Chapters 31 & 32:Plant Structure & Reproduction

2. Plant Reproduction & Development

1. Flowering Plant Structure

1. Flowering Plant Structure

“Roots & Shoots”2 basic parts of

flowering plants:shoot system

• stems• leaves

root system

• flowers, fruits

• taproot (dicots)• roots

Dicot stemVascular bundle

Cortex

Pith

Epidermis

Monocot stemVascular bundle

Epidermis

Epidermis

Vascular cylinder

XylemPhloem

Cortex

Dicot root

Key

Dermal tissueGround tissueVascular tissue

Plant Tissue Types1) Dermal tissue

• outer, protective covering of the plant

2) Vasculartissue

• transport of fluids &structural support

3) Groundtissue

• everythingelse!

Vascular Tissue

• transports products of photosynthesis (sugars) throughoutplant from sugar sources

Phloem

to sugar sinks

Xylem• transports water & minerals “upward”(towards shoots, leaves)

Low water pressure

High sugarconcentration

High water pressure

PHLOEM XYLEM

sugar

water

Sourcecell

sugar

water

Sinkcell

SUGARSINK

1

2

3

4

Low sugarconcentration

Low water pressure

• driven by osmosis, increased pressure due to more sugar solutesnear source

Root hair

Flow

of w

ater

Soil particle

Water

Water uptake from soil

Adhesion

Cellwall

Cohesion,by hydrogenbonding

XylemcellsCohesion and

adhesion in the xylem

Xylem sap

Mesophyll cells

Air space within leafStoma

Outside air

Transpiration

Watermolecule

How is water moved “upward”?Water lost bytranspiration from leaves“pulls” waterupward through xylemto replace whatwas lost.

Depends on:• cohesion dueto H-bonding

• adhesion toxylem cells

Leaf Structureepidermis

palisade mesophyll

spongy mesophyllphloem

stomataguard cells

xylemsheath

Epidermis• outer cell layer on both sides of leaf• secrete waxy cuticle to waterproof the leaf

Mesophyll (ground tissue of leaf)• loosely packed photosynthetic cells• palisade or spongy arrangement

Vascular Bundles• phloem & xylem• surrounding sheath

Stomata (singular = “stoma”)• openings for gas exchange, transpiration• regulated by guard cells

CO2

O2

H2O

Minerals

Root Function

• anchorage in the soil

Roots supply the plant with:

• water• mineral nutrients• oxygen (O2)

• for respiration since plants make ATP just aswe do

• over-watering cansuffocate a plant!

N2

N2

SoilH+

Organic material

Nitrogen-fixingbacteria

Ammonifying bacteria

NH3 NH4+

(ammonium) Nitrifying bacteria

NO3–

(nitrate)

Root

NH4+

Amino acids, etc.

ATMOSPHERE

Importance of Nitrogen FixationPlants require the element nitrogen in the form ofammonium (NH4

+) or nitrate (NO3-) ions, however they

CAN’T “fix” atmospheric nitrogen (N2) into these forms.

Soil bacteria and some fungi CAN fix nitrogen, thusplants depend on these microbes for useable nitrogen.

ammonium & nitrate ions taken up by roots

Fibrousroot system

MONOCOTSSeed Leaves Leaf veins Stems Flowers Roots

Onecotyledon Main veins usually parallel

Vascular bundles in complex

arrangement

Floral parts usually in

multiples of three

Twocotyledons Main veins usually branched

Vascular bundles arranged in ring

Floral parts usually in

multiples of four or five

Taprootusually present

DICOTS

Monocots vs DicotsFlowering plants are of 2 basic types:

Monocot vs Dicot FeaturesCotyledons (embryonic “seed leaves”)

• nourish the seedling: monocots have 1, dicots have 2

Roots• dicots have a central taproot, monocots do not

Stems• dicots have a vascular structure organized into rings

Leaves• monocots have narrow, smooth leaves w/parallel veins• dicots have broader leaves w/branched vein patterns

Flowers• monocots – layered flower parts come in groups of 3• dicots – layered flower parts come in groups of 4 or 5

2. Plant Reproduction & Development

Basic Modes of ReproductionPlants reproduce in 2 basic ways:

