Chapter 17 The Evolution of Plant and Fungal Diversity Green algae (charophytes) are the ancestors...

Chapter 17 The Evolution of Plant and Fungal Diversity

Green algae (charophytes) are the ancestors of plants

© 2012 Pearson Education, Inc.

More than 500 million years ago, the algal ancestors of plants may have carpeted moist fringes of lakes and coastal salt marshes.

Plants and green algae called charophytes

– are thought to have evolved from a common ancestor,

– have complex multicellular bodies, and

– are photosynthetic eukaryotes.

– Algae do not have tissues like plants

17.1 Plants have adaptations for life on land



Life on land offered many opportunities for plant adaptations that took advantage of

– unlimited sunlight,

– abundant CO2, and

– initially, few pathogens or herbivores.



But life on land had disadvantages too. On land, plants must

– maintain moisture inside their cells, to keep from drying out,

– support their body in a nonbuoyant medium,

– reproduce and disperse offspring without water, and

– obtain resources from soil and air.



Unlike land plants, algae

– generally have no rigid tissues,

– are supported by surrounding water,

– obtain CO2 and minerals directly from the water surrounding the entire algal body,

– receive light and perform photosynthesis over most of their body,

– use flagellated sperm that swim to fertilize an egg, and

– disperse offspring by water.


Figure 17.1C

Key

Vasculartissue

Spores

Leaf

Stem

Roots

Flagellatedsperm

Flagellatedsperm

Leaf

Stem

Roots

Spores

AlgaSurroundingwater supportsalga. Whole algaperforms photo-synthesis; absorbswater, CO2, andminerals fromthe water.

Flagellatedsperm

Holdfast(anchors alga)

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

FernStomata; roots anchorplants, absorb water;lignified cell walls;vascular tissue;fertilization requiresmoisture

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

Stem

Roots

Leaf

Seed

Pollen


Land plants maintain moisture in their cells using

– a waxy cuticle and

– cells that regulate the opening and closing of stomata.

Land plants obtain

– water and minerals from roots in the soil and

– CO2 from the air and sunlight through leaves.

Growth-producing regions of cell division, called apical meristems, are found near the tips of stems and roots.



In many land plants, water and minerals move up from roots to stems and leaves using vascular tissues.

– Xylem

– consists of dead cells and

– conveys water and minerals.

– Phloem

– consists of living cells and

– conveys sugars.



In all plants, the

– gametes and embryos must be kept moist,

– fertilized egg (zygote) develops into an embryo while attached to and nourished by the parent plant, and

– life cycle involves an alternation of a

– haploid generation, which produces eggs and sperm, and

– diploid generation, which produces spores within protective structures called sporangia.

Pines and flowering plants have pollen grains, structures that contain the sperm-producing cells.


Fig. 17.2 Plant diversity reflects the evolutionary history of the plant kingdom

Ancestralgreenalga

Origin of land plants(about 475 mya)

Origin of vascular plants(about 425 mya)

Liverworts

Hornworts

Mosses

Lycophytes (club mosses,spike mosses, quillworts)

Pterophytes or Monilophytes (ferns,horsetails, whisk ferns)Gymnosperms

Angiosperms

Origin of seed plants(about 360 mya)

0300350400450500Millions of years ago (mya)

3

2

1

Seed

plan

tsS

eedless

vascular

plan

ts

No

nvascu

larp

lants

(bryo

ph

ytes)

Lan

d p

lants

Vascu

lar plan

ts

17.2 Plant diversity reflects the evolutionary history of the plant kingdom

Early diversification of plants gave rise to seedless, nonvascular plants called bryophytes, including

– _____, that we saw in laboratory

– liverworts, and

– hornworts.



These plants resemble other plants in having apical meristems and embryos retained on the parent plant, but they lack

– true roots,

– leaves, and

– stems.


Figure 17.2B

Bryophytes

_____ LiverwortHornwort


About 425 million years ago, vascular plants evolved with lignin-hardened vascular tissues.

