Transcript Plant cell structure

Plant cell structure
Plant cell organelles
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Cell Membrane
Nucleus
Cytoplasm
Mitochondria
Golgi Complex
Ribosomes
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Smooth Endoplasmic Reticulum
Rough Endoplasmic Reticulum
Cell Wall
Chloroplast
Central Vacuole
Lysosomes
Plant and animal cells: both have many
common components such as :
Nucleus, Mitochondria, ER, Golgi,
Ribosomes, Plasma membrane,
Cytosol, & Microtubules and
microfilaments (cytoskeleton)
• But Plant Cell has these unique
components:
• Cell wall
• Chloroplast
• Central Vacuole
By contrast, Animal Cell has:
• Centrioles
• Lysosomes
Mitochondria
Produces energy and involved in
cellular respiration
Golgi apparatus
Packaging and transport
center of the cell
Ribosomes for protein synthesis
RE for protein synthesis
SE for lipid synthesis
VACUOLE (Plant cell only) Filled with fluid
Helps maintains pressure and shape of cell
•Contains
Chlorophyll
• Transforms
solar energy
into ATP and
sugar in a
process called
photosynthesis
The cell wall
Cell wall consists of:
(1) Middle lamella –mostly pectin, cements
adjacent cells together
(2) Primary cell wall
• Found in all plant cells
• Cellulose matrix with hemicellulose, proteins,
pectin, lignin, cutin, and wax
• Characteristic of undifferentiated cells or
ones that still are growing
(3) Secondary cell wall
• Just inside primary cell wall
• Characteristic of mature cells
• Comprised of hemicellulose and lignin
•10-25 nm in
diameter
• Consists of longchain
polysaccharides
• The composition
varies between
different species
•The polysaccharide
chain folded into
fibers and microfibrils
Primary & Secondary wall
• Growing cells have primary
cell walls that are usually thin
and extensible, although
tough.
• Mature cells no longer needs
to be extensible: a rigid,
secondary cell wall is
produced by either:
• hardening of primary cell wall
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• adding secondary cell wall
between plasma membranes
and primary wall
Primary Cell Wall
• The cell wall is a network of
1.Microfibril threads (chains of
cellulose)
2.Cross-linking polysaccharides
(hemicellulose)
3.Matrix of mainly acidic
polysaccharides (pectins)
4.Calcium bridges pectin chains
• Cellulose and crosslinking glycans
(hemicellulose) provides
tensile strength,
• Pectin is the sticky
polysaccharide.
• The middle lamella is rich
in pectin and cement
adjacents cells together.
• Proteins Constitutes
about 5%.
Connections
between Cells:
Plasmodesmata
•Are microscopic
channels through
the cell walls and
middle lamella.
• Link adjacent
plasma membranes
and cytoplasm
•They enable
intercellular
transport and
communication
between cells.
Cellulose
• Linear polymer of glucose,
with (β1-4)linkages to form long straight
chains (2-250K residues).
• About 36 cellulose chains are associated by
hydrogen bonds to a crystalline structure
known as a microfibril.
• These structures are impermeable to water,
of high tensile strength, very resistant to
chemical and biological degradations
Structure of cellulose
Hemicellulose
• Hemicellulose is a heterogeneous group of
branched polysaccharides polymers that
cross-link cellulose fibrils forming a network.
• They all have a long linear backbone
composed of one type of sugar (glucose,
xylose, or mannose) with several branches
Structure of hemicellulose
Pectin
• Pectins are a heterogeneous group of
branched polysaccharides that contain
many negatively charged Galacturonic
acid.
• They form negatively charged, hydrophilic
network that gives compressive strength to
primary walls and contributes to cell-cell
adhesion.
•Pectin is a soluble
compound in the
absence of
Ca2+/Mg2+, but forms
amorphous
deformable gel in their
presence.
• Food industries use
of this property when
preparing jellies and
jams.
Structure of pectin
Lignin
• The most common additional polymer in
secondary walls is lignin
• Found mostly in the walls of the xylem
vessels and fiber cells of woody tissues.
• Lignin causes the walls to become thick, stiff,
and incompressible. Lignin provides the
structural strength needed by large trees to
reach heights in excess of 100 m. Without
lignin these trees would collapse on
themselves
Structure of lignin
Cell wall and Turgor
• Cell walls is made of neutral and charged
polysaccharides
absorbs H2O because it
has a hypotonic environment.
• Increased H2O in the cell
Turgor Pressure
• If a plant cell is turgid, It is very firm, a healthy
state in most plants
• If a plant cell is flaccid, It is in an isotonic or
hypertonic environment
PLANT CELL
ANIMAL CELL
• Hypertonic solution→
Plasmolysed cell
• Isotonic solution→
Non-turgid or wilted cell
• Hypotonic solution→
Turgid cell (Usual
environment
• Hypertonic
solution→Cell shrinks
• Isotonic
solution→Normal
(Usual environment)
• Hypotonic
solution→Cell swells