Transcript Chapter 23: Plant Tissues & Systems

Section 1
Specialized Plant Cells
• Remember plant
cells have unique
structures
• Cell wall
• Central vacuole
• 3 types of
specialized plant
cells
1.
Parenchyma
2.
Collenchyma
3.
Sclerenchyma
Paranchyma “puh-REN-kuhmuh”
• Usually loosely packed cubeshaped or elongated cells
• Contain large central vacuole
• Have thin, flexible cell walls
• Involved in many metabolic
functions: photosynthesis,
storage of water and nutrients,
healing
• Usually form main part of
nonwoody plants
• Ex. Fleshy part of apple
Collenchyma “koh-LEN-kuhmuh”
 Cells walls thicker than
parenchyma
 Cell walls irregular in shape
 Thicker walls provide more
support for plant
 Usually grouped in strands
 Specialized for supporting
areas of plant that are still
lengthening
 Ex. Celery stalks – lots of
collenchyma
Sclerenchyma “skluh-REN-kuhmuh”
 Thick, even, stiff cell walls
 Support and strengthen
plant in areas where
growth is finished
 Usually dies at maturity
 Rough texture of pear is
from presence of
sclerenchyma cells
Tissue Systems
• Cells that work together to
perform specific function
make tissue
• In plants, arranged into
systems
1. Dermal system
2. Ground system
3. Vascular system
•
Systems further
organized into 3 major
plant organs – roots,
stems, leaves
Dermal Tissue System
Forms outside covering of plants
In young plants, made of epidermis “ep-uhDURH-muhs” – the outer layer made of
parenchyma cells
In some species, epidermis more than 1 cell
thick
Outer epidermal wall often covered by waxy
layer called the cuticle  prevents water
loss
 Some epidermal cells of roots develop
hairlike extensions that increase water
absorption
 Openings in leaf and stem epidermis are
stomata  help regulate the passage of
gases and moisture in and out of plant
 In woody stems and roots, epidermis
replaced by dead cork cells
Ground Tissue System
 Dermal tissue surrounds the ground tissue
system
 Has all 3 types of cells
 Functions in storage, metabolism, support
 Paranchyma most common cell
 Nonwoody roots, stems, leaves made mostly of
ground tissue
• Cactus stems have large amounts of parenchyma
cells for storing water
• Plants growing in very wet soil have parenchyma with
large air spaces to allow air to reach roots
• Nonwoody plants that need to be flexible to withstand
wind have large amount of collenchyma cells
• Sclerenchyma found where hardness is advantage,
i.e. seed coats, cacti spines
Vascular Tissue
Vascular tissue supports the plant
body and transports water and
nutrients throughout the plant.
The two kinds of vascular tissue
are xylem, a water-conducting
tissue, and phloem, a tissue that
carries dissolved food.
Both xylem and phloem consist of
long, slender cells that connect
almost like sections of pipe, as
shown in the figure.
Xylem: Tracheids
All seed plants have xylem
cells called tracheids.
As they mature, tracheids die,
leaving only their cell walls.
These cell walls contain
lignin, a complex molecule
that gives wood much of its
strength.
Xylem: Tracheids
Openings in the walls
connect neighboring cells
and allow water to flow
from cell to cell.
Thinner regions of the
wall, known as pits, allow
water to diffuse from
tracheids into
surrounding ground
tissue.
Xylem: Vessel Elements
Angiosperms have a second
form of xylem tissue known
as vessel elements, which are
wider than tracheids and are
arranged end to end on top
of one another like a stack of
tin cans.
After they mature and die,
cell walls at both ends are left
with slit-like openings
through which water can
move freely.
Xylem: Sieve Tube
Elements
Unlike xylem cells,
phloem cells are alive at
maturity. The main
phloem cells are sieve
tube elements, which
are arranged end to end,
forming sieve tubes. The
end walls have many
small holes through
which nutrients move
from cell to cell.
Xylem: Sieve Tube
Elements
As sieve tube elements
mature, they lose their
nuclei and most other
organelles. The
remaining organelles hug
the inside of the cell wall
and are kept alive by
companion cells.
Phloem: Companion Cells
The cells that surround
sieve tube elements are
called companion cells.
Companion cells keep
their nuclei and other
organelles through their
lifetime.
Growth in Meristems
• Plant growth starts in
meristems “MER-i-stemz”
 regions where cells
continuously divide
• Apical “AP-i-kuhl”
meristems  plant grows in
length
• Located at tips of stems and
roots
• Some monocots
have intercalary
“in-TUHR-kah-leree” meristems
located above bases
of leaves and stems
• Allow grass leaves
to quickly regrow
after being cut
• Gymnosperms and most dicots also have lateral
meristems  allow stems and roots to increase in
diameter
• Located near outside of stems and roots
• 2 types
1.
Vascular cambium
2.
Cork cambium
 Vascular cambium  produces additional
vascular tissues
 Located between xylem and phloem
 Cork cambium  produces cork
 Located outside phloem
 Cork cells replace epidermis in woody stems
and roots
 Protects plant
 Cork  dead cells that provide protection
and prevent water loss
• Primary growth  increase in length
• Made by apical and intercalary meristems
• Secondary growth  increase in diameter
• Made by lateral meristems
• By vascular cambium and cork cambium