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