Plant SciencePlant Science

Structure, Transport, and Structure, Transport, and ReproductionReproduction

PLANT EVOLUTION AND DIVERSITYPLANT EVOLUTION AND DIVERSITY

The following 24 slides are for general reference and not required material The following 24 slides are for general reference and not required material

Do not take notes, just listen and ask questions. Do not take notes, just listen and ask questions.

Kingdom PlantaeKingdom Plantae

Eukaryotes Eukaryotes Possess cellulose-rich cell wallsPossess cellulose-rich cell walls Store energy in the form of starch Store energy in the form of starch PhotosynthesizePhotosynthesize Multi-cellularMulti-cellular Life cycles display both haploid and diploid Life cycles display both haploid and diploid

multi-cellular forms multi-cellular forms (alternation of generations)(alternation of generations)

Origin of PlantsOrigin of Plants ‘‘Plants’ are believed have evolved Plants’ are believed have evolved

from green algaefrom green algae

Charophyceans, a group of green Charophyceans, a group of green algae, are the ancestors of plantsalgae, are the ancestors of plants

Algae are… Algae are… single-celledsingle-celled colonialcolonial multi-cellularmulti-cellular

……and do not possess…and do not possess… leavesleaves vascular tissue vascular tissue rootsroots flowersflowers seeds seeds

A multi-cellular Charophycean, the nearest living relative to plants

Alternation of Alternation of GenerationsGenerations All plants undergo a life cycle that takes them through All plants undergo a life cycle that takes them through

both haploid and diploid generations.both haploid and diploid generations.

The multicellular diploid plant structure is called the The multicellular diploid plant structure is called the sporophyte, which produces spores through meiotic sporophyte, which produces spores through meiotic (asexual) division. (asexual) division.

The multicellular haploid plant structure is called the The multicellular haploid plant structure is called the gametophyte, which is formed from the spore and give gametophyte, which is formed from the spore and give rise to the haploid gametes. rise to the haploid gametes.

The fluctuation between these diploid and haploid stages The fluctuation between these diploid and haploid stages that occurs in plants is called the alternation of that occurs in plants is called the alternation of generations. generations.

Alternation of Alternation of GenerationsGenerations

Plant Diversity

There are four main groups of plantsThere are four main groups of plants Bryophytes : mosses and alliesBryophytes : mosses and allies Filicinophytes: ferns and alliesFilicinophytes: ferns and allies Coniferophytes: conifersConiferophytes: conifers Angiospermophytes: flowering plantsAngiospermophytes: flowering plants

The groups can be distinguished by The groups can be distinguished by morphology and methods of reproductionmorphology and methods of reproduction

Plant DiversityPlant Diversity

BryophytesBryophytes

Most primitive of land plantsMost primitive of land plants Includes mosses, liverworts, and Includes mosses, liverworts, and

hornwortshornworts Do not have roots Do not have roots Do not have vascular tissues (do not Do not have vascular tissues (do not

circulate internal liquids)circulate internal liquids) Do not flower or produce seedsDo not flower or produce seeds Reproduce via sporesReproduce via spores

MossesMosses

Moss Reproduction

Spores, haploid cells, are produced in a capsule.Spores, haploid cells, are produced in a capsule. Capsule develops at end of stalkCapsule develops at end of stalk

Moss FactsMoss Facts Max. height – 0.5 mMax. height – 0.5 m

Number of known species ~ 10,000Number of known species ~ 10,000

Moss will grow wherever there is an adequate amount of Moss will grow wherever there is an adequate amount of moisture and sunlight. (not just the north side of a tree)moisture and sunlight. (not just the north side of a tree)

Mosses prefer deciduous trees instead of conifers Mosses prefer deciduous trees instead of conifers because conifers have more acidic bark. (that’s why you because conifers have more acidic bark. (that’s why you don’t see mosses on redwoods very often)don’t see mosses on redwoods very often)

Mosses cannot survive in polluted air. Like the lichens, Mosses cannot survive in polluted air. Like the lichens, they need a healthy atmosphere to survivethey need a healthy atmosphere to survive

FilicinophytesFilicinophytes

Commonly known as fernsCommonly known as ferns Have roots, leaves, and short, non-Have roots, leaves, and short, non-

woody stemswoody stems Have vascular tissues to circulate water Have vascular tissues to circulate water

and nutrientsand nutrients Do not flower or produce seedsDo not flower or produce seeds Reproduce via sporesReproduce via spores

Fern sorus, sporangia (2n), Fern sorus, sporangia (2n), and spores (n)and spores (n)

Fern gametophyte (n)Fern gametophyte (n)

Pinnate Leaves: Pinnate Leaves: Resembling a feather; having parts or Resembling a feather; having parts or branches arranged on each side of a common branches arranged on each side of a common

axisaxis Simple Pinnate

Bi-pinnateTri-pinnate

FernsFerns

Fern FactsFern Facts

The fern was one of the first plants on The fern was one of the first plants on Earth. Earth.