Asexually:• piece of parent plant gives rise to new plant

Sexually:• fusion of haploid gametes generates offspring

• involves mitotic cell division only

• offspring are genetically identical to parent

• offspring are genetically unique

Life Cycle of Plants (sexual)

• fertilizationproduces a zygote that develops into a diploidsporophyte

• haploid spores produced by meiosisin flowers grow intomulticellular haploidgametophytes, somecells of which aregametes

The Plant Sexual Life CycleThe sexual life cycle of plants is unique, occurring by “Alternation of Generations”:

The sporophyte stage (diploid)• the plant is made of diploid cells

The gametophyte stage (haploid)

• grows from haploid spore (via mitosis)• produces gametes (sperm and/or egg)

• produces haploid spores by meiosis in thereproductive structures (e.g., flowers)

• fertilization then produces a new diploid sporophyte!

sporophyte (2n)gametophyte (n)

• gametophyte

Life Cycle in different Plant Phyla

is moreprominent inmore primitiveplant species

• in more advanced plant species,the sporophyteis much moreprominant

The Structure of Flowers

reproductiveorgan of

angiosperms

…more on Flower StructureFlowers have 4 main parts:

Petals• usually colored, inside sepals

Sepals• outermost structure (encloses flower bud)

Stamen (anther & filament)• male reproductive structure

Carpel (stigma, style & ovary)

• female reproductive structure• produces female gametophytes (embryo sacs)

• anthers produce male gametophytes (pollen grains)

Fertilization in Angiosperms

• pollen grains adhere to the stigma(pollination)

• tube cell in pollenelongates downstyle to penetrateovule in ovary

• 2 sperm are releasedto fertilize the egg & fuse with a special diploid cell in ovule

Seed Production

• zygote develops into embryo, triploid cell forms endosperm• seed coat derived fr. ovule wall encloses embryo, endosperm• fruit develops from ovary wall to aid seed dispersal

endosperm = nutrients for plant embryo

Seed DispersalSeeds can be dispersed via fruits by:

Water• floating on water (e.g., coconuts)

Air• lightweight seeds can be transported by the wind

(e.g., dandelion, maple)

Animal• edible fruits entice animals to eat them• “hitchhiker” fruits stick to animals

Terminal bud

Axillary buds

Root tips

Arrows = direction of

growth

Plant GrowthPlant growth occurs in 2 basic ways:

Primary growth• growth in length ofroots & shoots

• due to special “stemcell” tissue calledapical meristem

Secondary growth• growth in width dueto lateral meristem

• occurs in “woody”perennial plants

Apical meristem

Leaves

Axillary bud meristems

1 2

LM 1

03×

Primary (1o) GrowthVascular cylinder

Root hair

Cortex

Epidermis

Zone of maturation

Zone of elongation

Zone of cell division

Root cap

Apical meristem

regionKey

Dermal tissue systemGround tissue system

Vascular tissue system

1o RootGrowth

1o ShootGrowth

Year 1Early Spring

Year 1Late Summer

Year 2Late Summer

GrowthGrowth

Growth

Primary xylem

Vascular cambium

Primary phloem

Cortex

EpidermisSecondary

xylem (wood)

Cork

Corkcambium

Secondary phloem

Bark

Shed epidermis

Secondary xylem (2 years’ growth)

Key

Dermal tissue system

Ground tissue system

Vascular tissue system

Secondary (2o) GrowthDue to lateral meristem tissue which consists of:Vascular Cambium (new phloem & xylem)Cork Cambium (cork replaces the epidermis during 2o growth)

Heartwood

Sapwood

Rings

Wood rays

Heartwood

Vascular cambium

Sapwood

Secondary phloem

Cork cambiumCork

Bark

Secondary Growth in Woody PlantsVascular cambium produces new phloem & xylem ea yr:

• spring & summer growth look diff., producing an annual ring

Heartwood• old, dead xylem fromprevious years

Sapwood• new, functioning xylem from most recent 2o growth

Key Terms for Chapters 31 & 32

• carpel – stigma, style, ovary (ovule, embryo sac)

Relevant Review Questions: Ch. 31 – 2-4, 6-11 Ch. 32 – 1, 3

• sporophyte, gametophyte

• stamen – anther & filament (pollen, tube cell)

• asexual vs sexual, “alternation of generations”

• sepal, petal

• monocot, dicot

• mesophyll, stomata, phloem, xylem