+

Mrs. Valdes

AP Biology

Chapter 35: Plant

Structure, Growth, and

Development

+Developmental Plasticity DEFINE: ability to alter itself in response to its environment

more marked in plants than animals environment more greatly affects phenotype than genetic make-

up plant species by natural selection accumulate

characteristics of morphology that vary little within the species

TWO typesof leaves

+Concept 35.1: The plant body has a hierarchy of organs, tissues, and cells

Plants have organs composed of different tissues, composed of cells

Three basic organs: Roots Stems Leaves

Basic morphology of vascular plants reflect evolution as organisms that draw nutrients from below ground and to be used above ground

Organs organized into root system and shoot system

Roots rely on sugar produced by photosynthesis in shoot system

Shoots rely on water and minerals absorbed by root system

+ Roots• Roots: multicellular organs with

important functions: Anchor plant Absorb minerals and water Store organic nutrients

• Taproot system: consists of one main vertical root that gives rise to lateral roots, or branch roots

• Adventitious roots: arise from stems or leaves

• Seedless vascular plants and monocots:• have fibrous root system

characterized by thin lateral roots with no main root

• Most plants absorption of water and minerals occurs near root hairs, where vast numbers of tiny root hairs increase the surface area

+ Prop Roots: Aid in support of

tall, top-heavy plants Storage Roots: store food &

water in roots; “Strangling” aerial roots:

seeds of strangler fig tree germinate in branches of other trees, then send lots of aerial roots around host tree until it is totally shaded out and dies

Buttress roots: Look like buttress and support large trunk

Pneumatophores: “air roots”; roots go above water to get oxygen since oxygen is poor in muddy mangrove waters

+StemsStem: organ consisting of

: alternating system of nodes,

points at which leaves are attached Internodes: stem segments

between nodes

Axillary bud: structure that has potential to form a lateral shoot, or branch

Apical bud: AKA terminal bud; located near shoot tip and causes elongation of young shoot

Apical dominance: helps to maintain dormancy in most nonapical buds

+ Rhizomes: horizontal shoot

that grows just below surface; vertical shoots arise from axillary buds on rhizome

Bulbs: vertical underground shoots consisting of mostly enlarged bases of leaves that store food

Stolons: horizontal shoots that grow along surface; “runners” enable plant to reproduce asexually

Tubers: enlarged ends of rhizomes or stolons that specialize in storing food

+LeavesLeaf: main photosynthetic

organ of most vascular plantsgenerally consist of

flattened blade and stalk called the petiole, which joins leaf to node of stem

Monocots and eudicots differ in arrangement of veins, vascular tissue of leaves Most monocots have parallel veins Most eudicots have branching veins

In classifying angiosperms, taxonomists may use leaf morphology as criterion

+ Tendrils: usually modified

leaves but can be modified stems; “lassoed” support anchors plant and brings it closer to support

Spines: modified leaves; photosynthesis carried out by fleshy green part of cacti

Storage leaves: most succulents modified to store water

Reproductive leaves: adventitious plantlets can fall off and take root in soil

Bracts: NOT petals but modified leaves that surround a group of flowers

+Dermal, Vascular, and Ground TissuesEach plant organ has dermal, vascular, and ground tissues

Tissue system: functional unit connecting all plant’s organs

Dermal tissue system: plants outer protective coveringCuticle: waxy coating helps

prevent water loss from epidermisPeriderm: in woody plants,

protective tissues that replace epidermis in older regions of stems and rootsTrichomes: outgrowths of shoot

epidermis; can help with insect defense

+Vascular tissue system:

carries out long-distance transport of materials between roots and shoots two vascular tissues :

Xylem: conveys water and dissolved minerals upward from roots into the shoots

Phloem: transports organic nutrients (FOOD) from where they are made to where they are needed

Stele: vascular tissue of stem or root In angiosperms stele of root is

a solid central vascular cylinder

stele of stems and leaves divided into vascular bundles, strands of xylem and phloem

+Ground tissue system: tissues neither dermal nor vascular includes cells specialized

for storage, photosynthesis, and support

Pith: ground tissue internal to vascular tissue

Cortex: ground tissue external to vascular tissue

+Common Types of Plant CellsPlant characterized by cellular differentiation, the specialization of cells in structure and function

Plant cell types: Parenchyma Collenchyma Sclerenchyma Water-conducting

cells of the xylem Sugar-conducting

cells of the phloem

+• Mature parenchyma cells

– Have thin and flexible primary walls– Lack secondary walls– Are least specialized– Perform most metabolic functions– Retain ability to divide and differentiate

