Download Ground tissue

The
Plant
Body
A plant has two organ systems, each of
which has an apex that extends growth.
Shoot system
Above ground and includes organs such as
leaves, buds, stems, flowers (if the plant
has any) and fruits (if the plant has any).
Root system
Below ground and includes those parts of the
plant such as the roots, tubers, and rhizomes.
2
Organ
Systems
Plant Cells
Plant cell walls consist of cellulose
 Primary cell wall
- Found in all cells
- Cellulose fibers parallel to microtubules
 Secondary cell wall
- Found in some cells
- Additional layers of cellulose and lignin
increase mechanical strength of wall
Plant Cells
Roots: take up
water, support
plant, store food
Stems: support
plant, store food
and water
Leaves:
photosynthesis
Flowers:
reproduction
Plant Body Organization
Plants contain three basic tissue systems:
 Dermal tissue: protection
- Wax and bark
 Ground tissue: storage, photosynthesis,
and secretion; Bulk of the plant!
 Vascular tissue: conduction
- Xylem – Water and dissolved minerals
- Phloem – Nutrient-containing solution
Plant Meristems
Meristems are
clumps of small cells
with dense cytoplasm
and large nuclei. They
act as stem cells do in
animals. One cell
divides producing a
differentiating cell and
another cell that
remains meristematic.
Meristems may be:
• Apical
• Lateral
Apical Meristems
Apical meristems are located at the tips of
stems and roots.
- Give rise to primary tissues which are
collectively called the primary plant body
- Three primary meristems
- Protoderm  Epidermis
- Procambium  1o vascular tissue
- Ground meristem  Ground tissue
Apical Meristems
(make plants longer)
Intercalary Meristems
• Located above the bases of
leaves and stems in grasses,
bamboo, and related plants
that do not increase in girth
(They do not have vascular
cambium or cork cambium.)
• Allows stems to regrow
quickly after being cut
down!
Lateral Meristems
(make plant wider/increase girth)
Lateral meristems are found in plants that
exhibit secondary growth.
- Give rise to secondary tissues which are
collectively called the secondary plant body
- Woody plants have two types
- Cork cambium  Outer bark
- Vascular cambium  2o vascular tissue
Secondary
Growth
MUST know
sequence of tissues!
Cambium = layer of
cells just one cell thick,
inside the inner bark, that is
actively growing. Cambium
makes xylem and phloem
cells. As new phloem cells
are made, the old ones dry
out, adding to the bark. On
the inside of the cambium,
newly fashioned wood cells
add to the sapwood (xylem).
This is where growth
occurs each year!
Rings can also provide rainfall history!
Year Rings
(secondary xylem)
• Cold in winter  Slow growth  Small xylem
• Warm in summer  Fast growth  Large xylem
• No year rings in tropical wood
Plants
have
only
3
tissue
types
Plant Tissues
Plant Tissues
•
Dermal
•
Ground
•
- Dermal
- Ground
- Vascular
Vascular
Dermal Tissue
• Outer surface of herbaceous plants
• Composed of epidermal cells, closely packed
cells (usually 1 cell thick) that secrete a waxy
cuticle that aids in the prevention of water loss.
• Acts as a barrier to fungi
and other invaders.
• Epidermis contains guard
cells, trichomes, and root
hairs.
Guard cells
To facilitate gas exchange
between the inner parts of
leaves, stems, and fruits,
plants have a series of
openings known as stomata
(singular stoma). These
openings allow gas exchange,
but at a cost of water loss.
Guard cells are bean-shaped cells covering the stomata
opening. They regulate the exchange of water vapor,
oxygen and carbon dioxide through the stoma.
Trichomes
Glandular bulb
of trichome
Trichomes are a hair like or bristle like outgrowth from
the epidermis of a plant. Trichomes function as devices
against animals, as glands, as weapons, in keeping the leaf
surface cool, and in reducing the rate of evaporation.
Root Hairs
SURFACE AREA!
Ground Tissue
Consists of three types of cells:
Parenchyma – Collenchyma – Sclerenchyma
Ground Tissue
Parenchyma
Cells are the most abundant & least specialized. They
are loosely packed, cube shaped or elongate cells with
a large central vacuole and
thin cell walls. They store
food and water and can be
photosynthetic.
