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Plants, Fungi, and the Colonization of Land

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1 Plants, Fungi, and the Colonization of Land
Chapter 17 Plants, Fungi, and the Colonization of Land

2 Plants and Fungi-A Beneficial Partnership
Mycorrhizae are mutually beneficial associations of plant roots and fungi The fungi help plants obtain nutrients and water and protect plant roots from parasites Sugars produced by the plant nourish the fungi Modern agricultural practices often disrupt mycorrhizal fungi, making fertilizers necessary Beneficial relationships with fungi may have been important as plants adapted to life on land



17.1 Plants evolved from green algae Plants and present-day green algae called charophyceans probably evolved from a common ancestor Morphological, biochemical, and genetic similarities Adaptations enabling permanent life on land appeared in ancestral green algae about 475 million years ago Early environment suitable for plant life



8 17.2 Plants have adaptations for life on land
Plants and algae are both multicellular photosynthetic eukaryotes A set of derived characteristics distinguishes plants as a clade Plants and algae interact differently with their environments

9 Key adaptations of plants to four challenges of terrestrial life
Obtaining resources from both soil and air Roots provide anchorage and absorb water and minerals from soil Leaves absorb CO2 from the air Elongation of apical meristems maximizes exposure to resources Vascular tissue (xylem and phloem) connects subterranean and aerial parts

10 Supporting the plant body
Lignin thickens and strengthens cell walls Maintaining moisture Waxy cuticle covering aerial parts prevents direct gas exchange Stomata control gas exchange and prevent water loss

11 Plants are embryophytes
Reproducing on land Male and female gametangia (protective jackets) surround gamete-producing cells Plants are embryophytes Fertilized egg develops into an embryo while attached to and nourished by the parent plant All plant life cycles have alternation of generations Haploid spores are produced in protective sporangia

12 LE 17-2a Plant Reproductive structures (flowers)
contain spores and gametes Leaf performs photosynthesis Cuticle reduces water loss; stomata allow gas exchange Stem supports plant and may perform photosynthesis Surrounding water supports alga Alga Whole alga performs photosynthesis; absorbs water, CO2, and minerals from the water Roots anchor plant; absorb water and minerals from the soil Holdfast anchors alga

13 17.3 Plant diversity reflects the evolutionary history of the plant kingdom
Diversification of plants about 475 million years ago gave rise to bryophytes Mosses, hornworts, and liverworts Lack vascular tissue Need to be covered with a film of water for sperm to swim to egg


15 Vascular plants originated about 420 million years ago
Have supportive vascular tissues Seedless vascular plants Lycophytes: club mosses Pterophytes: ferns and their relatives Well-developed roots and rigid stems Flagellated sperm that swim to eggs


17 Vascular plants with seeds evolved about 360 million years ago
Seed: embryo packaged with food supply within a protective covering Seed plant lineage accounts for over 90% of plants living today Key adaptations of seed plants Seeds allow embryos to spread to diverse habitats Pollen allows for passive transfer of sperm to egg

18 Gymnosperms are among the earliest seed plants
Seeds not protected in specialized chambers Largest clade comprises cone-bearing confers


20 Angiosperms (flowering plants) evolved about 140 million years ago
Flowers are complex reproductive structures that develop seeds within protective ovaries The great majority of living plants are angiosperms


22 Summary: Four key adaptations for life on land distinguish the main lineages of the plant kingdom
Dependent embryos: all plants Lignified vascular tissues: all vascular plants Seeds: gymnosperms and angiosperms Flowers: angiosperms

23 Seedless vascular plants Origin of vascular plants
LE 17-3a Land plants Vascular plants Bryophytes (nonvascular plants) Seedless vascular plants Seed plants Gymnosperms Angiosperms Liverworts Hornworts Mosses Lycophytes (club mosses and relatives) Pterophytes (ferns and relatives) Origin of seed plants (about 360 mya) Origin of vascular plants (about 420 mya) Origin of land plants (about 475 mya)

17.4 Haploid and diploid generations alternate in plant life cycles Haploid gametophyte produces eggs and sperm by mitosis Fertilization results in a diploid zygote Zygote develops into the diploid sporophyte, which produces haploid spores by meiosis Spores grow into gametophytes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

