Seed Plant Structure and
Function
Chapter 23
Seed Plant Overview:
• The plant body consists of two basic parts--- the shoot
system and the root system
• Shoot system is above ground and includes organs
such as leaves, buds, stems, flowers, and fruits
• The functions of the shoot system include
photosynthesis, reproduction, storage, transport, and
hormone production
• The root system is below ground and includes roots as
well as modified stem structures such as tubers and
rhizomes
• The functions of the root system include anchorage,
absorption, storage, transport, and production of
certain hormones
Seed Plant Overview Cont.:
• Seed plants contain 2 types of vascular tissue
(xylem & phloem) to help transport water,
minerals, & food throughout the root & shoot
systems
• Plant cells have several specialized structures
including a central vacuole for storage, plastids
for storage of pigments, and a thick cell wall of
cellulose
• Plant cells are all box-shaped in appearance
Plant Cell Organization
• Plant cells are arranged into
tissues and tissue systems
• A simple tissue is composed of
only one type of cell; a complex
tissue is composed of more than
one cell type.
• Plants are composed of
specialized cells and tissues
• In plants, the formation of new
cells, tissues and organs is
restricted almost entirely to
regions known as meristems
Meristems:
• There are 3 main types of meristematic
tissue in vascular seed plants ---- apical,
intercalary, & lateral meristems
Meristems:
• Apical Meristem occur at
the tips of roots and
shoots and are
responsible for the
length-wise extension of
the plant body known as
primary growth
• Cells in apical meristems
are produced by mitosis
& then differentiate into
specialized cells &
tissues
Intercalary Meristems
• Some monocots, such as grasses &
bamboo, have intercalary meristems
located above the bases of leaves and
stems allowing them to regrow quickly
after being cut down
Growth in Plants
• Woody plants have meristem between xylem &
phloem to produce wood
• Lateral meristems produce outward growth in
plants or secondary growth
• Lateral meristems are called cambium (cambia,
plural)
• Vascular cambium makes wood & vascular
tissues and cork cambium makes cork & bark
• Plants without lateral meristems have only
primary, not secondary growth and are called
herbaceous plants
Specialized Plant Cells:
• Plants have 3 basic types of cells --parenchyma, collenchyma, &
sclerenchyma
• Parenchyma cells are the most abundant
& least specialized
• Parenchyma are loosely-packed, cube
shaped or elongate cells with a large
central vacuole & thin cell walls
Parenchyma
• Parenchyma cells can specialize
for various functions (storage,
photosynthesis, etc.)
• Parenchyma form the bulk of non-woody
plants such as the fleshy part of an apple
• Collenchyma cells are irregular in shape
with thicker cell walls & support the
growing parts of plants
Collenchyma
 Collenchyma cell walls are also flexible
to support new growth regions of the
plant (example: tough strings on a celery
stalk)
Sclerenchyma
• Sclerenchyma cells support non-growing parts of plants
because they have thick, rigid, non-stretchable cell walls
•
Sclerenchyma Cells
• Sclerenchyma cells often die at maturity leaving empty,
box-like structures
• Two types of sclerenchyma cells are fibers & sclereids
• Fibers are cells up to 50cm long that usually occur in
strands such as linen & flax
•
Sclerenchyma Fibers
• Sclereids have thicker cell walls & come in many shapes
• Sclereids may be single cells or groups of cells and give
pears their gritty texture & give hardness to peach pits &
walnut shells
Sclerynchyma Fibers
Sclerynchyma
Sclereid Fibers
Other Plant Tissues & Systems:
• Tissues are groups of cells with similar
structures & functions
• Plants have 3 tissue systems --- ground, dermal,
and vascular tissues
• Plant tissues make up the main organs of a
plant --- root, stem, leaf, & flower
• Ground tissue makes up most of the plant's
