Transcript Plant Cells & Tissues

Plant Cells
& Tissues
Plant Cells
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Plant Cells have
a few unique
organelles:
 Vacuoles
 Plastids (e.g.,
chloroplasts)
 Cell wall
Vacuoles
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Definition: membranous
sacs filled with water that
serve a variety of functions:
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Storage of “food”, water, oil,
pigments, toxins, & waste).
Helps to maintain turgor
pressure.
Young plant cells often
contain many small
vacuoles, but as the cells
mature, these unite to form
a large central vacuole.
Plasmolysis
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Definition: the contraction of
cells within plants due to the
loss of water through osmosis.
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It is when the cell membrane
“shrinks away” from the cell
wall and the vacuole collapses.
Occurs when water is drawn
out of the cell (high water
concentration  low water
concentration).
Causes plants to wilt.
Plastids
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Definition: large organelles that
are associated with pigments
and other storage products (e.g.,
starch).
A typical plant cell will usually
have 20-40 plastids.
Several Types:
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Chloroplasts
Amyloplasts/Leucoplasts
Chromoplasts
Chloroplasts
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Definition: plastids that
capture light energy
from the sun to make
“food”; contain
chlorophyll (Elodea)
Amyloplasts
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Definition: colorless
plastids that store
starch
Leucoplasts are pretty
similar.
Found in things like
potatoes & onions
Chromoplasts
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Definition: plastids that make
& store carotenoid pigments
Found in red & yellow
peppers, tomatoes, flower
petals …
When leaves change color in
autumn, it is the result of the
conversion of chloroplasts
into chromoplasts.
Cell Wall
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Definition: a flexible outer
barrier made of cellulose
fibrils that surrounds plant
cells.
Functions:
 Protection & Support
 Determines plant shape
& size
 Maintains turgor pressure
 Regulates movement in
and out
 Cell-cell communication
Plasmodesmata
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Definition: small tubes that
connect plant cells to each
other, establishing living
bridges between cells.
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Allow certain molecules to pass
directly from one cell to another.
These channels, penetrate the
cell wall and are lined with
plasma membrane, uniting all
connected cells with essentially
one continuous cell membrane.
Stomata
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Definition: pores found in the
underside of plant leaves in the
epidermis that allow for the
exchange of gases (CO2) and H20.
The stomata are flanked by two half
moon shaped guard cells, which
contains chloroplasts and regulates
the opening and closing of the
stoma.
Normally stomata open when the
light strikes the leaf in the morning
and close during the night.
Pea leaf stoma (SEM x 3, 520)
Trichomes
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Definition: epidermal hairs
or scales found on nearly
all plants.
Functions:
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Glandular secretions
Absorb nutrients
Protect against predators
Reduce evaporation
Reflect solar radiation
Collect water
Cell Division
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The mechanism that
allows the nuclei of
cells to split and provide
each daughter cell with
a complete set of
chromosomes during
cellular division.
Permits plants to grow
& develop.
Garlic Root Tip
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In plants cell
division occurs in
tissues called
meristems, which
are often found in
root tips.
Apical meristem
Root cap
Phases of Cell Division
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Interphase
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Mitosis:
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G1 phase
S phase
G2 phase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Interphase
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Cellular growth
Preparation for mitosis
Mitosis
Prophase
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Appearance of stringlike chromosomes due
to condensing of
chromatin.
Metaphase
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Chromosomes line up
in the middle of the
cell (equator)
Anaphase
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Chromosomes
separate and move to
opposite ends of the
cell (poles).
Telophase & Cytokinesis
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Two new nuclei are
formed and the
cytoplasm is beginning
to separate.
Tissues
Plant Tissues
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Definition: a group of cells that forms a structural and
functional unit.
Three tissue systems in plants:
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Ground tissue: variety of functions including support
and photosynthesis
Vascular tissue: “Plumbing system” throughout plants;
conducts water, food (CHO), and dissolved minerals;
also strengthens and supports the plant.
Dermal tissue: Provides covering for the plant body.
SIMPLE
TISSUES
The Ground
Tissue System
Parenchyma cells
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Definition: a simple tissue composed
of spherical-shaped cells; most
common type of tissue (most of
apples & potatoes); found throughout
plant
Have thin primary walls
Living, metabolizing tissue
Functions:
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Photosynthesis & Respiration
Storage (starch, oil droplets, water,
and salts)
Wound healing & regeneration
Collenchyma
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Definition: a simple tissue found
beneath the epidermis in young
stems and in large veins of
leaves (“strings” in celery).
Provides a flexible support
system (like our skeletal
system).
Found uniformly throughout the
plant.
Elongated cells that have
unevenly thickened cell walls
(especially in the corners)
Alive at maturity
Sclerenchyma
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Definition: a simple tissue
specialized for structural
support; occurs in many
areas
Two types:
 Fibers
 Sclereids
Have both primary and
secondary cell walls.
At functional maturity cells
are often dead.
Fibers
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Long, tapered cells that
often occur in groups or
clumps (abundant in the
wood and bark of
flowering plants)
Found in leaves &
stems.
Primary function is
support.
These sclerenchyma fibers
clearly show the thick cell walls.
Notice the pits (identified by the
arrows) which allow materials to
pass from one fiber to another
Sclereids
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Short, cuboidal cells
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common in shells of
nuts and pits of fruits
(peaches, cherries)
Found in all plant parts,
usually clustered.
Primary function is for
protection.
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The red cells in this picture are
sclereids from a pear.
Notice the irregular shape.
The surrounding cells are
parenchyma cells.