25 Gametophyte plant (n) Mitosis Mitosis Mitosis Sporophyte plant (2n)
LE 17-4 Key Gametophyte plant (n) Haploid (n) Diploid (2n) Mitosis Mitosis Sperm Spores (n) Gametes (n) Egg Meiosis Fertilization Zygote (2n) Mitosis Sporophyte plant (2n)

26 17.5 Mosses have a dominant gametophyte
A mat of moss is mostly gametophytes, which produce eggs and swimming sperm Haploid gametes develop in gametangia After fertilization, diploid zygote remains in the gametophyte Mitosis produces a smaller sporophyte, which remains attached to the gametophyte

27 Animation: Moss Life Cycle
Meiosis in sporangia produces haploid spores, which are released from sporangium Spores undergo mitosis and develop into gametophytes Animation: Moss Life Cycle

28 LE 17-5 Gametophytes (n) Key Haploid (n) Male Diploid (2n) Mitosis and
development Sperm (n) (released from gametangium) Spores (n) Female Egg (n) Fertilization Sporangium Stalk Sporophytes (growing from gametophytes) Meiosis Sporophyte (2n) Zygote (2n) Mitosis and development

29 17.6 Ferns, like most plants, have a dominant sporophyte
Small haploid gametophyte produces sperm that swim to the egg Zygote remains on the gametophyte Zygote undergoes mitosis and develops into independent diploid sporophyte Meiosis in sporangia produces haploid spores Spores are released and develop into gametophytes by mitosis

30 LE 17-6 Key Haploid (n) Diploid (2n) Sperm (n) (released from male
gametangium) Mitosis and development Gametophyte (n) (underside) Female gametangium (n) Spores (n) Egg (n) Meiosis Fertilization Clusters of sporangia Zygote (2n) New sporophyte (2n) growing out of gametophyte Mitosis and development Mature sporophyte (independent of gametophyte)

31 Animation: Fern Life Cycle

32 17.7 Seedless plants dominated vast "coal forests"
Ferns and lycophytes were once the dominant plants on Earth Tropical swamp forests of the Carboniferous period generated a lot of organic matter Their remains formed the fossil fuels peat and coal After the Carboniferous period, climate change provided opportunities for seed plants Gymnosperms dominated through the Mesozoic era


34 17.8 A pine tree is a sporophyte with tiny gametophytes in its cones
Roles of haploid and diploid generations changed drastically as plants evolved on land All reproductive stages of conifers are on sporophytes in cones; ovule is the key adaptation Ovulate cone has scales bearing ovules Smaller pollen cones make haploid spores that develop into pollen grains

35 Pollination occurs; meiosis occurs in a spore mother cell in the ovule
One surviving haploid spore develops into the female gametophyte Tube grows out of each pollen grain and releases sperm near an egg Zygote develops into sporophyte embryo; ovules transform into seeds Seeds disperse, germinate; embryo grows into seedling

36 LE 17-8 A haploid spore cell in ovule develops into
female gametophyte, which makes eggs. Ovulate cone bears ovules. Scale Female gametophyte (n) Ovule Meiosis Sporangium (2n) Male gametophyte (pollen) grows tube to egg and makes and releases sperm. Spore mother cell (2n) Integument Eggs (n) Pollen grains (male gametophytes) (n) Pollination Sperm (n) Fertilization Meiosis Male gametophyte (pollen grain) Sporangia in pollen cone produce spores by meiosis; spores develop into pollen grains. Mature sporophyte Seed coat Embryo (2n) Zygote (2n) Food supply Zygote develops into embryo, and ovule becomes seed. Key Haploid (n) Seed germinates, and embryo grows into seedling. Diploid (2n) Seed

37 Animation: Pine Life Cycle

38 17.9 The flower is the centerpiece of angiosperm reproduction
Flowers are the site of pollination and fertilization Generate fruits, which contain seeds A flower is a short stem with modified leaves Sepals enclose flower before it opens Petals are important in attracting pollinators

