Plants Chapter 22. Setting the Stage for Plants Earth’s atmosphere was originally oxygen free Ultraviolet radiation bombarded the surface Photosynthetic

PlantsPlants

Chapter 22Chapter 22

Setting the Stage for PlantsSetting 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

Invading the LandInvading the Land

• 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

The Plant KingdomThe Plant Kingdom

• Nearly all are multicelled

• Vast majority are

photoautotrophs

– Energy from sun

– Carbon dioxide from air

– Minerals dissolved in water

22.1 Evolutionary Trends22.1 Evolutionary Trends

• 295,00 species of plants

• Most plants are vascular-internal

tissue conducts water and solutes

through roots, stems, and leaves

• 19,000 species are nonvascular-called

bryophytes-liverworts, hornworts

mosses


• Seedless vascular plants-wisk ferns,

lycophytes, horsetails and ferns

• Gymnosperms- cycads, ginkgos,

gnetophytes and conifers (seed-

bearing vascular plants)

• Angiosperms-Dicots and monocots-

two classes of flowering plants


• Simple roots began to form when

plants colonized the land. Later

became more specialized roots.

• Most root systems have many

underground absorptive structures

with increased surface area.


• Above grounds shoots evolved-

stems, leaves that absorb energy

from the sun and carbon dioxide

from the air.

• Plants changed as they began to

move into higher and drier places.


• Diploid zygote forms at fertilization,

mitotic cells divide and cell

enlargements convert it into a

sporophyte.

• After some of its cells undergo

meiosis, haploid resting cells (spores)

form.


• Seed-bearing plants produce two types of

spores. This condition is known as

heterospory.

• One type of spore is known as homospory.

• In gymnospers and angiosperms,

macrospores tive rise to female

gametophytes in which eggs form and get

fertilized.

22.1 Evolutionary Trends22.1 Evolutionary Trends• Smaller microspores are the start of pollen grains-

cellular structures that become mature, sperm-

bearing male gametophytes.

• Pollen grains travel with the help of wind, birds,

insects, and other animals.

• In drier habitats, seed production also adapted.

Female gametophytes of seed-bearing plants form

within sporophyte tissue.


• In most lineages, structural adaption ot life

on land included a root system, shoot

system, waxy cuticle, stomata, vascular

tissues and lignin-reinforced tissue.

• Lignin- found in cell walls; an organic

compound that helps give plant cell its

structure.

Milestones in Plant EvolutionMilestones in Plant Evolution

ancestral green algae

PROGYMNOSPERMS

RHYNIOPHYTES

FLOWERING PLANTS

CONIFERS

CYCADS

GINKGOS

FERNS

HORSETAILS

LYCOPHYTES

BRYOPHYTES

CENOZOIC

?

PALEOZOIC MESOZOIC

Ordovician Silurian Devonian Carboniferous Permian Triassic Jurassic CretaceousPresent505 435 410 360 290 240 205 138 65

Time (millions of years ago)

Pg. 343.

22.3 Bryophytes- 22.3 Bryophytes- Nonvascular PlantsNonvascular Plants

• Bryophytes

• Fewer than 19,000

species

• Three groups

Liverworts

Hornworts

Mosses

Nonvascular PlantsNonvascular Plants

• Adapted to grow well in fully

or seasonally moist

habitats. (Mosses are

sensitive to pollution, but

will grow in almost all other

environments-including

deserts and Antarctica.)


