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

Plant body organization

• Plant body• Systems

• Shoot & root systems• Organs

• Vegetative: root, stem, leaf• Reproductive: flower, fruit

• Tissue Systems• Dermal, ground, vascular

• Tissues• Cells

Meristem classification:

• apical • root tip & shoot tip• produce primary growth

• lateral• to the side of stems and

roots• produce secondary growth

• intercalary• between mature tissues• help regenerate parts that

are removed (grass leaves and herbivory)

• primary (formed first)• produce primary tissue

systems• three types

• protoderm• ground meristem• procambium

• secondary (formed after 1°)• produce secondary tissue

systems• two types

• vascular cambium• cork cambium

LOCATION FUNCTION

1° Tissue Systems

• Dermal tissue system• covers and protects

plant surface• epidermis

• Ground tissue system• parenchyma,

collenchyma and sclerenchyma cells

• mesophyll of leaves• young green stems

(pith and cortex)• Vascular tissue

system• conducts water and

solutes (xylem)• conducts sugars

(phloem)

leaf

stem

root

Plant body organization

Tissues with cell typesSimple

• Parenchyma• Chlorenchyma• Sclerenchyma• Collenchyma

Complex• Epidermis

• Ground cells• Guard cells

• Xylem• Vessel elements• parenchyma

• Phloem• Sieve tube elements• Companion cells• Sclerenchyma fiber

parenchyma

collenchyma

collenchyma

sclerenchyma fibers

sclerenchyma fibers

vessel elements

sclerenchyma fibers

tracheid

Primary Meristems

• Forms primary tissue• Elongates root and

shoot• types

• protoderm• epidermis

• procambium• primary xylem and

phloem• ground meristem

• pith and cortex of stems and root, mesophyll of leaves

ground meristem

procambium

protoderm

Secondary Meristems

• Forms secondary tissue• Growth in lateral

direction• leads to increase in girth or

circumference• wood in trees

• 2 types• vascular cambium

• secondary xylem • secondary phloem

• cork cambium• periderm

2 xylem

2 phloem

vascular cambium

periderm