The seedless vascular plants include

– lycophytes (including club mosses) and

– Pterophytes or monilophytes (ferns and their relatives).


Figure 17.2CSeedless vascular plants

fern (a pterophyte or monilophyte), spores under ____

Club moss (a lycophyte).Spores are produced in theupright tan-colored structures.


The first vascular plants with seeds evolved about 360 million years ago.

A seed consists of an embryo packaged with a food supply within a protective covering.



Vascular plants with seeds include

– gymnosperms (including ginkgo, cycad, and conifer species) and

– angiosperms (such as flowering trees and grasses).



Gymnosperms

– have naked seeds that are not produced in fruits and

– include ginkgo, cycad, and conifer species.


Figure 17.2D

Ginkgo

Cycad Ephedra(Mormon tea)

Gymnosperms

A conifer


Angiosperms

– are flowering plants and

– include flowering trees and grasses.


Figure 17.2EAngiosperms

A tropical jacaranda tree Green foxtail, a grass

ALTERNATION OF GENERATIONS

AND PLANT LIFE CYCLES


Plants have an alternation of generations in which the haploid and diploid stages are distinct, multicellular bodies.

– The haploid gametophyte produces gametes (eggs or sperm) by mitosis.

– Fertilization results in a diploid zygote.

– The zygote develops into the diploid sporophyte, which produces haploid spores by meiosis.

– Spores grow into gametophytes.

17.3 Haploid and diploid generations alternate in plant life cycles


Figure 17.3

Key Haploid (n) Diploid (2n)

Sperm (n)

Egg (n)

Zygote (2n)

Spores (n)

Gametophyteplant (n)

FertilizationMeiosis

Sporophyteplant (2n)

THE PLANT LIFE CYCLE

Gametophytes make up a bed of moss.

– Gametes develop in male and female gametangia.

– Sperm swim through water to the egg in the female gametangium.



The zygote

– develops within the gametangium into a mature sporophyte,

– which remains attached to the gametophyte.

Meiosis occurs in sporangia at the tips of the sporophyte stalks.

Haploid spores are released from the sporangium and develop into gametophyte plants.



Figure 17.3

Key Haploid (n)

Diploid (2n)

Malegametangium

Sperm

Femalegametangium

Egg

Fertilization

ZygoteGametophyte

Sporophyte

Sporangium

Meiosis

Spores (n)Gametophyte plants (n)

A Moss Life Cycle

Gametophyte or sporophyte?


Fern gametophytes are small and inconspicuous.

Gametophytes produce flagellated sperm that swim

to the egg and fertilize it to produce a zygote.

The zygote initially develops within the female

gametangia but eventually develops into an

independent sporophyte.



Sporangia develop on the underside of the leaves of the sporophyte.

Within the sporangia, cells undergo meiosis to produce haploid spores.

Spores are released and develop into gametophytes.


Figure 17.3

Sperm

Key Haploid (n)

Diploid (2n)

Gametophyteplant (n)

Spores

MeiosisMature

sporophyte

New sporophytegrowing from the

gametophyte

Fertilization

Egg

Femalegametangium

Malegametangium

A Fern Life Cycle

Zygote

17.4 Seedless vascular plants dominated vast “coal forests”

Two groups of seedless plants formed vast ancient forests in low-lying wetlands during the Carboniferous period (360–299 million years ago):

– lycophytes (such as club mosses) and

– Pterophytes or monilophytes (such as ferns).

When these plants died, they formed peat deposits that eventually formed coal.


Figure 17.4

17.4 Seedless vascular plants dominated vast “coal forests”

As temperatures dropped during the late Carboniferous,

– glaciers formed,

– the climate turned drier,

– the vast swamps and forests began to disappear, and

– wind-dispersed pollen and protective seeds gave seed plants a competitive advantage.


