Plant Cell Walls
Chapter 3
Where is the cell wall of plant cells located?
A. Inside the plasma membraneB. Outside the plasma membraneC. Between the plasma membranes of two
adjacent cells
The Eukaryotic Plant Cell
• cell wall• plasma
membrane• cytoplasm
• various organelles
• cytoplasmic streaming
• nucleus• vacuole
bound by tonoplast
Cell Wall Functions
• constrains protoplast expansion• gives turgidity to plant
• determines size/shape of cell• cells classified largely
based upon cell wall traits• contain enzymes, absorb,
transport and secrete substances
• play important role in defense
• NOT JUST A CONTAINER BOUNDARY
Primary Cell Walls
• outside of the plasma membrane
• deposited while cell grows• contain thin areas
• primary pit fields• plasmodesmata connect cell-
to-cell • (cytoplasmic connections)
• shared with adjacent cell• middle lamella
• joins primary cell walls of adjacent cells
Plasmodesmata
Chemistry of Primary Cell Walls
• cellulose• glucose monomers• bundled into microfibrils• wound and coiled into
macrofibrils• hemicelluloses
• polysaccharides that limit cell wall extensibility
• pectins• primary cell walls and middle
lamella• give wall pliability; act as
cement• glycoproteins• lignins• cutin• suberin• waxes
Cell growth
determined by cellulose microfibril orientation
Secondary Cell Walls• formed inside the primary
wall• different staining qualities
than primary cell wall• very thick• not present in all cells• formed after cell growth• function in strength and
water transport• abundant cellulose and
hemicellulose• pectins and glycoproteins
absent - thus not elastic• lignins common - gives
hardness and rigidity
Basswood stem (angiosperm stem)
dicot stem
Secondary Cell Wall Examples
• Vascular Tissue• xylem
• vessel elements• tracheids
(gymnosperms)• schlerenchyma fibers
• phloem• schlerenchyma fibers
• Ground Tissue• schlerenchyma fibers
monocot stem
Pine stem
dicot stem
The primary cell wall of plant cells is located inside the plasma membrane.TrueFalse
The secondary cell wall is located inside the plasma membrane.TrueFalse