Chapter 17
Plants, Fungi, and the Colonization of Land PowerPoint Lectures for Biology: Concepts and Connections, Fifth Edition – Campbell, Reece, Taylor, and Simon
Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
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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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
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• 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
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• 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Roots anchor plant; absorb water and minerals from the soil
Whole alga performs photosynthesis; absorbs water, CO2, and minerals from the water Holdfast anchors alga
Alga
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
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• 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
– Gymnosperms are among the earliest seed plants • Seeds not protected in specialized chambers • Largest clade comprises cone-bearing confers
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– 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
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• 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
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LE 17-3a Land plants Vascular plants Bryophytes (nonvascular plants)
Seedless vascular plants
Seed plants
Origin of seed plants (about 360 mya)
Origin of vascular plants (about 420 mya)
Origin of land plants (about 475 mya)
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
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LE 17-4
Key Haploid (n)
Gametophyte plant (n)
Diploid (2n) Sperm Spores (n)
Gametes (n)
Meiosis
Egg
Fertilization
Zygote (2n)
Sporophyte plant (2n)
17.5 Mosses have a dominant gametophyte •
A mat of moss is mostly gametophytes, which produce eggs and swimming sperm 1. Haploid gametes develop in gametangia
2. After fertilization, diploid zygote remains in the gametophyte 3. Mitosis produces a smaller sporophyte, which remains attached to the gametophyte
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4. Meiosis in sporangia produces haploid spores, which are released from sporangium 5. Spores undergo mitosis and develop into gametophytes
Animation: Moss Life Cycle Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 17-5 Gametophytes (n)
Key Haploid (n) Diploid (2n)
Male Mitosis and development
Sperm (n) (released from gametangium)
Spores (n)
Female
Egg (n) Fertilization
Sporangium Stalk Meiosis
Sporophytes (growing from gametophytes) Zygote (2n)
Sporophyte (2n)
Mitosis and development
17.6 Ferns, like most plants, have a dominant sporophyte 1. Small haploid gametophyte produces sperm that swim to the egg 2. Zygote remains on the gametophyte 3. Zygote undergoes mitosis and develops into independent diploid sporophyte
4. Meiosis in sporangia produces haploid spores 5. Spores are released and develop into gametophytes by mitosis Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 17-6 Key Haploid (n) Diploid (2n)
Sperm (n) (released from male gametangium)
Mitosis and development
Spores (n)
Female gametangium (n)
Gametophyte (n) (underside) Egg (n)
Fertilization
Meiosis
Clusters of sporangia
Zygote (2n) New sporophyte (2n) growing out of gametophyte Mitosis and development
Mature sporophyte (independent of gametophyte)
Animation: Fern Life Cycle
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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
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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 1. Ovulate cone has scales bearing ovules 2. Smaller pollen cones make haploid spores that develop into pollen grains
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3. Pollination occurs; meiosis occurs in a spore mother cell in the ovule
4. One surviving haploid spore develops into the female gametophyte 5. Tube grows out of each pollen grain and releases sperm near an egg 6. Zygote develops into sporophyte embryo; ovules transform into seeds 7. Seeds disperse, germinate; embryo grows into seedling Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 17-8 A haploid spore cell in ovule develops into female gametophyte, which makes eggs.
Scale
Ovulate cone bears ovules. Ovule
Pollen grains (male gametophytes) (n)
Female gametophyte (n)
Meiosis Sporangium (2n) Spore mother cell (2n) Integument Eggs (n) Pollination
Male gametophyte (pollen) grows tube to egg and makes and releases sperm.
Sperm (n)
Fertilization
Male gametophyte (pollen grain)
Meiosis 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) Diploid (2n)
Seed germinates, and embryo grows into seedling.
Seed
Animation: Pine Life Cycle
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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
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– 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 17-9b
Stigma Anther Style Stamen Ovary
Filament
Petal Sepal Ovule
Receptacle
Carpel
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 1. Meiosis and mitosis in anther result in male gametophytes (pollen grains)
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2. Meiosis and mitosis in ovule lead to female gametophytes, one of which becomes an egg 3. Tube grows from pollen grain, carries sperm to egg in ovule 4. Zygote forms 5. A seed develops from each ovule 6. Ovary's wall thickens, forming fruit 7. Seed germinates, embryo grows and develops into mature sporophyte Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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.
Stigma Anther
Pollen grain Pollen tube
Meiosis Egg (n) Ovule Ovary Ovule
Sporophyte (2n)
Sperm Seed germinates, and embryo grows into plant.
Seeds
Food supply Fruit (mature ovary) Key Haploid (n) Diploid (2n)
Fertilization
Seed coat Seed Embryo (2n)
Zygote (2n)
Video: Flowering Plant Life Cycle (time lapse) Animation: Fruit Development
Animation: Plant Fertilization Animation: Seed Development
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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
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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
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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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Video: Bee Pollinating Video: Bat Pollinating Agave Plant
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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
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FUNGI 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
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LE 17-15b
Hypha
Mycelium
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
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LE 17-16
Key Heterokaryotic stage
Haploid (n) Heterokaryotic (n + n) (unfused nuclei) Diploid (2n)
Fusion of nuclei
Fusion of cytoplasm Zygote (2n)
Spore-producing structures Spores (n)
Asexual reproduction
Sexual reproduction
Meiosis
Mycelium Spore-producing structures Germination
Germination Spores (n)
Animation: Fungal Reproduction and Nutrition
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• 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
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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
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LE 17-17a
• 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Basidiomycetes (club fungi) – Have a club-shaped spore-producing basidium – Mushrooms, puffballs, shelf fungi
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Video: Allomyces Zoospore Release Video: Phlyctochytrium Zoospore Release
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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)
•
The life cycle of a basidiomycete has five stages
1. A heterokaryotic mycelium forms by fusion of two different mating types 2. A mushroom develops and grows 3. Specialized cells from the gills contain the diploid nuclei from nuclei fusion
4. Haploid spores are formed by meiosis and then released 5. Germination takes place, and a haploid mycelium grows Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 17-18b
Key
Diploid nuclei
Haploid (n) Heterokaryotic (n+n)
Fusion of nuclei Meiosis
Diploid (2n)
Basidia
Spores released
Haploid nuclei
Spores (n)
Mushroom
Germination of spores and growth of mycelia Growth of heterokaryotic mycelium
Fusion of two hyphae of different mating types
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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 17-20b
Fungal hyphae
Colorized SEM 1,000
Algal cell
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"
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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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 17-22b
Staphylococcus aureus
Penicillium Zone of inhibited growth