17.5 Pollen and seeds are key adaptations to life on land

A pine tree is a sporophyte. Tiny gametophytes grow in sporophyte cones. The ovule is a key adaptation, a protective device

for all the female stages in the life cycle, as well as the site of– pollination,

– fertilization, and

– embryonic development.


17.5 Pollen and seeds are key adaptations to life on land

A sperm from a pollen grain fertilizes an egg in the female gametophyte.

The zygote develops into a sporophyte embryo.

The ovule becomes the 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.


Figure 17.5

Sporangia

Longitudinalsection of

ovulate cone

Longitudinalsection of

pollen cone

Figure 17.5B

Ovulate cone

Spore (n)

Spore wall

Sporangium (2n)(produces spore)

Male gametophyte(within a germinated

pollen grain) (n)

Pollen grain (n)

Femalegametophyte (n)

Egg nucleus (n)

Dischargedsperm nucleus (n)

Pollen tube

Seed coat

Sporewall

Food supply

Embryo (2n)(new sporophyte)

17.6 The flower is the centerpiece of angiosperm reproduction

Flowers house separate male and female sporangia and gametophytes.

Flowers are the sites of

– pollination and

– fertilization.



Flowers usually consist of

– sepals, which enclose the flower before it opens,

– petals, which attract animal pollinators,

– stamens, which include a filament and anther, a sac at the top of each filament that contains male sporangia and releases pollen, and

– Carpels or pistils, the female reproductive structure, which produce eggs.



Ovules develop into seeds.

Ovaries mature into fruit.


Figure 17.6B

_____

ReceptacleOvule

_____

_____

_____

Anther

Filament

OvaryStyle

Stigma

17.6 The angiosperm plant is a sporophyte with gametophytes in its flowers

Key events in a typical angiosperm life cycle

1. Meiosis in the anthers produces haploid spores that form the male gametophyte (pollen grains).

2. Meiosis in the ovule produces a haploid spore that forms the few cells of the female gametophyte, one of which becomes the egg.

3. Pollination occurs when a pollen grain lands on the stigma. A pollen tube grows from the pollen grain to the ovule.

4. The tube carries a sperm that fertilizes the egg to form a zygote.


17.6 The angiosperm plant is a sporophyte with gametophytes in its flowers

Key events in a typical angiosperm life cycle, continued

5. Each ovule develops into a seed, consisting of

– an embryo (a new sporophyte) surrounded by a food supply and

– a seed coat derived from the integuments.

6. While the seeds develop, the ovary’s wall thickens, forming the fruit that encloses the seeds.

7. When conditions are favorable, a seed germinates.


Figure 17.7

Anther1

2

3

4

5

6

7

Meiosis

Pollen grains (n)(male gametophytes)

Meiosis

Stigma

Pollen grain

Pollen tube

OvuleOvary

Sperm

Fertilization

Zygote(2n)

SeedEmbryo (2n)

Seed coat

Foodsupply

Fruit(mature ovary)

Seeds

Germination

Sporophyte (2n)

Egg withina female

gametophyte (n)

Ovulecontaining

female sporangium(2n)

KeyHaploid (n)

Diploid (2n)

17.8 The structure of a fruit reflects its function in seed dispersal

Fruits are

– ripened ovaries of flowers and

– adaptations that disperse seeds.

Seed dispersal mechanisms include relying on

– wind,

– hitching a ride on animals, or

– fleshy, edible fruits that attract animals, which then deposit the seed in a supply of natural fertilizer at some distance from the parent plant.


Figure 17.8A-C

Fruit

Seeddispersal

17.9 Angiosperms sustain us—and add spice to our diets

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 like pepper (Piper nigrum)

and cumin are also angiosperm

fruits.


17.10 EVOLUTION CONNECTION: Pollination by animals has influenced angiosperm evolution

About 90% of angiosperms use animals to transfer their pollen.

– Birds are usually attracted by colorful flowers, often red, but without scent.

– Most beetles are attracted by fruity odors, but are indifferent to color.

