Transcript Monocot root

Chapter 9: Plant Organization
9-1
Plant Organs
The flowering plants, or angiosperms,
have characteristic organs and tissues.
An organ is a structure that contains
different types of tissues and performs
one or more specific functions.
The vegetative organs of a flowering
plant – the root, stem, and leaf – allow
the plant to live and grow.
The body of a plant has a root system
and a shoot system.
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Organization of the plant body
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Roots
The root system of a plant has a main
root, or taproot, and many branch or
lateral roots.
The root system absorbs water and
minerals from the soil for the plant.
The cylindrical shape of the root allows it
to penetrate the soil.
Root hairs greatly increase the
absorptive capacity of the root.
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Roots can also have other functions.
Roots produce hormones that stimulate
the growth of stems and coordinate
their size with the size of the root.
Generally the root system is equivalent in
size and extent to the shoot system.
Perennial plants often store the products
of photosynthesis in their roots.
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Root system
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Stems
The shoot system of a plant includes
both stems and leaves.
A stem is the main axis of the plant along
with its lateral branches.
At the tip of the stem is tissue that allows
the stem to elongate and produce
leaves.
A leaf attached to a stem at a node; and
internode is the region beween nodes.
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Shoot system
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Stems also contain vascular tissue that
transports water and minerals from
roots to leaves, and also transports the
products of photosynthesis in the
opposite direction.
A cylindrical stem can expand in girth as
well as in length.
Some stems have functions other than
transport; some are specialized for
storage.
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Leaves
A leaf is a broad, thin organ that carries
on photosynthesis.
This shape maximizes the surface area
for collection of solar energy and
absorption of carbon dioxide.
The wide portion of a leaf is the blade, a
petiole is the stalk of the leaf, and
axillary buds are found at the leaf axil.
Some leaves have other functions.
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Leaves
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Monocot Versus Dicot Plants
Flowering plants are divided into two
groups depending on their number of
cotyledons (seed leaves).
Monocots (monocotyledons) have one
cotyledon; dicots (dicotyledons) have
two.
Cotyledons provide nutrients for
seedlings before true leaves begin
photosynthesizing.
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The vascular (transport) tissue is
organized differently in monocots and
dicots.
Monocot roots have vascular tissue in a
ring; in stems, vascular bundles are
scattered.
Dicot roots have vascular tissue in a star
shape with phloem located between
arms of xylem.
Dicot stems have vascular bundles in a
ring.
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Monocot and dicot traits
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Leaf veins are vascular bundles within a
leaf.
Monocots usually have parallel venation.
Dicots exhibit netted venation, which
may be either pinnate or palmate.
Adult monocots and dicots differ in the
number of flower parts, and dicot
pollen grains have three apertures
while monocot pollen grains have one
aperture.
Important monocots are rice, wheat and
corn; oak trees and dandelions are
dicots.
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Dicot leaves
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Plant Tissues
A plant grows throughout its lifespan
because of meristem (embryonic
tissue) in stem and root tips (apexes).
Three specialized tissues are in plants:
1) Epidermal tissue – forms the outer
protective covering
2) Ground tissue – fills interior of a plant
3) Vascular tissue – transports water and
nutrients and provides support.
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Epidermal Tissue
Epidermal tissue forms the outer
protective covering of a herbaceous
plant and is modified in roots, stems,
and leaves.
Exposed epidermal cells are covered
with waxy cuticle to minimize water
loss.
Epidermal cells in roots have root hairs.
Lower leaf epidermal cells have guard
cells and stomata.
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Root hairs
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Stoma of leaf
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In older woody plants, the epidermis of
the stem is replaced by cork tissue.
Cork, a component of bark, is made up of
dead cells that may be sloughed off.
New cork cells are made by a meristem
called cork cambium.
As cork cells mature, they fill with
suberin, a lipid that makes them
waterproof and chemically inert.
Cork protects woody plants and helps
them resist fungi, bacteria, and
animals.
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Cork of older stem
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Ground Tissue
Ground tissue forms the bulk of the
plant.
Ground tissue contains parenchyma
cells, which are thin-walled and capable
of photosynthesis when they contain
chloroplasts.
Collenchyma cells have thicker walls for
flexible support.