Bryophytes

radially symmetrical rhizoids multicellularleaves usually with midrib

Mosses

Thallose liverwort - bilaterally symmetricalrhizoids unicellular

BryophytesBryophytes• Small, nonvascular, nonwooody

• Gametophyte dominates life

cycle; has leaflike, stemlike, and rootlike parts

• Usually live in wet habitats• Flagellated sperm require

water to reach eggs

Types of BryophytesTypes of Bryophytes

Liverworts (simplest)

Hornworts

Mosses (most common)

Marchantia:Marchantia: A Liverwort A Liverwort

• Reproduces asexually by way of

gemmae cups

• Sexual reproduction

•Gametophytes are male or female

•Gametes are produced on elevated

structures

Moss Life CycleMoss Life Cycle

Fertilization MeiosisDiploid Stage

Haploid Stage

malegametophytetip

femalegametophytetip

Zygote

Development of mature sporophyte (still attached to gametophyte)

Male gametophyte

Female gametophyte

Spores released

Egg

Sperm

Peat MossesPeat 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

Seedless Vascular PlantsSeedless Vascular Plants• Like bryophytes

– Live in wet, humid places

– Require water for fertilization

• Unlike bryophytes

– Sporophyte is free-living and

has vascular tissues

Types of Types of Seedless Vascular PlantsSeedless Vascular Plants

Whisk ferns (Psilophyta)

Lycophytes (Lycophyta)

Horsetails (Sphenophyta)

Ferns (Pterophyta)

Corksonia

Ferns (Pterophyta)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

Fern Life CycleFern Life Cycle

The sporophyte (still attached to the gametophyte) grows, develops.

zygote fertilization

Diploid Stage

Haploid Stage

egg

sperm

egg-producing structure

sperm-producing structure

mature gametophyte (underside)

Spores develop.

meiosis

Sori

Spores are released

Spore germinates

rhizome

gametophyte


Bryophytes

Thallose liverwort - bilaterally symmetricalrhizoids unicellular

Liverwort


Bryophytes are nonvascular plants with flagellated sperm that require liquid water to reach and fertilize the eggs.

A sporophyte of these plants develops within gametophyte tissues. It remains attached to the gametophyte and receives some nutritional support from it.

22.4 Vascular Plants22.4 Vascular Plants

• Majority of plants

• Have internal tissues that carry

water and solutes

• Two groups

– Seedless vascular plants

– Seed-bearing vascular plants

Seedless Vascular PlantsSeedless Vascular Plants• Arose during the Devonian period• Produce spores but no seeds• Four main groups

Whisk fernsLycophytesHorsetails

Ferns

Seedless Vascular PlantsSeedless Vascular Plants• Most seedless vascular plants live in

wet, humid places. Their gametophytes lace vascular tissues. Water clinging to these plants are the only means for flagellated sperm to reach the eggs.

http://www.plantapalm.com/vce/evolution/timetable.htm

Geologic Time Table

Evolutionary TrendEvolutionary Trend

zygote

SPOROPHYTE (2n)

GAMETOPHYTE (n)

GREEN ALGA BRYOPHYTE FERN GYMNOSPERM ANGIOSPERM

Seedless Vascular PlantsSeedless Vascular Plants• Psilotum grows

wild in Florida woodlands and all members of the division, Psilophyta, today are tropical plants

Seedless Vascular PlantsSeedless Vascular Plants• Psilotum grows

wild in Florida woodlands and all members of the division, Psilophyta, today are tropical plants

Seedless Vascular PlantsSeedless Vascular Plants• Running pine or

Lycopodium complanatum, an Ohio native

Seedless Vascular PlantsSeedless Vascular Plants

Horsetails Strobili Equisetum palustre

Seedless Vascular PlantsSeedless Vascular Plants

22.5 Seed-Bearing 22.5 Seed-Bearing Vascular PlantsVascular Plants

• Gymnosperms arose first– Cycads– Ginkgos– Gnetophytes– Conifers

• Angiosperms arose later– Monocots– Dicots

GymnospermsGymnosperms• Plants with “naked seeds”

• Seeds don’t form inside an

ovary

• Four groups

Conifers Ginkgos

Cycads Gnetophytes

Conifer Characteristics Conifer Characteristics • Widest known, largest

number of living species

• Woody trees or shrubs

• Most are evergreen

• Bear seeds on exposed cone scales

• Most produce woody cones

CycadsCycads• Most diverse during age of dinosaurs• Only 100 living species• Two species of Zamia are native to

