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Lab 6—Roots, Stems, Leaves
Willow shoot
Plant Parts
Monocot vs Dicot
Plant organs are composed of
three tissue systems:
1. Dermal tissue
2. Vascular tissue
3. Ground tissue
Plant Cell Structure
cell wall
chloroplast
nucleus
central vacuole
Cell Wall Structure
secondary cell wall
primary cell wall
middle lamella
Cell Wall Structure
plasmodesmata
Plant Cell Types
• Xylem
–Tracheids
–Vessel elements
• Phloem
–Sieve-tube
members
–Companion cell
Vascular Tissue
Vascular tissue:
• runs continuous throughout the plant
• transports materials between roots and
shoots.
– Xylem transports water and dissolved minerals
upward from roots into the shoots.
(water the xylem)
– Phloem transports food from the leaves to the
roots and to non-photosynthetic parts of the
shoot system.
(feed the phloem)
Xylem
The water conducting elements
of xylem are the tracheids and
vessel elements.
Xylem
• Tracheids
– Characteristics
• tapered elongated cells
• connect to each other through pits
• secondary cell walls strengthened with
lignin
• dead at functional maturity
– Functions
• transport of water plus dissolved minerals
• support
Xylem
• Vessel Elements
–Characteristics
• shorter and wider than tracheids
• possess thinner cell walls than tracheids
• Aligned end-to-end to form long
micropipes
• dead at functional maturity
–Functions
• transport of water plus dissolved
minerals
• support
Water conducting cells of the xylem
Phloem
• Food and minerals move through
tubes formed by chains of cells,
sieve-tube members.
–sieve plates
–companion cell
Phloem
• Sieve-tube Members
– Characteristics
• living cells arranged end-to-end to form foodconducting cells of the phloem
• lack lignin in their cell walls
• mature cells lack nuclei and other cellular
organelles
• alive at functional maturity
– Functions
• transport products of photosynthesis
Phloem
• Companion Cells
– Characteristics
• living cells adjacent to sieve-tube members
• connected to sieve-tube members via
plasmodesmata
– Functions
• support sieve-tube members
• may assist in sugar loading into sieve-tube
members
Food conducting cells of the phloem
Ground Tissue
Ground tissue fills the interior of the plant. It
contains three basic cell types:
Dermal tissue
– Parenchyma cells
– Collenchyma cells
– Sclerenchyma cells
Ground tissue
Vascular tissue
Parenchyma
• Characteristics
– least specialized cell type
– only thin primary cell wall is present
– possess large central vacuole
– generally alive at functional maturity
• Functions
– make up most of the ground tissues of the plant
– storage
– photosynthesis
– can help repair and replace damaged organs by
proliferation and specialization into other cells
Parenchyma
Collenchyma
• Characteristics
–possess thicker primary cell walls the
that of parenchyma
–no secondary cell wall present
–generally alive at functional maturity
• Functions
–provide support without restraining
growth
Collenchyma
Sclerenchyma
• Characteristics
–have
secondary
cell
walls
strengthened by lignin
–often are dead at functional maturity
–two forms: fibers and sclereids
• Functions
–rigid cells providing support and
strength to tissues
• Two other sclerenchyma cells, fibers
and sclereids, are specialized entirely
in support.
– Fibers are long, slender and tapered,
and usually occur in groups.
• Those from hemp fibers are used for making
rope and those from flax for weaving into
linen.
– Sclereids, shorter than fibers and
irregular in shape, impart the hardness to
nutshells and seed coats and the gritty
texture to pear fruits.
Fiber Cells
Sclereids
Plant Growth & Development
• Meristems– embryonic tissue.
– These cells divide to generate additional cells.
– Initials- generative cells that remain in the
meristem.
– Derivatives- Those that are displaced from the
meristem,and continue to divide for some time
until the cells they produce begin to specialize
within developing tissues.
Locations of Meristematic Tissues
• Apical meristems: located at the tips of
roots and in the buds of shoots, supply
cells for the plant to grow in length.
–Primary growth
• initial root and shoot growth
• produced by apical meristem
• elongation occurs
• restricted to youngest parts of the
plant, i.e, tips of roots & shoots
Locations of Meristematic Tissues
• Lateral meristems: allow the plant to
increase in girth
–Secondary growth: thickening of
roots and shoots.
• Produced by lateral meristems
• Develop in slightly older regions of
roots and shoots
• Examples: vascular and cork cambium.
Meristems
Types of Primary Meristems
• Protoderm: forms dermal tissue system
• Procambium: forms vascular tissue
system
• Ground Meristem: forms ground tissue
system
Primary Growth in Roots
• Root Cap: covers root tip & protects the
meristem as the root pushes through the abrasive
soil during primary growth.
– The cap also secretes a lubricating slime.
• Growth in length is concentrated near the root’s
tip, where three zones of cells at successive
stages of primary growth are located.
– zone of cell division
– zone of elongation
– zone of maturation
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• The procambium gives rise to the stele,
which in roots is a central cylinder of
vascular tissue where both xylem and
phloem develop.
Stele
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Dicot Root
Monocot Root
Monocot
Root
Anatomy
cortex
epidermis
cortex
endodermis
pericycle
stele
pith
pith
phloem
xylem
cortex
Dicot Root
Anatomy
endodermis
pericycle
epidermis
cortex
stele
xylem
phloem
Plant Shoot
Primary
Growth of
the Shoot
Stem Anatomy
Dicot Stem
Monocot Stem
Monocot
Stem
Anatomy
sclerenchyma
phloem
epidermis
vascular
bundles
ground
tissue
xylem
parenchyma
epidermis
Dicot Stem
Anatomy
phloem
cortex
vascular
bundle
pith
vascular
cambium
xylem
Anatomy of a Tree Trunk
• After several years
of secondary
growth, several
zones are visible
in a stem.
Leaf Anatomy
Typical Dicot Leaf X-Section
Cuticle
Palisade
Parenchyma
Epidermis
Vascular
bundles
Guard
Cells
Spongy
Parenchyma
Stoma
Typical Monocot Leaf X-Section
Midvein
Vein
Bundle
sheath cell
Epidermis
Phloem
Xylem
Bulliform
Cells
Stoma
Leaf Stomata: Allow Gas Exchange
Guard cells
Stoma