Plant Structure

Chapter 35

Angiosperms

MonocotsSeed one cotyledon (seed leaf)Leaves parallel veinsRoots fibrousVascular tissue scatteredFlower parts 3’s or multiples of 3’sBulbs, grasses, grains, orchids

Angiosperms

Dicots (eudicots)Seed with 2 cotyledon (seed leaf)Leaves with network of veinsTaproot Vascular tissue arranged in a ringFlowers in groups of 4 & 5 or multiplesAnnuals, trees, shrubs, roses, peas

Angiosperms

Organs

RootStemLeaves

Angiosperms

Organs

Root systemAnchors the plantAbsorbs nutrientsWater & ionsShoot system Stems & leaves

Roots

Tap rootOne large root with small rootsLateral rootBranched rootsAdventitious rootRoot grows from another part of plant Fibrous rootMat of thin roots

Modified roots

Prop rootsGrow from stem, cornAerial rootsRoots extend in airPlant does not grow into dirtPneumatophoresPlant grows in waterRoots above water to get oxygen

Modified roots

Parasitic rootsTake nourishment from host plantsFood storage rootsXylem of roots such as sweet potatoWater storage rootsGrow in water deprived areasButtress rootsAdds to stability,very large

Root

Shoot system

Stem positions leavesLeaves-food productionNode:Leave attachmentInternode:Area on stem between nodes

Stem (external)

Axillary bud:Bud along stem may be a branchTerminal bud:Bud at end where apical meristem

Modified stems

Shoots with diverse functions Stolons:Such as “runners” of strawberry plantsGrow on the surface Enable a plant to colonize large areasRhizomes: (iris) Horizontal stems that grow underground.

Modified stems

Tubers: (potatoes) Swollen ends of rhizomesFood storage.Bulbs: (onions, tulips) Vertical, underground shoots Swollen bases of leaves-store food.

Modified stems

Tendrils:Grapes, ivy give support for climbingCladphylls:Flattened modified stemsCactus

Leaf (external)

Extension of shoot apical meristemPrinciple site of photosynthesisExpand by cell enlargementNot cell divisionGrowth stops at maturityBlade (flattened)Stalk (petiole) mostly eudicots

Leaf (external)

Veins (vascular bundles)Found in leafParallel in monocotsNetwork in eudicots Many shapes & arrangementsSpiral, paired or whorled

Leaf (external)

Simple leaves:One blade with indentations or teethCompound leaves:Blade divided into leaflets

Modified Leaves

Other functions.Tendrils (peas) to cling to supportsSpines of cacti for defenseLeaves modified for water storageBrightly colored leaves that attract pollinators.

Modified Leaves

Modified leaves

Tissue types

1. Dermal tissueEpidermis (primary growth)One cell layer thickOuter protective layerCuticle wax cover-water lossPeriderm (secondary growth)Replaces epidermis in woody plants

Trichomes

Hair like growthEpidermis from shoot“fuzzy” Keep surface coolMinimize evaporationKeep herbivores from eating (sticky surface)

Root hairs

Extensions of epidermal cellsOccur behind root tipsIncrease surface area Absorption

Tissue type

2. Vascular tissueTransport Xylem: Water & dissolved mineralsPhloem: Carbohydrates (sucrose)

Tissue type

3. Ground tissueThin-walled parenchyma cellsStorage, photosynthesis, supportPith:Internal to vascular tissueCortex:External to vascular tissue

Tissue type

Plant cells

1. Parenchyma cellsLarge vacuolesThin walled14 sidesMost common type of plant cell

Parenchyma Cells

Perform most metabolic functions Synthesize & stores various organic products.Fleshy tissue of most fruit.

Parenchyma

Plant cells

2. Collenchyma cellsUsually little longer than wideCell wall thickness variesSupport for organsAllows stems to bend & not break

Collenchyma

Plant cells

3. Sclerenchyma cellsSupporting elements of the plantThick secondary wallsMuch more rigid Cannot elongate Plant regions-stopped lengthening.

Plant cells

Lignin:Highly branch polymerStrengthens wallsTypes sclerenchymaFibers: Long cells grouped in strands (linen)Sclereids: Branched (pears, seed coats, nutshells)

Sclerenchyma cells

4.Water-conducting cells

Xylem (water minerals, inner)Vessel members (elements) Continuous tubes Hollow, dead cylindrical cells end to endTracheids Dead cells that overlap each otherTapered endsThick walled Wood is secondary xylem

Xylem

5. Sugar-conducting cells

Phloem (outer)Sieve cellsSieve-tube members (elements)Conduct carbohydrates Away from where formedSieve-tube more advanced

5. Sugar-conducting cells

Companion cells: Next to sieve-tube cellsPlasmodesmata: Connection between cells

Phloem

Vascular tissue

Growth

Meristems:Embryonic tissuesClumps of small cells Dense cytoplasm & large nucleiSimilar to stem cellsOne cell remains meristematic IndeterminateGive rise to other tissues

Meristems

Apical meristemsCell divisionElongation of roots & stems (tips)Primary growth

Meristems

Apical meristems

Primary tissues Tissues resulting from primary growth Primary plant bodyMade up of primary tissuesYoung soft shoots, roots Some plants entire plant body

Root

4 regions in developing roots1. Root capProtects new cells Moves through soilPerception of gravityHelp root to bend downNitrogen fixing bacteria

Root

2. Region of divisionArea in center of root tipApical meristemCells divide every 12-36 hours3. Region of elongationCells produced are longer than wider4. Region of maturation (differentiation)

Root

Epidermal cells: Root surface have thin cuticleRoot hairsCortex: Parenchyma tissue Between epidermis & vascular tissue

Root

Endodermis: Inner boundary of cortex thin layer Casparian strips: Surround the endodermal cellsWater cannot pass through the strips

Root

Root

Root

Roots

Stele: Tissues interior to endodermPericycle: Layer of cells inside endodermGive rise to lateral or branched rootsPith: Center of rootPrimary xylem form around the pithPrimary phloem form in groups near xylem

Root

Lateral roots

Root

Stem

Primordia:Bulges produced by apical meristem Leaves, other shoots, or flowersIntercalary meristems:Add more length at plant internodesCorn

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 35.18

Leaf

Stomata:Tiny poresGap between guard cells Guard cells: Specialized epidermal cellsRegulate openingTranspiration:Evaporation of water

Leaf

More stomata on lower epidermisDecrease water lossContain chloroplastsResult from asymmetrical cell division

Leaf

Surface covered with epidermisCuticleMesophyll: Ground tissueLayer between the epidermis layersContains veins (vascular bundles)

Leaf

Palisade mesophyll:Closest to upper epidermisTightly packed cellsContains parenchyma with chloroplastsSpongy mesophyll:Loosely arrangedContains air spaces

Leaf

Leaf

Secondary growth

Secondary tissues:Lateral meristemsVascular cambium (xylem-wood, phloem)Cork cambium Secondary growth-increases girth

Secondary growth

Periderm:Protective layer replaces epidermisCork plus the cork cambium Lenticels:Raised areas in periderm Areas for gas exchange

Secondary growth

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 35.22

Stem