23.1
Specialized Tissues in Plants
Essential Question
What are plant tissues and organs?
Seed Plant
Structure
• Three main organs of
seed plants are roots,
stems, and leaves
• These organs are
linked together by
systems that transport
nutrients, protect it,
and coordinate
activities
Roots
• Absorb and transport
water and dissolved
nutrients to rest of plant
• Anchor plant in ground,
holding soil in place, and
preventing erosion
• Keeps plants upright
against forces such as
wind and rain
• Protects plant form
harmful soil bacteria and
fungi
• Two types: fibrous and
taproot
Stems
• Have three important
functions:
– Produce leaves,
branches, and flowers
– Hold leaves up to
sunlight
– Transport substances
between roots and
leaves
Leaves
• Principle organs in
which plants carry out
photosynthesis
• Vary widely according
to species
• Have adjustable pores
called stomata that
help to conserve water
and exchange gases
Tissue Systems- 3 types
• Dermal – outermost layer of cells functions
to protect plant and exchange gases and
water
• Ground – cells that lie between the dermal
and vascular systems
• Vascular – transports water and nutrients
throughout plant
Dermal Tissue
• Outermost layer of
plant
• Consists of single
layer of epidermal
cells
• Often covered with
waxy layer called the
cuticle that protects
against water loss
and injury
Dermal Cont’d
• Some cells have
projections called
trichomes that help
protect leaf and give
it a fuzzy
appearance
• Root dermal tissue
contains root hair
cells that aid in
absorption
Dermal Cont’d
• Underside of leaves
have stomata which
contain guard cells
that regulate water
loss and gas
exchange
Leaf Structure
Vascular Tissue
• Forms transport system m; conducts water
and nutrients through plant
• Made up of a network of hollow connected
cells
• Consists of:
– xylem (water-conducting tissue)
• consists of tracheids (conifers) and vessel
elements (angiosperms only)
– phloem (food conducting tissue).
• Phloem consists of sieve tube elements and
companion cells
Tracheids
•
•
•
•
•
Found in all seed plants
type of xylem cell
Found first in fossil record
Only xylem cell found in conifers and ferns
long, narrow cells with walls made of lignin and
cellulose that are impermeable to water
• Walls are pierced with openings that connect
them to other cells
• Mature cells die and cytoplasm disintegrates
Vessel elements
• Only found in angiosperms
• Conduct water
• much wider than tracheids and are
arranged end to end like stacked tin cans
• Angiosperms have both tracheids and
vessel elements but rely on vessel
element to move water
• Both types of cells mature and die before
they can conduct water
Compare Vessel element and
Tracheid
Phloem
• Phloem tissue transports carbohydrates
made during photosynthesis.
• Made of sieve tube elements and
companion cells
• sieve tube elements are arranged end to
end to form sieve tubes
• Sieve tubes are mature cells that die and
lose nuclei and most organelles
• remaining organelles hug cell wall to form
“pipeline” for movement of fluids.
Cont’d
• Ends of sieve tubes have many small
holes to allow movement of sugars and
other foods
• Companion cells surround sieve tube
elements and help support phloem cells
and aid in movement of substances in and
out of phloem
Xylem and Phloem Vessel
Cross Section of a Stem
Ground Tissue
• Made up of cells that lie between dermal and
vascular tissues
• Site of photosynthesis; helps support plants
• May have three types of cells (depending on
plant type)
– parenchyma cells – thin cell walls and large central
vacuole; in leaves are packed with chloroplasts
• Function in storage and photosynthesis
– collenchyma cells have thick strong flexible cell walls
that help support larger plants
– sclerenchyma cells have extremely thick, rigid cell
walls that make ground tissue tough and strong.
– Both collenchyma cells and sclerenchyma cells
function as support
Types of Cells in Ground Tissue
Meristematic Tissue
• Meristems are clusters of meristematic cells
(undifferentiated cells) that are found in zones of the
plant and help it grow throughout its entire life
• Its function is to begin growth of new cells in seedlings at
the tips of roots and shoots
• Meristematic tissue produces meristems (meristematic
cells) that are not yet specialized to perform specific
functions (undifferentiated or embryonic)
• Meristematic tissue is the only plant tissue that
produces new cells by mitosis
• Classified by location in plant:
– apical meristems – found at the end or tip of growing roots and
stems (shoots)
– Lateral meristems -- found in the vascular cambium and cork
cambium
– intercalary meristems -- at internodes, or stem regions between
the places at which leaves attach
Plant Tissue Types
Dermal tissue
Vascular tissue
Ground tissue
Meristematic
tissue
Meristematic Tissue
Root Meristem
Differentiation
• At first cells in meristem look alike
• Then they divide rapidly and mature in a
process called differentiation
• Cells develop into each of the tissue
systems of the plant (dermal, ground, and
vascular)