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Origin and Evolution of Plants: Algae

• Green algae – closest relatives to

modern terrestrial plants (outgroup)

– Chlorophyll

– Cell walls composed of cellulose

– Starch = primary NRG reserve

• Photosynthetic and often multicellular

Life in Water vs. Life on Land• Life in water is pretty easy compared to life on

land…

• Why?– Bathed in fluid—don’t worry about desiccation!

– Algae are surrounded by medium from which they get nutrients and O2---no need for long distance transport in plant!

– Algae supported by surrounding water, gravity not a problem.

– Gametes and adults can disperse (or swim)

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Plant Adaptations to Life on Land

• Life on land offered new opportunities

– Unlimited sunlight

– Abundant CO2

– Initially, few pathogens or herbivores

• Land plants are a clade, defined by a set

of derived characters

– Alternation of haploid and diploid generations

–Walled spores produced in sporangia

– Male and female gametangia

– Multicellular, dependent sporophyte embryos

Today’s Goals

• Four major groups of land plants

• Origin of major plant characteristics

• Each group represents a different major evolutionary radiation associated with increasing adaptations to life on land.

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The Mosses: Bryophytes

• Exhibit two crucial adaptations to life on land

– Cuticle reduces desiccation

– Protection of the embryo: retained on the “maternal plant”

• Still restricted to moist habitats

– Lack a well developed vascular system

– Fairly little structural support

– Rely on moisture for sperm to reach the eggs

• Haploid gametophyte more conspicuous than Diploid sporophyte.

• Only plant group where dominant form is the haploid gametophyte.

• Water is required in order for the flagellated sperm to reach the egg. The sporophyte is tiny and attached to the moss plant. Water is required in order for spores to germinate and form a new gametophyte moss plant.

http://www.sbs.auckland.ac.nz/info/schools/nzplants/con_reproduction.htm

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The Ferns

(Second Radiation of Land Plants)

• Tracheophyta

– In addition to a cuticle and protected embryo, ferns have

• Well developed vascular tissues for transport within

• Vascular system invested with lignin (structural support)

• Can now get large (some early seedless plants > 40m)

– But…

• Still rely on water for transport of gametes

• Sporophyte more conspicuous than gametophyte

• Dominant form is the diploid sporophyte

• Water is required in order

for spores to germinate and form a tiny thumbnail-sized

gametophyte on the soil surface.

Water is required in order for the flagellated sperm

to locate an egg.

http://www.sbs.auckland.ac.nz/info/schools/nzplants/con_reproduction.htm

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• Seedless plants formed vast ancient forests in

low-lying wetlands during the Carboniferous

period (360–299 million years ago)

– When they died, the plants formed peat deposits that eventually formed coal

• Coal, oil, and natural gas are fossil fuels

– Oil and natural gas formed from marine organisms; coal formed from seedless plants

– Burning fossil fuels releases CO2, causing climate warming

Gymnosperms & the 3rd Radiation

• ~ 700 living species

• In addition to cuticle, protected embryo, vascular tissue for transport and support…

– Seed

• Embryo enclosed in durable, desiccation resistant seed.

Can wait for favorable conditions to develop and can be

dispersed.

– Reduced Gametophyte.

• Male gametophyte small enough to be dispersed by

wind!

• REPRODUCTION FREE FROM WATER!

• Heterosporous (Produce two types of spores)

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Sporangia producespores; spores developinto pollen grains.

Spore mother cell (2n)

Meiosis

1

Sporangium (2n)

Scale

Integument

Pollination

Ovule

Meiosis

2

3Pollen grains(male gameto-phytes) (n)

Ovulate conebears ovules.

Haploid (n)

Diploid (2n)

Key

Mature sporophyte

Egg (n)

Fertilization

Femalegametophyte (n)

Male gametophyte (pollen grain)

Sperm (n)

A haploid spore celldevelops into femalegametophyte, whichmakes eggs.

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Pollen growstube to eggand makesand releasessperm.

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Seed coat

Zygote(2n)

Zygote developsinto embryo, andovule becomes seed.

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Food supply

Embryo (2n)Seed

7 Seed germinates,and embryo grows into seedling.

Pollination in gymnosperms• In pollination, a pollen grain lands on a scale

in an ovulate cone and enters an ovule

• Fertilization occurs a year after pollination,

when a sperm moves down a pollen tube to the

egg to form a zygote

– The zygote develops into a sporophyte embryo, and the ovule becomes a seed, with stored food and a protective seed coat

• The seed is a key adaptation for life on land

and a major factor in the success of seed plants

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Angiosperms & the 4th Radiation

• ~250,000 living species

• Reasons for this diversification may include– A more complex and efficient vascular system

– Ovules protected in ovary

– Fruit promoting dispersal• Eat and poop – move the seeds!