Photosynthetic parenchyma
is called chlorenchyma.
Ground Tissue
Collenchyma
Support the growing parts of
plants. The cell walls are
thicker than those of
parenchyma cells. Collenchyma
cell walls are also irregular in
shape.
Collenchyma cells are usually
grouped in strands. The tough
string of a celery stalk (stems)
are made of collenchyma cells!
Ground Tissue
Sclerenchyma
Cells have lignin thickened walls and
strengthen plant tissues. They may
be non-living at maturity.
Two types:
Fibers – long, slender cells that are
usually grouped together in strands.
Sclereids – usually branched cells
occurring in groups or singly. They are
NOT elongated and come in a variety of
shapes. Provide hardness of nuts.
Vascular Tissue
Transports food, water, hormones and minerals within
the plant, as well as provides support.
Xylem
Carries water and
minerals (ex: nitrates)
from the roots to stems
and leaves; supports
the plant body
Phloem
Carries dissolved sugars
from the leaves to all
parts of the plant
Remember?
Vascular bundles: arranged in rings in dicot stems.
Vascular bundles: scattered throughout monocot stems.
Xylem
Vessels:
continuous tubes of dead
cylindrical cells arranged
end-to-end; shorter &
wider than tracheids;
conduct water more
efficiently than tracheids
Tracheids:
dead cells that taper at
the end and overlap one
another
Vessels and tracheids are both
sclerenchyma cells!
Angiosperms
have tracheids
and vessel
elements.
Gymnosperms
only have
tracheids.
Phloem
Sieve-tube members
living cells stacked to form
tubes called sieve tubes
with porous sieve plates
between the cells for
movement of sugars.
Companion cells
along each sieve tube
member; help in loading
sugar into the sieve tube.
Remember?
Plasmodesmata
small tubes that connect
plant cells to each other,
establishing living bridges
between cells.
They allow certain
molecules to pass directly
from one cell to another.
Each plasmodesmata
contains a smaller tube
that connects the
endoplasmic reticula of the
connected cells.
ROOTS
• Anchor plants
• Absorb water & nutrients
• May store carbohydrates
(carrots, turnips, radishes)
• May store water for dry
periods
Root Structure
There are 4 zones in developing roots:
• Root cap
• Zone of cell division
• Zone of elongation
• Zone of maturation
Root Structure
Root Cap
• Covers and protects the
delicate growing tip from
injury and damage as the
root pushes its way through
the soil; perception of gravity
• Secretes polysaccharide
slime that lubricates the soil
• Constantly sloughed off and
replaced.
Zone of Cell Division
Three areas just above the apical meristem that continue
to divide for some time:
Protoderm - outermost primary meristem –
produces cells which will become dermal tissue.
Ground meristem - central primary meristem produces cells which will become ground tissue.
Procambium - innermost primary meristem produces cells which will become vascular tissue.
Root Structure
Zone of Elongation
• Cells rapidly elongating
• Vacuoles grow
tremendously  major
water uptake
• More highly developed
organelles  Mature
mitochondria and plastids
• Cells are converting from
meristem to parenchyma.
Zone of Maturation
• Differentiation is
completed in this
zone.
• This zone is easily
distinguishable by
the presence of
several root hairs.
Mature Root
Epidermis - covers the entire root except for the root cap.
Unlike the epidermis covering other plant organs, the
epidermis of the root lacks a cuticle.
Cortex - parenchyma tissue that functions in food storage.
Endodermis - layer of cells which surrounds the stele.
Unlike the cortex cells to its outside, the endodermis cells
are very tightly packed with no intercellular air spaces. The
cell walls of the endodermis cells are impregnated with
lignin and suberin (waterproofing) which forms a
structure known as the Casparian strip.
Mature Root
Stele (All tissues interior to endodermis):
o Pericycle – root cells immediately
adjacent and interior to the endodermis;
can divide and may ultimately give rise to
lateral (branch) roots
o Pith – parenchyma cells at the very
center of the root; storage tissue.
Stele
pericycle
Root Systems
Most plants produce either/or …
Taproot
single large root
with smaller branch roots
Fibrous
many smaller roots
of similar diameter
Modified Roots
Aerial roots
•
Roots formed in/exposed to air.