39 Video: Flower Blooming Time Lapse
Reproductive structures Stamen: a stalk bearing an anther in which pollen grains develop Carpel: a stalk with an ovary and a sticky stigma that traps pollen Ovary: protective chamber containing ovules in which eggs develop Video: Flower Blooming Time Lapse


41 Stigma Anther Style Carpel Stamen Ovary Filament Petal Sepal Ovule
LE 17-9b Stigma Anther Style Carpel Stamen Ovary Filament Petal Sepal Ovule Receptacle

42 17.10 The angiosperm plant is a sporophyte with gametophytes in its flowers
The angiosperm life cycle differs in two main ways from the gymnosperm life cycle Gametophytes develop in flowers Seeds are produced in an ovary and packaged inside a fruit Steps of the angiosperm life cycle Meiosis and mitosis in anther result in male gametophytes (pollen grains)

43 Meiosis and mitosis in ovule lead to female gametophytes, one of which becomes an egg
Tube grows from pollen grain, carries sperm to egg in ovule Zygote forms A seed develops from each ovule Ovary's wall thickens, forming fruit Seed germinates, embryo grows and develops into mature sporophyte

44 LE 17-10 Haploid spores in anthers develop into pollen grains:
male gametophytes. Pollen grains (n) Pollination and growth of pollen tube Meiosis Stigma Haploid spore in each ovule develops into female gametophyte, which produces egg. Pollen grain Stigma Anther Pollen tube Meiosis Egg (n) Ovule Ovary Sporophyte (2n) Ovule Sperm Seed germinates, and embryo grows into plant. Seeds Food supply Fertilization Fruit (mature ovary) Seed coat Key Haploid (n) Seed Zygote (2n) Diploid (2n) Embryo (2n)

45 Video: Flowering Plant Life Cycle (time lapse)
Animation: Fruit Development Animation: Plant Fertilization Animation: Seed Development

46 17.11 The structure of a fruit reflects its function in seed dispersal
Fruits are adaptations that disperse seeds Largely depend on wind and animals for dispersal




50 17.12 Agriculture is based almost entirely on angiosperms
CONNECTION 17.12 Agriculture is based almost entirely on angiosperms Angiosperms provide most of our food and other important commercial products Humans intervened in plant evolution by selectively breeding to improve quality

51 17.13 Interactions with animals have profoundly influenced angiosperm evolution
Angiosperms are a major source of food for land animals Most angiosperms depend on animals to aid in pollination Coevolution is the mutual evolutionary influence between two species Various plant and animal adaptations benefit both species Examples: color, shape, timing




55 Video: Bee Pollinating Video: Bat Pollinating Agave Plant

56 CONNECTION 17.14 Plant diversity is a nonrenewable resource
Plant biodiversity is being reduced at an unprecedented rate The threat is especially noteworthy in forests The majority of plant genetic diversity is found in the world's rain forests What is lost is irreplaceable Medicinal plants, food, timber, clean water and air, animal habitat Efforts are underway to develop sustainable forest management



59 17.15 Fungi absorb food after digesting it outside their bodies
Fungi are heterotrophic eukaryotes that digest their food externally and absorb the nutrients Like animals, must obtain organic molecules from other organisms Fungi are vital as mycorrhizal partners of plants and as decomposers Fungi are found virtually everywhere


61 Fungi usually consist of a mass of threadlike hyphae
Branch repeatedly into a feeding structure called a mycelium Are surrounded by a cell wall made of chitin Grow at a phenomenal rate, extending into new territory Develop a huge surface area for digesting food

62 LE 17-15b Hypha Mycelium


64 17.16 Fungi produce spores in both asexual and sexual life cycles
Many fungal species can reproduce sexually or asexually Many sexually reproducing fungi have a heterokaryotic phase Fusion of haploid hyphae produces cells containing nuclei from two parents After varying lengths of time, parent nuclei fuse and form short-lived diploid phase Haploid spores are produced by meiosis in specialized structure

65 LE 17-16 Key Heterokaryotic stage Haploid (n) Heterokaryotic (n + n)
(unfused nuclei) Fusion of nuclei Diploid (2n) Fusion of cytoplasm Zygote (2n) Spore-producing structures Sexual reproduction Meiosis Spores (n) Asexual reproduction Mycelium Spore-producing structures Germination Germination Spores (n)

