Chapter 9: Plant Organization
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9-1
Plant Organs
The flowering plants, or angiosperms,
have characteristic organs and tissues.
An organ is a structure that contains
different types of tissues and performs
one or more specific functions.
9-2
Organization of the plant body
Shoot System
Fig. 9.1
Vegetative organs
are the leaf, stem
and root
The body of a plant
has a root system
and a shoot
system.
Root System
9-3
The Root System
Consists of a main root
(taproot) and many lateral
roots, which absorb water
and minerals from the soil
for the plant.
9-4
Root systems
Fig. 9.2
-Produce hormones
-Perennial plants often
store the products of
photosynthesis in their
roots.
9-5
Shoot System - Stems
Fig. 9.1
A stem is the main
axis of the plant
along with its lateral
branches.
Transports water
and minerals from
roots to leaves, and
products of
photosynthesis in
the other direction.
A cylindrical stem can expand in
girth as well as in length.
9-6
Shoot System - Leaves
A leaf is a broad, thin organ (maximizes surface area) that
carries on photosynthesis (some have other functions).
Fig. 9.1
A leaf attaches to a
stem at a node; an
internode is the
region beween
nodes.
9-7
Blade
Petiole
Attaches to the
node here
9-8
Monocot Versus Dicot Plants
Flowering plants are divided into two
groups depending on their number of
cotyledons (seed leaves).
Monocots (monocotyledons) have one
cotyledon; dicots (dicotyledons) have
two.
Cotyledons provide nutrients for
seedlings before true leaves begin
photosynthesizing.
9-9
Monocot and dicot traits
Fig. 9.3
9-10
Fig. 9.3
Monocots:
Parallel veins (sugarcane,
corn)
Flowers have 3 or multiples of
3 (6,9,12, etc.) parts
Dicots:
Veins form a net pattern (oak
tree)
Flowers have 4 or 5 or
multiples of 4 or 5 (8,10, etc.)
parts
9-11
Dicot leaves
From Page 150
9-12
Plant Tissues
1) Epidermal tissue – outer covering
2) Ground tissue – majority of plant
tissue
3) Vascular tissue – transport
9-13
Epidermal Tissue
Epidermal tissue forms the outer
protective covering of a herbaceous
(non-woody) plant.
Exposed epidermal cells are covered
with waxy cuticle to minimize water
loss.
9-14
Root Hairs are Epidermal Tissue
Fig. 9.4
Root hairs
greatly increase
the absorptive
capacity of the
root.
9-15
Stoma of leaves are part of the
Fig. 9.4
epidermal tissue
9-16
Cork (an epidermal tissue) of an
older stem
Fig. 9.4
Cork is a component
of bark.
New cork cells are
made by a meristem
called cork
cambium.
As cork cells
mature, they fill with
suberin, a lipid that
makes them
waterproof and
chemically inert.
9-17
Ground Tissue
-forms the bulk of the plant.
Fig. 9.5
-thin-walled and
capable of
photosynthesis
when they
contain
chloroplasts.
-have thicker
walls for flexible
support (celery
strands).
-are hollow,
nonliving
support cells
with secondary
walls.
9-18
Vascular Tissue
Two types of vascular (transport) tissue:
Xylem transports water and minerals
from roots to leaves and contains two
types of conducting cells: tracheids
and vessel elements.
Phloem transports organic nutrients from
leaves to roots and has sieve-tube
elements with companion cells;
plasmodesmata extend between cells
at sieve plates.
9-19
Xylem structure
Xylem transports
water and minerals
from roots to leaves
Contains two types
of conducting cells:
tracheids and
vessel elements.
Water
Leaves
Roots
9-20
Phloem structure
Transports organic
nutrients from
leaves to roots
Has sieve-tube
elements with
companion cells
Plasmodesmata
extend between
cells at sieve plates.
Organic nutrients
Leaves
Roots
9-21
Leaves (produce organic nutrients by photosynthesis)
Phloem
Carries Organic Nutrients
Xylem
Carries Water and Nutrients
Roots (absorb water and minerals from the soil)
9-22
Organization of Roots
Within a root are zones where cells are in
various stages of differentiation.
9-23
Dicot root tip
In the zone of maturation,
mature cells are differentiated
and epidermal cells have root
hairs.
In the zone of elongation, cells
become longer as they
specialize.
The root apical meristem is in
the zone of cell division; the
root cap is a protective
9-24
covering for the root tip.
