Chapter 10 Chapter 10 Rotational motion Rotational motion Part 2 Part 2.
HMM1414 Chapter 5 Part 2
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Transcript of HMM1414 Chapter 5 Part 2
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Cells displaced from meristem,
derivatives, continue to divide for sometime until the cells they produce
differentiate within developing tissues.
Pattern of plant growth depends
on the location of meristems.
Two major types of meristems
(i) Apical Meristem Located at tips ofroots & in buds of shoots
Supply cells for plant to grow in length.
This elongation, primary growth, enablesroots to extend through soil and shoots to
increase their exposure to light and CO2. In herbaceous plants, primary growth
produces almost all of plant body.
(ii) Lateral Meristems(Cambium)
Add thickness to woody plants, a processcalled secondary growth (progressivethickening of roots and shoots where
primary growth has ceased.)
Two lateral meristems: vascularcambium and cork cambium.
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Vascular cambium adds layers of vascular
tissue called secondary xylem (wood) and
secondary phloem.
Cork cambium replaces epidermis with
periderm, which is thicker and tougher.
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5.6.2 PLANT CELL TYPESThree Tissue Systems:1. Dermal - epidermis,2. Vascular-Xylem + Phleom , and3. Ground- Parenchyma,collenchyma
(See Figure 35.8, Campbell, page 717)
Each system is continuous throughout
plant body.
(1) Dermal Tissue Outer covering.
In non-woody plants, it is a single layer of
tightly packed cells, orepidermis thatcovers and protects all young parts ofplant.
Epidermis has other specialized
characteristics consistent with function of
organ it covers.
Example:
Root hairs - extensions of epidermalcells near root tips.
Cuticle waxy coating secreted byepidermis of leaves and most stems -
helps aerial parts of plant retain water.
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In woody plants, protective tissues called
periderm replace epidermis in olderregions of stems and roots.
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(2) Vascular Tissue Continuous throughout plant - involved in
transport of materials between roots andshoots.
The two types of vascular tissues:
(i) Xylem Conveys water and dissolved
minerals upward from roots into
shoots.
(ii) Phloem Transports food (organic nutrients)
made in mature leaves to roots; to
non-photosynthetic parts of shoot
system; and to sites of growth, such
as developing leaves and fruits.
Vascular tissue of a root or stem is called
the stele. In angiosperms, stele of root forms a
solid central vascular cylinder. The stele of stems and leaves is divided
into vascular bundles, strandsconsisting of xylem and phloem.
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(3) Ground Tissue Tissue that is neither dermal nor vascular
tissue. In eudicot stems, ground tissue divided
into pith, internal to vascular tissue, andcortex, external to the vascular tissue.
Functions - photosynthesis, storage, and
support.
Example, the cortex of a eudicot stem
has both fleshy storage cells and thick-
walled support cells.
Some major types of plant cells:
(See Figure 35.8, Campbell, page 718 719)
(a) Parenchyma(b) Collenchyma(c) Sclerenchyma(d)Water-conducting cells of the xylem(e) Sugar-conducting cells of thephloem
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(a) Parenchyma Primary wall relatively thin and
flexible Most lack secondary wall.
Protoplast usually has large central
vacuole.
Often depicted as typical plant cells
because they generally are the least
specialized, but there are exceptions.
For example, highly specialized sieve-
tube members of phloem are parenchyma
cells.
Perform most of metabolic functions of
plant, synthesizing and storing various
organic products.
For example, photosynthesis occurs
within chloroplasts of parenchyma cells
in leaf.
Some parenchyma cells in stems and
roots have colorless plastids that store
starch.
Fleshy tissue of most fruit is composed of
parenchyma cells.
Most parenchyma cells retain
ability to divide and differentiate into other
cell types under special conditions, such as
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repair & replacement of organs after injury
to plant.
Possible to regenerate entire plant from
single parenchyma cell in lab.
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/groundtsa.jpg
(b) Collenchyma Thicker primary walls than parenchyma
cells.
Walls unevenly thickened.
Grouped into strands or cylinders,
collenchyma cells help support youngparts of plant shoot.
Young stems and petioles often have
strands of collenchyma just below
epidermis, providing support without
restraining growth.
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Mature collenchyma cells are living and
flexible and elongate with stems and
leaves they support.
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/groundtsb.jpg
(c) Sclerenchyma Have thick secondary walls usually
strengthened by lignin and function as
supporting elements of plant.
Much more rigid than collenchyma cells.
Unlike parenchyma cells, they cannot
elongate. Occur in plant regions that have stopped
lengthening.
Many are dead at maturity, but they
produce rigid secondary cells walls before
protoplast dies.
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In parts of plant that are still elongating,
secondary walls are deposited in a spiral
or ring pattern, enabling the cell wall to
stretch like a spring as the cell grows.
Two types: fibers and sclereids -
specialized entirely for support.
(i) Fibers Long, slender, and tapered, and
usually occur in groups. Hemp fibers are used for making rope;
those from flax are woven into linen.
(ii) Sclereids (Stone cells) Irregular in shape and shorter than
fibers.
Very thick, lignified secondary walls. Gives hardness to nutshells and seed
coats and gritty texture to pear fruits.
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Sclerenchyma fibers
Stone cells or sclereids
http://www2.volstate.edu/msd/BIO/1020/lab10planttissues.htm
(d) Xylem Water-conducting elements of xylem,tracheids and vessel elements, areelongated cells that are dead at maturity.
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Thickened wall
Pit
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Thickened cell walls remain as a
nonliving conduit (tube) through which
water can flow.
