Chapter 23
Roots, Stems and Leaves
Section 23-1 Learning Targets
Describe the organs and tissues of
vascular plants
 Identify the specialized cells of vascular
tissue
 Contrast meristematic tissue with other
plant tissues

Specialized Tissues in Plants

Three main organs of plants:

ROOTS: underground organs that absorb
water and minerals


STEMS: supporting structures that connect
roots and leaves



Also anchor the plant and hold it upright
Carry water and nutrients
Holds leaves up to light
LEAVES: carry out photosynthesis

Capture light, flat so cover more surface area

Cuticle and adjustable pores protect leaves from water loss
Tissue Systems

Within the roots, stems and leaves are
FOUR specialized tissue systems:
DERMAL TISSUE: forms the skin of a plant (is
the outermost layer of cells)
 VASCULAR TISSUE: like the plant’s
bloodstream (transports water and nutrients
throughout the plant)
 GROUND TISSUE: cells between the dermal and
vascular tissues
 MERISTEMATIC TISSUE: found only in the tips
of shoots and roots

Leaf
Stem
Root
Dermal tissue
Vascular tissue
Ground tissue
Three
tissues of
plants
Dermal Tissue
Outer covering
of a plant
 Consists of:

Epidermis: outermost layer
 Cuticle: thick, waxy layer that protects
against water loss and injury (covers
epidermis)
 On under side of leaves, contains guard cells
which regulate water loss and gas exchange

Vascular Tissue
Transport system: “bloodstream”
 Consists of xylem and phloem


Xylem: water-conducting tissue
 Transports

water to leaves
Phloem: food-conducting tissue
 Takes
sugar to the roots
Ground Tissue

Tissue that lies between dermal and
vascular tissue

Consists of parenchyma, collenchyma and
sclerenchyma
Meristematic Tissue
New growth is produced in cells that make
up meristematic tissue
 It is the ONLY plant tissue that produces
new cells by mitosis!!


Best place to see this at the tip of a
shoot/root where apical
meristem is located
Section 23-2 Roots Learning Targets
Describe the two main types of roots
 Identify the tissues and structures in a
mature root.
 Describe the different functions of roots.

Roots

Functions:



Absorb water and nutrients
Anchor plant
TWO MAIN TYPES OF ROOTS:

Taproots: found mainly in dicots


EX: carrot, dandelions, beets, radishes,
oak tree
Fibrous Roots: found mainly in monocots


Help to prevent erosion
EX: grass
ROOTS
Root Structure

Epidermis of root is covered with
tiny projections called root hairs


Increase surface area of root to absorb more
water
Roots grow in length as their apical meristem
produces new cells near the root tip

The fragile new cells are covered by a tough root
cap that protects the root as it forces its way
through soil
Root Function
 Roots
anchor the plants into the
ground and absorb water and
nutrients.
 Roots use osmosis and active
transport to move water and
nutrients into the plant roots to
support the plants growth
Section 23-3 Stems
 Describe
the main functions of
stems
 Contrast monocot and dicot
stems
 Explain how primary growth
and secondary growth occur in
stems
Stems

3 IMPORTANT FUNCTIONS:
Produce Leaves, branches and flowers
 Hold leaves up in the sunlight
 Transport substances between roots and
leaves


Composed of dermal, vascular and
ground tissue (like the rest of the
plant)
Stem Parts
Nodes: where
leaves are
attached
 Internodes:
regions between
the nodes
 Buds: contain
undeveloped
tissue that can
produce new
stems and leaves

Monocot v. Dicot Stems

Moncots: vascular bundles are scattered
throughout the stem
Monocot v. Dicot Stems

Dicots: vascular bundles are arranged in a
cylinder
Primary vs. Secondary Growth
 Plants
grow in two main ways:
 Primary
Growth: produced by cell
divisions in the apical meristem (tips
of roots and shoots)
 Secondary
Growth: the type of
growth in which the stem increases
in width.
P
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Secondary Growth:WOOD