– Night-flying bats and moths are usually attracted by large, highly scented flowers that are often white.

– Wind-pollinated flowers typically produce large amounts of pollen.


Figure 17.10B

17.11 CONNECTION: Plant diversity is vital to the future of the world’s food supply

Some new crops may come from the hundreds of species of nutritious fruits, nuts, and grains that people gather and use locally.

Figure 17.11a-0 Sugar plums (left) and African plums (right), two wild fruits that may be ripe for domestication

DIVERSITY OF FUNGI


17.12 Fungi absorb food after digesting it outside their bodies

Fungi

– are absorptive heterotrophic eukaryotes,

– secrete powerful enzymes to digest their food externally,

and

– acquire their nutrients by absorption.



Most fungi consist of a mass of threadlike hyphae

making up a mycelium.

Hyphal cells

– are separated by cross-walls with pores large enough for

organelles to cross, and

– have a huge surface area to secrete digestive enzymes

and absorb food.


Figure 17.12A

Figure 17.12B

Hyphae

Reproductivestructure

Spore-producingstructures (tips of hyphae)

Mycelium


Fungal hyphae

– are surrounded by a cell wall made of chitin instead of

cellulose as in plants and some algae.

Some fungi

– are parasites and

– obtain their nutrients at the expense of living plants or

animals.


17.13 Fungi produce spores in both asexual and sexual life cycles

In many fungi, sexual fusion of haploid hyphae leads to a heterokaryotic stage, in which cells contain two genetically distinct haploid nuclei.

– Hours or centuries may pass before parental nuclei fuse to form a short-lived diploid phase.

– Zygotes undergo meiosis to produce haploid spores.



In asexual reproduction, spore-producing structures arise from haploid mycelia that have undergone neither a heterokaryotic stage or meiosis.

Many fungi that reproduce sexually can also produce spores asexually.



Molds are any rapidly growing fungus that reproduces asexually by producing spores.

Yeasts are single-celled fungi that reproduce asexually by cell division or budding.


Figure 17.13

Key

1

2

3

4

Haploid (n)

Heterokaryotic (n + n)(unfused nuclei)

Diploid (2n)

Spores(n)

Zygote(2n)

Spores (n)

Heterokaryoticstage

Fusion of nuclei

Fusion of cytoplasm

Spore-producingstructures

Asexualreproduction

Mycelium

Sexualreproduction Meiosis

Spore-producingstructures

GerminationGermination

The life cycle of a black bread mold is typical of zygomycetes.

Hyphae reproduce asexually by producing spores in sporangia

at the tips of upright hyphae. When food is depleted, the

fungus reproduces sexually. Mycelia of different mating types

join and produce a zygosporangium, a thick-walled cell

containing heterokaryotic nuclei from two parents that can

tolerate dry, harsh conditions. When conditions are

favorable, the

parental nuclei fuse

to form diploid

zygotes, which

undergo meiosis

producing haploid

spores.


17.14 Fungi are classified into five groups

There are over 100,000 described fungi species. Suspected but as yet undescribed species may

number as many as 1.5 million. Sexual reproductive structures are often used to

classify fungi. Fungi and animals may have diverged

– from a flagellated ancestor

– more than 1 billion years ago.



Chytrids are the

– only fungi with flagellated spores and

– earliest lineage of fungi.

Chytrid fungi are

– common in lakes, ponds, and soil and

– linked to the widespread decline of amphibian species.


Figure 17.14A

Chytrids

Zygomycetes(zygote fungi)

Glomeromycetes(arbuscularmycorrhizal fungi)

Ascomycetes(sac fungi)

Basidiomycetes(club fungi)


Zygomycetes, or zygote fungi

– are characterized by their protective zygosporangium, where zygotes produce haploid spores by meiosis.

– This diverse group includes fast-growing molds that attack

– bread

– peaches,

– strawberries,

– sweet potatoes, and

– some animals.



