Plant Structure, Growth, and Development

(Ch. 35)

What are Angiosperms?

Angiosperm Body2 Taxonomic classes• monocots• eudicotsMonocots• One cotyledon • Parallel veins • Floral parts in 3’s • Fibrous RootsEudicots • Two cotyledons -• Netlike veins• -Floral parts in 4’s and 5’s• Tap root

Angiosperm BodyNeed to be able to inhabit soil and air at the same time• roots and shoots

Plant morphology• study of the external structure• arrangement of flower parts, etc.

Plant anatomy• study of the internal structure• arrangement of cells, tissues in a leaf, etc.• Tissue – groups of cells, consisting of one or more types,

that perform a specialized function• Organ – consists of several types of tissues that together

carry out specific functions

Angiosperm Body

Two basic systems• root system• aerial shoot system

(stems, leaves, flowers)

Vascular Tissues• transport materials• xylem transports

water and dissolved minerals

• phloem transports food

Root System• Anchoring, absorbing water

and minerals, storing carbohydrates

Taproot system• one large, vertical root• mostly eudicots• firm anchorage; one large

vertical root• stores lots of reserve food• gives rise to lateral roots

Root SystemFibrous root system• mat of threadlike

roots• mostly monocots• extensive exposure to

soil, water, minerals• concentrated in

topsoil; prevents erosion

Root SystemAdventitious roots

• plant organ that grows in an unusual location

• arising above ground or from stems/leaves

Root hairs

• thin, tubular extension of a root epidermal cells

• increase SA near root tip

Root SystemMycorrhizae

• mutualistic relationship between fungi and roots

Root nodules

• contain symbiotic bacteria to convert atmospheric nitrogen to compounds usable by the plant

Modified Roots

(a) Prop roots (b) Storage roots (c) “Strangling” aerialroots

(d) Buttress roots (e) Pneumatophores

Shoot SystemVegetative shoots• Stems and leavesFloral shoots• FlowersStem• Alternating system of

nodes and internodes• Raises or separates

leaves• Raise reproductive

structures

Shoot System - StemsNodes• where leaves attach to stemsInternodes• segment of stem between nodesAxillary bud• embryonic side shoot• has potential to form a branch shoot• usually dormant in young plants• pruning

Shoot System - Stems

Terminal (apical) bud

• bud on shoot tip; composed of developing leaves and a compact series of nodes and internodes

• where most of the growth of a young plant occurs

• May inhibit growth of axillary buds– apical dominance

Modified StemsStolons• Runners allow plant to colonize a large

area & reproduce asexuallyRhizomes• Horizontal stem that grows below groundTubers• Swollen ends of rhizomes; store foodBulbs• Vertical, underground shoots

Modified Stems

Rhizomes. The edible base of this ginger plant is an example of a rhizome, a horizontal stem that grows just below the surface or emerges and grows along thesurface.

(d)

Tubers. Tubers, such as these red potatoes, are enlarged ends of rhizomes specializedfor storing food. The “eyes” arranged in a spiral pattern around a potato are clusters of axillary buds that markthe nodes.

(c)Bulbs. Bulbs are vertical,underground shoots consistingmostly of the enlarged bases of leaves that store food. You can see the many layers of modified leaves attached to the short stem by slicing an onion bulb lengthwise.

(b)

Stolons. Shown here on a strawberry plant, stolons are horizontal stems that grow along the surface. These “runners”enable a plant to reproduce asexually, as plantlets form at nodes along each runner.

(a)

Storage leaves

Stem

Root Node

Rhizome

Root

Shoot System - Leaves

Main photosynthetic organ

• Blade

• Joined to node by a petiole

Venation (vascular tissue)

• parallel

• netted

Classification

• shape

• spatial arrangement

• venation

Petiole

(a) Simple leaf. A simple leafis a single, undivided blade.Some simple leaves are deeply lobed, as in anoak leaf.

(b) Compound leaf. In acompound leaf, theblade consists of multiple leaflets.Notice that a leaflethas no axillary budat its base.

(c) Doubly compound leaf. In a doubly compound leaf, each leaflet is divided into smaller leaflets.