body, dermal tissue covers the outside of the
plant, & vascular tissue conducts water &
nutrients
Dermal Tissue:
• Covers the plant body and
consists of epidermis in
young plants & non-woody
plants that is replaced later
by periderm in woody plant
• Epidermis is made of
parenchyma cells in a single
layer
• Epidermis on stem and
leaves prevents water loss
by transpiration & produces
a waxy material called
cuticle
Dermal Tissue:
Guard Cells
surrounding stoma
• Openings in the
epidermis on the
underside of a leaf
where gases are
exchanged are called
stomata (stoma, singular)
• Sausage-shaped guard
cells are found on each
side of the stoma to help
open and close the pore
to prevent water loss
• Dead cork cells replace
epidermis in woody
stems & roots
Ground Tissue:
• Ground tissue constitutes the majority of
the plant body and contains parenchyma,
collenchyma, and sclerenchyma cells
• Ground tissue of the leaf (called
mesophyll) uses the energy in sunlight to
synthesize sugars in a process known as
photosynthesis
• Spongy Mesophyll of Leaf
• Ground tissue of the stem (called pith and cortex)
develops support cells to hold the young plant upright
• Ground tissue of the root (also called cortex) often
stores energy- rich carbohydrates
Vascular Tissue:
• Vascular tissues transport water and dissolved
substances inside the plant and helps support
the stem
• The 2 types of vascular tissue are xylem &
phloem
• Xylem carries water and dissolved ions from
the roots to stems and leaves
• Phloem carries dissolved sugars from the
leaves to all other parts of the plant
• Xylem has 2 kinds of conducting cells --tracheids & vessel elements
Vascular Tissue:
• Tracheids are long, narrow sclerenchyma cells
with walls and pits for water to move between
them
• Vessel elements are short, wide sclerenchyma
cells without end walls stacked on top of each
other
• Angiosperms (flowering plants) have tracheids
& vessel elements, while gymnosperms (cone
bearers) only have tracheids
• Phloem moves sap (dissolved sugars &
minerals) from source (where they are made) to
sink (where they will be used)
Phloem Cells
Xylem Cells
Vascular Tissue:
• Phloem is made of cells called sieve tube
members and companion cells
• sieve tube members are stacked to form
tubes called sieve tubes with porous
sieve plates between the cells for
movement of sugars
• Companion cells are along each sieve
tube member & help in loading sugar
into the sieve tube
Root and Shoot system of a plant
Root System:
• Roots grow underground (subterranean
part of the plant)
• Roots have 3 main functions --- (1)anchor
plants (2) absorb and conduct water &
minerals (3) store food
• The first root to emerge from the most seeds
is called the primary root or taproot & can
grow deep to reach water
• Taproots may store food (carrot & beet)
Root Systems
• Monocots have highly branched, roots called
fibrous roots that grow near the surface &
spread out to collect water
• Fibrous roots such as in grasses often help
prevent erosion
• Adventitious roots grow from a stem or leaf
above ground in some plants and serve to prop
up or support the plant (corn)
• Aerial roots obtain water & minerals from the
air & enable the plant to climb (orchids & ivy)
Adventitious
Roots 
Arial Roots
Taproots
Fibrous Roots
Structure of the Root:
• Root cap covers the apical meristem
(growth tissue) at the tip of the root &
produces a slimy substance so roots can
more easily grow through the ground
• Apical meristem replaces cells of the root
cap as they are damaged
• Epidermis covers the outside of the root
& has extensions called root hairs that
absorb water & minerals and increase the
surface area of the root
Structure of the Root:
• The core of the root is called the vascular
cylinder, contains xylem & phloem
• A band of ground tissue called cortex
surrounds the vascular cylinder
• A single cell layer called endodermis separates
the cortex & vascular tissue
• Endodermal cells are coated with a waxy layer
called the Casparian strip so water is
