政府采购限额标准和公开招标数额标准.pptVIP

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