Fungi

Fungi 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

Fungal Life Cycles 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)

Fungal Spore-Producing Structures

Zygomycetes: Zygote Fungi Include molds that grow on foods (fruits, breads) A few species are dangerous pathogens Hyphae: Continuous tubes with no cross-walls

Ascomycetes: Sac Fungi The most diverse group Single-celled yeasts and multicelled species

Predatory Sac Fungus

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

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

Fungal Infections A number of pathogenic fungi can destroy crops, spoil food, and cause diseases in humans Examples: Athlete’s foot, apple scab, ergot

Poisonous Mushrooms

Plant Evolution

Plant Adaptations to Land Most groups are adapted to dry and often cold habitats through structural modifications Stomata across epidermal surfaces Waterproof cuticle Xylem and phloem (vascular tissues)

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

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 wind-dispersed

Life Cycle: Bryophytes

female gametophytes male gametophyte thallus (leaflike part) close-up of gemmae

Peat Bogs: Sphagnum

Seedless Vascular Plants Lycophytes, horsetails, whisk ferns, true ferns

Life Cycle: Seedless Vascular Plants Dominated by the sporophyte Spore-bearing structures Sori of ferns Sperm swim through water to reach eggs

The sporophyte (still attached to the gametophyte) grows, develops. zygote rhizome sorus Diploid Stage fertilization meiosis Haploid Stage Spores are released. Spores develop. egg-producing structure egg mature gametophyte (underside) sperm-producing structure A spore germinates, grows into a gametophyte. sperm

Fern Diversity

Seed-Bearing Vascular Plants Gymnosperms and flowering plants (angiosperms)

Life Cycle: Seed Plants 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)

Gymnosperms: Naked Seeds 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

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 section through a pollen sac (red cut) surface view of a scale of a male strobilus (houses two pollen sacs) mature sporophyte seed coat embryo nutritive tissue zygote seedling seed formation Diploid Stage fertilization meiosis meiosis pollen tube Haploid Stage sperm-producing cell (view inside an ovule) pollination (wind deposits pollen grain near ovule) Microspores form, develop into pollen grains. Megaspores form; one develops into the female gametophyte. Germinating pollen grain (the male gametophyte). Sperm nuclei form as the pollen tube grows toward the egg. eggs female gametophyte

Angiosperms: Flowering Plants Only angiosperms have flowers Many coevolved with birds, bees, bats, and other animal pollinators Most widely distributed and diverse plant group Two largest classes: Dicots and monocots

angiosperms (flowering plants) cycads ferns gymnosperms ginkgo other genera

Evolution of Flowering Plants

petal stamen (microspores form here) sepal carpel (megaspores form here) ovule in an ovary

Life Cycle: Flowering Plants 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

Monocot Life Cycle: Lily

Summary: Plant Evolutionary Trends