• Types of fruits

• Flowers and insects (don’t have to rely on just wind)– Recruit other organisms to work for them!

• The gametophytes is even more reduced than in Gymnosperms – seeing a trend here?

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Pollination

• 90% of angiosperms use animals to transfer pollen– Birds are attracted by colorful flowers, but not

scent

– Beetles are attracted by fruity odors, but not color

– Bats are attracted by large, highly scented flowers

–Wind-pollinated flowers produce large amounts of pollen

Meiosis

1

Haploid (n)

Diploid (2n)

Key

Egg (n)

Fertilization

Sperm

Seed coat

Zygote(2n)

Food supply

Embryo (2n)

Seeds

Haploid spores in anthers develop intopollen grains: male gametophytes.

2

Meiosis

Pollen grains (n)

Ovule

Haploid spore in each ovuledevelops into female gameto-phyte, which produces an egg.

3 Pollination andgrowth of pollen tube

Stigma

Pollen grain

Pollen tube

4

Fruit(matureovary)

6

Seed5

Ovary

Ovule

Stigma

Anther

Sporophyte (2n)

Seed germinates,and embryogrows intoplant.

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Angiosperms

• Flowers contain separate male and female sporangia and gametophytes

• Flowers usually consist of sepals, petals, stamens (which produce pollen), and carpels(which produce eggs)– Sepals enclose and protect the flower before it opens

– Petals attract animal pollinators

• Stamens include a filament and anther, a sac at the top of each filament that contains male sporangia and releases pollen

Angiosperms

• The carpel is the female reproductive

structure, including the ovary

– The ovary encloses the ovules, which contain sporangia that will produce a female gametophyte

• Ovules develop into seeds; ovaries mature

into fruit

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Stamen

Anther

Filament

Petal

Receptacle

Ovule

Sepal

Stigma

Style

Ovary

Carpel

Ovary, containingovule

Mature plant withflowers, wherefertilization occurs

Fruit (mature ovary),containing seed

Embryo

Seed

Germinatingseed

Seedling

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Seeds

• The zygote divides many times via mitosis to produce the embryo

• The embryo consists of tiny root and shoot apical meristems and one or two cotyledons

• A tough seed coat develops

• Seed dormancy

– Embryo growth and development are suspended

– Allows delay of germination until conditions are favorable

Cotyledon

Cotyledons

Embryonicshoot

EmbryonicShoot

Embryonicroot

EndospermEmbryonicleaf

Fruit tissue

Seed coat

Sheath

Corn (monocot)

Common bean (eudicot)

Seed coat

Embryonicroot

Embryonicleaves

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MONOCOTS

EUDICOTS

Seed leaves Leaf veins Stems Flowers Roots

Onecotyledon Veins usually parallel

Vascular bundles in

complex arrangement

Floral parts usually

in multiples of threeFibrous

root system

Taprootusually present

Floral parts usually inmultiples of four or five

Vascular bundlesarranged in ringVeins usually branched

Twocotyledons

• Dicots—most plants• Two cotyledons

• Branched leaf

venation

• Ring of vascular bundles

• Flower parts in 4s or 5s (or multiples)

• Taproot system

– Monocots• One cotyledon

• Parallel leaf venation

• Scattered vascular

bundles

• Flower parts in 3s or multiples of 3

• Fibrous root

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Ovary, containingovule

Mature plant withflowers, wherefertilization occurs

Fruit (mature ovary),containing seed

Embryo

Seed

Germinatingseed

Seedling

Fruits

Hormonal changes induced by fertilization

trigger the ovary to develop into a fruit

• Fruits are adaptations that disperse seeds

– Some rely on wind for seed dispersal

– Some hitch a ride on animals

– Fleshy, edible fruits attract animals

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Upper partof carpel

Ovule

Ovarywall

Sepal

Seed

Pod(opened)

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• Most human food is provided by the fruits

and seeds of angiosperms

– Corn, rice, wheat, and other grains are dry fruits

– Apples, cherries, tomatoes, and squash are

fleshy fruits

– Spices such as nutmeg, cinnamon, cumin, cloves, ginger, and licorice are also angiosperm fruits