WOOD is actually layers
of XYLEM

Heartwood: older xylem
in center of wood, that no
longer conducts water
 Darkens
with age as it
accumulates impurities

Sapwood: surrounds
heartwood, active in
transport
WOOD
Growth Rings
 Indicate age of tree and
environmental conditions

Thick rings indicate the
growing season
experienced adequate
moisture
 Thin rings indicate there
was less water (draught)

Wood
Bark
Cork
Contains old,
nonfunctioning
phloem that
protects the tree
Xylem:
Heartwood
Contains old,
nonfunctioning
xylem that helps
support the tree
Cork Cambium
Produces
protective layer
of cork
Phloem
Transports sugars
produced by
photosynthesis
Xylem: Sapwood
Contains active xylem
that transports water
and minerals
Vascular Cambium
Produces new xylem
and phloem, which
increase the width of
the stem
Section 23-4 Leaves
 Describe
how the structure of
a leaf enables it to carry out
photosynthesis
 Describe how gas exchange
takes place in a leaf
Leaf Structure

Main organs of photosynthesis


Makes food for plants (glucose: C6H12O2)
Structure is optimized for absorbing light
and carrying out photosynthesis

Blades: thin, flattened to increase surface
area to absorb sunlight
 Attached
to stem by petiole
Epidermis: outer layer
 Cuticle: waxy, protective layer

 Protects
tissues and limits water loss
Leaf Structure
Leaf Function

Photosynthesis

Most of photosynthesis carried out in
MESOPHYLL layer
 Packed

with chloroplasts
Palisade Mesophyll: column-shaped cells just
under epidermis
 Absorb
most of light coming into leaf
Leaf Function
Cuticle
Veins
Epidermis
Palisade
mesophyll
Xylem
Phloem
Vein
Spongy
mesophyll
Epidermis
Stoma
Guard
cells
Leaf Structure/Function

Spongy Mesophyll: loose tissue layer beneath
palisade with air spaces between cells

Air spaces connect with outside through
STOMATA
Leaf Structure/Function

STOMATA: pores in underside of leaf
that let carbon dioxide and oxygen diffuse
in and out of the leaf

Each stoma consists of two GUARD CELLS
 Guard
Cells: cells in the epidermis that control the
opening and closing of the stomata by responding to
water pressure changes
Single stomata
Multiple stomata
Stomata/Guard Cells
Guard cells
Guard cells
Inner cell wall
Inner cell wall
Stoma
Stoma Open
Stoma Closed
Leaf Structure/Function

Gas Exchange


Leaves take in CO2 and give off O2 during photosynthesis
Plant leaves allow gas exchange by opening their stomata
 If kept open all the time, there would be large
amounts of water loss due to transpiration
 Plants keep stomata open just enough to allow
photosynthesis to take place, not long enough to lose
too much water
 Guard
cells regulate opening/closing of the
stomata
 If
water pressure is high, they open the stomata
 If water pressure is low, they close the stoma
Leaf Structure/Function
Cuticle
Veins
Epidermis
Palisade
mesophyll
Xylem
Phloem
Vein
Spongy
mesophyll
Epidermis
Stoma
Guard
cells
Section 22-5 Transport in Plants
 Explain
how water is
transported throughout the
plant
 Describe how the products of
photosynthesis are
transported throughout the
plant.
Water Transport

Combo of root pressure, capillary action and
transpiration provides force to move water through
the xylem


Root Pressure: pressure created by water entering
the tissues of a root that pushes water upward in a
plant stem
Capillary Action: tendency of water to rise in a THIN
tube
 Water
is attracted to the walls of the tube and to
other water molecules

Transpiration: loss of water through plant leaves by
evaporation

When water is lost through transpiration the leaf “pulls”
water upward from the roots

Moves water from HIGH to LOW pressure
Water Movement
Evaporation of water
molecules out of leaves.
Pull of water molecules upward
from the roots.