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Plant Tissues
Chapter 26
Jin Hoe Huh
March 28, 2005
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Angiosperms – flowering plants
• The angiosperms are seed-bearing vascular plants
• In terms of distribution and diversity, they are the most successful plants on Earth
• The structure and function of this plant group help explain its success
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Flowering Plant Life
Cycle Double fertilization Meiosis Meiosis
microspores
Female gametophyte
pollination
Mitosis without cytoplasmic division
Two sperms enter ovule
Diploid
Haploid
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Plant Life Histories
• Annuals complete life cycle in one
growing season
• Biennials live for two seasons; flowers
form in second season
• Perennials grow and produce seeds
year after year
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Shoot System
Root System
Root system
- anchors the plant
- penetrates the soil and absorbs water and minerals
- stores food
Shoot system
- produces sugars by photosynthesis
- carries out reproduction
Shoot and Root Systems
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water & minerals
sugar
SHOOT SYSTEM
ROOT SYSTEM
Shoot and root systems are interdependent
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Plant Tissue Systems
VASCULAR TISSUES
GROUND TISSUES
SHOOT SYSTEM
ROOT SYSTEM
EPIDERMIS
• Ground tissue system
• Vascular tissue system
• Dermal tissue system
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Meristems – Where Tissues Originate
• Regions where cell divisions produce plant growth
• Apical meristems– Lengthen stems and roots– Responsible for primary growth
• Lateral meristems– Increase width of stems– Responsible for secondary growth
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Apical Meristems
activity atmeristems
new cellselongateand start todifferentiateinto primarytissues
procambium primary vascular tissues
protoderm epidermis
Cells that form at apical meristems:
ground meristem ground tissues
Lengthen shoots and roots:SAM and RAM
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Lateral Meristems
vascular cambium secondary vascular tissues
periderm cork cambium
thickening
Increases girth of older roots and stems
Cylindrical arrays of cells
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Simple Tissues
Made up of only one type of cell
Parenchyma
Collenchyma
Sclerenchyma
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collenchymaparenchyma sclerenchyma
Morphology of three simple tissue types
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Parenchyma: A Simple Tissue
• Comprises most of a plant’s soft primary growth
• Cells are pliable, thin walled, many sided
• Cells remain alive at maturity and retain capacity to divide
• Mesophyll is a type of parenchyma that contains chloroplasts
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Collenchyma: A Simple Tissue
• Specialized for support for primary tissues
• Cells are elongated, with walls (especially corners) thickened with pectin
• Makes stems strong but pliable
• Cells are alive at maturity
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Sclerenchyma: A Simple Tissue
• Supports mature plant parts• Protects many seeds• Cells have thick, lignified walls and are dead
at maturity• Two types:
– Fibers: Long, tapered cells– Sclereids: Stubbier cells
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Complex Tissues
Composed of a mix of cell types
Xylem
Phloem
Epidermis
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Xylem
• Conducts water and dissolved minerals
• Conducting cells are dead and hollow at maturity
vessel membertracheids
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Phloem: A Complex Vascular Tissue
• Transports sugars
• Main conducting cells are sieve-tube members
• Companion cells assist in the loading of sugars
sieve plate
sieve-tubemember
companioncell
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Epidermis: A Complex Plant Tissue
- Covers and protects plant
surfaces
- Secretes a waxy,
waterproof cuticle
- In plants with secondary
growth, periderm replaces
epidermis
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Monocots and Dicots – same tissues, different features
Parallel veinsNetlike veins
3 pores1 pore
4 or 5 floral parts
3 floral parts
1 cotyledon 2 cotyledons
Vascular bundles dispersed
Vascular bundles in ring
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Shoot Development
ground meristem
primary xylempithprocambriumcortex
procambriumprotoderm
shoot apicalmeristem
primary phloem
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Bud = undeveloped shoot of meristematic tissue
Internode
Leaves
Axillary bud at node
Longitudinal section of terminal bud
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Roots also have meristems
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Internal Structure of a Dicot Stem
- Outermost layer is epidermis
- Cortex lies beneath epidermis
- Ring of vascular bundles separates the cortex from the pith
- The pith lies in the center of the stem
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Internal Structure
of a Monocot
Stem
• The vascular bundles
are distributed
throughout the ground
tissue
• No division of ground
tissue into cortex and
pith
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Dicots
Dicots and Monocots have different stem and root anatomies
Ground tissuesystem
Vascular tissue system
Dermal tissuesystem
Monocots
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Leaf Gross Structure
petiole
blade
axillarybud
node
blade
sheath
node
DICOT MONOCOT
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Adapted for Photosynthesis
• Leaves are usually thin – High surface area-to-volume ratio
– Promotes diffusion of carbon dioxide in, oxygen out
• Leaves are arranged to capture sunlight– Are held perpendicular to rays of sun
– Arrange so they don’t shade one another
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Leaf StructureUPPER
EPIDERMIS
PALISADEMESOPHYLL
SPONGYMESOPHYLL
LOWEREPIDERMIS
one stoma
cuticle
O2CO2
xylem
phloem
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Mesophyll:Photosynthetic Tissue
• A type of parenchyma tissue
• Cells have chloroplasts
• Two layers in dicots
– Palisade mesophyll
– Spongy mesophyll
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Parenchyma
Collenchyma
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Leaf Veins: Vascular Bundles
• Xylem and phloem –
often strengthened with fibers
• In dicots, veins are netlike
• In monocots, they are parallel
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Root Systems
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Root Structure
• Root cap covers tip
• Apical meristem produces the cap
• Cell divisions at the apical meristem cause the root to lengthen
• Farther up, cells differentiate and mature
root apical meristem
root cap
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Internal Structure of a Root
• Outermost layer is epidermis
• Root cortex is beneath the epidermis
• Endodermis, then pericycle surround
the vascular cylinder
• In some plants, there is a central pith
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pericycle
phloem
xylem
root hair
endodermis
epidermis
cortex
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Root Hairs and Lateral Roots
• Both increase the surface area
of a root system
• Root hairs are tiny extensions
of epidermal cells
• Lateral roots arise from the
pericycle and must push
through the cortex and
epidermis to reach the soil
newlateralroot
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Secondary Growth
• Occurs in perennials
• A ring of vascular cambium produces
secondary xylem and phloem
• Wood is the accumulation of these
secondary tissues, especially xylem
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Secondary Growth
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Woody Stem
periderm (consists ofcork, cork cambium,and secondary cortex)
secondaryphloem
BARK
HEARTWOOD SAPWOOD
vascular cambium
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Annual Rings
• Concentric rings of secondary xylem
• Alternating bands of early and late wood
• Early wood– Xylem cells with large diameter, thin walls
• Late wood– Xylem cells with smaller diameter, thicker
walls
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Types of Wood
• Hardwood (oak, hickory)– Dicot wood– Xylem composed of vessels, tracheids,
and fibers
• Softwood (pine, redwood)– Gymnosperm wood– Xylem composed mostly of tracheids– Grows more quickly