U.S.• Palmlike appearance• Pollen-bearing and seed-bearing

cones on different plants

GinkgosGinkgos• Diverse during age of dinosaurs• Only surviving species, Ginkgo

biloba, is native to China• Deciduous tree with fan-shaped

leaves• Trees are male or female• Female trees produce seeds covered

with a fleshy, foul-smelling coat

3 Genera of Gnetophytes3 Genera of Gnetophytes

• Gnetum - Tropical climbing vines

• Ephedra (joint fir, Mormon tea)

• Welwitschia mirabilis

Pine ConesPine Cones

• Woody scales of a “pine cone” are

the parts of where megaspores

formed and developed into female

gametophytes

• Male cones, where microspores and

pollen are produced, are not woody

PinePineLifeLife

CycleCycle Sporophyte

Female cone

Male cone

ovule

fertilization meiosis

microsporesmegaspores

Pollen sac

egg View insideovule

Pollen tube

Seed

Conifer DistributionConifer Distribution

• Conifers dominated during Mesozoic

• 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

Rise of Seed-Bearing Rise of Seed-Bearing PlantsPlants

• Seeds appeared about 360

million years ago

• Seed ferns and gymnosperms

were dominant at first

• Angiosperms arose later

Special Traits of Special Traits of Seed-Bearing PlantsSeed-Bearing Plants

• Pollen grains– Arise from megaspores– Develop into male gametophytes– Can be transported without water

• Seeds– Embryo sporophyte inside nutritive

tissues and a protective coat– Can withstand hostile conditions

Vascular Plants

Adaptations to LandAdaptations to Land

• Root systems• Shoot systems• Vascular tissues • Waxy cuticle for

water conservation

Seed-Bearing Vascular Seed-Bearing Vascular PlantsPlants

Conifers

Bristle-coned pines

The oldest trees

Giant redwoods- the tallest trees

http://www.mcwdn.org/Plants/Angiosperm.html

AngiospermsAngiosperms• Flowering plants• Dominant land plants (260,000

species)• Defining feature: Ovules and (after

fertilization) seeds are enclosed in an ovary

• Two classes: Monocots and dicots

Structure of Flower and Structure of Flower and SeedSeed

ovaryovule

embryo

endosperm

seed coat

FlowerinFlowering Plant g Plant

Life Cycle Life Cycle

Double fertilization Meiosis Meiosis

microspores

Female gametophyte

pollination

Mitosis without cytoplasmic division

Two sperm enter ovule

Diploid

Haploid

Seed-Bearing Plants Seed-Bearing Plants

• Microspores that give rise

to pollen grains

• Megaspores inside ovules

• More water-conserving

than seedless vascular

plants

Pollen Pollen

• Pollen grains are sperm-bearing male gametophytes that develop from microspores

• Allows transfer of sperm to egg without water

• Can drift on air currents, or be carried by pollinators

OvulesOvules

• Female reproductive structures that become seeds

• Consist of:– Female gametophyte with egg cell

– Nutrient-rich tissue

– Jacket of cell layers that will form seed coat

Double Fertilization Double Fertilization • Distinctive feature of angiosperms• Male gametocyte delivers two

sperm to an ovule• One fertilizes egg; other fertilizes a

cell that gives rise to endosperm that supports embryo

People and PlantsPeople 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

Nonfood Uses of Plants Nonfood Uses of Plants • Lumber, paper, and fuel from conifers• Furniture from hardwoods• Rope from agave, hemp• Thatched roofing from grasses, palms• Natural insecticides• Drugs from foxglove, periwinkle

Plants of AbusePlants of Abuse• Tobacco plants are Nicotiana sp. • Cannabis sativa is source of

marijuana• Coca leaves are used to produce

cocaine• Toxic plant alkaloids, such as

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

ReviewReview• Chart pg. 354• Summary and Review Questions, Self

Quiz and end of chapter readings.

Documents

Plants Chapter 22. Setting the Stage for Plants Earth’s atmosphere was originally oxygen free Ultraviolet radiation bombarded the surface Photosynthetic