Chapter 23
Roots, Stems and Leaves
Learning Targets 23.1
What are the principal organs and
tissues of vascular plants?
How is meristematic tissue
different from other plant tissues?
What specialized cells make up
vascular tissue?
Specialized Tissues in Plants
 Three main organs of plants:
ROOTS: underground organs that absorb water and
minerals
 Also anchor the plant and hold it upright
STEMS: supporting structures that connect roots and
leaves
 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
Dermal Tissue
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
Ground Tissue
Parenchyma:
Thin cell walls and large vacuoles
In leaves, these cells are packed with
chloroplasts and are the site of
photosynthesis
Collenchyma
Cells with strong, flexible walls that help to
support larger plants
This is what makes up the stringy part of
celery
Ground Tissue
Sclerenchyma
Cells that have an extremely thick, ridged,
cell wall that makes ground tissue tough
and strong.
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
Learning Targets 23.2
What are the two main types of
roots?
What are the main tissues in a
mature root?
What are 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
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
Learning Targets 23.3
What are the three main functions
of stems?
How do monocot and dicot stems
differ?
How do primary growth and
secondary growth occur in stems?
Stems
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 Growth
For a plant’s entire life, new cells
are produced at the tips of roots
and shoots
This is called primary growth
They increase in length
It takes place in all seed plants
Secondary Growth
The pattern of growth in which
stems increase in width is called
secondary growth
In conifers and dicots, secondary growth
takes place in lateral meristematic tissue
called the vascular cambium and cork
cabium
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
Learning Targets 23.4
How does the structure of a leaf
enable it to carry out
photosynthesis?
How does gas exchange take place
in a leaf?
Leaves
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
Leaves
Simple and
Compound Leaves
Leaf Structure/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 Structure/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
Cuticle
Veins
Epidermis
Palisade
mesophyll
Xylem
Phloem
Vein
Spongy
mesophyll
Epidermis
Stoma
Guard
cells
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
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
Leaf Structure/Function
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
Stomata/Guard Cells
Guard cells
Guard cells
Inner cell wall
Inner cell wall
Stoma
Stoma Open
Stoma Closed
Leaf Structure/Function
Cuticle
Veins
Epidermis
Palisade
mesophyll
Xylem
Phloem
Vein
Spongy
mesophyll
Epidermis
Stoma
Guard
cells
Learning Targets 23.5
How is water transported
throughout a plant?
How are the products of
photosynthesis transported
throughout the plan?
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
Water Transport
Transpiration: loss of water through
plant leaves
• 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.