Fossil fern remains, dating back 450 Fossil fern remains, dating back 450 million years, have been found in coal million years, have been found in coal beds. beds.

There are about 12,000 species in the There are about 12,000 species in the world today. world today.

ConifersConifers

Coniferophytes: conifersConiferophytes: conifers

Also known as gymnospermsAlso known as gymnosperms

Produce naked seeds in conesProduce naked seeds in cones

Have leaves, stems, roots, and Have leaves, stems, roots, and vascular tissuevascular tissue

Most are trees, some shrubsMost are trees, some shrubs

All are woodyAll are woody

Leaves are reduced and waxyLeaves are reduced and waxy

Conifer Conifer Life Life Cycle: Cycle: sporophyte sporophyte phase phase dominantdominant

Naked Seeds (no flesh like Naked Seeds (no flesh like fruit) are produced in Conesfruit) are produced in Cones

Cones can be male (produce pollen) or Cones can be male (produce pollen) or female (contain ovules), these are all female (contain ovules), these are all femalefemale

Conifer factsConifer facts Typical examples of conifers include cedars, douglas-Typical examples of conifers include cedars, douglas-

firs, cypresses, firs, junipers, kauris, larches, pines, firs, cypresses, firs, junipers, kauris, larches, pines, redwoods, spruces, and yews.redwoods, spruces, and yews.

Conifers are of immense economic value, primarily for Conifers are of immense economic value, primarily for timber and paper production.timber and paper production.

The division contains approximately 700 living species.The division contains approximately 700 living species. The world's tallest, largest, thickest and oldest living The world's tallest, largest, thickest and oldest living

things are all conifers. things are all conifers.

Phylogeny of PlantsPhylogeny of Plants

AngiospermsAngiosperms

AngiospermsAngiosperms

Flowering PlantsFlowering Plants Plant group with the most recent originPlant group with the most recent origin Have roots, leaves, vascular tissueHave roots, leaves, vascular tissue Produce seeds within endosperm (fruit)Produce seeds within endosperm (fruit) Two main types – monocots and dicotsTwo main types – monocots and dicots Can be shrubs, vines, trees, grasses, Can be shrubs, vines, trees, grasses,

cacti, etc.cacti, etc.

Monocot vs. DicotMonocot vs. Dicot Angiosperms typically belong to two general Angiosperms typically belong to two general

groups monocots and dicotsgroups monocots and dicots

Monocots have 1 embryonic leaf (cotyledon)Monocots have 1 embryonic leaf (cotyledon) include all grasses (rice, corn, wheat), palms, and include all grasses (rice, corn, wheat), palms, and

many ornamentals (orchids,lilies, tulips)many ornamentals (orchids,lilies, tulips)

Dicots have 2 embryonic leavesDicots have 2 embryonic leaves Include beans, apples, roses, and oaksInclude beans, apples, roses, and oaks

Flower FactsFlower Facts There are an estimated 350,000 species of There are an estimated 350,000 species of

angiosperms, over ¾ of the worlds plantsangiosperms, over ¾ of the worlds plants

Fossil evidence of first flowering plants dates back to Fossil evidence of first flowering plants dates back to 125 mya125 mya

Many plants have co-evolved with insects in mutual Many plants have co-evolved with insects in mutual symbiosis, symbiosis, ex. bees pollinateex. bees pollinate

The value of angiosperms to humans are priceless, they The value of angiosperms to humans are priceless, they are the source of nearly all terrestrial based food are the source of nearly all terrestrial based food production, production, ex. Fruits, veggies, grains, grass for livestockex. Fruits, veggies, grains, grass for livestock

Xerophytes: Xerophytes: plants adapted to grow in dry environmentsplants adapted to grow in dry environments

Spines instead of leaves, to reduce Spines instead of leaves, to reduce transpirationtranspiration

