Lewis/Life - Review of Key Concepts

Review of Key Concepts - Chapter 24

Fungi are eukaryotes with chitinous cell walls. They do not photosynthesize, do not have nervous tissue, use glycogen as a carbohydrate source, and are symbionts or saprophytes.
Fungi may be unicellular yeasts, multicellular with hyphae strands organized into mycelia, or dimorphic, undergoing both phases during the life cycle. The visible portion of a fungus is a thallus. Hyphae may be coenocytic (continuous) or septate (consisting of distinct cells).
Fungal reproduction may be asexual, as in budding or when a parental cell divides in two, or sexual, so that haploid sex cells combine, either in one mycelium or between two individuals. Insects may assist fungi in distributing sex cells.
Fungi occupy many habitats, range greatly in size, and are genetically diverse. Molecular data place them most closely related in an evolutionary sense to animals.
Type of reproductive structure distinguishes the zygomycetes, ascomycetes, and basidiomycetes. Zygomycetes have zygospores and feed on decaying plant and animal matter. Ascomycetes have asci containing eight haploid nuclei each. Fungi growing on spoiled foods are ascomycetes. The basidiomycetes, including mushrooms, have clublike hyphal tips. The deuteromycetes cannot be classified by reproductive structures. Lichens consist of a fungus associated with an alga or cyanobacterium. A lichen has properties its constituent organisms lack.
Fungi are decomposers, forming soil and recycling carbon and other elements. Fungal fossils are rare. This kingdom split from other eukaryotes about a billion years ago.
Saprophytic fungi secrete digestive enzymes that break down macromolecules in the environment, which the fungus then absorbs. Mycorrhizae are associations between fungi and the roots of vascular plants. Ectomycorrhizae surround roots; endomycorrhizae infiltrate deeper into the plant. Both help plant roots absorb water and minerals, while obtaining sugars from the plant.
Mycoses, or fungal infections, affect many types of organisms. Human mycoses, classified by their effect on the body, may be superficial, cutaneous, subcutaneous, systemic, or opportunistic.