COMPLEX
TISSUES
The Vascular
Tissue System
Two Complex Tissues
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Xylem
Phloem
Both are continuous
throughout the plant
body.
Xylem
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Conducts water and dissolved
minerals from the roots and the
stems and leaves & provides
support.
Composed of four types of
cells:
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Tracheids*
Vessel elements*
Parenchyma cells
Fiber
(*Both of these conduct water!)
Tracheids
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Tracheids are
typically found in
gymnosperms and
seedless vascular
plants and aid in
transporting water.
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The hollow cells
that are stained
red are tracheids
from a fern.
Vessel Elements
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Vessel elements are typically
found in angiosperms and aid
in transporting water.
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Upper right is a long section
of vessel elements showing
the perforation plate
Lower right is a cross section
of vessel elements.
Phloem
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Conducts food materials,
carbohydrates, in solution and
provides support.
Composed of four different cells:
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Sieve-tube members (carry food)
Companion cells (aid STM)
Schlerenchyma fibers (support)
Parenchyma cells (storage)
Sieve-tube
members (STM)
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Long, thin cells that are stacked endto-end to form extended sieve tubes.
Some of the most-specialized cells
in nature that are alive, but lose their
organelles at maturity.
The end of the cells are called sieve
plates.
Adjacent to STM are companion
cells, which assist in the STM by
moving food into the sieve-tube for
transport.
Sieve-tube Members (STM)
This is a sieve tube
member from
milkweed.
Notice how STM’s are
connected by sieve
plates (identified by the
arrows).
Sieve-tube Members (STM)
This picture show several
sieve tube member in
cross section.
Notice the perforated
sieve plate near the top
that would connect two
sieve tube members.
Sieve-tube Members (STM)
Sieve tube members can
secrete a protein called
callose to plug the seive
plates and stop the flow
of food if there is
damage in the phloem.
This picture shows an
example.
Companion Cells
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Companion Cells are
alive and regulate the
movement of material
through sieve tubes.
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The arrows point out
several companion cells
adjacent to the sieve
tube members.
Notice the sieve plate as
well.
Dermal Tissue
System
Dermis
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In herbaceous plants the
dermis is a single layer of
cells called the epidermis.
Epidermis
Epidermis
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Comprised of two types
of cells:
 Parenchyma cells
(storage)
 Guard cells (together
create stoma)
Epidermal parenchyma
contain no chloroplasts, so
they appear transparent
allowing light to penetrate
into interior photosynthetic
tissues.
This picture shows the single
layer of parenchyma cells that
makes up the epidermis and
also a very thick cuticle.
Epidermis
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Functions:
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Absorption of water
Secretion of cuticle
Protection
Control of gas
exchange
Epidermis--Cuticle
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This picture shows
the single layer of
parenchyma cells
that makes up the
epidermis and also a
very thick cuticle.
Cuticle
Parenchyma cells
Cuticle
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A waxy layer that is
secreted by epidermal
cells of stems and
leaves.
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Functions to prevent
water loss.
Also prevents important
gases like CO2 from
diffusing into leaf/stem.
Epidermis—Guard Cells
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This picture shows
the single layer of
parenchyma cells
that makes up the
epidermis along with
the cuticle and a pair
of guard cells
creating a stoma.
Epidermis—Guard Cells
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This picture shows
the parenchyma
cells that makes up
the epidermis and a
couple pairs of
guard cells (and
stomata) from the
top.
Stomata & Guard Cells
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Stomata are tiny pores in the
epidermis between two cells
called guard cells.
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Many gases, including CO2,
O2 and H2O vapor, pass
through stomata by diffusion.
Stomata are generally open
during the day during
photosythesis. The water
lost when stoma are open
elps to cool the leaf!
Usually closed at night to
conserve water.
Peridermis
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Woody plants initially
produce an epidermis
that splits as the plant
grows.
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These plants also
have periderm, which
is several cells thick
and forms under the
epidermis.
Periderm composes
the outer bark.
Peridermis
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Composed of two
types of cells:
 Cork Cells that
secrete suberin to
help waterproof
the plant.
 Cork Parenchyma
that function for
storage.
Peridermis from an ivy stem.
Plants Exhibit
Localized Growth
at Meristems
Meristems
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Definition: specific areas of plant growth, which
are composed of cells that do not differentiate.
These cells retain the ability to divide, which
other plant cells lose.
Meristems allow plants to grow their entire
lives.
Types:
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Apical
Lateral
Intercalary
Types of Growth
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Primary growth: an increase in the length
of a plant.
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All plants have primary growth.
Secondary growth: an increase in girth of
a plant.
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Only select plants (gymnosperms and woody
dicots) have extensive secondary growth.
Wood and bark are produced by secondary
growth.
Types of
Meristematic
Tissues
Apical Meristems
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Found at or near tips of roots and the
buds of stems.
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Cells are small and “boxy” in shape due
to parenchyma cells.
Responsible for the increase in length
of roots and stems.
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Root tips have a root cap at the tip of the
apical meristem, which is followed by an
area of cell elongation and an area of cell
differentiation.
Stem buds have a dome-like apical
meristem in addition to leaf primordia
and bud primordia, which protect the
apical meristem.
Lateral meristems
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Definition: areas that extend the
entire lengths of stems and roots
except at tips, which are
responsible for secondary growth in
trees & shrubs.
Two types:
 Vascular cambium —a layer of
cells that forms a thin cylinder
around the stem and root trunk,
between the wood and bark.
 Cork cambium —a thin cylnder
of cells in the outer bark region.
Intercalary meristems
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Growth regions that
occur at the base of
nodes.
Found in many plants
that don’t have a
vascular cambium
(grasses).