Fungi Fungi. Chapter 22. Heterotrophs that secrete digestive enzymes on organic matter and absorb released nutrients

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1 22.1 Fungi Fungi Chapter 22 Heterotrophs that secrete digestive enzymes on organic matter and absorb released nutrients Saprobes feed on organic remains (major decomposers in ecosystems) Symbionts, harmless or beneficial Parasites Include single-celled yeasts and large multicelled species A Fungal Symbiont: Lichen Fungal Groups Three major groups Zygote fungi, sac fungi, and club fungi 1

2 Fungal Life Cycles Fungal Spore-Producing Structures Sexual and asexual spore production In multicelled species Spores germinate, give rise to filaments (hyphae) Filaments grow into extensive mesh (mycelium) Sexual reproduction Hyphae form short-lived, spore-producing reproductive structures (mushrooms) 22.2 Zygomycetes: Zygote Fungi Include molds that grow on foods (fruits, breads) A few species are dangerous pathogens 22.3 Ascomycetes: Sac Fungi The most diverse group Single-celled yeasts and multicelled species Hyphae: Continuous tubes with no cross-walls 2

3 Predatory Sac Fungus 22.4 Basidiomycetes: Club Fungi Multicelled club fungi also have hyphae with cross-walls and can produce complex reproductive structures (mushrooms) Many club fungi are major decomposers in forest habitats Life Cycle: Club Fungi Lichen A composite organism that consists of a fungal symbiont and one or more photoautotrophs (green algae or cyanobacteria) The fungus makes up most of the lichen, and obtains nutrients from its photosynthetic partner 3

4 Lichens Mycorrhizae (Fungus-Roots) Symbiotic interaction between fungus and plant Fungal hyphae surround or penetrate roots and supplement their absorptive surface area Fungus shares some absorbed mineral ions with the plant, gets some carbohydrates back A Mycorrhiza 22.6 Fungal Infections A number of pathogenic fungi can destroy crops, spoil food, and cause diseases in humans Examples: Athlete s foot, apple scab, ergot 4

5 Poisonous Mushrooms Plant Evolution Chapter Evolutionary Trends Plants evolved about 475 million years ago from charophytes (a group of green algae) Most modern plants are photoautotrophs on land Plant Adaptations to Land Most groups are adapted to dry and often cold habitats through structural modifications Stomata across epidermal surfaces Waterproof cuticle Lignin-reinforced tissues Xylem and phloem (vascular tissues) 5

6 Alternation of Generations Land plants alternate between gametophyte (haploid) and sporophyte (diploid) generations From Haploid to Diploid Dominance Dominant stages Haploid body (algae and nonvascular plants) Diploid body (most modern plants) Complex sporophytes retain, nourish, and protect new generations through seasons Production of two spore types allows evolution of pollen grains and seeds in two lineages Evolutionary Trends in Plant Life Cycles Fig. 21.3, p.335 6

7 21.2 Bryophytes Mosses, liverworts, and hornworts Nonvascular (no xylem or phloem) Life Cycle: Bryophytes Sperm swim through water droplets or film of water to eggs Sporophytes stay attached to larger gametophytes Spores that give rise to gametophytes are winddispersed Life Cycle: Bryophytes female gametophytes male gametophyte thallus (leaflike part) close-up of gemmae Fig. 21.7, p.337 7

8 Peat Bogs: Sphagnum 21.3 Seedless Vascular Plants Lycophytes, horsetails, whisk ferns, true ferns Life Cycle: Seedless Vascular Plants Dominated by the sporophyte The sporophyte (still attached to the gametophyte) grows, develops. Spore-bearing structures Sori of ferns Sperm swim through water to reach eggs zygote fertilization egg sperm eggproducing structure spermproducing structure Diploid Stage Haploid Stage rhizome mature gametophyte (underside) sorus meiosis Spores develop. Spores are released. A spore germinates, grows into a gametophyte. Fig. 21.9, p.339 8

9 Fern Diversity 21.5 Seed-Bearing Vascular Plants Gymnosperms and flowering plants (angiosperms) Life Cycle: Seed Plants 21.6 Gymnosperms: Naked Seeds Microspores become pollen grains in which sperm-producing male gametophytes develop Megaspores give rise to female gametophytes (with eggs) inside ovules Seed: A mature ovule Part of ovule forms nutritive tissue and seed coat (protects embryo sporophyte) Conifers, cycads, ginkgos, and gnetophytes Many are well adapted to dry climates Life cycle: No ovaries Ovules form on exposed surfaces of strobili or (in conifers) female cones 9

10 Gymnosperms section through one ovule (the red cut in the diagram to the left) surface view of a female cone scale (houses two ovules) ovule spermproducing cell mature sporophyte seedling pollen tube Germinating pollen grain (the male gametophyte). Sperm nuclei form as the pollen tube grows toward the egg. seed coat embryo nutritive tissue seed formation surface view of a scale of a male strobilus (houses two pollen sacs) zygote fertilization (view inside an ovule) eggs female gametophyte Diploid Stage Haploid Stage pollination (wind deposits pollen grain near ovule) section through a pollen sac (red cut) meiosis Microspores form, develop into pollen grains. meiosis Megaspores form; one develops into the female gametophyte. Fig , p Angiosperms: Flowering Plants Only angiosperms have flowers Many coevolved with birds, bees, bats, and other animal pollinators angiosperms (flowering plants) Most widely distributed and diverse plant group Two largest classes: Dicots and monocots cycads ferns gymnosperms ginkgo other genera Fig , p

11 Evolution of Flowering Plants petal stamen (microspores form here) carpel (megaspores form here) sepal ovule in an ovary Fig , p Life Cycle: Flowering Plants Monocot Life Cycle: Lily Monocot life cycle: An example of sexual reproduction in flowering plants Formation of pollen and eggs Double fertilization produces an embryo sporophyte and nutritive tissue that supports it Protective seeds form in ovaries Outer ovary tissues later develop into fruits 11

12 Summary: Comparison of Major Plant Groups Summary: Plant Evolutionary Trends 12