29.1 Why Do Biologists Study Fungi?

• Fungi that live in close association with plant roots are said to be mycorrhizal

• The fungi along with the roots they are associated with are referred to as mycorrhizae

• Fungi are critical to the productivity of forests, croplands, and rangelands.

• Fungi that make their living by digesting dead plant material are called saprophytes.

• Note that there are two basic components of the carbon cycle on land:

  • The fixation of carbon by land plants-meaning that carbon in atmospheric C02 is reduced to form sugar, which is then used to synthesize cellulose, lignin, and other complex organic compounds in the bodies of plants.

  • The release of C02 from nearly all organisms as the result of cellular respiration-meaning the oxidation of glucose and production of the ATP that sustains life

29.2 How Do Biologists Study Fungi?

• Only two growth forms occur among fungi:

  • single celled forms called yeasts

  • multicellular, filamentous structures called mycelia

• The filaments making up a mycelium are called hyphae

• In most terrestrial fungi, each filament is divided into cells by cross-walls called septa

• Some fungal lineages have hyphae that are coenocytic meaning that they are not divided into separate cells

• Fungi produce reproductive cells called spores by sexual or asexual reproduction that are resistant to drying

• Most fungal species that undergo sexual reproduction produce one of four types of distinctive reproductive structures:

  • Swimming gametes and spores

  • Zygosporangia- Cells from yoked hyphae fuse to form a distinctive spore-producing structure called a zygosporangium

  • Basidia- Mushrooms, brackets, and puffballs form specialized club-shaped cells at the ends of hyphae called basidia

  • Asci- Cups, morels, and some other types of fungi form specialized sac-like cells called asci

• Conidia can be dispersed by water or wind currents and grow into new hyphae when conditions are right.

• Fungicides are substances at can kill fungi or slow their growth

29.3 What Themes Occur in the Diversification of Fungi?

• Fungi and land plants often have a symbiotic (“together-living”) relationship

• Scientists categorize these symbiotic relationships as:

  • mutualistic if they benefit both species

  • parasitic if one species benefits at the other’s expense

  • commensal if one species benefits while the other is unaffected.

• The name αrbuscular (“little-tree”) was inspired by the bushy, highly branched hyphae that form between the cell walls and the plasma membrane of root cells.

• AMF are also called endomycorrhizal fungi, because they grow inside root cell walls.

• Endophytes (“inside-plants”) are organisms that live between and within plant cells.

• Extracellular digestion is a digestion that takes place outside the organism.

• When genetically distinct nuclei from the two different mating types exist within a single mycelium, it is considered heterokaryotic

• Dikaryotic (“two-kernel”) occurs when their cells are divided by septa, and each cell contains two nuclei, one from each mating type.

• The fusion of nuclei is called karyogamy

29.4 Key Lineages of Fungi

• Yeasts reproduce when daughter cells pinch off from the parent cell after mitosis. This asexual reproductive process is called budding.

• Fungi are a large and diverse group of organisms. They are economically important, and they also play important roles in the environment.