Both have secondary walls interrupted bypits, thinner regions where only primarywalls are present.
(i) Tracheids Long, thin cells with tapered ends.Water moves from cell to cell mainly
through pits. Because their secondary walls are
hardened with lignin, tracheids function
in support as well as transport.
(ii) Vessel elements
Generally wider, shorter, thinner walled,
and less tapered than tracheids.
Aligned end to end, forming long
micropipes orxylem vessels. Ends are perforated, enabling water to
flow freely.
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Tracheids Vessel elements
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http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPLANTANAT.html
Other xylem cells: fibers & parenchyma
not conductive.
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Pit
Perforationplate
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPLANTANAT.htmlhttp://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPLANTANAT.html -
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(e) Phloem Sucrose, other organic compounds, and
some mineral ions move through tubesformed by chains of cells called sieve-tube members. Alive at maturity, although cell lacks
nucleus, ribosomes, and vacuole.
End walls (sieve plates) have pores thatfacilitate flow of fluid between cells.
Each sieve-tube member has non-
conducting nucleated companion cell,connected to sieve-tube member by
numerous plasmodesmata.
Nucleus and ribosomes of companion cell
serve both that cell and adjacent sieve-
tube member.
In some plants, companion cells in leaves
help load sugar into sieve-tube members,
which transport sugars to other parts of
plant.
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http://io.uwinnipeg.ca/~simmons/2153/lb1pg6.htm
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5.6.3 STRUCTURE OF EUDICOT &MONOCOT STEMS, ROOTS ANDLEAVES
(1) Tissue Organization of Stems In gymnosperms and most eudicots,
vascular tissue consists of vascular
bundles arranged in a ring
In most monocot stems, vascular bundles
are scattered throughout ground tissue.
(a) Structure of eudicot stem
Epidermis (dermal tissue):
Outer surface covered with cuticle.
May be perforated with stomata.
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Cortex (ground tissue)
Several layers of collenchyma cells
immediately below epidermis
Parenchyma cells below collenchyma
cells.
Vascular bundles
Arranged in a ring.
Xylem towards inner side, and phloem
towards outside. Xylem and phloem separated by
cambium.
Pith (ground tissue)
Made up of living parenchyma cells.
Secondary growth
Woody dicot plants undergo
secondary growth, an increase in girth of
stems.
Cambium divides, forming secondary
xylem (wood) on inside and secondary
phloem (inner bark) on outside.
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(b) Structure of monocotyledonous stem
Epidermis (dermal tissue):
Outer surface covered with cuticle.
May be perforated with stomata.
Does not have distinct area of cortex.
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Vascular bundles
Not arranged in a circle/ring but are
scattered throughout ground tissues.
Does not possess lateral meristems
(cambium) that give rise to secondary
growth.
Monocot does not produce wood.
(2) Tissue Organization of Roots In roots of typical gymnosperms and
eudicots, as well as some monocots, the
stele is a vascular cylinder consisting of a
lobed core of xylem with phloem between
lobes.
Stele of many monocot roots is a vascular
cylinder with a core of parenchyma
surrounded by a ring of alternating xylem
and phloem.
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(a) Internal structure of eudicot root
http://sps.k12.ar.us/massengale/plant_structure_bi1.htm
Epidermis
No cuticle.
Have root hairs. Cortex
Contains thin-walled parenchyma
cells.
Endodermis
One layer of cells. Each cell has a
special bandlike region, called a
Casparian strip. Pericycle
One layer of cells.
Surrounds vascular bundle.
Vascular cylinder
Xylem arranged like a star in
transverse section with several spokes.
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Phloem located in between spokes
of xylem.
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(b) Internal structure of monocot root
Epidermis
No cuticle.
Have root hairs.
Cortex
Contains thin-walled parenchyma
cells.
Endodermis
One layer of cells.
Pericycle
One layer of cells.
Surrounds vascular bundle.
Vascular cylinder
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Xylem does not arrange like a star in
transverse section.X AND P ARRANGED
ALTERNATELY
Phloem and xylem are in separate
alternating bundles arranged around
central pith.
Pith consists of parenchyma cells.
(3) Tissue Organization of Leaves Epidermis in leaves is interrupted by
stomata, which allow CO2 exchange
between air and photosynthetic cells in a
leaf.
Ground tissue in a leaf is sandwiched
between upper and lower epidermis.
Vascular tissue of each leaf is continuous
with vascular tissue of stem.
(a) Internal structure of eudicot leaf
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http://home.earthlink.net/~dayvdanls/plant_structure.html
Epidermis
On upper and lower surface.
Outer surface covered with cuticle.
Lower epidermis perforated by
stomata.
Palisade mesophyll.
Very little air spaces between
palisade cells.
Cells contain chloroplast performs
most of the photosynthesis.
Spongy mesophyll
Loosely arranged allows CO2 to
diffuse easily.
Cells contain fewer chloroplasts.
Vascular bundles
Xylem and phloem surrounded by
bundle sheath.
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Xylem and phloem in leaves form in
strands called veins.
Most dicots have netted venation.
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(b) Internal structure ofmonocotyledonous leaf
Epidermis
On upper and lower surface.
Outer surface covered with cuticle.
Lower epidermis perforated by
stomata.
Although most monocots have both
palisade and spongy mesophylls, some
monocots lack distinct regions of palisadeand spongy mesophylls.
Vascular bundles
Leaves of most monocots have
parallel venation.
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http://www.cbu.edu/~seisen/LeafStructure.htm
http://www.cbu.edu/~seisen/LeafStructure.htmhttp://www.cbu.edu/~seisen/LeafStructure.htm