Fungi

• Biologists who study fungi have described more than

  100,000 species, but recent studies suggest that this

  number represents less than 10% of fungal diversity.
• The lineages that gave rise to fungi and animals are

  thought to have diverged from a flagellated unikont

  ancestor more than 1 billion years ago
• All fungi are heterotrophs that acquire their nutrients by

  absorption.
• They secrete powerful enzymes that digest

  macromolecules into monomers and then absorb the

  small nutrient molecules into their cells.
• Some fungi produce enzymes that digest cellulose and

  lignin, the major structural components of plants.

  Consequently, fungi are essential decomposers in most

  ecosystems.
• For example, the symbiosis between fungi

  and plant roots, called a mycorrhiza (plural, mycorrhizae), is of

  special significance.
• Mycorrhizae absorb phosphorus and

  other essential minerals from the soil and

  make them available to the plant.
• The feeding structures of a fungus are a network of

  threadlike filaments called hyphae
• Hyphae branch repeatedly as they grow, forming a mass

  known as a mycelium
• Above ground, the mushroom produces tiny reproductive

  cells called spores at the tips of specialized hyphae, and

  the spores are then dispersed on air currents.
• Fungal hyphae are surrounded by a cell wall.
• most fungi have cell walls

  made of chitin,
• Fungal Hyphae, a strong, flexible nitrogen-containing

  polysaccharide,
• Fungal reproduction typically involves

  the release of vast numbers of haploid

  spores, which are transported easily over

  great distances by wind or water.
• However, spores can be produced either

  sexually or asexually.
• heterokaryotic stage

  (from the Greek, meaning “different nuclei”), in which cells

  contain two genetically distinct haploid nuclei.

  Hours, days, or even centuries may pass before the parental nuclei fuse
• fungi

  In asexual reproduction,

  ➍ spore-producing

  structures arise from

  haploid mycelia that

  have undergone neither

  a heterokaryotic stage

  nor meiosis.
• asexual reproduction is the only known means

  of spore production in some fungi, informally known as

  imperfect fungi. Many species commonly called molds

  and yeasts.
• The chytrids, the only fungi with flagellated spores, are

  thought to represent the earliest lineage of fungi to

  diverge.

  ▫ They are common in lakes, ponds, and soil.
• Zygomycetes

  ▫ are characterized by their protective zygosporangium,

  where zygotes produce haploid spores by meiosis.
• This diverse group includes fast-growing molds, such as

  black bread mold and molds that rot produce such as

  peaches, strawberries, and sweet potatoes. Some zygote

  fungi are parasites on animals.

  Zygomycetes
• Glomeromycetes

  ▫ (from the Latin glomer, ball) form a distinct type of

  mycorrhiza in which hyphae invade plant root cells,

  where they branch into tiny treelike structures known as

  arbuscules
• About 80% of all plants have such

  symbiotic partnerships with

  glomeromycetes,
• The ascomycetes, or sac fungi, are named for saclike

  structures called asci (from the Greek asco, pouch) that

  produce spores in sexual reproduction.
• Ascomycetes live in a

  variety of marine, freshwater,

  and terrestrial habitats and

  range in size from unicellular

  yeasts to elaborate morels

  and cup fungi
• Other species of ascomycetes live with green algae or

  cyanobacteria in symbiotic associations called lichens
• A lichen is not a single

  organism, but the result of a

  partnership (mutualistic

  symbiosis) between a fungus

  and an alga or cyanobacteria.
• Ascomycetes include some of the most-devastating

  plant pathogens.
• Basidiomycetes

  ▫ Known as club fungi,
• club-shaped, spore-producing structure, called a basidium
• Basidiomycetes

  a basidium

  (meaning “little pedestal” in Latin;
• The basidiomycetes also

  include two groups of

  particularly destructive plant

  parasites, the rusts and smuts
• Many basidiomycete species excel at breaking down the

  lignin found in wood
• As symbiotic partners in mycorrhizae, fungi supply

  essential nutrients to plants and are enormously

  important in natural ecosystems and agriculture
• Fungi, along with prokaryotes, are essential

  decomposers in ecosystems, breaking down organic

  matter and restocking the environment with vital

  nutrients essential for plant growth
• Some fungi have the useful ability to break down toxic

  pollutants, including the pesticide DDT and certain

  chemicals that cause cancer.
• TRUE OR FALSE

  Fungi have a number of culinary uses.

  TRUE
• The distinctive flavors of certain

  cheeses, including Roquefort

  and blue cheese, come from

  fungi used to ripen them.
• Truffles, which are produced by

  certain mycorrhizal fungi

  associated with tree roots, are

  highly prized by gourmets.
• Humans have used yeasts for

  thousands of years to produce

  alcoholic beverages and cause

  bread to rise.