Transcript Chapter 35

The Plant Body
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Vegetative Organs of the Flowering Plant Body
• Flowering plants possess three kinds of vegetative
(nonreproductive) organs: roots, stems, and leaves.
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Vegetative Organs of the Flowering Plant Body
• Most flowering plants belong to one of two major
lineages.
• Monocots are generally narrow-leaved flowering
plants such as grasses.
• Eudicots are broad-leaved flowering plants such
as roses.
• Monocots and eudicots account for 97 percent of
the species of flowering plants.
• Most of the remaining species (including water
lilies and magnolias) are structurally similar to
eudicots.
Figure 35.1 Monocots versus Eudicots
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Vegetative Organs of the Flowering Plant Body
• The shoot system of a plant consists of the stems and the
leaves, as well as flowers.
• Leaves are the main sites of photosynthesis.
• Stems hold and display the leaves to the sun and provide
connections for the transport of materials between roots
and leaves.
• A node is the point where a leaf attaches to a stem.
• Regions of stem between nodes are the internodes.
• The root system provides support and nutrition.
Figure 35.2 Vegetative Organs and Systems
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Vegetative Organs of the Flowering Plant Body
• There are two main types of
root system: taproot and
fibrous root.
• Taproot (many eudicots): a
single, large, deep-growing
primary root with smaller
lateral roots.
• Fibrous root system
(monocots and some
eudicots): composed of
numerous thin roots roughly
equal in diameter – holds soil
in place very effectively.
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Vegetative Organs of the Flowering Plant Body
• A bud is an embryonic shoot.
• A stem bears leaves at its nodes, and where each leaf
meets the stem, there is a lateral bud.
• At the tip of each stem or branch there is an apical
bud, which produces the cells for the growth and
development of that stem or branch.
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Vegetative Organs of the Flowering Plant Body
• A potato is a portion of the
plant’s stem, and its “eyes”
contain lateral buds = tuber
• The runners of strawberries
are horizontal stems.
• In some plant species the
leaves are highly modified,
such as the thorns of a cactus.
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Vegetative Organs of the Flowering Plant Body
• Leaves are well
adapted for gathering
light.
• The blade of a leaf is
a thin, flat structure,
attached to the stem
by the petiole, which
holds the leaf at an
angle almost
perpendicular to the
sun.
Figure 35.5 The Diversity of Leaf Forms
A simple leaf
has a single
blade.
A compound
leaf has
multiple
blades (or
leaflets)
arranged
along an axis
or radiating
from a central
point.
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Plant Cells
• Plant cells have all the organelles common to eukaryotes.
• Plant cells have additional distinguishing features:
1) chloroplasts (or other plastids)
2) vacuoles
3) cell wall
• Each plant cell has its own
primary cell wall. Some plant
cells produce a thick secondary
wall.
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• Plasmodesmata are
pore-like structures
that pass through
primary cell walls,
allowing substances
to move freely from
cell to cell without
crossing the plasma
membrane.
Plant Cells
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Plant Cells
• Parenchyma cells are the most numerous type
of cell in young plants.
• Parenchyma cells usually have thin walls and
large central vacuoles.
• The photosynthetic cells in leaves are
parenchyma cells filled with chloroplasts.
• Some parenchyma cells store lipids or starch.
• Other parenchyma cells serve as “packing
material” and play a vital role in supporting the
stem.
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Plant Cells
• Collenchyma cells are supporting cells that lay
down primary cell walls that are thick in the corners.
• Collenchyma cells provide support to leaf petioles,
nonwoody stems, and growing organs.
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• Sclerenchyma cells are
the main supporting cells
of a plant.
• There are two types of
sclerenchyma cells:
elongated fibers and
variously shaped
sclereids.
• Fibers often organize
into bundles.
• Sclereids may pack
together very densely.
Plant Cells
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• The xylem conducts water
from roots to above ground
plant parts. It contains
conducting cells called
Tracheids .