Thick stems store waterThick stems store water Very thick cuticle prevents water lossVery thick cuticle prevents water loss Wide, shallow root network absorbs Wide, shallow root network absorbs

occasional rain falloccasional rain fall

Xerophytes:Xerophytes: cacti cacti

Plant StructurePlant Structure

Plant StructurePlant Structure

Angiosperms may take on a wide variety of Angiosperms may take on a wide variety of morphologies and adaptationsmorphologies and adaptations

Species are distinguished primarily by flower Species are distinguished primarily by flower characteristicscharacteristics

Areas of focus:Areas of focus: Basic FeaturesBasic Features Leaf CharacteristicsLeaf Characteristics Vascular system (stem and root)Vascular system (stem and root) Generalized FlowerGeneralized Flower

Basic FeaturesBasic Features FlowerFlower: :

reproductionreproduction

FruitFruit: : seed dispersalseed dispersal

LeafLeaf: : energy absorptionenergy absorption

BudBud: : growth sitegrowth site

Vascular tissueVascular tissue: : water and nutrient transportwater and nutrient transport

Ground tissueGround tissue: : basic supportbasic support

Root system: Root system: water and mineral absorptionwater and mineral absorption acts as anchoracts as anchor

The LeafThe Leaf Site of photosynthesis, highest concentration of Site of photosynthesis, highest concentration of

chloroplast in plantchloroplast in plant

COCO22 enters, and H enters, and H22O exits, through stomataO exits, through stomata Stoma Stoma – opening in epidermis– opening in epidermis Guard cell Guard cell – swells or shrinks to close or open – swells or shrinks to close or open

stomastoma

Vessels bring water to cells, and transport Vessels bring water to cells, and transport sugar away to rest of plantsugar away to rest of plant

Leaf PartsLeaf Parts

MesophyllMesophyll – ground tissue – ground tissue SpongySpongy – bottom part of leaf, air pocket – bottom part of leaf, air pocket

allow for gas exchangeallow for gas exchange PalisadePalisade – top layers of cells, tightly packed – top layers of cells, tightly packed

to absorb maximum amount of sunlightto absorb maximum amount of sunlight

CuticleCuticle – – waxy coating prevents water loss, thicker on waxy coating prevents water loss, thicker on

upper epidermisupper epidermis

Vascular TissueVascular Tissue

Specialized cells form Specialized cells form tubes to allow tubes to allow movement of solutionmovement of solution

Xylem:Xylem: Transports water and Transports water and

minerals up from the minerals up from the rootsroots

Phloem:Phloem: Transports sugar down Transports sugar down

from the leaves where it from the leaves where it was madewas made

XylemXylem Technically ‘dead’: no nucleus, cell membrane, Technically ‘dead’: no nucleus, cell membrane,

organelles, cytoplasm, etc.organelles, cytoplasm, etc. Modified cell wall containing lignin for increased Modified cell wall containing lignin for increased

strengthstrength TracheidsTracheids::

Long, thin cells with high surface area to volume ratio; Long, thin cells with high surface area to volume ratio; highly poroushighly porous

Vessel ElementsVessel Elements:: Larger diameter and shorter, lower surface to area ratio Larger diameter and shorter, lower surface to area ratio

than tracheids; highly porousthan tracheids; highly porous

PhloemPhloem Composed of cells known as Composed of cells known as

sieve tube cells and companion sieve tube cells and companion cellscells

Sieve tubes lacked nucleus, Sieve tubes lacked nucleus, ribosomes, and vacuoleribosomes, and vacuole

Companion cells maintain Companion cells maintain functioning of sieve cells and functioning of sieve cells and transport carbohydrates into transport carbohydrates into tubestubes

Vascular CellsVascular Cells

Dicot Stem Cross SectionDicot Stem Cross Section

Ground Tissue:Ground Tissue: PithPith – interior to cambium – interior to cambium Cortex Cortex – exterior to cambium– exterior to cambium

EpidermisEpidermis Prevents water loss, can be specialized to become root hairs Prevents water loss, can be specialized to become root hairs

or create cuticleor create cuticle

Vascular BundleVascular Bundle

CambiumCambium: : actively dividing tissue, gives rise to both actively dividing tissue, gives rise to both

xylem and phloemxylem and phloem

Dicot RootDicot Root

RootsRoots Absorb minerals (nitrogen, phosphorous) by active Absorb minerals (nitrogen, phosphorous) by active

transporttransport

Water follows by osmosis because root has high Water follows by osmosis because root has high solute concentrationsolute concentration

