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NOTES: CH 35 - Plant Structure
& Growth
In their evolutionary journey, plants
adapted to the problems of a
terrestrial existence as they moved
from water to land
ANGIOSPERMS
(flowering plants)
-most diverse and widespread of plants
(about 275,000 species!)
-characterized by FLOWERS and
FRUITS (adaptations for reproduction
and seed dispersal)
*Angiosperms are divided into two
taxonomic classes:
1) MONOCOTS
2) DICOTS
Terrestrial plants faced a divided
habitat:
 air is the source of CO2 for
photosynthesis (not dissolved
in water)
 sunlight cannot penetrate
soil
 soil provides water and
dissolved minerals to plant
To accommodate this divided habitat,
plants have two basic systems:
1) ROOT SYSTEM
(subterranean)
2) SHOOT SYSTEM
(aerial)
Roots and Shoots are interdependent!!!
*Roots depend on shoots
for sugar and other
organic nutrients
*Shoots depend on
roots for minerals,
water and support
THE ROOT SYSTEM:
Root structure is well adapted to:
> Anchor plants
> Absorb and conduct water and nutrients
> Store food
Two major types of root systems:
1) TAPROOT SYSTEM:
-one large, vertical root
-provides firm
anchorage in soil
-modified taproots:
carrots, turnips,
sweet potatoes
2) FIBROUS ROOT SYSTEM:
-mat of threadlike roots spread out
below soil
-provides exposure to soil water and
minerals
-roots concentrated in upper
few cm of soil
-helps to prevent soil
erosion
*Absorption of water is greatly enhanced
by ROOT HAIRS
THE SHOOT SYSTEM:
• Stem morphology includes:
-axillary buds = embryonic side shoots in
angle of leaf and stem; usually dormant
-terminal bud = bud on a shoot tip
• Growth of a shoot is concentrated at the apex
of the shoot (TERMINAL BUD)
**the terminal bud inhibits development of
axillary buds – this is called
APICAL DOMINANCE
LEAVES
*the main photosynthetic organs of a plant
*leaves of monocots and dicots differ:
-monocot leaves have parallel veins
-dicot leaves have a branched network of
veins
PLANT CELL OVERVIEW:
*Recall: in addition to the structures in
other eukaryotic animal cells, PLANT
CELLS have unique organelles:
-CELL WALL
-CHLOROPLASTS
-LARGE, CENTRAL VACUOLE
-TONOPLAST (membrane around
vacuole)
Typical
Plant
Cell
Specialized Plant Cells:
1) Parenchyma cells:
-least specialized of plant cells
-function in synthesizing and storing
organic products
Specialized Plant Cells:
2) Collenchyma cells:
-usually grouped in strands to support young
parts of plants
-elongate as the stems and leaves grow
-e.g.: make up the strings
in celery
Specialized Plant Cells:
3) Sclerenchyma cells:
-function in support
-FIBERS: long, slender, tapered cells
-SCLERIDS: shorter, irregularly-shaped
cells
Each organ of a plant (leaf, stem, root)
has three tissue systems:
1) DERMAL
2) VASCULAR
3) GROUND
• DERMAL TISSUE SYSTEM (epidermis)
-covers and protects plant
-root hairs are extensions of epidermal
cells near root tips
-waxy CUTICLE secreted by epidermal
cells of the leaf and stem
• VASCULAR TISSUE SYTEM
-xylem and phloem
-functions in transport and support;
continuous throughout plant
Specialized Plant Tissues:
● XYLEM: water-conducting vessels
● PHLOEM: sugar / sap-conducting
vessels
Specialized Plant Tissues (continued):
Food-conducting cells of PHLOEM include:
● at least one COMPANION CELL is connected to
each phloem segment by openings called
PLASMODESMATA 
• GROUND TISSUE SYSTEM
-predominantly parenchyma
-occupies space between dermal and
vascular tissues
-functions in: photosynthesis, storage,
support
PLANT GROWTH!