Parenchyma Cells

+• Collenchyma cells: grouped in strands; help support young parts of plant shoot• have thicker and uneven cell walls• lack secondary walls• provide flexible support without restraining

growth

Collenchyma Cells

+• Sclerenchyma cells: rigid because of thick secondary walls strengthened with lignin• dead at functional maturity• Two types:

Sclereids: short & irregular shape; thick lignified secondary walls

Fibers: long and slender; arranged in threads

Sclerenchyma Cells

+• Two types of water-conducting cells:• BOTH DEAD at

maturity • Tracheids: found in

xylem of all vascular plants

Vessel elements: common to most angiosperms and few gymnospermsalign end to end to

form long micropipes called vessels

Water Conducting Cells of Xylem

+• Sieve-tube elements: alive at functional maturity, though lack organelles

• Sieve plates: porous end walls that allow fluid to flow between cells along sieve tube• Each sieve-tube

element has a companion cell whose nucleus and ribosomes serve both cells

Sugar-Conducting Cells of Phloem

+Concept 35.2: Meristems generate cells for new organs

Indeterminate growth: plant growth throughout its life

Determinate growth: some plant organs cease to grow at a certain size

Annuals: complete life cycle in a year or less

Biennials: require two growing seasonsPerennials: live for many years

+Meristems: perpetually

embryonic tissue; allow for indeterminate growth

Apical meristems: located at tips of roots and shoots and at axillary buds of shoots elongate shoots and roots, AKA

primary growthLateral meristems: add

thickness to woody plants, AKA secondary growth two lateral meristems:

vascular cambium: adds layers of vascular tissue called secondary xylem (wood) and secondary phloem

cork cambium: replaces epidermis with periderm, which is thicker and tougher

+Fig. 35-11

Shoot tip (shootapical meristemand young leaves)

Lateral meristems:

Axillary budmeristem

Vascular cambiumCork cambium

Root apicalmeristems

Primary growth in stems

Epidermis

Cortex

Primary phloem

Primary xylem

Pith

Secondary growth in stems

Periderm

Corkcambium

Cortex

Primaryphloem

Secondaryphloem

Pith

Primaryxylem

Secondaryxylem

Vascular cambium

+Meristems give rise to: initials: remain in

meristem, derivatives:

become specialized in developing tissues

In woody plants, primary and secondary growth occur simultaneously but in different locations

+Concept 35.3: Primary growth lengthens roots and shoots

Primary plant body: produced by primary growth; parts of root and shoot systems produced by apical meristems

Root cap: covers root tip; protects apical meristem as root pushes through soil

Growth occurs just behind the root tip, in three zones of cells: Zone of cell division Zone of elongation Zone of maturation

+Primary growth of roots produces: epidermisground tissuevascular tissue

In most roots, stele is vascular cylinder

Ground tissue fills cortex (region between vascular cylinder and epidermis)Endodermis:

innermost layer of the cortex is called the

+Fig. 35-15-3

Cortex

Emerginglateralroot

Vascularcylinder

100 µm Epidermis

Lateral root

321

Lateral roots arise from within pericycle outermost cell layer in vascular cylinder

+Primary Growth of ShootsShoot apical meristem: dome-shaped mass of dividing cells at shoot tip

Leaves develop from leaf primordia along sides of apical meristem

Axillary buds develop from meristematic cells left at bases of leaf primordia

+Tissue Organization of Stems Lateral shoots develop from axillary

buds on stem’s surface In most eudicots, vascular tissue

consists of vascular bundles arranged in ring

In most monocot stems, the vascular bundles scattered throughout the ground tissue, rather than forming a ring

+Tissue Organization of Leaves• Epidermis in leaves

interrupted by stomata, which allow CO2 exchange between air and photosynthetic cells in leaf

• Each stomatal pore is flanked by two guard cells, which regulate its opening and closing

• Mesophyll: ground tissue in a leaf; sandwiched between the upper and lower epidermis

• Spongy mesophyll: where gas exchange occurs; below palisade mesophyll in upper part of leaf

• vascular tissue of each leaf is continuous with vascular tissue of the stem

• Veins: leaf’s vascular bundles; function as leaf’s skeleton• Each vein enclosed by protective bundle sheath

