chapter 17 plants, fungi, and the colonization of...

PowerPoint Lectures for

Biology: Concepts & Connections, Sixth Edition

Campbell, Reece, Taylor, Simon, and Dickey

Chapter 17

Lecture by Joan Sharp

Plants, Fungi, and the

Colonization of Land

Introduction: Plants and Fungi—A Beneficial Partnership

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

PLANT EVOLUTION AND DIVERSITY

500 million years ago, the algal ancestors of plants formed a green carpet on the edge of lakes and coastal salt marshes

Green algae called charophytes are the closest living relatives of plants

17.1 Plants have adaptations for life on land

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

Life on land offered new opportunities

– Unlimited sunlight

– Abundant CO2

– Initially, few pathogens or herbivores

Challenges of terrestrial life

– Maintaining moisture within cells

– Obtaining resources from soil and air

– Supporting body in air

– Reproducing and dispersing offspring without water

Spores

Flagellatedsperm

Stem Leaf

Pollen

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

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

Vasculartissue

Holdfast(anchors alga)

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

Flagellatedsperm

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

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

Spores

Flagellatedsperm

Vasculartissue

Holdfast(anchors alga)

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

Spores

Pollen

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

Vasculartissue

In all plants, the zygote develops into an embryo while attached to and nourished by the parent plant

Plants are embryophytes, with multicellular, dependent embryos

17.2 Plant diversity reflects the evolutionary history of the plant kingdom

Four key adaptations for life on land distinguish the main lineages of the plant kingdom

– Dependent embryos (characteristic of all plants)

– Lignified vascular tissues

– Seeds

– Flowers

Ancestralgreenalga

Origin of land plants(about 475 mya)

Origin of vascular plants(about 425 mya)

Origin of seed plants(about 360 mya)

Mosses

Lycophytes (club mosses,spike mosses, quillworts)

Pterophytes (ferns,horsetails, whisk ferns)

Gymnosperms

Angiosperms

Millions of years ago (mya)

500 450 350 300400 0

Liverworts

Hornworts

ALTERNATION OF GENERATIONS

AND PLANT LIFE CYCLES

The haploid gametophyte produces gametes (eggs and 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

Haploid (n)

Diploid (2n)

Key Gametophyteplant (n)

Gametes (n)

Mitosis

Haploid (n)

Diploid (2n)

Gametes (n)

Fertilization

Zygote (2n)

Mitosis

Haploid (n)

Diploid (2n)

Gametes (n)

Fertilization

Zygote (2n)

Sporophyteplant (2n)

Mitosis

Haploid (n)

Diploid (2n)

Gametes (n)

Fertilization

Zygote (2n)

Meiosis

Spores (n)

Mitosis

Haploid (n)

Diploid (2n)

Gametes (n)

Fertilization

Zygote (2n)

Meiosis

Spores (n)

Mitosis

Gametophytes make up a bed of moss

– They produce eggs and flagellated sperm in gametangia

– Sperm swim through water to the egg

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 stalk

– Haploid spores are released from the sporangium and develop into gametophytes

17.4 Mosses have a dominant gametophyte

Animation: Moss Life Cycle

MaleHaploid (n)

Diploid (2n)

KeyGametophytes (n)

Female

Sperm (n)

Egg (n)

Fertilization

Femalegametangium

MaleHaploid (n)

Diploid (2n)

KeyGametophytes (n)

Female

Sperm (n)

Egg (n)

Fertilization

Femalegametangium

Zygote (2n)

MaleHaploid (n)

Diploid (2n)

KeyGametophytes (n)

Female

Sperm (n)

Egg (n)

Fertilization

Femalegametangium

Zygote (2n)Sporophyte (2n)

3 Mitosis

and development

Sporangium

MaleHaploid (n)

Diploid (2n)

KeyGametophytes (n)

Female

Sperm (n)

Egg (n)

Fertilization

Femalegametangium

3 Mitosis

and development

Sporangium

Meiosis

Spores (n)

MaleHaploid (n)

Diploid (2n)

KeyGametophytes (n)

Female

Sperm (n)

Egg (n)