Axillary bud

Leaflet

Petiole

Axillary bud

Axillary bud

Leaflet

Petiole

Modified Leaves• Tendrils on vines

• Spines of cacti

• Storage

• Reproductive

• Bracts

Dermal, Vascular, and Ground TissuesTissue system• A functional unit

connecting all of the plant’s organs

Dermal tissue system• Outer protective

covering• Epidermis in

nonwoody plants• Cuticle

• Periderm in woody plants

Dermal, Vascular, and Ground TissuesVascular tissue system• Long distance

transport b/w roots and stems

• Xylem and phloem• Collectively called the

steleGround tissue system• If internal to the

vascular tissue pith• If external to the

vascular tissue cortex

Plant CellsProtoplast• contents of a plant cell not

including the cell wallLignin• Structural component of cell

wallsAll start out similar to

parenchyma cells; become more specialized

• Can generate an entire plant from one parenchyma cell

Plant CellsParenchyma cells• “typical” plant cell• chloroplasts for photosynthesis• large central vacuole• store starch• comprise fleshy tissue of fruits

Collenchyma cells• unevenly thick primary walls• support for young plants

without restraining growth• living and flexible throughout

life

Plant CellsSclerenchyma cells• rigid, thick secondary walls

with lignin• function only in support• may be dead at maturity but

produce secondary walls before protoplast dies

• Sclereids– Very thick cell lignified cell

walls; nutshells & seed coats

• Fibers – Long, slender and tapered

Plant CellsWater-conducting cells of xylem

• dead at functional maturity

• allow water to flow from cell to cell

• tracheids

– In nearly all vascular plants

– Water moves through pits

• vessel elements

– Angiosperms and some gymnosperms

– Water moves through perforation plates

Plant CellsFood-conducting cells of phloem

• alive at functional maturity

• sieve-tube cells make the sieve tube elements/members that transport sucrose and other organic nutrients

• sieve plate

– Pores that allow flow from cell to cell

• companion cells

– Ribosomes and nucleus serve the sieve tube cell too

Figure 35.12 Locations of major meristems: an overview of plant growth

Meristems generate cells for primary and secondary growth

Begins with germination and occurs throughout life of plant

• Indeterminate growth

Meristems• perpetually undifferentiated tissues

Apical meristems• Responsible for primary growth

(growth in length)

Lateral meristems• Responsible for secondary growth

(growth in thickness)

Meristems generate cells for primary and secondary growth

Two types of lateral meristems

Vascular cambium• Add layers of vascular

tissue called secondary xylem (wood) and secondary phloem

Cork cambium• Replaces the epidermis with

thicker, tougher periderm

Plant GrowthFinite life span

• genetically & environmentally determined

• annuals, biennials, and perennialsAnnuals• Complete their life cycle in a year• Cereal grains, legumes, wildflowersPerennials• Live many years• Trees, shrubs, some grassesBiennials• Life span –generally 2 years• Live through an intervening cold period between vegetative

growth and flowering• Beets, carrots

Figure 35.14 Primary growth of a root

Primary Growth Lengthens Roots and ShootsPrimary growth of roots• pushes roots through soil;

root cap covers apical meristem

• Zone of cell division – apical and primary

meristems• Zone of cell elongation

– elongate in size• Zone of maturation

– specialize in function

Primary Growth Lengthens Roots and ShootsEpidermisGround tissueVascular tissueSteleEndodermisPericycle

Primary Growth Lengthens Roots and Shoots

Primary growth of shoots• Apical meristems give rise

to primary meristems• Leaf primordia give rise

to leaves• Shoot elongation is due to

lengthening of internode cells below the shoot tip

• Branching occurs due to activation of axillary buds

Tissue Organization of Stems

Epidermis• Covers stemsVascular tissue in bundlesAxillary buds meristems

develop lateral shootsParenchyma, collenchyma,

and scelerenchyma cells are present

Tissue Organization of Leaves Epidermis• tightly locked cells• protect from damage &

pathogens• waxy cuticleStomata • pores on underside of leaf• site of gas exchangeGuard cells• control stomata opening for

gas exchange• Flaccid stomata are closed

due to lack of water

Tissue Organization of LeavesMesophyll• Ground tissue of leaf

between epidermal layers

• palisade parenchyma – upper half of leaf

• spongy parenchyma

– air spaces to allow O2 and CO2 to circulate

– lower half of leaf

Tissue Organization of Leaves

Vascular Cambium and Secondary Vascular Tissue

Secondary growth of stems• Stems and roots of woody plants• vascular cambium

– transport and storage of starch– Adds secondary xylem (wood) and secondary phloem

• cork cambium – protective layers

• Bark (refers to all tissues external to vascular cambium)

• phloem, phelloderm, cork cambium, corkSecondary growth of roots

An overview of primary and secondary growth

Cork Cambium and Production of Periderm

Phelloderm• Thin layer of parenchyma cells that forms to

the interior of the cork cambiumAccumulation of cork cells• Deposit suberin in walls then die

– Protects from water loss, physical damage, pathogens

Lenticels• Small, raised areas in the periderm• Help cells to exchange gases

Growth, Morphogenesis, and Cell Differentiation Produce the Plant Body

Development• Specific series of changes by which cells form tissues, organs, and

organismsGrowth• Irreversible change in size• Cell division and expansionMorphogenesis• Process that gives a tissue, organ, or organism its shape and

determines the positions of cell types• Pattern formationDifferentiation• Process by which cells with the same genes become different from

one another• Control of gene expression