+Fig. 35-18

Keyto labels

Dermal

Ground

VascularCuticle Sclerenchyma

fibersStoma

Bundle-sheathcell

Xylem

Phloem

(a) Cutaway drawing of leaf tissues

Guardcells

Vein

Cuticle

Lowerepidermis

Spongymesophyll

Palisademesophyll

Upperepidermis

Guardcells

Stomatalpore

Surface view of a spiderwort(Tradescantia) leaf (LM)

Epidermalcell

(b)

50 µ

m10

0 µ

m

Vein Air spaces Guard cells

Cross section of a lilac(Syringa)) leaf (LM)

(c)

+Fig. 35-18a

Keyto labels

Dermal

Ground

VascularCuticle Sclerenchyma

fibersStoma

Bundle-sheathcell

Xylem

Phloem

(a) Cutaway drawing of leaf tissuesGuardcells

Vein

Cuticle

Lowerepidermis

Spongymesophyll

Palisademesophyll

Upperepidermis

+Fig. 35-18b

Guardcells

Stomatalpore

Surface view of a spiderwort(Tradescantia) leaf (LM)

Epidermalcell

(b)

50 µ

m

+Fig. 35-18c

Upperepidermis

Palisademesophyll

Keyto labels

Dermal

Ground

Vascular

Spongymesophyll

Lowerepidermis

Vein Air spaces Guard cells

Cross section of a lilac(Syringa) leaf (LM)

(c)

100

µm

+Concept 35.4: Secondary growth adds girth to stems and roots in woody plantsSecondary growth occurs in stems and roots of woody plants but rarely in leaves

Secondary plant body: tissues produced by vascular cambium and cork cambiumcharacteristic of

gymnosperms and many eudicots, but NOT monocots

+Fig. 35-19a1

Epidermis

Cortex

Primary phloem

Vascular cambium

Primary xylem

Pith

Primary and secondary growthin a two-year-old stem

(a)

Periderm (mainlycork cambiaand cork)

Secondary phloem

Secondaryxylem

Epidermis

Cortex

Primary phloem

Vascular cambiumPrimary xylem

Pith

+Fig. 35-19a2

Epidermis

Cortex

Primary phloem

Vascular cambium

Primary xylem

Pith

Primary and secondary growthin a two-year-old stem

(a)

Periderm (mainlycork cambiaand cork)

Secondary phloem

Secondaryxylem

Epidermis

Cortex

Primary phloem

Vascular cambiumPrimary xylem

Pith

Vascular ray

Secondary xylem

Secondary phloem

First cork cambium

Cork

Growth

+Fig. 35-19a3

Epidermis

Cortex

Primary phloem

Vascular cambium

Primary xylem

Pith

Primary and secondary growthin a two-year-old stem

(a)

Periderm (mainlycork cambiaand cork)

Secondary phloem

Secondaryxylem

Epidermis

Cortex

Primary phloem

Vascular cambiumPrimary xylem

Pith

Vascular ray

Secondary xylem

Secondary phloem

First cork cambium

Cork

Growth

Cork

Bark

Most recent corkcambium

Layers ofperiderm

+Fig. 35-19b

Secondary phloemVascular cambium

Secondary xylem

Bark

Early woodLate wood Cork

cambium

Cork

Periderm

0.5

mm

Vascular ray Growth ring

Cross section of a three-year-old Tilia (linden) stem (LM)

(b)

0.5 mm

+Vascular Cambium and Secondary Vascular Tissue

Vascular cambium: cylinder of meristematic cells one cell layer thickdevelops from undifferentiated parenchyma cells in cross section appears as a ring of initials

initials increase vascular cambium’s circumference and add secondary xylem to inside and secondary phloem to outside

+Secondary xylem accumulates as wood, and consists

of: tracheids vessel elements (only in angiosperms) fibers

Early wood: formed in spring, has thin cell walls to maximize water delivery

Late wood: formed in late summer, has thick-walled cells and contributes more to stem support

In temperate regions, vascular cambium of perennials dormant through winter

Tree rings visible where late and early wood meet; can be used to estimate a tree’s age

Dendrochronology: analysis of tree ring growth patterns; can be used to study past climate change

What does this graph tell you?