Fertilization

Femalegametangium

3 Mitosis

and development

Sporangium

Meiosis

Spores (n)

5 Mitosis and

development

17.5 Ferns, like most plants, have a dominant sporophyte

Fern gametophytes are small and inconspicuous

– They 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

17.5 Ferns, like most plants, have a dominant sporophyte

Animation: Fern Life Cycle

Haploid (n)

Diploid (2n)

Gametophyte (n)

Sperm (n)

Egg (n)

Fertilization

Female

gametangium (n)

Haploid (n)

Diploid (2n)

Gametophyte (n)

Sperm (n)

Egg (n)

Fertilization

Zygote (2n)

Female

gametangium (n)

Haploid (n)

Diploid (2n)

Gametophyte (n)

Sperm (n)

Egg (n)

Fertilization

Female

gametangium (n)

Zygote (2n)New sporophyte (2n)

Mitosis and

development

Mature sporophyte

Clusters of

sporangia

Haploid (n)

Diploid (2n)

Gametophyte (n)

Sperm (n)

Egg (n)

Fertilization

Female

gametangium (n)

Zygote (2n)New sporophyte (2n)

Mitosis and

development

Meiosis

Mature sporophyte

Clusters of

sporangia

Mitosis and

development

Spores (n)

17.6 Seedless plants dominated vast “coal forests”

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

17.7 A pine tree is a sporophyte with gametophytes in its cones

A pine cone holds all of the tree’s reproductive stages: spores, eggs, sperm, zygotes, and embryos

– Each scale of the cone contains sporangia that produce spores by meiosis

– The spores produce gametophytes within the cone

The male gametophyte is a pollen grain, released from pollen cones and carried by wind to female cones

Female ovulate cones carry two ovules on each stiff scale

– Each ovule contains a sporangium surrounded by the integument

Animation: Pine Life Cycle

Sporangia producespores; spores developinto pollen grains.

Spore mother cell (2n)

Meiosis

Sporangium (2n)

Integument

Pollination

Meiosis

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

Ovulate conebears ovules.

Haploid (n)

Diploid (2n)

Mature sporophyte

Meiosis

Sporangium (2n)

Integument

Pollination

Meiosis

Haploid (n)

Diploid (2n)

Mature sporophyte

Egg (n)

Fertilization

Femalegametophyte (n)

Male gametophyte (pollen grain)

Sperm (n)

A haploid spore celldevelops into femalegametophyte, whichmakes eggs.

Pollen growstube to eggand makesand releasessperm.

Meiosis

Sporangium (2n)

Integument

Pollination

Meiosis

Haploid (n)

Diploid (2n)

Mature sporophyte

Egg (n)

Fertilization

Sperm (n)

Seed coat

Zygote(2n)

Zygote developsinto embryo, andovule becomes seed.

Food supply

Embryo (2n)Seed

Meiosis

Sporangium (2n)

Integument

Pollination

Meiosis

Haploid (n)

Diploid (2n)

Mature sporophyte

Egg (n)

Fertilization

Sperm (n)

Seed coat

Zygote(2n)

Zygote developsinto embryo, andovule becomes seed.

Food supply

Embryo (2n)Seed

7 Seed germinates,and embryo grows into seedling.

17.7 A pine tree is a sporophyte with gametophytes in its cones

In pollination, a pollen grain lands on a scale in an ovulate cone and enters an ovule

– The scales then grow together, sealing up the cone

– Within the sealed cone, the gametophytes produce gametes

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

17.8 The flower is the centerpiece of angiosperm reproduction

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 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

Video: Flower Blooming (time lapse)

Stamen

Anther

Filament

Receptacle

Stigma

Carpel

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

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

The 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 a tiny female gametophyte, including the egg

3. A pollen tube from the pollen grain to the ovule carries a sperm that fertilizes the egg to form a zygote

4. Each ovule develops into a seed, consisting of an embryo (a new sporophyte) with a food supply and a seed coat

5. The ovary wall forms a fruit

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

Animation: Plant Fertilization

Video: Flowering Plant Life Cycle (time lapse)

Animation: Seed Development

Meiosis

Egg (n)

Haploid spores in anthers develop intopollen grains: male gametophytes.

