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Plant Tissue Growth
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Key Concepts
• Overview of Plant Tissues
• Seed-bearing vascular plants have a shoot system with
stems, leaves, and reproductive parts
• Most also have a root system
• These systems consist of ground, vascular, and dermal
tissues
• Plants lengthen or thicken at meristems
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Introducing Meristems
• Plant tissues originate at meristems, which are regions of
undifferentiated cells that retain their ability to divide
• Primary growth (or lengthening) arises from apical
meristems
• Secondary growth (or thickening) arises from lateral
meristems
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Key Terms
• meristem
• Zone of undifferentiated plant cells
• Cells of meristem tissue can divide rapidly
• primary growth
• Plant growth from apical meristems in root and shoot tips
• secondary growth
• Thickening of older stems and roots
• In woody plants, secondary growth occurs when cells of a
thin cylindrical layer of meristem divide
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A
B
B
C
D
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25.3 Components of Plant Tissues
• Simple tissues consist primarily of one type of cell
• Examples: Parenchyma, collenchyma, and sclerenchyma
• Complex tissues have two or more cell types
• Examples: Xylem, phloem, and epidermis
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Simple Tissues
• Parenchyma cells are typically thin-walled, flexible, and are
alive in mature tissue
• Function in storage, secretion, wound repair, photosynthesis,
and other specialized tasks
• Mesophyll is photosynthetic parenchyma
• parenchyma
• Simple plant tissue made up of living cells
• Main component of ground tissue
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Simple Tissues
• Collenchyma cells have thick, flexible walls that support fast-
growing plant parts, and are alive in mature tissue
• collenchyma
• Simple plant tissue composed of living cells with unevenly
thickened walls
• Provides flexible support
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Simple Tissues
• Cells in sclerenchyma die at maturity, but their lignin-
reinforced walls remain and support the plant
• sclerenchyma
• Simple plant tissue that is dead at maturity
• Its lignin-reinforced cell walls structurally support plant
parts
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Complex Tissues
• Complex tissues consist of simple tissues in varying
arrangements and proportions
• Complex tissues:
• Dermal
• Ground
• Vascular
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Dermal Tissues
• The first dermal tissue to form on a plant is epidermis, which
is usually a single layer of cells on the plant’s outer surface
• Epidermal secretions form a cuticle that helps the plant
conserve water and repel pathogens
• epidermis
• Outermost tissue layer of a plant
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Some Dermal Tissues
• Dermal tissues include specialized cells, hairs, and other
epidermal cell outgrowths
• Pairs of specialized epidermal cells form stomata, which
control diffusion of water vapor, oxygen, and carbon dioxide
gases across the epidermis
• Periderm replaces epidermis in woody stems and roots
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Vascular Tissues
• Xylem and phloem are vascular tissues composed of
elongated conducting tubes often surrounded by
sclerenchyma fibers and parenchyma
• Xylem conducts water and dissolved mineral ions
• Consists of dead tracheids and vessel members with
perforated, interconnected walls
• Phloem conducts sugars and other organic solutes
• Consists of live sieve-tube members interconnected to
form sieve tubes
• Companion cells load sugars into sieve tubes
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Fig. 25.7, p. 401
fibers of
sclerenchyma
companion
cell
sieve plate
of sieve-
tube cell
pit in
wall
one
cell’s
wall
parenchyma vessel
of xylem
phloem
A B C
Vascular
Tissues
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Simple Graphic
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Ground Tissues
• Ground tissue (everything other than dermal and vascular
tissue) makes up the bulk of a plant
• Consists mostly of parenchyma, but can also include other
simple tissues
• mesophyll
• Photosynthetic parenchyma
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Overview
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Key Terms
• xylem
• Complex vascular tissue of plants; its tracheids and vessel
members distribute water and mineral ions
• tracheid
• Tapered cell that forms water-conducting tubes in xylem
• Dead at maturity
• vessel member
• Cell that forms water-conducting tubes in xylem
• Dead at maturity
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Key Terms
• phloem
• Complex vascular tissue of plants; distributes sugars
through its sieve tubes
• sieve tube
• Conducting tube of phloem
• companion cell
• In phloem, parenchyma cell that loads sugars into sieve
tubes
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Complex Tissues in a Sunflower
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Overview of Flowering Plant Tissues