66 Animation: Fungal Reproduction and Nutrition

67 Asexually reproducing fungi
Molds: fungi that reproduce by producing spores, often at the tips of specialized hyphae Yeast: single-celled fungi that reproduce by cell division or budding

68 17.17 Fungi can be classified into five groups
Fungi probably evolved from an aquatic, flagellated ancestor shared with animals Animals and fungi diverged about 1.5 billion years ago Fungi classification is often based on sexual reproductive structures Those with no known sexual stage are called imperfect fungi

69 LE 17-17a Chytrids Zygomycetes (zygote fungi) Ascomycetes (sac fungi)
Basidiomycetes (club fungi) Glomeromycetes (arbuscular mycorrhizal fungi)

70 Most biologists recognize five groups of fungi
Chytrids Have flagellated spores Decomposers and parasites Zygomycetes Form haploid spores in resistant zygosporangia Fast-growing molds such as black bread mold; animal parasites


72 Glomeromycetes Similar to zygomycetes but genetically distinct Form distinctive mycorrhizae with treelike arbuscules Ascomycetes (sac fungi) Have saclike asci that produce spores in sexual reproduction Some devastating plant pathogens; part of symbiotic lichens



75 Basidiomycetes (club fungi)
Have a club-shaped spore-producing basidium Mushrooms, puffballs, shelf fungi


77 Video: Allomyces Zoospore Release
Video: Phlyctochytrium Zoospore Release

78 17.18 Fungal groups differ in their life cycles and reproductive structures
Much of the success of fungi is due to their reproductive capacity Black bread mold life cycle is typical of zygomycetes As hyphae expand through its food, the fungus reproduces asexually When the food is depleted, the fungus reproduces sexually Ascomycetes are similar

79 LE 17-18a Key Haploid (n) Heterokaryotic (n + n)
Zygosporangium (n  n) Diploid (2n) Mycelia of different mating types Cells fuse Fusion of nuclei Young zygosporangium (heterokaryotic) Meiosis Sporangium Spores (n)

80 The life cycle of a basidiomycete has five stages
A heterokaryotic mycelium forms by fusion of two different mating types A mushroom develops and grows Specialized cells from the gills contain the diploid nuclei from nuclei fusion Haploid spores are formed by meiosis and then released Germination takes place, and a haploid mycelium grows

81 LE 17-18b Key Diploid nuclei Haploid (n) Fusion of nuclei
Heterokaryotic (n+n) Diploid (2n) Meiosis Spores released Haploid nuclei Basidia Spores (n) Mushroom Germination of spores and growth of mycelia Growth of heterokaryotic mycelium Fusion of two hyphae of different mating types

82 17.19 Parasitic fungi harm plants and animals
CONNECTION 17.19 Parasitic fungi harm plants and animals Of 100,000 known species of fungi, about 30% are parasites, mostly of plants Fungi have changed landscapes Example: Dutch elm disease Fungi are serious agricultural pests Example: corn smut, ergot A mycosis is a fungal infection of animals Examples: ringworm, vaginal yeast infections




86 17.20 Lichens consist of fungi living mutualistically with photosynthetic organisms
Lichens consist of algae or cyanobacteria held in a mass of fungal hyphae Fungus receives food from the photosynthesis of its partner Alga or cyanobacterium receives housing, water, and the minerals trapped by the hyphal network Lichens are able to live in difficult conditions but cannot withstand air pollution


88 LE 17-20b Fungal hyphae Algal cell Colorized SEM 1,000

89 17.21 Fungi also form mutualistic relationships with animals
The digestive abilities of fungi benefit some animals Break down plant material in guts of grazing animals Digest plants in ant or termite "farms"


91 17.22 Fungi have enormous ecological benefits and practical uses
CONNECTION 17.22 Fungi have enormous ecological benefits and practical uses As mycorrhizae, fungi supply essential nutrients to plants Fungi are essential decomposers in ecosystems Consume almost any carbon-containing substance Fungi also have practical uses for humans Provide antibiotics and food Are useful in research


93 LE 17-22b Staphylococcus aureus Penicillium Zone of inhibited growth

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