•
Found in diverse plant species,
including epiphytes (Plants,
such as a tropical orchid, that
grows on another plant upon
which it depends for mechanical
support but not for nutrients),
tropical coastal swamp trees
such as mangroves, and vines
like irritating poison ivy.
Aerial Roots of an Orchid
Aerial roots …
Prop roots
keep the plant
upright and
brace against the
wind.
Mangrove tree
Aerial roots …
Adventitious roots
Ivy
… arise from
any place
other than
the
plant’s root
Modified Roots
Pneumatophores
Erect roots that rise up above the soil or water and promote
gas exchange. Pneumatophores, or breathing roots, are formed
by certain swamp-dwelling
trees, such as mangroves,
since there is little oxygen
available to the roots in
waterlogged conditions.
They have numerous
pores or lenticels over
their surface, allowing
gas exchange.
Modified Roots
Contractile Root
Thickened root at the
base of a bulb or other
organ that spirals like
a corkscrew; helps
position the root at an
appropriate level in
the ground.
Modified Roots
Parasitic Root
Parasitic plants have no
chlorophyll and are
dependent on chlorophyllbearing plants for nutrition.
Haustoria are peglike
parasitic roots
that penetrate the host
plant.
Modified Roots
Food Storage Root
Roots which
produce many
extra parenchyma
cells that store
large quantities of
carbohydrates.
Carrots and Beets
Modified Roots
Water Storage Root
Roots which
produce many
extra parenchyma
cells that store
large quantities of
water.
Modified Roots
Buttress Roots
Thick roots that flare
out from the base of
large canopy trees,
often found on
rainforest trees;
provide support as
well as additional
nutrients.
Stems
• Support of main
body of plant and
leaves.
• Conduct water
and food.
• Photosynthesis in
new green stems.
Firetoad
Stems
• Like roots, stems contain the three types of
plant tissue and undergo growth from cell
division in apical and lateral stems
• Shoot apical meristem initiates
stem tissue and intermittently
produces primordia 
develop into leaves, other
shoots and even flowers
The domeshaped
structure at
the tip of the
stem is the
shoot apical
meristem.
All tissues of
the stem and
leaves arise
from this
terminal
meristem.
bulges
from
which
stem &
leaves
form
External Stem Structure
Node = point of attachment of leaf to stem
Internode = area of stem between two nodes
Blade = flattened part of leaf
Petiole = stalk of leaf
Axillary bud = develops into branches
With leaves or may form flowers
Terminal bud = Extends the shoot
system during the growing season
Sessile leaf
petiole is missing
Leaf is attached
directly to stem.
A stipule refers to outgrowths borne on either side of
the base of a petiole. A pair of stipules is considered
part of the anatomy of the leaf of a typical flowering
plant, although in many species the stipules are
inconspicuous or entirely absent. Stipules are
morphologically variable and might appear as glands,
scales, spines, or leaf-like structures.
WOW
Leaf scars
tiny bundle scars
within mark where
vascular connections
were.
Internal Stem Structure
Monocot :
Vascular bundles are usually scattered
throughout ground tissue system
Eudicot :
Vascular bundles are arranged in a ring with
internal ground tissue (pith) and external
ground tissue (cortex)
Stem Structure
Internal
Monocot or Dicot?
Internal Stem Structure
Vascular tissue arrangement is directly related
to the stem’s ability for secondary growth.
 In eudicots, a vascular cambium develops
between the primary xylem and phloem
-Connects the ring of primary vascular
bundles
 In monocots, there is no vascular cambium
 Therefore, no secondary growth
In woody eudicots and
gymnosperms, the cork
cambium arises in the
outer cortex  produces
boxlike cork cells on
outside and parenchymalike cells on inside.
Cork tissue cells get
impregnated with
suberin shortly after
they are formed  They
then die and constitute
the outer bark.
The cork cambium also produces
cells without suberin 
lenticels = small, pores or
narrow lines on the surface of
the stems of woody plants that
permit gas exchange to continue.
Modified Stems
• Tubers
• Bulbs
• Corms
• Rhizomes
• Runners/Stolons
• Tendrils
• Cladophylls
Tubers
• Swollen tips of rhizomes that contain carbohydrates
• The potato is a stem because it has many nodes
(eyes) with spaces between eyes (internodes).
