The Plant Body
35
Vegetative Organs of the Flowering Plant Body
• Flowering plants possess three kinds of vegetative
(nonreproductive) organs: roots, stems, and leaves.
35
Vegetative Organs of the Flowering Plant Body
• Most flowering plants belong to one of two major
lineages.
• Monocots are generally narrow-leaved flowering
plants such as grasses.
• Eudicots are broad-leaved flowering plants such
as roses.
• Monocots and eudicots account for 97 percent of
the species of flowering plants.
• Most of the remaining species (including water
lilies and magnolias) are structurally similar to
eudicots.
Figure 35.1 Monocots versus Eudicots
35
Vegetative Organs of the Flowering Plant Body
• The shoot system of a plant consists of the stems and the
leaves, as well as flowers.
• Leaves are the main sites of photosynthesis.
• Stems hold and display the leaves to the sun and provide
connections for the transport of materials between roots
and leaves.
• A node is the point where a leaf attaches to a stem.
• Regions of stem between nodes are the internodes.
• The root system provides support and nutrition.
Figure 35.2 Vegetative Organs and Systems
35
Vegetative Organs of the Flowering Plant Body
• There are two main types of
root system: taproot and
fibrous root.
• Taproot (many eudicots): a
single, large, deep-growing
primary root with smaller
lateral roots.
• Fibrous root system
(monocots and some
eudicots): composed of
numerous thin roots roughly
equal in diameter – holds soil
in place very effectively.
35
Vegetative Organs of the Flowering Plant Body
• A bud is an embryonic shoot.
• A stem bears leaves at its nodes, and where each leaf
meets the stem, there is a lateral bud.
• At the tip of each stem or branch there is an apical
bud, which produces the cells for the growth and
development of that stem or branch.
35
Vegetative Organs of the Flowering Plant Body
• A potato is a portion of the
plant’s stem, and its “eyes”
contain lateral buds = tuber
• The runners of strawberries
are horizontal stems.
• In some plant species the
leaves are highly modified,
such as the thorns of a cactus.
35
Vegetative Organs of the Flowering Plant Body
• Leaves are well
adapted for gathering
light.
• The blade of a leaf is
a thin, flat structure,
attached to the stem
by the petiole, which
holds the leaf at an
angle almost
perpendicular to the
sun.
Figure 35.5 The Diversity of Leaf Forms
A simple leaf
has a single
blade.
A compound
leaf has
multiple
blades (or
leaflets)
arranged
along an axis
or radiating
from a central
point.
35
Plant Cells
• Plant cells have all the organelles common to eukaryotes.
• Plant cells have additional distinguishing features:
1) chloroplasts (or other plastids)
2) vacuoles
3) cell wall
• Each plant cell has its own
primary cell wall. Some plant
cells produce a thick secondary
wall.
35
• Plasmodesmata are
pore-like structures
that pass through
primary cell walls,
allowing substances
to move freely from
cell to cell without
crossing the plasma
membrane.
Plant Cells
35
Plant Cells
• Parenchyma cells are the most numerous type
of cell in young plants.
• Parenchyma cells usually have thin walls and
large central vacuoles.
• The photosynthetic cells in leaves are
parenchyma cells filled with chloroplasts.
• Some parenchyma cells store lipids or starch.
• Other parenchyma cells serve as “packing
material” and play a vital role in supporting the
stem.
35
Plant Cells
• Collenchyma cells are supporting cells that lay
down primary cell walls that are thick in the corners.
• Collenchyma cells provide support to leaf petioles,
nonwoody stems, and growing organs.
35
• Sclerenchyma cells are
the main supporting cells
of a plant.
• There are two types of
sclerenchyma cells:
elongated fibers and
variously shaped
sclereids.
• Fibers often organize
into bundles.
• Sclereids may pack
together very densely.
Plant Cells
35
• The xylem conducts water
from roots to above ground
plant parts. It contains
conducting cells called
Tracheids .
• Vessel elements are the
water “pipeline” system in
flowering plants, also
formed from dead cells.