channeled into the vascular tissue
• The Pericycle is the outermost layer of central
vascular tissue & forms lateral roots
Stem Structure & Function:
• Adapted to support leaves
• Transport water & minerals
• Transport sugars (usually sucrose) from Source (where
they're made) to Sink (where they're stored)
• Movement of sugars is called translocation
• Store food and/or water
• Tubers (potatoes) underground food storage stems
• Stems grow from the tip or apical meristem
• Stems increase in circumference by lateral meristems
• Leaves are attached to stems at nodes & have lateral
buds that can develop into new stems or branches
• Internode is space between nodes on a stem
• The tip of each stem usually has a Terminal
Bud enclosed by specialized leaves called Bud
Scales
• Vascular Tissue is arranged in bundles with
xylem toward the inside & phloem toward the
outside
• Vascular bundles are scattered throughout
monocot stems
• Vascular bundles are arranged in rings in dicot
stems
Stem Structure
• Secondary grow
(woody growth)
occurs in dicots, but
less often in
monocots
• Plants with only
primary growth
(non-woody) are
called herbaceous
• Darker wood in the center of a tree trunk is
called Heartwood and is composed of old, nonfunctional xylem
• New, functional xylem makes up lighter wood
in the tree trunk and is called Sapwood
• Sapwood gets wider, but heartwood remains
the same size
• Bark is the protective covering of Woody Plants
& consists of Cork, Cork Cambium, and
Phloem
Translocation of Sugars:
• Phloem cells move sugars through a plant
• Sugars made in photosynthetic cells are
PUMPED into Sieve Tubes by ACTIVE
TRANSPORT at the Source
• Turgor Pressure Increases as Water enters the
Sieve Tube by Osmosis
• TURGOR moves the SAP toward the SINKS
• Known as the PRESSURE-FLOW
HYPOTHESIS
Transport of Water:
• Transport of Water and mineral Nutrients occurs in the
Xylem
• Water movement in plants is driven by Transpiration
(evaporation of water from leaves & stems)
• As water evaporates, more water is pulled into the
roots
• Transpiration produces a NEGATIVE pressure in the
xylem pulling water UPWARD
• Water molecules are cohesive (attracted to each other)
which also pulls water upward
• Water is also adhesive sticking to the walls of the
xylem
• Known as Cohesion Theory of water movement
Leaf Structure & Function:
• Flat surfaces helps leaves capture
sunlight for photosynthesis
• Convert carbon dioxide and water into
simple sugars (glucose)
• Some leaves store food (onion) and water
• Protect (cactus spines)
• Used Dyes, Fibers, Fuels, Drugs, Wax,
Soap, Spices and Food
Leaf Structure & Function:
• Attached by a stem-like petiole to the plant
• Simple leaves have one blade, while
compound leaves have several leaflets
• Covered with a single layer of cells called
epidermis (upper & lower)
• A waxy cuticle prevents water loss
• Openings called stomata on the underside of
leaves for gas exchange (CO2 & O2)
• Two guard cells on either side of the stomata
open & close the openings
• Two guard cells on
either side of the
stomata open & close
the openings
• When guard cells
LOSE water, the
stoma CLOSE, while
the stoma OPEN
when guard cells
gain water & swell
• Stomata are CLOSED during the HOTTEST parts of
the day to prevent water loss from leaves
• Below the epidermis are 2 types of chlorophyll
containing MESOPHYLL cells ---palisade & spongy
• PALISADE mesophyll cells are closely packed
columnar cells (most photosynthesis occurs here)
• SPONGY mesophyll cells are loosely packed with air
spaces containing CO2 & O2
• VASCULAR BUNDLES (xylem & Phloem) in the
spongy mesophyll appear as VEINS on the surface of
the leaf
• VENATION is the
arrangement of veins in
a leaf
• Monocots leaves (such as
Grasses or Corn Plants)
have Parallel Venation
• Dicots leaves form a
Branched network called
Net Venation
• In carnivorous plants
(Venus Fly Trap), the
leaves trap insects for
food so the plant can get
enough nitrogen (grow
in N2 poor soil)