Download The Plant Body

Topic 14.1
The Structure & Growth of Flowering Plants
Biology 1001
November 4, 2005
I. The structure of Flowering Plants
The Plant Body
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Plants are multicellular
organisms with organs and
organ systems, tissues, and
cells (see Fig. 1.3)
The three basic plant organs
are roots, stems, and leaves
They are organized into a
root system and a shoot
system
The two systems are
interdependent and each
accesses a different part of
the plant’s environment
Figure 35.2(!!)
Plant Organs - Roots
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A root is an organ that
anchors a vascular
plant, absorbs water
and minerals, and may
store organic nutrients
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Root hairs increase the
surface area of the root
for absorption
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Variations of a theme:
taproots, lateral roots,
fibrous roots, storage
roots, aerial roots,
adventitious roots…
Plant Organs - Stems
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A stem is a shoot organ consisting of alternating nodes and
internodes that supports leaves and flowers
Axillary buds are located at the apexes of leaves and have the
potential to form lateral shoots (branches)
The terminal bud contains developing leaves and a compact
series of nodes and internodes, and is the site at which most
shoot elongation occurs
Stem variations include stolons, bulbs, tubers, rhizomes
Plant Organs - Leaves
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The leaf is the main
photosynthetic organ of most
plants, and consists of a blade
and petiole (stalk)
Flowers, the reproductive organs
of flowering plants, are shoots
composed of highly modified
leaves and stems
Leaves also contain veins of
vascular tissue
Leaf morphology and venation
pattern are used to classify plants
Modified leaves include tendrils,
spines, storage leaves, bracts,
and reproductive leaves
Plant Tissues Systems
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Each plant organ has dermal,
vascular and ground tissue systems
These tissue systems are continuous
throughout the plant and connect the
organs
The dermal tissue system is the outer
protective covering of the plant –
usually a single layer of tightly
packed cells called the epidermis
The vascular tissue system contains
xylem & phloem which are used for
long-distance transport in the plant
The ground tissue functions in
storage, photosynthesis, and support
Figure 35.8(!) The three
plant tissue systems
Plant Cells
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Fig. 6.9 - a generic plant cell
Like other multicellular
organisms, plant cells are
differentiated into specialized
types with particular functions
Differentiation can be at the
level of the protoplast (living
part of the cell) or at the level of
the cell wall
Plant cells can have primary and
secondary cell walls
Plants cells can be living or dead
at functional maturity
Figure 35.9(!) - Exploring Examples of
Differentiated Plant Cells
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Parenchyma cells are living cells with
flexible primary cell walls, large vacuoles,
and no secondary cell walls
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They are the least differentiated of plant cells
and perform most of the metabolic synthesis and
storage functions of the plant
They retain the ability to divide and differentiate
into other cell types
Examples include photosynthetic cells, the
fleshy part of a fruit, and cells that store starch in
plastids
Figure 35.9(!) - Exploring Examples of
Differentiated Plant Cells
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Collenchyma cells are living
cells with unevenly thickened
primary walls that remain
flexible
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Grouped in strands or cylinders,
they provide support for a young
growing plant
Figure 35.9(!) - Exploring Examples of
Differentiated Plant Cells
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Sclerenchyma cells are dead
at functional maturity, and
they have thick secondary
cell walls strengthened with
lignin
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They support the non-growing
parts of the plant
Sclereids and fibers are two
types of sclerenchyma cells
Figure 35.9(!) - Exploring Examples of
Differentiated Plant Cells
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Phloem contains two types of sugarconducting cells called sieve-tube
members and companion cells
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Both types are alive at functional
maturity
Sieve-tube members lack organelles,
and are connected end-to-end to form
sieve tubes with porous sieve plates at
the ends of each cell. These are the cells
that conduct organic nutrients
Companion cells are adjacent to sievetube members and perform the
metabolic functions for both cell types;
they also function to load sugars into the
sieve tubes
Figure 35.9(!) - Exploring Examples of
Differentiated Plant Cells
 Xylem
contains two types of waterconducting cells called tracheids
and vessel elements
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Tubular, elongated cells with
thickened secondary walls that are
dead at functional maturity and act as
conduits for the flow of water
Tracheids are thin tapered cells whose
secondary walls are thickened by
lignin; water moves laterally between
tracheids via pits
Vessel elements are connected end-toend to form vessels. Water moves into
vessel elements laterally via pits, and
then flows vertically through porous
end plates