• Vessel elements are
generally larger in diameter
than tracheids and are laid
down end-to-end to form
hollow tubes.
Plant Cells
35
• Cells of the phloem
are alive when they do
their job, unlike those
of the xylem.
• The characteristic cell
of the phloem is the
sieve tube member.
• Cells of the phloem
are arranged end-toend and form long
sieve tubes, which
transport
carbohydrates and
other materials.
Plant Cells
35
Plant Cells
35
Plant Tissues and Tissue Systems
• A tissue is an organization of cells that work
together as a functional unit.
• Tissues are grouped into tissue systems that
extend throughout the body of the plant from
organ to organ.
• There are three plant tissue systems: vascular,
dermal, and ground.
Figure 35.12 Three Tissue Systems Extend throughout the Plant Body
35
Plant Tissues and Tissue Systems
• The vascular tissue system includes the xylem and
phloem; it is the conductive or “plumbing” system of the
plant – occurs in vascular bundles.
• The phloem transports carbohydrates from photosynthesis
from sites of production (sources such as leaves) to sites of
utilization (sinks) elsewhere in the plant ( live cells).
• The xylem conducts water and minerals from the roots to
above ground plant parts (dead cells).
35
Plant Tissues and Tissue Systems
• The dermal tissue system is the outer covering of the
plant.
• All parts of the young plant body are covered by an
epidermis, which is a single layer or multiple layers of cells.
• The epidermis contains epidermal cells and other
specialized cells such as guard cells.
• The shoot epidermis secretes a layer of wax (the cuticle)
which helps retard water loss from stems and leaves.
35
Plant Tissues and Tissue Systems
• The ground tissue system
makes up the rest of a
plant.
• Ground tissue functions
primarily in storage,
support, photosynthesis,
and the production of
defensive and attractive
substances.
Cross sections of
eudicot leaves.
35
Forming the Plant Body
• In plants, the growth of leaves, flowers, and fruits is
determinant (ceases to grow once adulthood is
reached).
• In plants the growth of roots and stems is indeterminate
and is generated from specific regions of active cell
division.
• Plants exhibit regions of:
 Primary growth – leads to lengthening of the plant
body and organ formation.
 Secondary growth – growth in the diameter of stems
and roots (wood and bark).
Figure 35.14 A Woody Twig
35
Forming the Plant Body
• The root cap protects the delicate growing area of the root
as it pushes through the soil.
• The root cap also detects the pull of gravity and controls the
downward growth of roots.
• Tissues of the root are divided into three zones: cell
division, cell elongation, and cell differentiation.
Root
cap
Root
tip
Figure 35.15 Tissues and Regions of the Root Tip
35
Forming the Plant Body
• Cross sections of most tree trunks in temperate
zone forests have annual rings.
• Wood consists of secondary xylem.
• Annual rings form due to differential rates of
growth in spring (when water is plentiful) and in
summer.
• Wood that is no longer conducting water is known
as heartwood.
• Sapwood is wood that is actively conducting
water and minerals in the tree.
Figure 35.21 Annual Rings
Figure 35.19 Vascular Cambium Thickens Stems and Roots (Part 2)
35
Leaf Anatomy Supports Photosynthesis
• Leaf anatomy is adapted to carry out
photosynthesis, limit evaporative water loss, and
transport the products of photosynthesis to the
rest of the plant.
• The zones in leaf that photosynthesize are the
called mesophyll.
• Within the mesophyll is air space through which
CO2 can diffuse to the photosynthesizing cells.
Figure 35.23 (a) The Eudicot Leaf
35
Leaf Anatomy Supports Photosynthesis
• Veins supply mesophyll cells with
water and minerals, and they
transport the products of
photosynthesis to the rest of the
plant.
• Leaf epidermis: outermost cell
layer, covered by a waxy cuticle.
Functions to keep water and
photosynthetic products in the
leaf.
• Guard cells allow controlled gas
exchange through pores in the
leaf (the stomata).