Fungi Overview and Organization

Fungi Overview

• Fungi are a distinct kingdom, often multicellular, but sometimes unicellular.
• Fungi are heterotrophic, meaning they obtain their nutrients from other organisms.
• Their cell walls are made of chitin.
• Fungi primarily exist in a haploid state throughout most of their life cycle.
• A key characteristic is their mode of carbohydrate storage, which is in glycogen.

Fungal Organization

• Fungi primarily exist in a filamentous form, called hyphae —long strands of cells that can associate to form larger structures.
• Hyphae can be dikaryotic (containing two nuclei)
  • Genetically different nuclei: heterokaryon
  • Genetically similar nuclei: homokaryon
• Hyphae can also be monokaryotic (single nuclei) and cannot reproduce sexually.
• Fungi tend to organize into a mycelium, which are densely branched masses of hyphae.
• Fungi grow in size via cell division.
• Fungi digest organically through secretion of digestive enzymes into their environment and absorption of molecules back into their bodies.
• Fungi can be carnivorous or herbivorous.

Fungal Reproduction

• Structures:

  • Gametangia: Specialized organs that form haploid gametes (in sexual reproduction) formed by extensions of hyphae that are compatible.
  • Sporangia: Organs that form haploid spores (in sexual and asexual reproduction). Spore names may differ by the phylum.

• Processes:

  • Plasmogamy: Fusion of cytoplasm in two gametangia.
  • Karyogamy: Fusion of two haploid nuclei to form a diploid nucleus.

• Fungi practice both sexual and asexual reproduction depending on the species.

• Asexual via mitosis and germination.

• Sexual via fusion of compatible nuclei (environmental factors).

Key Phyla (and reproduction modes)

• Zygomycota
  • Fast-growing
  • Cells of the hyphae are haploid and fuse to form diploid nuclei, which then undergo meiosis to create haploid spores.
  • Sexual and asexual reproduction mechanisms.
• Ascomycota
  • Live in marine, freshwater, and terrestrial habitats; often edible fruiting bodies.
  • Asexual reproduction through budding and via conidia formation (asexual non-motile spores).
  • Sexual reproduction occurs through sac-like structure (asci).
• Basidiomycota
  • Long-lived and dikaryotic (two nuclei in cells).
  • Sexual reproduction occurs via sexual basidiospores in club-like structures (basidia).
  • Fruiting bodies and basidiocarps are characteristic features.
  • Asexual reproduction is uncommon.

Imperfect Fungi (Deuteromycota)

• Not a formal taxonomic group; classified based on a lack of observed sexual reproduction.
• A large group containing a wide variety of fungi.
• They reproduce asexually via conidia (asexual non-motile spores).

Lichens

• Symbiotic associations between fungi and photosynthetic organisms. (usually blue-green algae).
• Fungi act as a photosynthetic partner, providing structural support and protection for algae.
• Lichens are categorized by their shapes (crustose, foliose, fruticose).
• They are often the first colonizers of new environments and sensitive to pollution.

Lichen-Fungi Relationship

• Fungi in lichens usually create a sac-like or club-like structure.
• Lichen body (thallus) varies by shape, color, and species.
• Reproductive structures vary in color (pink, red, green).
• Lichens show tolerance to harsh environments.