• Potato tubers develop at
the end of rhizomes. Eyes
of potatoes are axillary
buds. These buds can
expand to form
shoots which can
form whole plants.
Although the common potato is a stem, the sweet potato is a modified root!
Bulbs
• Swollen underground
stems, consisting of fleshy
leaves
• Two basic bulb types:
Layered and Scaly
Corms
Superficially resemble
bulbs, but have no
fleshy leaves
Gladiolus
Gladiolus, crocus, and tuberous begonias all arise from corms.
Bulb or Corm ?
Bulb
Corm
Rhizomes
• Horizontal underground stems, w/adventitious roots.
• Typically have short
internodes and scale
leaves.
• Store food for renewing
growth of the shoot after
periods of stress.
• Example: ginger
Runners/Stolons
• Horizontal stems with long internodes that grow
along the surface of the ground
• Function is vegetative production.
• Examples:
Some grasses,
spider plant,
strawberries are
sometimes
propagated
asexually by runners.
Tendrils
Coil around to
grab onto
branches or the
bark of larger
plants; help
support the
plant.
Passiflora
Cladophylls
Flattened
photosynthetic stems
resembling leaves
In cacti, the real leaves
are actually
modified as spines!
Leaves
• Major function is photosynthesis.
• Initiated as primordia by the apical meristems.
• The leaf may have three parts: a blade, a petiole ,
and a pair of stipules.
• The leaves of most plants have petioles that help
orient the blade of the leaf to the sun.
Phyllotaxy:
Leaves may be arranged in one of three ways:
The spiral (alternate) arrangement is the most common.
 May optimize the exposure of leaves to the sun.
Leaves
Veins consist of both xylem and phloem and are
distributed throughout the leaf blades.
Monocot leaves
have parallel veins
Eudicot leaves have
netted (reticulate) veins
Leaves
The leaf’s surface is covered by
transparent epidermal cells,
most having no chloroplasts.
Epidermis has a waxy cuticle.
The lower epidermis contains numerous mouth
shaped stomata flanked by guard cells.
Leaves
The bulk of most leaves is a specialized ground tissue
called mesophyll. Mesophyll cells are packed with
chloroplasts!
• Palisade mesophyll (parenchyma) – just under
the upper epidermis / closely packed column-shaped
cells that absorb most of the light that enters the leaf.
• Spongy mesophyll (parenchyma) – beneath the
palisade layer / a loose tissue with many air spaces /
These air spaces connect to the outside by stomata
mesophyll
Rich in
chloroplasts
Air spaces
function in
gas & water
vapor
exchange.
Modified Leaves
• Floral leaves (bracts)
• Spines
• Reproductive leaves
• Window leaves
• Shade leaves
• Insectivorous leaves
Floral Leaves (bracts)
Surround the
true flowers
and serve the
same function
as showy
petals.
Poinsettia
Spines
• Modified leaves
that reduce
surface area and
therefore water
loss.
• Spines may also
deter predators.
Reproductive Leaves
in vivo regeneration
The leaves of the
Walking Fern
actually bend
over and form
roots for another
plant, causing it
to "walk!"
Window Leaves
Succulent, cone-shaped leaves that allow photosynthesis
underground
Leaves of Sandy Arid Regions: The leaves are buried in the
sand, leaving the transparent dime-sized tip of the leaf
exposed at the surface. The transparent surface is covered
with a thick epidermis and cuticle and
has virtually no stomata. This
arrangement allows light nearly direct
access to the mesophyll with
chloroplasts inside. The plant, for the
most part, is buried and away from
drying winds and abrasive blowing
sands.
Shade Leaves
• Larger and thinner than sun leaves
• On a weight basis have more chlorophyll
• Chloroplasts move within
cells to take up a position
where they will absorb the
maximum light without
shading other chloroplasts
below them.
Insectivorous Leaves
Plants that trap insects; usually occur in swampy
areas and bogs of tropical and temperate regions.
Generally, the soil is lacking some vital ingredient
for life and the plants utilize trapped insects and
small organisms to fill the gap.
Pitcher Plants  drowning trap
Sundews  sticky trap
Venus Flytrap  hinged trap
Bladderworts  underwater trapdoor trap
Sundews
Pitcher Plant
Bladderworts
Venus Flytrap