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Spores

Flagellatedsperm

Stem Leaf

Seed

Pollen

Leaf

FernStomata; roots anchor plants,absorb water; lignified cellwalls; vascular tissue;fertilization requires moisture

Roots

Stem

Roots

Pine treeStomata; roots anchor plants, absorb water; lignified cell walls; vascular tissue;fertilization does not require moisture

MossStomata only on sporophytes; primitive roots anchor plants,no lignin; no vascular tissue;fertilization requires moisture

Spores

Flagellatedsperm

Leaf

Stem

Roots

Flagellatedsperm

Vasculartissue

Key

Holdfast(anchors alga)

AlgaWater supportsalga. Whole algaperforms photo-synthesis;absorbs water,CO2, andminerals fromwater.

Shoot system

(photosyntheticcenter)

Root system(anchors,

absorbsnutrients,

and stores

food)

Root hairs

(microscopic;increase surface

area for absorption)

Leaf (mainphotosynthetic organ)

Blade

Petiole

Node

Internode

Axillary bud (produces a branch)

Stem (supports leavesand flowers)

Terminal bud (grows stem)

Flower (reproductive organ)

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Typical Plant Body

– Plants absorb water and minerals from soil through roots

– Plants absorb the sun’s energy and carbon dioxide from the air through shoots (stems and leaves)

– Plant roots depend on shoots for carbohydrates produced via photosynthesis

– Plant shoots depend on roots for water and minerals

Typical Plant Body

• Plant roots

– Anchor plant

– Absorb water and nutrients

– Store food

• Plant shoots

– Stems, leaves, and reproductive structures

– Stems provide support

– Leaves carry out photosynthesis

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Plant Body Modifications

• Modifications of plant parts are

adaptations for various functions–Food or water storage

–Asexual reproduction

–Protection

–Climbing

–Photosynthesis

Root Modifications

• Food Storage

– Large taproots store starches

– carrots, turnips, sugar beets, sweet potatoes

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Stem modifications

• Stem modifications

– Stolon: asexual reproduction

– Rhizomes: storage, asexual reproduction

– Tubers: storage, asexual reproduction

– Cactus stem: water storage

& photosynthesis

Leaf modifications

– Protection–Cactus spine

–Climbing– Pea plant tendril

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Three tissue systems in the plant body

• Dermal tissue

– Outer protective covering

– Layer of tightly packed cells called the epidermis

– First line of defense against damage and infection

– Waxy layer called cuticle reduces water loss

• Vascular tissue

– Support and long-distance transport (xylem, phloem)

• Ground tissue

– Bulk of the plant body

– Food production, storage, support

Eudicot leaf

XylemPhloem

Vein

Guardcells

Stoma

Sheath

Eudicot stemVascularbundle

Pith

Cortex

Epidermis

Eudicot root

Endodermis

Cortex

Epidermis

PhloemXylem Vascular

cylinder

Mesophyll

Cuticle

Upper epidermis

Lower epidermis

Monocot stem

Vascularbundle

Epidermis

Key

Ground tissue systemDermal tissue system

Vascular tissue system

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Xylem and Phloem

• Xylem

– Transports water throughout plant

• Phloem

– Transports food throughout plant

Plant vs. Animal cells

• Plants cells have three structures that

distinguish them from animals cells

– Chloroplasts used in photosynthesis

– A large, fluid-filled vacuole

– A cell wall composed of cellulose

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How do plants grow?

• Animal growth is determinate

– Growth stops after a certain size is reached

• Plant growth is indeterminate

– Growth occurs throughout a plant’s life

– Plants are categorized based on how long they live

–Annuals complete their life cycle in one year

–Biennials complete their life cycle in two years

– Perennials live for many years

Primary Growth

• Plant growth occurs in specialized tissues called meristems– Regions of active cell division

• Apical meristems are found at the tips of roots and shoots–Where primary growth occurs

– Primary growth allows roots to push downward through the soil and shoots to grow upward toward the sun

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Primary Growth

• The apical meristems of shoot tips occur as buds at the stem tip and at the base

of leaves

• Cells produced in the shoot apical meristem differentiate into dermal, vascular and ground tissues

Axillary buds

Terminal bud

Arrows =directionof growth

Roottips

Secondary Growth

• Plants grow thicker over time

• Secondary growth occurs at lateral meristems

– areas of active cell division that exist in two cylinders that extend along the length of roots and shoots

– Vascular cambium is a lateral meristem that lies between primary xylem and phloem

