Fungi

• Fungi


  • Eukaryotes that grow as single cells or as large, branching networks of multicellular filaments
• Fungi that absorb nutrients from dead organisms


  The world's most important decomposers
• Other fungi


  Specialize in absorbing nutrients from living organisms
• Most fungi that live in association with other organisms


  Benefit their hosts and thus are mutualists
• Roots of most land plants

  Colonized by mutualistic fungi that provide water and nitrogen and phosphorus to host plant
• Fungi living inside shoots of certain plants


  Help ward off herbivores by making toxic compounds
• Many insects


  Harbor single-celled fungi in their guts that aid digestion of plant material
• Some insects


  Grow gardens of fungi that they feed with pieces of leaves
• Fungi can be thought of as the master traders and recyclers in terrestrial ecosystems
• Some fungi


  Release nutrients from dead plants and animals
• Some fungi


  Transfer nutrients they obtain to living plants
• Because they recycle key elements and transfer key nutrients to plants, fungi profoundly influence productivity and biodiversity
• A handful of species can cause debilitating diseases in humans and crop plants
• Fungi nourish the plants that nourish us
• They affect climate change because they are critical to the carbon cycle on land
• There are about 300 species of parasitic fungi that cause human illness
• The incidence of fungal infections is relatively low, compared with the frequency of illness caused by other organisms
• The major destructive impact of fungi on people is through the food supply
• Fungi known as rusts, smuts, mildews, wilts, and blights


  Cause billions of dollars of crop losses each year
• Saprophytic fungi


  Responsible for losses due to spoilage of fruits and vegetables
• Fungi


  Have important economic and ecological impacts
• Beneficial impacts of fungi on humans


  • Source for many antibiotics, including penicillin
  • Mushrooms eaten in many cultures
  • Yeast used to make bread, cheese, soy sauce, tofu, beer, wine, and other foods
  • Fungal species ferment cacao seeds before chocolate is edible
  • Fungal enzymes used to improve characteristics of foods such as fruit juice, candy, and meat
• Mycorrhizal fungi


  Fungi that live in close association with plant roots
• Mycorrhizae


  Fungi along with roots
• Mycorrhizal fungi are absent


  Plant growth suffers
• Saprophytic Fungi Accelerate the Carbon Cycle on Land

  • Saprophytes are fungi that make their living by digesting dead plant material

  • The carbon cycle on land has two basic components:

  1. The fixation of carbon by land plants

  2. The release of CO2 from plants, animals, and fungi

  as the result of cellular respiration

  • For most carbon atoms, fungi connect the two components
• Analyzing Morphological Traits

  • Fungi have very simple bodies

  • Two growth forms exist

  1. Single-celled forms—yeasts

  2. Multicellular, filamentous forms—mycelia (singular: mycelium)

  • Some species adopt both forms
• Fungal Mycelium


  • All mycelia are dynamic
  • They constantly grow in the direction of food sources and die back in areas where food is running out
  • The body shape of a fungus can change almost continuously throughout its life
• Hyphae


  The long, narrow, frequently branching filaments, making up a mycelium
• Structure of Hyphae


  1. Each filament is separated into cells by cross-walls called septa

  2. Gaps in septa called pores enable materials to flow between compartments

  3. Nutrients can move rapidly through these pores, from regions of uptake to regions of growth
• Coenocytic Fungi


  • They lack septa entirely
  • These species are a single, gigantic, multinucleate cell
• Mycelia


  • Composed of branching networks of very thin hyphae
  • Have the highest surface-area-to-volume ratio observed in a multicellular organism
  • Nutrient and water absorption are extremely efficient
  • Prone to drying out
  • Most abundant in moist environments
• Reproductive spores


  • Resistant to drying out
  • Can endure dry periods and then germinate to form a new mycelium when conditions improve
• Mycelia


  An adaptation that supports external digestion and the absorptive lifestyle of fungi
• Fungi also produce thick, fleshy reproductive organs
• Many species of fungi do not reproduce sexually
• There are important morphological differences among lineages in those species of fungi that do reproduce sexually
• Distinctive reproductive structures in sexually reproducing fungi


  • Swimming gametes and spores
  • Zygosporangia
• Swimming gametes and spores

  The only known motile fungal cells
• Zygosporangia


  Spore-producing structures formed from the fusion of cells from joined-together haploid hyphae from two individuals