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

5. PLANT EVOLUTION AND DIVERSITY
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)

24. ALTERNATION OF GENERATIONS AND PLANT LIFE CYCLES
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