– Cork cambium is a lateral meristem that lies at the outer edge

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Secondary Growth

• Vascular cambium produces cells in two directions– Secondary xylem produces wood toward the

interior of the stem

– Secondary phloem produces the inner bark toward the exterior of the stem

• Cork cambium produces cells in one direction– Cork cambium produces the outer bark

Secondary xylem(2 years’ growth)

Growth

Shedepidermis

Year 1Late Summer Key

Ground tissue system

Dermal tissue system

Vascular tissue system

GrowthGrowth

Year 2Late Summer

Year 1Early Spring

Bark

Secondaryxylem (wood)

Secondaryphloem

Corkcambium

Cork

Primaryphloem

Primaryxylem

Vascularcambium

Epidermis

Cortex

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Secondary Growth

• Most transport occurs near the vascular

cambium

– Sapwood near the vascular cambium transports water

– Heartwood stores resins and wastes

– Transport of sugars occurs in the secondary phloem near the vascular cambium

Sapwood

Heartwood

Bark

Rings

Woodrays

Heartwood

Sapwood

Vascular cambium

Secondary phloemCork cambiumCork

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Secondary Growth

• Wood annual rings show layers of secondary

xylem

– In temperate regions, periods of dormancy stop growth of secondary xylem

– Rings occur in areas when new growth starts each

year

• The bark (secondary phloem and cork) is

sloughed off over time

Reproductive structures, as in flowers,contain spores and gametes

Cuticle covering leaves and stemsreduces water loss

Stomata in leaves allow gas exchangebetween plant and atmosphere

Lignin hardens cell walls of someplant tissues

Stem supports plant; may performphotosynthesis

Vascular tissues in shoots and rootstransport water, minerals, and sugars;provide support

Leaves carry out photosynthesis

Roots anchor plant; mycorrhizae (root-fungus associations) help absorb waterand minerals from the soil

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Copyright © 2009 Pearson Education, Inc.

Plants and Fungi

– Plants and fungi colonized land together

– Mycorrhizae, mutually beneficial associations of plant roots and fungi hyphae, enabled plants to colonize land– Mycorrhizal fungi absorb water,

phosphorus, and other minerals from soil and make them available to the plant

– The sugars produced by the plant nourish the fungus

Fungi

• Fungi are absorptiveheterotrophic eukaryotes that digest their food externally and absorb the nutrients

• Most fungi consist of a mass of threadlike hyphae making up a mycelium

• Fungal hyphae are surrounded by a cell wall with chitin

Hypha

Mycelium

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Fusion of cytoplasm

Heterokaryoticstage

Spore-producingstructures

Asexualreproduction

Spores(n)

Diploid (2n)

Haploid (n)

Heterokaryotic (n + n)(unfused nuclei)

Key

Sexualreproduction

Zygote(2n)

Fusion of nuclei

Spore-producingstructures

Spores (n)

Mycelium

Meiosis

Germination

Germination

Chytrids

Zygomycetes(zygote fungi)

Glomeromycetes(arbuscularmycorrhizal fungi)

Ascomycetes(sac fungi)

Basidiomycetes(club fungi)

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Chytrids

• Chytrids, which have flagellated spores, are the earliest lineage of fungi

• In 1999, a new species was described that infects amphibians and causes a deadly disease.

• Travels easily on water and moist surfaces

• Where the fungus thrives, 50% of amphibian species and 80% of individuals can be expected to disappear within one year (Lips et al. 2006)

• 80% of plant diseases are caused by fungi– Between 10 and 50% of the world’s fruit harvest is

lost each year to fungal attack

– A variety of fungi, including smuts and rusts, infect grain crops

• Only 50 species of fungi are parasitic on animals, causing mycoses– Human infections include athlete’s foot (caused by

ringworm)

– Systemic mycoses are rare but serious fungal infections that spread through the body from inhaled spores

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Lichens

• Lichens consist of algae or cyanobacteria within a fungal network

– Many lichen associations are mutualistic

– The fungus receives food from its photosynthetic partner

– The fungal mycelium helps the alga absorb and retain water and minerals

• Lichens are important pioneers on new land, where they help to form soil

– Lichens are sensitive to air pollution, because they obtain minerals from the air

For Next Week

• Lab– Invertebrate questions due at 8:40 AM

– Bring dissecting kit and gloves to lab

• Lecture – Assignment: Collect 5 branches from trees, put in

plastic bags – For each,• Identify if it is from a gymnosperm or an angiosperm

• Try to identify the tree – common name and latin name

– Extra credit: 1-2 page earthworm paper with references