Meiosis

Pollen grains (n)

Haploid (n)

Diploid (2n)

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

Meiosis

Haploid (n)

Diploid (2n)

Egg (n)

Meiosis

Pollen grains (n)

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

3 Pollination andgrowth of pollen tube

Stigma

Pollen grain

Pollen tube

Fertilization

Meiosis

Haploid (n)

Diploid (2n)

Egg (n)

Fertilization

Zygote(2n)

Meiosis

Pollen grains (n)

Stigma

Pollen grain

Pollen tube

Meiosis

Haploid (n)

Diploid (2n)

Egg (n)

Fertilization

Seed coat

Zygote(2n)

Food supply

Embryo (2n)

Meiosis

Pollen grains (n)

Stigma

Pollen grain

Pollen tube

Fruit(matureovary)

Meiosis

Haploid (n)

Diploid (2n)

Egg (n)

Fertilization

Seed coat

Zygote(2n)

Food supply

Embryo (2n)

Meiosis

Pollen grains (n)

Stigma

Pollen grain

Pollen tube

Fruit(matureovary)

Stigma

Anther

Sporophyte (2n)

Seed germinates,and embryogrows intoplant.

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

Fruits, ripened ovaries of flowers, are adaptations that disperse seeds

– Some rely on wind for seed dispersal

– Some hitch a ride on animals

– Fleshy, edible fruits attract animals

Animation: Fruit Development

17.11 CONNECTION: 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 such as nutmeg, cinnamon, cumin, cloves, ginger, and licorice are also angiosperm fruits

17.12 EVOLUTION CONNECTION: Pollination by animals has influenced angiosperm evolution

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

17.13 CONNECTION: Plant diversity is an irreplaceable resource

More than 50,000 square miles of forest are cleared every year

– Replanted areas have greatly reduced biological diversity

Loss of forests has greatly reduced diversity of life on Earth

– The loss of plant diversity removes potentially beneficial medicines

– More than 25% of prescription drugs are extracted from plants

17.14 Fungi absorb food after digesting it outside their bodies

Fungi are absorptive heterotrophic eukaryotes that digest their food externally and absorb the nutrients

Most fungi consist of a mass of threadlike hyphaemaking up a mycelium

– Hyphal cells are separated by cross-walls with pores large enough for ribosomes, mitochondria, and nuclei to cross

– Some are multinucleate without cross-walls

– Hyphae have a huge surface area to secrete digestive enzymes and absorb food

Fungal hyphae are surrounded by a cell wall with chitin

Animation: Fungal Reproduction and Nutrition

Mycelium

17.15 Fungi produce spores in both asexual and sexual life cycles

Many fungal species can reproduce both sexually and asexually

Fungi produce huge numbers of asexual spores, each of which can germinate to form a new fungus

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 inside specialized reproductive structures and disperse haploid spores

17.15 Fungi produce spores in both asexual and sexual life cycles

Video: Allomyces Zoospore Release

Video: Phlyctochytrium Zoospore Release

Fusion of cytoplasm

Heterokaryoticstage

Spore-producingstructures

Asexualreproduction

Spores(n)

Diploid (2n)

Haploid (n)

Heterokaryotic (n + n)(unfused nuclei)

Sexualreproduction

Zygote(2n)

Fusion of nuclei

Spore-producingstructures

Spores (n)

Mycelium

Meiosis

Germination

17.16 Fungi are classified into five groups

Sexual reproductive structures are used to classify fungi

– Fungi with no known sexual stage are known as imperfect fungi

Fungi likely evolved from an aquatic, flagellated ancestor shared with animals

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

Animals and fungi diverged into separate lineages 1.5 billion years ago

The oldest fungal fossils are 460 million years old

Chytrids

Zygomycetes(zygote fungi)

Glomeromycetes(arbuscularmycorrhizal fungi)

Ascomycetes(sac fungi)

Basidiomycetes(club fungi)

Zygomycetes

– Zygote fungi form resistant zygosporangia in which haploid spores form by meiosis

– This group includes black bread mold

Glomeromycetes

– These fungi form mycorrhizae, in which invasive hyphae branch into treelike arbuscules within plant roots

