Starr & Taggart – 11th Edition

Plant Evolution

AP Biology: Chapter 23

Chapter 23

Key Concepts:

The plant kingdom consists mostly of multicelled photoautotrophs

Almost all plants live on land

Plants have structural adaptations that allow them to photosynthesize, absorb water and ions, and conserve water

Land plants are reproductively adapted to withstand dry periods

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Key Concepts:

Seed producers were more successful in radiating into drier environments based on an evolutionary scale

Gymnosperms and angiosperms are vascular plants

Angiosperms include two classes of flowering plants Dicots and Monocots

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Impacts, Issues Video

Beginnings and Endings

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Setting the Stage for Plants

Earth’s atmosphere was originally oxygen free Ultraviolet radiation bombarded the surface Photosynthetic cells produced oxygen and allowed formation

of a protective ozone layer

Cyanobacteria were probably the first to spread into and up freshwater streams

Later, green algae and fungi made the journey together

Every plant is descended from species of green algae

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The Plant Kingdom

Nearly all are multicelled

Vast majority are

photoautotrophs

Energy from sun

Carbon dioxide from air

Minerals dissolved in water

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Evolutionary Trends Among Plants

Photoautotraphs

Vascular plants Roots, stems, leaves

Gymnosperms

Seed bearing

Gingko

Cycads

Conifers

Angiosperms Flowers and seeds

Dicots and Monocots

Non-vascular plants Bryophytes

Liverworts

Hornworts

Mosses

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Evolution of Roots, Stems, and Leaves

Roots and Stems Below ground

Shoot systems Stems and leaves

Above Ground

Sunlight and CO2

Support of cell wall

Lignin

Vascular tissue Xylem

Phloem

Water conservation Cuticle

Stomata

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Evolutionary Trends

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Evolution of Pollen and Seeds

Homospory Heterospory

Pollen grains Sperm-bearing gametophytes Female gametophytes

Spread by air, insects, birds

Seeds Embryo of gametophytes Nutritive tissues Protective coat

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Milestones in Plant Evolution

ancestral green algae

?

PALEOZOIC MESOZOICOrdovician Silurian Devonian

505 435 410

PROGYMNOSPERMS

RHYNIOPHYTES

FLOWERING PLANTS

CONIFERS

CYCADS

GINKGOS

FERNS

HORSETAILS

LYCOPHYTES

BRYOPHYTES

CENOZOICCarboniferous Permian Triassic Jurassic Cretaceous

present360 290 240 205 138 65Time (millions of years ago)

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Bryophytes

Characteristics: Nonvascular

Moist habitats mostly

Small

< 20 cm tall

Simplest plants

Fewer than 19,000 species

Mosses

Liverworts

HornwortsLiverwort

Mosses

Hornwort

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Moss Life CycleZygote grows, develops into a sporophyte while still attached to gametophyte.

Fertilization

zygote

sperm-producing structure

egg-producing structure

Diploid StageHaploid Stage

mature sporophyte

Meiosis

Spores germinate.

male gametophyte

female gametophyte

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Peat Mosses

350 species

Sphagnum is an example

Grow in acidic bogs; important

ecosystems of cold and temperate

regions

Peat can be harvested and burned as

fuel

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Seedless Vascular Plants

Like bryophytes

Live in wet, humid places

Require water for fertilization

Unlike bryophytes

Sporophyte is free-living and has

vascular tissues

Fern gametophyte

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Existing Seedless Vascular Plants

Whisk ferns, Lycophytes, Horsetails, Ferns 3 Differences from Bryophytes

Sporophyte: not attached to a gametophyte has vascular tissues longer phase in life cycle

Habitat Moist places

Gametophytes lack vascular tissue Sperm needs water to reach egg

Whisk Fern

Horsetail

Princess Pine

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Ferns (Pterophyta)