+As a tree or woody shrub ages, older layers of secondary xylem, AKA heartwood, no longer transport water and minerals

Outer layers, known as sapwood, still transport materials through the xylem

Older secondary phloem sloughs off and does not accumulate

+Cork Cambium and Production of Periderm

Cork cambium: gives rise to secondary plant body’s protective covering, or peridermPeriderm consists of cork cambium plus layers

of cork cells it producesBark: consists of all tissues external to vascular cambium, including secondary phloem and periderm

Lenticels: in periderm allow for gas exchange between living stem or root cells and outside air

+Concept 35.5: Growth, morphogenesis, and differentiation produce the plant bodyMorphogenesis: development of body form and organization

Three developmental processes act in concert to transform the fertilized egg into a plant:growth morphogenesiscellular

differentiation

+

Arabidopsis: model organism, and first plant to have its entire genome sequenced

Studying genes and biochemical pathways of Arabidopsis provide insights into plant development

Molecular Techniques Revolutionize the Study of Plants

+Growth: Cell Division and Cell ExpansionBy increasing cell number, cell division in meristems increases potential for growth

Cell expansion accounts for actual increase in plant size

Plane (direction) and symmetry of cell division are immensely important in determining plant form

If planes of division parallel to plane of first division, single file of cells is produced

If the planes of division vary randomly, asymmetrical cell division occurs

+Plane in which cell divides determined during late interphaseMicrotubules

become concentrated into ring called preprophase band that predicts future plane of cell division

+Orientation of Cell ExpansionPlant cells grow rapidly and “cheaply” by

intake and storage of water in vacuoles AKA “Water Weight”

Plant cells expand primarily along plant’s main axis

Cellulose microfibrils in cell wall restrict direction of cell elongation

+Morphogenesis and Pattern FormationPattern formation: development of specific structures in specific locations controlled by homeotic genes determined by positional

information in form of signals indicating to each cell its location may be provided by gradients of

molecules Polarity: having structural or

chemical differences at opposite ends of organism, provides one type of positional information

Polarization initiated by asymmetrical first division of plant zygote In gnom mutant of Arabidopsis,

establishment of polarity is defective

+Gene Expression and Control of Cellular Differentiation

Cellular differentiation depends on positional information and is affected by homeotic genes

Positional information underlies all processes of development: growth, morphogenesis, and differentiation

Cells NOT dedicated early to forming specific tissues and organs

Cell’s final position determines what kind of cell it will become

+Shifts in Development: Phase ChangesPhase changes: developmental phases from juvenile phase to adult phaseoccur within shoot

apical meristem

Most obvious morphological changes typically occur in leaf size and shape

+Genetic Control of FloweringFlower formation involves phase change from

vegetative growth to reproductive growthTriggered by combination of environmental

cues and internal signalsTransition associated with switching on of

floral meristem identity genesPlant biologists identified

several organ identity genes (plant homeotic genes) that regulate development of floral pattern

Mutation in plant organ identity gene abnormal floral development

+Researchers identified three classes of floral organ identity genes

ABC model of flower formation identifies how floral organ identity genes direct formation of four types of floral organs

Understanding mutants of organ identity genes depict how this model accounts for floral phenotypes

+Fig. 35-34a

Sepals

Petals

Stamens

CarpelsAB

C

A + Bgene

activity

B + Cgene

activity

C geneactivity

A geneactivity

(a) A schematic diagram of the ABC hypothesis

Carpel

Petal

Stamen

Sepal

+Fig. 35-34b

Activegenes:

Whorls:

StamenCarpel

Petal

Sepal

Wild type Mutant lacking A Mutant lacking B Mutant lacking C

(b) Side view of flowers with organ identity mutations

A A A AC C C CB B B B B B

C C C C C C C C C C C CA A A A A A A AB B B BB A A A AB

+You should now be able to:1. Compare the following structures or cells:

– Fibrous roots, taproots, root hairs, adventitious roots– Dermal, vascular, and ground tissues – Monocot leaves and eudicot leaves– Parenchyma, collenchyma, sclerenchyma, water-conducting cells of the

xylem, and sugar-conducting cells of the phloem– Sieve-tube element and companion cell

2. Explain the phenomenon of apical dominance3. Distinguish between determinate and indeterminate

growth4. Describe in detail the primary and secondary growth

of the tissues of roots and shoots5. Describe the composition of wood and bark6. Distinguish between morphogenesis, differentiation,

and growth7. Explain how a vegetative shoot tip changes into a

floral meristem

+

2. Explain the phenomenon of apical dominance

3. Distinguish between determinate and indeterminate growth

4. Describe in detail the primary and secondary growth of the tissues of roots and shoots

5. Describe the composition of wood and bark

+

6. Distinguish between morphogenesis, differentiation, and growth

7. Explain how a vegetative shoot tip changes into a floral meristem