STRUCTURAL

ORGANIZATION OF

VASCULAR PLANTS

STRUCTURAL ORGANIZATION OF

VASCULAR PLANTS

The vascular plant body

plan

Root system

Shoot system

Stems

Leaves

Flowers

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PLANT TISSUES

Tissue = collection of similar cells that

perform a common specialized function

Ground tissue

Bulk of the plant body

Vascular tissue

Conduct water (xylem) and nutrients

(phloem)

Dermal tissue

Cover plant outer surfaces

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Meristems

“Stem cells” that give rise to other plant

tissues and direct plant growth

Apical meristems

Lateral meristems

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Apical Meristems

Tips of shoots and roots

Growth in length & height

(primary growth)

Give rise to other tissue layers

Ground, vascular, dermal

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Tissue Development

Development of meristems

Ground meristem

Ground tissue

Procambium

Vascular tissue

Protoderm

Epidermis

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Lateral Meristems

Periphery of shoots and roots

Growth in width (secondary growth)

Woody plants…

Vascular cambium

Produces secondary vascular tissue

Cork cambium

Produces bark

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Ground Tissue

Tissues forming bulk of plant body

Simple tissues

1 type of cell

3 categories of ground tissue

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Ground Tissue

Parenchyma

Soft moist tissues

Roots, stems, leaves,

flowers, fruits

Function

Photosynthesis, food

storage, water storage

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Ground Tissue

Collenchyma

Function

Flexible support

Elongated cells layered with

pectin

Holds cellulose fibers

Maintains pliability

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Ground Tissue

Sclerenchyma

Function

Strength, protection, support

Lines water conducting cells

Thick cell walls fortified with lignin

Fibers or sclereids

Fibers support vascular system

E.g., woven rope (Agave)

Sclereids: e.g., peach stones, pear grit, coconut shell 11

Vascular Tissue

Conducting tissues

Xylem

Transport of water & dissolved minerals

Phloem

Transport of sugars and other solutes

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Transports water & dissolved minerals

Form continuous “pipelines” from roots to leaves

H2O diffuses through pores in walls

Mature cells die: provide support

2 types of elements

Tracheids

Tapered / overlap

Vessel members

End-end

Xylem

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Phloem

Transport of sugars and other

solutes

2 types of elements

Sieve tube members

Sieve plate

Pores (large) between cells

Companion cells

Assist in sugar loading

Sieve cells

No companion cells

Gymnosperms & seedless

vascular plants 14

Dermal Tissue

Epidermis

Provides protective outer covering over plant surfaces

Specialized structures

Cuticle

Waxy outer covering

Stomata

Pores (stoma)

Trichomes

Root hairs

Replaced with secondary growth (bark) in woody plants 15

Dermal Tissue

Carniverous plants

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SHOOT SYSTEM

Stems

Dicots

Vascular bundles

Arranged in ring

Large

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Dicot Stem

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Vascular Bundle

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Shoot System

Stems

Dicots

Monocots

Vascular bundles

Distributed throughout

Smaller

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Monocot Stem Dicot

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Shoot System

Leaves Structure

Node

Petiole / sheath

Blade

Forms

Simple

Undivided

May be lobed

Compound

Blades divided into leaflets

On same plane 22

Leaf Structure

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ROOT SYSTEM

Root structure

Primary root

Lateral roots

Root hairs

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Types of roots

Tap root

Fibrous root

Root Structure

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Fibrous Roots & Competition

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Root Structure

Vascularization

Dicots

Vascular cylinder at core of root

Surrounded by cortex (parenchyma)

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Dicot Root

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Root Structure

Vascularization

Dicots

Monocots

Vascular cylinders in ring

Divide ground tissue

Pith

Cortex

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Monocot Root

Dicot

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Growth in width

Occurs in woody plants over multiple

seasons

Due to cell proliferation at lateral meristems

Secondary Growth

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Secondary Growth

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Secondary Growth

secondary_growth

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Wood & Bark

Wood

Accumulated secondary

xylem

Heartwood

No longer transporting

water

Waste storage: resins

and gums

Darken, strengthen

heartwood

Sapwood

Actively transporting water

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Wood & Bark

Bark

Cork

Cork cambium

Secondary phloem

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Wood & Bark

Wood

Growth rings

Reflect seasonal

activity

Temperate regions

1 ring per year

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Growth Rings

Spring xylem (early wood)

Lighter / wider

Larger diameter xylem

Optimum growing season

(light, water, temp)

Summer xylem (late wood)

Darker / narrower

Smaller diameter xylem

Slower growth (heat/cold,

less water)

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Hardwood

E.g., oak, maple, cherry

Higher number of vessel members in xylem

Reinforced with collenchyma / sclerenchyma

fibers

Softwood

E.g., pine, fir, hemlock

Gymnosperms (conifers)

Xylem = tracheids (no vessel

members)

Lack supportive ground tissue

fibers

Hardwoods vs. Softwoods

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