Glomeromycetes

– form a distinct type of mycorrhizae, in which hyphae that

invade plant roots in a symbiotic relationship

– Mycorrhizal fungi absorb phosphorus and other essential materials from the soil and make them available to the plant and sugars produced by the plant through photosynthesis nourish the mycorrhizal fungi.

– About 90% of all plants have symbiotic partnerships with

glomeromycetes.



Ascomycetes, or sac fungi

– form saclike structures called asci, which produce spores in sexual reproduction,

– live in marine, freshwater, and terrestrial habitats, and

– range in size from unicellular yeast to elaborate morels and cup fungi.

– Some ascomycetes live with green algae or cyanobacteria in symbiotic associations called lichens.


Figure 17.14D

Ascomycetes

Edible morels Cup fungus


Basidiomycetes, or club fungi,

– include common mushrooms, puffballs, and shelf fungi and

– are named for their club-shaped, spore-producing structure called a basidium.

These fungi include

– important forest decomposers and

– particularly destructive plant parasites called rusts and smuts.


Figure 17.14E

Mushrooms

Basidiomycetes

Shelf fungi

A puffball

17.17 Fungal groups differ in their life cycles and reproductive structures

The life cycle of a black bread mold is typical of

zygomycetes.

Hyphae reproduce asexually by producing spores

in sporangia at the tips of upright hyphae.


17.15 CONNECTION: Fungi have enormous ecological benefits

Fungi

– supply essential nutrients to plants through symbiotic mycorrhyizae,

– along with prokaryotes are essential decomposers in ecosystems, breaking down organic matter and restocking the environment with vital nutrients essential for plant growth, and

– may also be used to digest petroleum products to clean up oil spills and other chemical messes.

17.16 CONNECTION: Fungi have many practical uses

Fungi have many practical uses for humans.

– We eat mushrooms and cheeses modified by fungi.

– Yeasts produce alcohol and cause bread to rise.

– Some fungi provide antibiotics that are used to treat bacterial disease.

Figure 17.16A

Figure 17.16B

Staphylococcusaureus (bacteria)

Penicillium(mold)

Zone ofinhibitedgrowth

17.17 Lichens are symbiotic associations of fungi and photosynthetic organisms

Lichens consist of algae or cyanobacteria within a mass of fungal hyphae.

– 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.


17.17 Lichens are symbiotic associations of fungi and photosynthetic organisms

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.


Figure 17.17A Two species of lichens commonly found on coastal rocks

Figure 17.17b

Algal cell

Fungalhyphae

Figure 17.17C Reindeer moss, a lichen fed on by caribou in the Arctic Tundra

17.18 SCIENTIFIC THINKING: Mycorrhizae may have helped plants colonize land

About 80% of all plant species establish symbioses with glomeromycetes, mycorrhizal fungi that form bushy structures called arbuscules in root cells, which increase surface area for nutrient absorbtion. The fungi obtain sugar from root cells. Both benefit in the symbiosis called _______________

The presence of mycorrhizal associations in almost all major lineages of present-day plants suggests an ancient origin for plant-fungus symbioses.

Fossils and molecular biology provide evidence for this ancient association

17.19 Parasitic fungi harm plants and animals

Of the 100,000 known species of fungi, about 30% are either parasites or pathogens in or on plants.

About 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.

– Dutch elm disease destroyed 70% elm trees across the eastern USA

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


Figure 17.19B

Figure 17.19C

Ergots

17.19 CONNECTION: Parasitic fungi harm plants and animals

Only about 500 species of fungi are parasitic on animals.

Skin diseases include– ringworm, named because it appears as circular red

areas on the skin,

– athlete’s foot, also caused by the ringworm fungus,

– vaginal yeast infections, and

– deadly lung diseases.


Chapter 17 The Evolution of Plant and Fungal Diversity Green algae (charophytes) are the ancestors...

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Transcript of Chapter 17 The Evolution of Plant and Fungal Diversity Green algae (charophytes) are the ancestors...