
At the tips of main and lateral shoots and in
tips of roots. Responsible for primary
growth and length.
• Lateral meristems
Parallel to the stem or the root e.g.
vascular cambium and cork cambium.
Responsible for increase in diameter
(secondary growth).
Permanent tissues
• Mature tissues of the plant
• Derived from meristematic tissue by cell
enlargement and differentiation
• Simple tissues: same cells that perform
the same function (parenchyma,
collenchyma, sclerenchyma)
• Complex tissues: different cells that
perform more than 1 function
(epidermis, xylem, phloem)
Permanent Tissues
• These tissues are grouped into three tissue systems
• 1. dermal tissue: covers the plant body
• 2. ground tissue: perform a variety of functions and make up the bulk of the plant body
• 3. vascular tissue:responsible for transport in the plant
Vascular tissue
• Conducts liquids around the plant
• Xylem transports water and inorganic
salts (strength and support)
• Phloem conducts food (sugar and
organic solutes)
Xylem • Four types of tissues:
– 1. tracheids
– 2. vessels
– 3. xylem fibres
– 4. xylem parenchyma
–Tracheids are elongated
dead cells with tapered ends
(not continuous)
–Cell walls are thickened with
lignin causing the protoplasm
to die leaving a lumen
–Water is transported from
tracheid to the next through
pits in the walls
Xylem
• Function: transport water and inorganic salts from the roots to the leaves
• Vessels are elongated tubes that extend sometimes meters in length (dead cells)
• Walls are lignified in different ways (strength for woody tissues) – Annular rings
– Spiral or helical
– Pitted
– Scalariform
– Reticulate
• Long, thin, perforated, hollow tubes stacked on top of each other
• This allows water to flow up stems to leaves as ascending sap – good water conduction
Xylem vessels
• Annular thickening:
2dry wall is laid over the
primary wall in rings. Allows for
stretching.
• Spiral/ helical thickening:
2dry wall laid down in the form
of spirals. Allows vessels to
stretch or bend.
• Pitted thickening:
2dry wall laid down everywhere
except small areas that form
pits. Pits allow movement of
water between cells.
• Scalariform thickening:
2dry wall covers the entire
primary wall except for
unthickened parts which are
left in parallel lines (looks like
a ladder).
• Reticulate thickening:
Like scalariform except
unthickened parts look like a
net.
Xylem
• Xylem fibres are
dead cells with
heavily thickened cell
walls. They do not
conduct water but
strengthen and
support the plant.
• Xylem Parenchyma
is the only living
tissue in mature
xylem. Walls are
thicker than ordinary
parenchyma cells.
Store starch and
water and can
conduct solutes for
short distances.
Phloem tissue • Phloem fibres and cells are
found in vascular bundles
in roots, stems and leaves
• Phloem transports
nutrients made in the
leaves to all parts of the
plant
• This is known as
descending sap
• 4 tissues:
– Sieve tube
– Companion cells
– Phloem fibres
– Phloem parenchyma
Phloem tissue• Consists of elongated cells
called sieve tubes
• The walls of the cells are
thickened with lignin
• Pores/ perforations in the walls
form a sieve-like structure
• Mature sieve tubes lack nuclei
and have thick slime in the
vacuole
• The conducting elements of
phloem
• Thin cellulose walls lined with
layer of cytoplasm. Few
organelles and no nuclei.
• Mass of tubules in the centre
called P-protein
• Cross walls between sieve
cells are perforated and are
called sieve plates and sieve
pores, respectively
Phloem
• Each sieve tube has a
companion cells.
• Smaller than sieve
cells and connected
to them by
plasmodesmata
• The companion cells
contain nuclei, which
controls the functions
of the sieve tubes
• Phloem fibres are
strengthening tissue
• Cell walls are lignified
• No water conduction
• Can form protective
cap
• Phloem parenchyma
are living cells that
store starch
Dermal Tissue• Epidermis is the outermost
layer of the plant
• Protection from drying out and mechanical injury
• These cells are:
• square shaped (bricks)
• closely packed with no air spaces
• Transparent (lack chlorophyll) –allow sunlight to penetrate inner tissues for photosynthesis
• Usually only a single layer of cells
• Thicker outer cell walls for mechanical protection
Modified Epidermis• Stem and leaf epidermal cells are modified to secrete a
waxy substance called cuticle
• The waxy cuticle reduces the amount of water lost by the aerial parts of the plant
Modified Epidermis
• Guard cells are bean-shaped cells with a
thick inner wall and thin outer wall
• They also contain chloroplasts allowing
them to regulate the opening and closing of the stoma
• This allows substances like water vapour, CO² and O² to
move in and out of leaves
Modified Epidermis
• Epidermis is different in roots
• No cuticle as roots need to absorb
water
• No guard cells and stomata
• Cells have microscopic extensions
called root hairs
Modified Epidermis
• Root hair cells have small outgrowths of the cell wall
• increases theabsorptive surface area
• The vacuole extends into the root hair to absorb more water
• Small enough to fitbetween soil particles
Summary of epidermal functions
• Protects plants against injury and
desiccation
• Cuticle prevents water loss
• Guard cells regulate gas exchange
and transpiration
• Root hairs absorb water and
mineral salts from the soil
Parenchyma
• Most abundant plant tissue:
• Large thin walled living cells
• Centrally situated nucleus
• Large vacuole
• Many plastids i.e. chloroplasts and leucoplasts
• Parenchyma cells containing chloroplasts are referred to as chlorenchyma
• Large intercellular air spaces between cells which allows gases to circulate
• Found in roots, stems and leaves
• Main function: storage and photosynthesis, gas movement, packing tissue
Types of parenchyma
• Spongy parenchyma:
– Large round cells
– Loosely packed with many airspaces
– Chloroplasts and leucoplasts
– Found in roots, stems and leaves
– Store substances like starch and water in fleshy organs
Types of parenchyma
• Palisade parenchyma
• Elongated cells arranged vertically
• contain many chloroplast
• Cytoplasm streams to ensure all chloroplasts receive maximum sunlight
• Main photosynthesizing tissue in leaves
• Aerenchyma
• Large air spaces in plants growing in water–logged soils
Functions of parenchyma
• Packing tissue
• Stores water and nutrients
• Air spaces allows for water
movement, photosynthesis and
respiration
Collenchyma • Spherical cells with cell
walls thickened in the
corners
• Long living cells
• Larger than parenchyma
cells
• Contain chloroplasts
• Usually found in young
growing stems
• Support and strength but
allows stretching
• To prevent collapse of
vascular tissue
• to prevent collapse
Sclerenchyma
• Cells with very thick cell walls
• Thickening due to lignin and sometimes suberin
• This causes the contents of the cells to die off leaving a hollow cavity or lumen
• Occur as stone cells or fibres
• Provide support and protection around vascular bundles, fruit, seeds and pips, twine, rope, hemp, linen and other textiles
Sclerenchyma• Fibres
• Elongated cells with
pointed tips
• Thick cells walls
• Mostly found in
vascular tissue
• Tough, strong and
flexible
• Occur in groups with
interlocking ends
• Used to make various
textiles and linen
• Stone cells/ sclereids
• Do not interlock
• Lignified cell walls
• Provide rigidity and
hardness