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Chapter 34
Lecture 8
The Plant Body
Dr. Angelika Stollewerk
The Plant Body
Aims:
• To be able to distinguish between monocot
and eudicot plants
• To be able to identify the component parts of
plants, including their modifications
• To introduce the three tissue systems of
plants
• To look at how leaf anatomy supports
photosynthesis
The Plant Body
Aims:
•
•
•
To be able to distinguish between monocot and eudicot plants
To be able to identify the component parts of plants, including their
modifications
To introduce the three tissue systems of plants
• To look at how leaf anatomy supports photosynthesis
These lecture aims form part of the knowledge
required for learning outcome 2:
Describe basic organism structure and
diversity (LOC2).
The Plant Body
Essential reading
• pages 744–750
• pages 752-754
• pages 760-761
• 34.1 How Is the Plant Body Organized?
• 34.3 How Do Meristems Build the Plant Body?
(Part)
• 34.4 How Does Leaf Anatomy Support
Photosynthesis?
34.1 How Is the Plant Body Organized?
Ninety-seven percent of angiosperms are
in two clades:
• Monocots: narrow-leaved; grasses,
lilies, orchids, palms
• Eudicots: broad-leaved; soybeans,
roses, sunflowers, maples
Remaining species have structure similar
to eudicots: water lilies and magnoliids.
Figure 34.1 Monocots versus Eudicots
34.1 How Is the Plant Body Organized?
Angiosperms are vascular plants with
double fertilization, a triploid
endosperm, seeds enclosed in modified
leaves called carpels.
Three types of vegetative organs: roots,
stems, leaves.
They are organized in two systems:
shoot system and root system.
Figure 34.2 Vegetative Organs and Systems
34.1 How Is the Plant Body Organized?
Shoot system: stems, leaves, flowers.
Leaves are the main organs of
photosynthesis.
Stems hold and display leaves in the
sun; connection between roots and
leaves.
Nodes: points of attachment of leaf to
stem. Regions in between are
internodes.
34.1 How Is the Plant Body Organized?
Root system: anchors plant and provides
nutrition.
Extreme branching of roots provides large
surface area for absorption of water and
mineral nutrients.
Structure of vegetative organs includes overall
form or morphology.
And arrangement of component cells and
tissues, or anatomy.
34.1 How Is the Plant Body Organized?
Water and minerals enter through the
root system in most plants.
Taproot systems: single, large, deepgrowing root and small side roots. The
root may also function as food storage.
Fibrous root systems: many thin roots of
equal diameter. Have large surface
area; cling to soil well.
Figure 34.3 Root Systems
34.1 How Is the Plant Body Organized?
Adventitious roots: arise above ground
from stem or leaves.
Cutting: piece of shoot cut or broken from
the plant. Adventitious roots may arise
from cuttings, and can start a new
plant—vegetative reproduction
(asexual).
Adventitious roots also help support
many plants, such as corn.
34.1 How Is the Plant Body Organized?
Stems elevate and support flowers and
leaves; have buds or embryonic shoots.
Stems bear leaves at the nodes, buds in
the angle or axil between shoot and leaf
are axillary buds. Can develop into a
branch.
Apical buds form at the tips—produce
cells for upward growth; some may
develop into flowers.
34.1 How Is the Plant Body Organized?
Stems can be modified:
Potato tuber is an underground stem.
Many desert plants have enlarged stems
that store water.
Runners are horizontal stems, roots grow
at intervals and independent plants can
arise from them.
Figure 34.4 Modified Stems
34.1 How Is the Plant Body Organized?
Most photosynthesis occurs in the
leaves.
The blade is a thin, flat organ attached to
stem by the petiole. Angle may be
perpendicular to sun’s rays to provide
maximum area for light gathering.
Some leaves change position during the
day to track the sun.
34.1 How Is the Plant Body Organized?
Leaves on one plant may have different
shapes, resulting from a combination of
genetic, developmental, and
environmental influences.
Simple leaves consist of a single blade.
Compound leaves have multiple blades
or leaflets.
Figure 34.5 Simple and Compound Leaves
34.1 How Is the Plant Body Organized?
Leaves can be highly modified during
development.
Some function as food storage, (e.g.,
onion bulbs). Leaves of succulents store
water.
Cacti spines are modified leaves.
Climbing plants have modified leaves
called tendrils that wrap around other
structures.
34.1 How Is the Plant Body Organized?
Tissue: organized group of cells with
similar structure and function.
Tissues are grouped into tissue
systems.
Vascular, dermal, and ground tissue
systems extend throughout the plant
body in a concentric arrangement.
Figure 34.6 Three Tissue Systems Extend Throughout the Plant Body
34.1 How Is the Plant Body Organized?
The vascular tissue system: the
transport system.
Xylem distributes water and minerals
taken up by roots to all parts of the
plant. Xylem can also function in
storage and support.
Phloem transports carbohydrates from
site of production (sources) to sites of
utilization or storage (sinks).
34.1 How Is the Plant Body Organized?
The dermal tissue system: the outer
covering.
The epidermis: single layer of cells or
several layers. May contain specialized
cells such as guard cells around
stomata.
Shoot and leaf epidermis secretes waxy
cuticle that retards water loss.
Stems and roots of woody plants have a
periderm.
34.1 How Is the Plant Body Organized?
The ground tissue system makes up
the rest of the plant.
Functions in storage, support,
photosynthesis, and production of
defensive and attractive chemicals.
34.3 How Do Meristems Build the Plant Body?
During early embryonic development, two
patterns contribute to the basic body
plan:
• Arrangement of cells and tissues along
the main axis from root to shoot.
• Concentric arrangement of tissue
systems.
34.3 How Do Meristems Build the Plant Body?
Growing stem consists of modules laid
down one after another.