Sclerenchyma cells are hollow, nonliving
support cells with secondary walls.
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Ground tissue cells
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Vascular Tissue
There are two types of vascular
(transport) tissue that extend from
roots to leaves.
Xylem transports water and minerals
from roots to leaves and contains two
types of conducting cells: tracheids
and vessel elements.
Phloem transports organic nutrients from
leaves to roots and has sieve-tube
elements with companion cells;
plasmodesmata extend between cells
at sieve plates.
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Xylem structure
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Phloem structure
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Organization of Roots
Within a root are zones where cells are in
various stages of differentiation.
The root apical meristem is in the zone of
cell division; the root cap is a
protective covering for the root tip.
In the zone of elongation, cells become
longer as they specialize.
In the zone of maturation, mature cells
are differentiated and epidermal cells
have root hairs.
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Dicot root tip
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Tissues of a Dicot Root
Epidermis – single layer of thin-walled,
rectangular cells; root hairs present in
zone of maturation
Cortex – thin-walled, loosely-packed
parenchyma; starch granules store
food
Endodermis – between cortex and
vascular cylinder, single layer of
endodermal cells bordered by the
Casparian strip; regulates entrance of
minerals into the vascular cylinder
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Movement of materials into
vascular cylinder
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Vascular Tissue – has star-shaped xylem
in dicots with phloem in separate
regions between arms of xylem; the
pericycle gives rise to lateral roots
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Branching of a dicot root
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Organization of Monocot Roots
Monocot roots have the same growth
zones as a dicot root but they do not
undergo secondary growth.
In a monocot root’s centrally located pith,
ground tissue is surrounded by a
vascular ring composed of alternating
xylem and phloem bundles.
Monocot roots also have pericycle,
endodermis, cortex, and epidermis.
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Monocot root
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Root Diversity
Roots have special adaptations and
associations to better perform the
functions of anchorage, absorption of
water and minerals, and carbohydrate
storage.
In some dicot plants, a primary root, or
taproot, grows straight down and is the
dominant root; it can be fleshy and
stores food.
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Taproot
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Monocots have no single main root but
instead have a large number of slender
roots.
These slender roots and their lateral
branches make up a fibrous root
system.
Fibrous roots develop from the lower
nodes of the stem rather than from the
root system, and are known as
adventitious roots.
Adventitious roots that emerge from the
surface to help anchor the plant are
called prop roots.
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Fibrous roots and prop roots
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Some plants (dodders and broomrapes)
are parasitic on other plants.
Their stems have rootlike projections
called haustoria that grow into the host
plant and extract water and nutrients
from the host.
Mycorrhizae are a mutualistic association
between roots and fungi that aid the
plant in extraction of nutrients and
water from soil.
Peas and other legumes have root
nodules in which nitrogen-fixing
bacteria live.
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Dodder
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Organization of Stems
During primary growth, the shoot apical
meristem at the shoot tip produces new
cells that elongate and add length to
the stem.
The shoot apical meristem is protected
within a terminal bud where leaf
primordia envelope it.
In the temperate zone, a terminal bud
stops growing in winter and is
protected by bud scales.
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Leaf primordia are produced at nodes;
the stem between two nodes is called
an internode.
Internodes increase in length as the stem
grows.
Axillary buds, which are dormant but
may develop into branch shoots or
flowers, form at the axes of leaf
primordia.
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Shoot tip
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In addition to leaf primordia, three
specialized types of primary meristem
that contribute to shoot length develop
from shoot apical meristem.
Protoderm gives rise to epidermis.
Ground meristem produces parenchyma
in the pith and parenchyma in the
cortex.
Procambium produces primary xylem
and primary phloem; later, vascular
cambium occurs between xylem and
phoem.
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Fate of primary meristems
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Herbaceous Stems
Mature nonwoody stems, or herbaceous
stems, exhibit only primary growth.
The outermost tissue is the epidermis,
which is covered by waxy cuticle.
These stems have distinctive vascular
bundles, with xylem toward the inside
and phloem toward the outside.
In dicot stems, vascular bundles are in a
distinct ring; monocot vascular
bundles are scattered throughout.
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Herbaceous dicot stem
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Monocot stem
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Woody Stems
A woody plant has both primary and
secondary tissues.