Roots can be used to store energy in tubersRoots can be used to store energy in tubers

SteleStele: the vascular tissue of the root: the vascular tissue of the root PericyclePericycle: the tissue immediately surrounding stele, : the tissue immediately surrounding stele,

gives rise to lateral branch rootsgives rise to lateral branch roots

Dicot Root Cross SectionDicot Root Cross Section

Root Hairs: Root Hairs: extensions of epidermis, extensions of epidermis, function in water and mineral absorption by function in water and mineral absorption by significantly increasing surface areasignificantly increasing surface area

Water AbsorptionWater Absorption Water moves toward Water moves toward

vascular tissue by vascular tissue by osmosisosmosis

ApoplasticApoplastic Water moves through cell Water moves through cell

walls, but not through cellswalls, but not through cells

SymplasticSymplastic Water moves directly Water moves directly

through cellsthrough cells

Casparian StripCasparian StripA band of modified cell A band of modified cell wall that separates the wall that separates the outer cortex from the outer cortex from the stelestele

Prevents passive flow of Prevents passive flow of water and materials into water and materials into stelestele

Forces water and Forces water and materials to exit materials to exit apoplastapoplast (cell wall) and enter (cell wall) and enter symplast symplast (cellular (cellular cytoplasm)cytoplasm)

The shape of root systems vary The shape of root systems vary between speciesbetween species

Special ModificationsSpecial Modifications

BulbsBulbs Stem TubersStem Tubers Storage RootsStorage Roots TendrilsTendrils

Plant GrowthPlant Growth

Plants exhibit two primary methods of Plants exhibit two primary methods of growthgrowth PrimaryPrimary – elongation from terminal or – elongation from terminal or

auxiliary shoot or root tipsauxiliary shoot or root tips SecondarySecondary – lateral growth of cambium – lateral growth of cambium

Tissue capable of active cell division is Tissue capable of active cell division is termed ‘termed ‘meristematicmeristematic’’

Primary Growth of ShootPrimary Growth of Shoot

MeristemMeristem Terminal bud Terminal bud Auxiliary budAuxiliary bud

A Root Branch: A Root Branch: note apical meristemnote apical meristem

Secondary Growth: Secondary Growth: division in the cambium

Secondary Growth Secondary Growth causes thickening causes thickening

of plant girthof plant girth

MeristemsMeristems

The actively dividing tissue of plantsThe actively dividing tissue of plants ApicalApical: located at end of branch or root: located at end of branch or root

ElongatingElongating Includes auxiliary budIncludes auxiliary bud

LateralLateral: located within existing stems, : located within existing stems, branches, or roots.branches, or roots. WideningWidening

Tissue known as the cambiumTissue known as the cambium

PhototropismPhototropism

The growth of the The growth of the shoot toward a light shoot toward a light sourcesource

Increased elongation Increased elongation of specific ground of specific ground tissue caused by tissue caused by plant hormone plant hormone auxinauxin

Phototropism and AuxinPhototropism and Auxin

Auxin is released from Auxin is released from apical meristemapical meristem

Auxin is released Auxin is released asymmetricallyasymmetrically In higher concentrations In higher concentrations

on side of plant away from on side of plant away from light sourcelight source

AuxinAuxin Polar TransportPolar Transport: :

auxins carrier found only auxins carrier found only on lower membranes of on lower membranes of cellscells

unidirectional hormone unidirectional hormone movementmovement

Acid Growth Acid Growth Hypothesis:Hypothesis: Auxin increases cell wall Auxin increases cell wall

acidity, causing cell to acidity, causing cell to expandexpand

Auxin and Cell ElongationAuxin and Cell Elongation-- Acid Growth HypothesisAcid Growth Hypothesis

1.1. Auxin increases the activity of proton pumpsAuxin increases the activity of proton pumps

2.2. The cell wall becomes more acidicThe cell wall becomes more acidic

3.3. Expansin proteins (activated by low pH) cause Expansin proteins (activated by low pH) cause cell wall fibers to loosen.cell wall fibers to loosen.

4.4. Turgor pressure causes cell to expandTurgor pressure causes cell to expand

Acid Growth HypothesisAcid Growth Hypothesis