Each module is a node with attached
leaves, the internode below, plus
axillary buds at the base of that
internode.
34.3 How Do Meristems Build the Plant Body?
Each branch may be thought of as a
separate module.
Branches form one after another (unlike
animal limbs). Branches may differ in
number of leaves, and number of
subsequent branches.
Branches are long-lived.
34.3 How Do Meristems Build the Plant Body?
Leaves are modules that are shortlived—weeks to a few years.
Root systems are also branching. Lateral
roots may be semi-independent. As root
systems grow, roots may die and be
replaced by new ones.
34.3 How Do Meristems Build the Plant Body?
All plants have a primary plant body: all
non-woody parts of the plant. Growth
lengthens the plant body.
Monocots consist entirely of primary plant
body.
Trees and shrubs have a secondary
plant body consisting of wood and
bark. Tissues are laid down as stems
and roots thicken. Grows throughout life
of plant.
34.3 How Do Meristems Build the Plant Body?
Meristems are localized regions of cell
division. Can produce new cells
indefinitely.
Cells that perpetuate the meristem are
called initials (comparable to stem cells
in animals).
When initials divide, one daughter cell
becomes specialized, the other remains
a meristem cell.
Figure 34.11 Apical and Lateral Meristems
34.3 How Do Meristems Build the Plant Body?
Animal growth is determinate; growth
ceases when adult state is reached.
Some plant growth is also determinate—
leaves, flowers, fruits.
Growth of stems and roots is
indeterminate—generated from specific
regions of cell division and expansion.
34.3 How Do Meristems Build the Plant Body?
Apical meristems at tips of roots and
stems, and in buds, give rise to the
primary plant body.
Shoot apical meristems extend stems
and branches.
Root apical meristems extend roots.
Apical meristems give rise to a set of
cylindrical primary meristems that
produce the three tissue systems.
34.3 How Do Meristems Build the Plant Body?
The primary meristems: protoderm,
ground meristem, procambium.
34.3 How Do Meristems Build the Plant Body?
Lateral meristems produce secondary
growth:
• Vascular cambium: supplies cells of
secondary xylem (towards the inside)
which become wood; and secondary
phloem (towards the outside) which
becomes bark.
• Cork cambium: produces waxy-walled
cork cells. Some of the cells become
the bark.
34.3 How Do Meristems Build the Plant Body?
• Wood is secondary xylem.
• Bark: everything external to the
vascular cambium (periderm plus
secondary phloem).
A twig illustrates both primary and
secondary growth. Apical meristems are
enclosed in buds.
Only the buds are entirely primary
tissues.
Figure 34.12 A Woody Tree Twig Has Both Primary and Secondary Growth
34.3 How Do Meristems Build the Plant Body?
As tree grows in diameter, outermost
layers, including the epidermis, dry and
crack off.
The cork cambium produces new
protective cells, called the periderm,
with walls impregnated with suberin.
34.3 How Do Meristems Build the Plant Body?
Meristems may remain active for years, or centuries.
Oldest known living plant: a bristlecone pine, about
4,900 years-old.
34.4 How Does Leaf Anatomy Support Photosynthesis?
Leaf anatomy is adapted to carry out
photosynthesis, and the exchange of O2
and CO2 with the environment, while
limiting water losses.
34.4 How Does Leaf Anatomy Support Photosynthesis?
Two zones of parenchyma cells make up
the mesophyll:
• Palisade mesophyll
• Spongy mesophyll
Also includes air space for diffusion of
gases.
Figure 34.23 The Eudicot Leaf (A)
Figure 34.23 The Eudicot Leaf
34.4 How Does Leaf Anatomy Support Photosynthesis?
Vascular tissue forms veins in leaves.
Veins extend to within a few cell
diameters of all the cells, so mesophyll
cells are well supplied with water and
minerals, and products of
photosynthesis can be conducted to the
phloem.
34.4 How Does Leaf Anatomy Support Photosynthesis?
The epidermal cells are
nonphotosynthetic, and have a waxy
cuticle that is impermeable to water.
The cuticle prevents water loss, but also
prevents diffusion of gases.
Pores called stomata allow gas
exchange. They are opened and closed
by guard cells.
34.4 How Does Leaf Anatomy Support Photosynthesis?
C4 plants have a modified leaf anatomy
that allows them to fix CO2 at low levels.
The photosynthetic cells are grouped
around the veins forming an outer
mesophyll and a bundle sheath.
CO2 is first fixed in mesophyll cells, then
moves to bundle sheath cells for
photosynthesis.
Figure 8.17 Leaf Anatomy of C3 and C4 Plants
The Plant Body
Check out
34.1 Recap, page 748
34.2 Recap, page 752, first two questions only
34.4 Recap, page 761
34.1 Chapter summary, page 762
34.2 Chapter summary, page 762
34.4 Chapter summary, page 762, see WEB/CD Activity 34.5
Self Quiz
Pages 762-763: Chapter 34 questions 1-6 and 10
The Plant Body
For Discussion
Page 763: Chapter 34, questions 3 and 5
Key terms:
adventitious root, apical bud, axillary bud, blade, bud,
chloroplast, collenchyma cell, compound leaf, cuticle, cutin,
dermal tissue, determinate growth, embryonic shoot (bud),
epidermis, Eudicot, flowering plant, fibrous root, ground tissue,
guard cell, indeterminate growth, internode, leaf (pl: leaves),
meristem, mesophyll cell, Monocot, node, parenchyma tissue,
petiole, phloem, plasmodesma (pl: plasmodesmata), palisade
cells, plastid, root, sclereid, sclerenchyma cell, shoot system,
simple leaf, spongy mesophyll, stem, taproot, vascular plant,
vascular tissue, vacuole, vegetative (non-reproductive), vein,
xylem