THE PLANT BODYTHE PLANT BODY

MeristemsMeristems

In flowering plants cells originate from In flowering plants cells originate from regions of active cell division known as regions of active cell division known as meristems.meristems.

The cells arising from meristems give The cells arising from meristems give rise to the many different cell types that rise to the many different cell types that make up a plant make up a plant

Types of MeristemsTypes of Meristems

Primary MeristemsPrimary Meristems (also called Apical (also called Apical Meristems) result in primary growth - Meristems) result in primary growth - growth in lengthgrowth in length

Secondary MeristemsSecondary Meristems result in result in secondary growth which in growth in secondary growth which in growth in width (increase in diameter)width (increase in diameter)

Apical meristemsApical meristems

Also known as primary meristemsAlso known as primary meristems Found at the tips of all roots and stems Found at the tips of all roots and stems Contribute to the increase in length of Contribute to the increase in length of

the plant which is called primary growth the plant which is called primary growth Give rise to the leaves, and non-woody Give rise to the leaves, and non-woody

stems and rootsstems and roots

Secondary MeristemsSecondary Meristems

Some plants have additional meristems Some plants have additional meristems that result in increases in diameter that result in increases in diameter which is secondary growth. which is secondary growth. • Vascular cambium Vascular cambium • cork cambium cork cambium

Multicellular OrganismsMulticellular Organisms

In multicellular organisms, certain cells are In multicellular organisms, certain cells are specialized in structure and functionspecialized in structure and function

Tissues are specialized cells that perform Tissues are specialized cells that perform specific functions specific functions

Plants composed of three basic tissues Plants composed of three basic tissues categoriescategories• DermalDermal• GroundGround• VascularVascular

Dermal TissueDermal Tissue

Dermal tissues are the outermost layers Dermal tissues are the outermost layers in a plantin a plant

They protect the plant They protect the plant Two types of dermal tissuesTwo types of dermal tissues• Epidermis Epidermis • PeridermPeriderm

EpidermisEpidermis

Outermost layer In Outermost layer In young plants and young plants and non-woody plants non-woody plants

Single layer of Single layer of flatten cellsflatten cells

Cells secrete Cells secrete cutincutin which makes up the which makes up the cuticlecuticle and and prevents water loss prevents water loss

Epidermal Cell

Cuticle

TrichomesTrichomes

Hairs (trichomes) Hairs (trichomes) may be present on may be present on the epidermis. the epidermis.

Sometime abundant Sometime abundant enough so leaves enough so leaves look fuzzylook fuzzy

Trichomes may also Trichomes may also be glandularbe glandular

Hair

Gland

Guard Cells and StomataGuard Cells and Stomata

Pores known as stomata (singular Pores known as stomata (singular stoma) occur on epidermisstoma) occur on epidermis

Gases exchange occurs through Gases exchange occurs through stomatastomata

A pair of sausage-shaped cells, guard A pair of sausage-shaped cells, guard cells, regulate the opening and closing cells, regulate the opening and closing of the stomataof the stomata

Guard Cells and StomaGuard Cells and Stoma

Guard Cell

Stoma (opening)

PeridermPeriderm

In woody plants when the tree increases In woody plants when the tree increases in diameter, the epidermis cracks and is in diameter, the epidermis cracks and is replaced by peridermreplaced by periderm

The periderm consists: The periderm consists: • Cork cellsCork cells• Cork cambiumCork cambium

Cork CellsCork Cells

Outer bark on mature treesOuter bark on mature trees Dead cells with walls containing Dead cells with walls containing

suberin, a waterproofing fatty suberin, a waterproofing fatty substance. substance.

Prevents water loss from underlying Prevents water loss from underlying tissues tissues

Produced by cork cambiumProduced by cork cambium

Ground tissues Ground tissues

Major tissue of non-woody plant organsMajor tissue of non-woody plant organs Perform a variety of functionsPerform a variety of functions The three types of ground tissue:The three types of ground tissue:• ParenchymaParenchyma• CollenchymaCollenchyma• SclerenchymaSclerenchyma

ParenchymaParenchyma

Almost any shape or sizeAlmost any shape or size Loosely arranged with intercellular Loosely arranged with intercellular

spacesspaces Many different functions: Many different functions: • Photosynthetic cells in leaves and green Photosynthetic cells in leaves and green

stems stems • Storage cells in plant organs for starch, Storage cells in plant organs for starch,

sugar, or watersugar, or water

Parenchyma CellsParenchyma Cells

Intercellularspaces

Parenchyma CellsParenchyma Cells

CollenchymaCollenchyma

Support tissue in young plant organsSupport tissue in young plant organs Found in stems, leaves, and petalsFound in stems, leaves, and petals Elongated cells with unevenly thickened Elongated cells with unevenly thickened

primary cell walls with the walls thickest primary cell walls with the walls thickest at the cornersat the corners

Found tightly packed together just Found tightly packed together just below the epidermisbelow the epidermis

Collenchyma CellsCollenchyma Cells

Longitudinal view

Cross sectionshowingunevenwall thickening

SclerenchymaSclerenchyma

Two cell typesTwo cell types• fibers fibers • sclereids. sclereids.

Non-living at maturityNon-living at maturity Thickened secondary wallsThickened secondary walls

FibersFibers

Elongate cellsElongate cells Function in supportFunction in support Leaf and stem fibers from many plants Leaf and stem fibers from many plants

used for cloth and rope. used for cloth and rope.