Dicot root tip
Fig. 9.8
Epidermis –
single layer of
thin-walled,
rectangular
cells; root hairs
present in zone
of maturation
9-25
Movement of materials into
vascular cylinder of the root
Endodermis – between
cortex and vascular
cylinder, single layer of
endodermal cells
bordered by the
Casparian strip
Fig. 9.8
Layer of impermeable lignin
and suberin
Cortex – thinwalled,
loosely-packed
parenchyma;
starch
granules store
food
regulates
entrance of
minerals into
the vascular
cylinder
9-26
In Dicot Roots Vascular Tissue is star-shaped;
phloem in separate regions between arms of
xylem
Fig. 9.8
9-27
Branching and Taproot of dicots
Fig. 9.9
Pericycle can
start the
development of
branch roots.
In some dicot plants, a
primary root, or taproot,
grows straight down and is
the dominant root; it can be
fleshy and stores food.
9-28
Organization of Monocot Roots
Monocot roots have the
same growth zones as a
dicot root but they DO
NOT undergo secondary
growth (become woody).
In a monocot root’s
centrally located pith,
ground tissue is
surrounded by a
vascular ring.
See Fig. 9.10
9-29
Monocot root
Fig. 9.11
Monocots have a large
number of slender
roots, which make up a
fibrous root system,
and are known as
adventitious roots.
Adventitious roots that
emerge from the surface to
help anchor the plant are
called prop roots.
-used for support
9-30
Fig. 9.11
Some plants are parasitic on other plants. Their
stems have rootlike projections called haustoria that
grow into the host plant and extract water and
nutrients from the host.
9-31
Other Root Diversity
Mycorrhizae - mutualistic association
between roots (better water absorption)
and fungi (receive sugars, etc.)
Peas and other legumes have root
nodules in which nitrogen-fixing
bacteria live.
9-32
Organization
of Stems
Shoot tip
Fig. 9.12
produces new cells
that elongate and
add length to the
stem.
9-33
Primary tissues are new tissues formed
each year from primary meristems right
behind apical meristem.
Meristem – Embryonic Tissue
(undifferentiated) that develops into
specialized tissue.
9-34
Fate of Primary Meristems
Fig. 9.12
Protoderm gives rise
to epidermis.
Ground meristem
produces parenchyma
in the pith and cortex.
Procambium produces
primary xylem and
primary phloem; later,
vascular cambium
occurs between xylem
and phoem.
9-35
Herbaceous (nonwoody) Stems
Mature herbaceous stems exhibit only
primary growth (not secondary).
The outermost tissue is the epidermis
(not bark), which is covered by a waxy
cuticle.
9-36
Herbaceous Dicot Stem
-vascular bundles are in a distinct ring
Fig. 9.13
9-37
Monocot stem
-vascular bundles are scattered throughout
Fig. 9.14
9-38
Woody Stems
A woody plant has both primary and
secondary tissues.
Secondary tissues develop during the
second and subsequent years of growth
from lateral meristems (vascular
cambium and cork cambium).
Secondary growth, (annual growth)
increases the girth of a plant.
9-39
Dicot stems
Fig. 9.15
The secondary tissues produced by the vascular
cambium, are called secondary xylem and secondary
phloem,
9-40
Secondary growth in a dicot
Fig. 9.15
stem
Pith rays are
composed of living
parenchyma cells
that allow materials
to move laterally.
Cork cambium
replaces epidermis
with cork cells
impregnated with
suberin.
9-41
Section of woody stem
Fig. 9.15
Spring wood
followed by
summer
wood makes
up one
year’s
growth or
annual ring.
The bark of a
tree contains
cork, cork
cambium, and
phloem.
A woody stem
has three
distinct areas:
the pith, the
wood, and the
bark.
9-42
Annual Rings
This tree had a pith
date of 256 BC and an
outer ring of about
AD 1320, making this
tree nearly 1,600
years old when it
died (it's about 3 feet
across)!
(photo © H.D.
Grissino-Mayer and
R.K. Adams).
9-43
Tree trunk
Fig. 9.16
9-44
Modified stems
Fig. 9.17
9-45
Organization of Leaves
Fig. 9.18
Helps prevent
water loss
Photosynthesis
Photosynthesis
and Increased
area for gas
exchange
gas exchange
9-46
The body of the leaf is composed of
mesophyll.
Parenchyma cells of these mesophyll
layers house chloroplasts.
9-47
Classification of leaves
Fig. 9.19
9-48
Leaf diversity
The leaves of a
cactus are spines
attached to a
succulent stem.
Climbing leaves
are modified
into tendrils.
Fig. 9.20
The leaves of a few
plants are
specialized for
catching insects.9-49