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Plant Plant Cells & Cells & TissuesTissues
Plant CellsPlant Cells Plant Cells have
a few unique organelles: Vacuoles Plastids (e.g.,
chloroplasts) Cell wall
VacuolesVacuoles Definition: membranous
sacs filled with water that serve a variety of functions: 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.
PlasmolysisPlasmolysis DefinitionDefinition: : the contraction of
cells within plants due to the loss of water through osmosis. 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.
PlastidsPlastids 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: Chloroplasts Amyloplasts/Leucoplasts Chromoplasts
ChloroplastsChloroplasts Definition: plastids that
capture light energy from the sun to make “food”; contain chlorophyll (Elodea)
AmyloplastsAmyloplasts Definition: colorless
plastids that store starch
Leucoplasts are pretty similar.
Found in things like potatoes & onions
ChromoplastsChromoplasts 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 WallCell Wall 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
PlasmodesmataPlasmodesmata Definition: small tubes that
connect plant cells to each other, establishing living bridges between cells. 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.
StomataStomata 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)
TrichomesTrichomes Definition: epidermal hairs
or scales found on nearly all plants.
Functions: Glandular secretions Absorb nutrients Protect against predators Reduce evaporation Reflect solar radiation Collect water
Cell DivisionCell Division 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 TipGarlic Root Tip In plants cell
division occurs in tissues called meristems, which are often found in root tips.
Root cap
Apical meristem
Phases of Cell DivisionPhases of Cell Division Interphase
G1 phase S phase G2 phase
Mitosis: Prophase Metaphase Anaphase Telophase
Cytokinesis
InterphaseInterphase Cellular growth Preparation for mitosis
MitosisMitosis
ProphaseProphase Appearance of string-
like chromosomes due to condensing of chromatin.
MetaphaseMetaphase Chromosomes line up
in the middle of the cell (equator)
AnaphaseAnaphase Chromosomes
separate and move to opposite ends of the cell (poles).
Telophase & CytokinesisTelophase & Cytokinesis Two new nuclei are
formed and the cytoplasm is beginning to separate.
TissuesTissues
Plant TissuesPlant Tissues Definition: a group of cells that forms a structural and
functional unit. Three tissue systems in plants:
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 SIMPLE TISSUESTISSUES
The Ground The Ground Tissue SystemTissue System
Parenchyma cellsParenchyma cells 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:
Photosynthesis & Respiration Storage (starch, oil droplets,
water, and salts) Wound healing & regeneration
CollenchymaCollenchyma 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
SclerenchymaSclerenchyma 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.
FibersFibers 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
SclereidsSclereids Short, cuboidal cells
common in shells of nuts and pits of fruits (peaches, cherries)
Found in all plant parts, usually clustered.
Primary function is for protection.
The red cells in this picture are sclereids from a pear.
Notice the irregular shape.
The surrounding cells are parenchyma cells.
COMPLEX COMPLEX TISSUESTISSUES
The Vascular The Vascular Tissue SystemTissue System
Two Complex TissuesTwo Complex Tissues Xylem Phloem Both are continuous
throughout the plant body.
XylemXylem Conducts water and dissolved
minerals from the roots and the stems and leaves & provides support.
Composed of four types of cells: Tracheids* Vessel elements* Parenchyma cells Fiber (*Both of these conduct water!)
TracheidsTracheids Tracheids are
typically found in gymnosperms and seedless vascular plants and aid in transporting water. The hollow cells
that are stained red are tracheids from a fern.
Vessel ElementsVessel Elements Vessel elements are
typically found in angiosperms and aid in transporting water. Upper right is a long section
of vessel elements showing the perforation plate
Lower right is a cross section of vessel elements.
PhloemPhloem Conducts food materials,
carbohydrates, in solution and provides support.
Composed of four different cells: Sieve-tube members (carry food) Companion cells (aid STM) Schlerenchyma fibers (support) Parenchyma cells (storage)
Sieve-tube Sieve-tube members (STM)members (STM) Long, thin cells that are stacked end-
to-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 Sieve-tube Members (STM)(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 Sieve-tube Members (STM)(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 Sieve-tube Members (STM)(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 CellsCompanion Cells Companion Cells are
alive and regulate the movement of material through sieve tubes. The arrows point out
several companion cells adjacent to the sieve tube members.
Notice the sieve plate as well.
Dermal Tissue Dermal Tissue SystemSystem
DermisDermis In herbaceous plants the
dermis is a single layer of cells called the epidermis.
Epidermis
EpidermisEpidermis 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.
EpidermisEpidermis Functions:
Absorption of water Secretion of cuticle Protection Control of gas
exchange
Epidermis--CuticleEpidermis--Cuticle This picture shows
the single layer of parenchyma cells that makes up the epidermis and also a very thick cuticle.
Cuticle Parenchyma cells
CuticleCuticle A waxy layer that is
secreted by epidermal cells of stems and leaves. Functions to prevent
water loss. Also prevents important
gases like CO2 from diffusing into leaf/stem.
Epidermis—Guard CellsEpidermis—Guard Cells 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 CellsEpidermis—Guard Cells 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 CellsStomata & Guard Cells Stomata are tiny pores in the
epidermis between two cells called guard cells. 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.
Woody plants initially produce an epidermis that splits as the plant grows. These plants also
have periderm, which is several cells thick and forms under the epidermis.
Periderm composes the outer bark.
PeridermisPeridermis
Composed of two types of cells: Cork Cells that
secrete suberin to help waterproof the plant.
Cork Parenchyma that function for storage.
PeridermisPeridermis
Peridermis from an ivy stem.
Plants Exhibit Plants Exhibit Localized Localized Growth at Growth at MeristemsMeristems
MeristemsMeristems 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:
Apical Lateral Intercalary
Types of GrowthTypes of Growth Primary growth: an increase in the length
of a plant. All plants have primary growth.
Secondary growth: an increase in girth of a plant. Only select plants (gymnosperms and woody
dicots) have extensive secondary growth. Wood and bark are produced by secondary
growth.
Types of Types of Meristematic Meristematic
TissuesTissues
Apical MeristemsApical Meristems Found at or near tips of roots and
the buds of stems. Cells are small and “boxy” in shape
due to parenchyma cells. Responsible for the increase in
length of roots and stems. 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 meristemsLateral meristems 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 meristemsIntercalary meristems Growth regions that
occur at the base of nodes.
Found in many plants that don’t have a vascular cambium (grasses).