Sclereids Sclereids

Various shapesVarious shapes FunctionsFunctions• mechanical support and mechanical support and • protectionprotection

Account for the hardness in nut shells Account for the hardness in nut shells and the grit of pear fruitand the grit of pear fruit

SclerenchymaSclerenchymaX-section of fiber showingthick secondary wall

Fiber

Sclereid x-sectionshowingthicksecondarywall

Sclereids

SclereidsSclereids

Vascular tissues Vascular tissues

XylemXylem - - conducts water and minerals conducts water and minerals from the roots upwardfrom the roots upward

PhloemPhloem - transports organic materials - transports organic materials (sugars) synthesized by the plant(sugars) synthesized by the plant

XylemXylem

Cells conducting water - non-living Cells conducting water - non-living • TracheidsTracheids - long thin cells with tapering - long thin cells with tapering

walls and numerous pits walls and numerous pits • VesselVessel elementselements - short, wide, with - short, wide, with

horizontal end walls with large openings horizontal end walls with large openings • Both cells have secondary walls Both cells have secondary walls

Fibers - non-living - provide supportFibers - non-living - provide support Parenchyma cells - metabolic activity Parenchyma cells - metabolic activity

Tracheids and VesselsTracheids and Vessels

Xylem Cells from Oak WoodXylem Cells from Oak Wood

Primary and Secondary Xylem Primary and Secondary Xylem

Primary xylemPrimary xylem develops from the develops from the apical meristem apical meristem

Secondary xylemSecondary xylem develops from the develops from the vascular cambium. vascular cambium.

In trees secondary xylem is very In trees secondary xylem is very extensiveextensive

PhloemPhloem

Cell Types in phloemCell Types in phloem• Sieve Tube Members - transport sugars Sieve Tube Members - transport sugars • Companion Cells - loading and unloadingCompanion Cells - loading and unloading• Fibers - supportFibers - support• Parenchyma - metabolic activityParenchyma - metabolic activity

Primary and Secondary phloemPrimary and Secondary phloem

Sieve Tube MemberSieve Tube Member

• Living cells with Living cells with only thin primary only thin primary wallswalls

• End walls have End walls have sieve plates (large sieve plates (large pores with large pores with large plasmodesmataplasmodesmata))

End wall with sieveplate

Companion cellsCompanion cells

• Specialized parenchyma cell develops Specialized parenchyma cell develops alongside a sieve tube memberalongside a sieve tube member

• Plasmodesmata connect it to sieve tube Plasmodesmata connect it to sieve tube member member

• Loading and unloading sugars for transportLoading and unloading sugars for transport

Plant Tissues and CellsPlant Tissues and Cells

Tissue TypeTissue Type Cell TypesCell Types FunctionFunction DermalDermal

EpidermisEpidermis epidermal cells epidermal cells protectionprotection Periderm Periderm cork cellscork cells protectionprotection

GroundGround ParenchymaParenchyma parenchyma cells parenchyma cells storage,storage,

photosynthesisphotosynthesis Collenchyma Collenchyma collenchyma cells collenchyma cells supportsupport Sclerenchyma Sclerenchyma sclereids, fibers sclereids, fibers support,support,

protectionprotection

Plant Tissues and CellsPlant Tissues and Cells Tissue TypeTissue Type Cell TypesCell Types FunctionFunction VascularVascular

Xylem Xylem tracheids water tracheids water

vessel elements conductionvessel elements conduction

fibers supportfibers support

parenchyma metabolismparenchyma metabolism

PhloemPhloem sieve tube transport sieve tube transport

member sugarsmember sugars

companion cellscompanion cells loadingloading

fibersfibers supportsupport

parenchyma metabolismparenchyma metabolism

Plant OrgansPlant Organs StemsStems• Support leavesSupport leaves• Conduct water and sugarsConduct water and sugars

RootsRoots• Anchor the plantAnchor the plant• Absorb water and mineralsAbsorb water and minerals

LeavesLeaves• PhotosynthesisPhotosynthesis• TranspirationTranspiration

Herbaceous Dicot StemHerbaceous Dicot Stem

X

P

EpidermisCortex (parenchyma cells)

Pith (parenchyma cells)

Vascular bundle

Cross-section

Monocot StemMonocot StemEpidermis

GroundTissue

Vascular bundle

ScatteredVascular Bundles

RootsRoots

SteleEpidermis

Xylem

Cortex

PhloemEndodermis

root hair

LeafLeaf

X

P

Epidermis

VeinsSpongy mesophyll (parenchyma)

Palisade Mesophyll (parenchyma)

Leaf from LigustrumLeaf from Ligustrum

Secondary Growth in DicotsSecondary Growth in Dicots

5 Year Old Woody Dicot Stem5 Year Old Woody Dicot StemOneannual ring

Periderm (cork)Cortex

Secondary phloem

Vascular Cambium

5 Years of Secondary Xylem

Three Year Old TreeThree Year Old Tree

DendrochronologyDendrochronology

Study of tree rings has added many Study of tree rings has added many fields of studyfields of study

Can tell us about past climatesCan tell us about past climates Can be used to date from archeological Can be used to date from archeological

sites artifacts sites artifacts Tree ring research lab at the University Tree ring research lab at the University

of Arizona of Arizona http://www.http://www.ltrrltrr..arizonaarizona..eduedu//

SummarySummary

Growth, replacement of cells, and Growth, replacement of cells, and asexual reproduction all depend on cell asexual reproduction all depend on cell divisiondivision

Tissues are groups of cells that perform Tissues are groups of cells that perform a common functiona common function

Stems, roots and leaves are made up of Stems, roots and leaves are made up of three basic tissue types: dermal, three basic tissue types: dermal, ground, and vascularground, and vascular