12,000 species, mostly tropical Most common sporophyte

structure Perennial underground stem

(rhizome) Roots and fronds arise from

rhizome Young fronds are coiled

“fiddleheads” Mature fronds divided into leaflets Spores form on lower surface of

some fronds

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Life Cycle of a Fern

Sporesare released

Sporophyte still attached to gametophyte

zygotefertilization

Diploid StageHaploid Stage

egg

spermmature gametophyte

Spores develop

meiosis

Spore germinates

rhizomesorus

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The Rise of the Seed-Bearing Plants

Seed ferns, gymnosperms, angiosperms Pollen grains from microspores

Male gametophytes (sperm)

Megaspores inside ovules

Egg producing gametophytes

Pollination

Pollen grains arrive on female reproductive structures (carried by air or pollinators)

Independent of water for fertilization

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Seed-Bearing Plants

Depend on Pollen grains

Ovules that mature into seeds

Tissue changes adapted to dry conditions

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Gymnosperms-Plants with “Naked” Seeds

Conifers, Cycads, Ginkgos, Gnetophytes Conifers – most produce woody cones

Seeds don’t form inside an ovary but on exposed cone scales Pines, cypress, firs, spruces, redwoods Most are evergreen

Male cones with pollen

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Pine Life Cycle

Conifers reproduce more slowly than angiosperms; at competitive disadvantage in many habitats

Still dominate in far north, at higher elevations, and in certain parts of southern hemisphere

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Lesser Known Gymnosperms

Cycads Tropical Subtropical areas Palm-like -♂ or ♀ Largest seed-bearing cones Only 100 living species

Gingko Diverse in dinosaur times One survives - Gingko biloba Deciduous trees -♂ or ♀

Gingko

Cycad

Fleshy coated seeds

Male micro-sporangia

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Lesser Known Gymnosperms

Gnetophytes Gnetum

Tropical tree

Ephedra

SW N. America

Welwitschia mirabilis

Desert shrub

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Angiosperms

Flowering plants Dominant land plants (260,000 species) Ovules and (after fertilization) seeds are

enclosed in an ovary Three main groups: magnoliids, monocots,

and eudicots

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AngiospermsThe Flowering Seed-Bearing Plants

Flowers

Coevolution with pollinators Insects

Bats

Birds

Seed

Ovary

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Double Fertilization

Distinctive feature of angiospermsMale gametocyte

delivers two sperm to an ovule One fertilizes egg;

other fertilizes a cell that gives rise to endosperm More details later!

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Overview of

Flowering Plant Life

Cycle

Double fertilization Meiosis Meiosis

microspores

female gametophyte

pollination

mitosis without cytoplasmic division

two sperm enter ovule

Diploid

Haploid

sporophyte

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Dicots and Monocots

Almost 180,000 Dicots are herbaceous Cabbage and Daisies

Flowering shrubs and trees

Water lilies

Cacti

About 80,000 Monocots Orchids, palms, grasses,

crop plants, rice

Chapter 23

People and Plants

Plant domestication began about 11,000 years ago About 3,000 species have been used as food

Now about 200 plants are major crops Non-food uses:

Lumber, paper, and fuel Furniture Rope Thatched roofing Natural insecticides Drugs

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Plants of Abuse

Tobacco plants are Nicotiana sp. Cannabis sativa is source of

marijuana Poppies used to produce opium Coca leaves are used to produce

cocaine Toxic plant alkaloids, such as

henbane and belladona, have been used as poisons and as medicine

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In Conclusion

Plants probably arose from green algae

Trends in evolution can be identified by comparing structural adaptations to dry conditions, shifts to diploid dominance, and the shift to heterospory

Bryophytes are nonvascular plants and require free water for fertilization

Vascular plants are adapted to life on land

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In Conclusion

Gymnosperms are vascular plants that produce pollen grains and seeds

Ovules contain the egg-producing female gametophytes

Evolution of pollen grains freed these plants from dependence on water for fertilization

Angiosperms produce flowers and coevolved with pollinators