Primary tissues are new tissues formed
each year from primary meristems right
behind apical meristem.
Secondary tissues develop during the
second and subsequent years of
growth from lateral meristems
(vascular cambium and cork cambium).
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Primary growth, which occurs in all plants,
increases the length of the plant.
Secondary growth, which occurs in
conifers and some dicots, increases the
girth of a plant.
Trees undergo secondary growth because
of a change in vascular cambium.
The secondary tissues produced by the
vascular cambium, called secondary
xylem and secondary phloem, add to the
girth of trunks, stems, branches, and
roots.
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Dicot stems
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Secondary growth in a dicot
stem
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As a result of secondary growth, a woody
dicot stem has an entirely different type of
organization.
A woody stem now has three distinct areas:
the pith, the wood, and the bark.
Pith rays are composed of living
parenchyma cells that allow materials to
move laterally.
The bark of a tree contains cork, cork
cambium, and phloem.
Cork cambium replaces epidermis with
cork cells impregnated with suberin.
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Section of woody stem
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Annual Rings
In trees that have a growing season,
vascular cambium is dormant during
winter.
In spring, with plentiful moisture, xylem
contains wide vessels with thin walls in
spring wood; summer wood has a
lower proportion of vessels.
Spring wood followed by summer wood
makes up one year’s growth or annual
ring.
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Tree trunk
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Stem Diversity
Plants use stems for such functions as
reproduction, climbing, survival, and
food storage.
Modified stems aid adaptation to different
environments.
Examples of stem modifications include:
Stolons
Rhizomes
Tubers
Corms
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Stolons and rhizomes
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Tubers and corms
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Organization of Leaves
Leaves are the organs of photosynthesis
in vascular plants.
Leaves have a flattened blade, that may
be single or composed of leaflets,
attached to a petiole.
The epidermal layers may bear protective
hairs or glands that produce irritating
substances; a waxy cuticle reduces
water loss and permits gas exchange.
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Guard cells surrounding stomata in the
lower epidermis allow gases to enter
and exit the leaf.
The body of the leaf is composed of
mesophyll.
Palisade mesophyll has elongated cells,
and spongy mesophyll has irregular
cells surrounded by air spaces.
Parenchyma cells of these mesophyll
layers house chloroplasts.
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Leaf structure
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Leaves are adapted to environmental
conditions and may be broad and wide
or reduced with sunken stomata.
The leaves of a cactus are spines
attached to a succulent stem.
Climbing leaves, such as those of peas,
are modified into tendrils.
The leaves of a few plants are specialized
for catching insects.
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Classification of leaves
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Leaf diversity
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Chapter Summary
A flowering plant (angiosperm) has three
vegetative organs: the root absorbs
water and minerals, the stem supports
and services leaves, and the leaf
carries on photosynthesis.
Flowering plants can be divided into
monocots and dicots based on
structural differences.
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Three types of meristem divide and
produce specialized tissues.
Dermal tissue consists of epidermis
composed of epidermal cells.
Ground tissue contains parenchyma,
collenchyma, and sclerenchyma cells.
Vascular tissue consists of xylem (vessel
elements and tracheids) that transports
water and minerals, and phloem (sievetube elements and companion cells)
that transports organic nutrients.
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A root tip has three zones: the zone of cell
division, the zone of elongation, and the
zone of maturation.
A herbaceous root has epidermis, cortex,
endodermis, and a vascular cylinder.
The dicot vascular cylinder is star-shaped,
while the monocot root has a ring of
vascular tissue with alternating bundles
of xylem and phloem surrounding pith.
Roots have diverse structures, including
taproots, adventitious roots, and prop
roots.
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Primary growth of a stem is due to the
shoot apical meristem, which is
protected within a terminal bud.
Stems have nodes and internodes.
In cross section, a nonwoody dicot has
epidermis, cortex, vascular bundles in a
ring, and an inner pith.
Monocots have scattered vascular
bundles.
Secondary growth is due to vascular
cambium; wood contains annual rings
of xylem.
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Stems are diverse; humans find many
uses for stems.
A leaf has an upper and a lower
epidermis, and mesophyll tissue forms
the bulk of the leaf.
Stomata regulate the passage of gases in
and out of leaves.
Leaves are diverse and are adapted to
environmental conditions.
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