• Vessel elements are the
water “pipeline” system in
flowering plants, also
formed from dead cells.
• Vessel elements are
generally larger in diameter
than tracheids and are laid
down end-to-end to form
hollow tubes.
Plant Cells
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• Cells of the phloem
are alive when they do
their job, unlike those
of the xylem.
• The characteristic cell
of the phloem is the
sieve tube member.
• Cells of the phloem
are arranged end-toend and form long
sieve tubes, which
transport
carbohydrates and
other materials.
Plant Cells
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Plant Cells
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Plant Tissues and Tissue Systems
• A tissue is an organization of cells that work
together as a functional unit.
• Tissues are grouped into tissue systems that
extend throughout the body of the plant from
organ to organ.
• There are three plant tissue systems: vascular,
dermal, and ground.
Figure 35.12 Three Tissue Systems Extend throughout the Plant Body
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Plant Tissues and Tissue Systems
• The vascular tissue system includes the xylem and
phloem; it is the conductive or “plumbing” system of the
plant – occurs in vascular bundles.
• The phloem transports carbohydrates from photosynthesis
from sites of production (sources such as leaves) to sites of
utilization (sinks) elsewhere in the plant ( live cells).
• The xylem conducts water and minerals from the roots to
above ground plant parts (dead cells).
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Plant Tissues and Tissue Systems
• The dermal tissue system is the outer covering of the
plant.
• All parts of the young plant body are covered by an
epidermis, which is a single layer or multiple layers of cells.
• The epidermis contains epidermal cells and other
specialized cells such as guard cells.
• The shoot epidermis secretes a layer of wax (the cuticle)
which helps retard water loss from stems and leaves.
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Plant Tissues and Tissue Systems
• The ground tissue system
makes up the rest of a
plant.
• Ground tissue functions
primarily in storage,
support, photosynthesis,
and the production of
defensive and attractive
substances.
Cross sections of
eudicot leaves.
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Forming the Plant Body
• In plants, the growth of leaves, flowers, and fruits is
determinant (ceases to grow once adulthood is
reached).
• In plants the growth of roots and stems is indeterminate
and is generated from specific regions of active cell
division.
• Plants exhibit regions of:
 Primary growth – leads to lengthening of the plant
body and organ formation.
 Secondary growth – growth in the diameter of stems
and roots (wood and bark).
Figure 35.14 A Woody Twig
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Forming the Plant Body
• The root cap protects the delicate growing area of the root
as it pushes through the soil.
• The root cap also detects the pull of gravity and controls the
downward growth of roots.
• Tissues of the root are divided into three zones: cell
division, cell elongation, and cell differentiation.
Root
cap
Root
tip
Figure 35.15 Tissues and Regions of the Root Tip
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Forming the Plant Body
• Cross sections of most tree trunks in temperate
zone forests have annual rings.
• Wood consists of secondary xylem.
• Annual rings form due to differential rates of
growth in spring (when water is plentiful) and in
summer.
• Wood that is no longer conducting water is known
as heartwood.
• Sapwood is wood that is actively conducting
water and minerals in the tree.
Figure 35.21 Annual Rings
Figure 35.19 Vascular Cambium Thickens Stems and Roots (Part 2)
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Leaf Anatomy Supports Photosynthesis
• Leaf anatomy is adapted to carry out
photosynthesis, limit evaporative water loss, and
transport the products of photosynthesis to the
rest of the plant.
• The zones in leaf that photosynthesize are the
called mesophyll.
• Within the mesophyll is air space through which
CO2 can diffuse to the photosynthesizing cells.
Figure 35.23 (a) The Eudicot Leaf
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Leaf Anatomy Supports Photosynthesis
• Veins supply mesophyll cells with
water and minerals, and they
transport the products of
photosynthesis to the rest of the
plant.
• Leaf epidermis: outermost cell
layer, covered by a waxy cuticle.
Functions to keep water and
photosynthetic products in the
leaf.
• Guard cells allow controlled gas
exchange through pores in the
leaf (the stomata).