– 90% of plants have symbiotic partnerships with glomeromycetes

Ascomycetes

– Sac fungi form saclike asci, which produce sexual spores

– They range in size from yeasts to elaborate morels and cup fungi

– Some form lichens in association with green algae or cyanobacteria

Basidiomycetes

– Club fungi are the mushrooms, puffballs, and shelf fungi

– They have club-shaped spore-producing structures called basidia

– These fungi are important forest decomposers

17.17 Fungal groups differ in their life cycles and reproductive structures

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, which develops into a thick-walled structure that can tolerate dry, harsh conditions

– Under favorable conditions, the parental nuclei fuse and the diploid nucleus undergoes meiosis to form haploid spores

Zygosporangium (n + n)

Spores(n)

Diploid (2n)

Haploid (n)

Heterokaryotic (n + n)

Meiosis

Mycelia ofdifferentmating types

Cells fuse

Youngzygosporangium(heterokaryotic)

Sporangium

1 Fusion ofnuclei

17.17 Fungal groups differ in their life cycles and reproductive structures

Hyphae of different mating types fuse to form a heterokaryotic mycelium, which grows to produce a mushroom

– Haploid nuclei fuse to form diploid nuclei in the club-shaped cells called basidia that line the gills of the mushroom

– Each diploid nucleus undergoes meiosis to form haploid spores

Diploid (2n)

Haploid (n)

Fusion of two hyphaeof different mating types

Diploid (2n)

Haploid (n)

1Growth ofheterokaryotic mycelium

Mushroom

Diploid (2n)

Haploid (n)

Mushroom

Diploid nuclei3

Basidia

Fusion ofnuclei

Diploid (2n)

Haploid (n)

Mushroom

Diploid nuclei3Fusion of

nuclei

Basidia

Meiosis

Haploidnuclei

Sporesreleased

Spores (n)

Diploid (2n)

Haploid (n)

Mushroom

Diploid nuclei3Fusion of

nuclei

Basidia

Meiosis

Haploidnuclei

Sporesreleased

Spores (n)

Germinationof sporesand growthof mycelia

17.18 CONNECTION: Parasitic fungi harm plants and animals

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

Ergots

17.19 Lichens consist of fungi living in close association with photosynthetic organisms

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

Fungal hyphae

Algal cell

Several species of ants and termites cultivate fungal gardens

The insects feed their fungi with leaves, weeding out undesirable fungi

– The fungi feed on the leaves

– The ants harvest the swollen hyphal tips

Farmer insects and fungal “crops” have been evolving together for over 50 million years

17.20 Some fungi have mutually beneficial relationships with ants

17.21 CONNECTION: Fungi have enormous ecological benefits and practical uses

Fungi have many practical uses for humans

– Some fungi can break down toxic pollutants, including pesticides like DDT and cancer-causing chemicals

– Fungi may be able to clean up oil spills and chemical messes

– We eat many fungi, from mushrooms to cheeses modified by fungi

– Yeasts produce alcohol and cause bread to rise

– Fungi provide antibiotics that are used to treat bacterial disease

– Fungi are playing important new roles in molecular biology and biotechnology

PenicilliumStaphylococcusaureus

Zone ofinhibitedgrowth

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

ANCESTRALGREEN ALGA

A. Pine tree, a gymnosperm B. Puffball, a club fungus

You should now be able to

1. Describe the key plant adaptations for life on land

2. Describe the alternation of generation life cycle; explain why it appears that this cycle has evolved independently in algae and land plants

3. Describe the key events of the moss, fern, and pine life cycles

4. Explain how coal was formed; explain why coal, oil, and natural gas are called fossil fuels

5. Describe the parts of a flower and explain their functions

6. Describe the stages of the angiosperm life cycle

7. Describe angiosperm adaptations that promote seed dispersal

8. Explain how flowers are adapted to attract pollinators

9. Compare the life cycles and reproductive structures in the fungal groups

10. Describe the structure and characteristics of lichens

11. Describe the positive ecological and practical roles of fungi

chapter 17 plants, fungi, and the colonization of...

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