*Plant growth begins with
germination of the seed and
continues for the lifespan of
the plants
MERISTEMS:
-perpetually embryonic tissues
-unspecialized and constantly dividing
Two types of plant
growth:
1) PRIMARY GROWTH:
elongation
2) SECONDARY
GROWTH: thickening
of roots and shoots
-APICAL MERISTEMS:
located in root tips and
shoot buds; involved in
primary growth
-LATERAL
MERISTEMS: cylinders
of dividing cells
extending along the
lengths of roots and
shoots; involved in
secondary growth
Primary Growth of Roots:
• root growth is concentrated near its tip and
results in roots extending through the soil
• the root is covered by a
ROOT CAP which
protects the meristem
and secretes a polysaccharide
coating that lubricates
the soil ahead of the
growing root
• the root tip contains 3 zones of cells:
*ZONE OF CELL DIVISION:
near tip of root;
-includes apical meristem
*ZONE OF CELL
ELONGATION: above
the zone of cell division
-cells elongate to at least
10x their original length
-elongation of cells here
pushes the root tip
through the soil
*ZONE OF MATURATION:
located farthest from the
root tip
-where new cells become
specialized
Primary Tissues of Roots:
1) PROTODERM:
gives rise to
epidermis
Primary Tissues of Roots:
2) PROCAMBIUM: forms a STELE (central
cylinder) where xylem and phloem
develop
*difference between monocots and dicots
Primary Tissues of Roots:
3) GROUND MERISTEM:
-gives rise to ground tissue system;
-fills the CORTEX (root area
between stele and epidermis);
-stores food;
-has ENDODERMIS (innermost layer
of cortex; forms boundary between
cortex and stele)
*LATERAL ROOTS may sprout from the
outermost layer of the stele (the
PERICYCLE)  as a result, the lateral
root maintains its vascular connection to
the stele of the main root
TISSUE ORGANIZATION OF STEMS:
• vascular tissue is organized into strands of
VASCULAR BUNDLES that run the
length of the stem;
• these converge at the shoot  root
transition to join the root stele
• each vascular bundle is surrounded by
ground tissue
DICOTS:
-ground tissue includes PITH
(inside) and CORTEX
(outside)
-bundles arranged in a RING
with:
XYLEM facing PITH
PHLOEM facing CORTEX
MONOCOTS:
-vascular bundles scattered throughout the
ground tissue of stem
TISSUE ORGANIZATION OF LEAVES:
• EPIDERMIS: protects against water loss and
pathogens
• STOMATA: pores flanked by GUARD CELLS
which regulate gas exchange and allow for
TRANSPIRATION (water loss)
 stomata are more numerous on the bottom
surface of the leaf…WHY?
MONOCOT =
parallel veins
DICOT =
network
veins
TISSUE ORGANIZATION OF LEAVES:
• the ground tissue inside the leaf is
called: MESOPHYLL
-consists mainly of parenchyma cells
equipped to perform photosynthesis
Mesophyll
TISSUE ORGANIZATION OF LEAVES:
*Dicots have two
mesophyll regions:
1) Palisade
parenchyma: upper half
of leaf; cells are columnshaped
2) Spongy parenchyma:
lower half of leaf;
irregularly shaped cells
surrounded by air spaces
TISSUE ORGANIZATION OF LEAVES:
**Vascular bundles from stem branch repeatedly
throughout leaf blade forming VEINS
 this brings the photosynthetic tissue of the leaf
in close contact with the xylem and phloem
 also forms a skeleton to support the shape of
the leaf
SECONDARY GROWTH:
• results in thickening of stems / roots
(seen in gymnosperms & some dicots)
• results from two lateral meristems:
1) VASCULAR CAMBIUM: produces
secondary xylem and phloem
2) CORK CAMBIUM: produces a tough,
thick covering for roots and stems that
replaces the epidermis
VASCULAR CAMBIUM:
• forms between the 1º xylem and phloem
of each vascular bundle
• a continuous cylinder of dividing cells:
-2º xylem cells form towards the inside
-2º phloem cells form
towards the outside
*accumulated layers of 2º xylem
produces WOOD
VASCULAR CAMBIUM:
**forms annual growth rings due to yearly
activity:
1) cambium dormancy (winter)
2) spring wood production
3) summer wood production
*2º phloem does
not accumulate
extensively; it
becomes part
of bark and
eventually
sloughs off the
tree trunk
CORK CAMBIUM:
• cylinder of meristematic tissue that forms in
the outer cortex of the stem
• cork cells form to the outside; as these cells
mature, they deposit a waxy material
(SUBERIN) in their walls and die
• these dead cork tissues protect the stem from
damage and pathogens and reduce water
loss
BARK = all tissues
external to the
vascular cambium
 phloem, cork
cambium and
cork
Secondary Growth in Roots:
-similar to stems
-in roots, the outer layer is impermeable to
water…consequently, the roots with 2º
growth function to anchor the plant and to
transport water and nutrients between the
younger roots and the shoot system