Biology

Fungi

Big Picture

Fungi are eukaryotes that belong to kingdom Fungi. While many fungi are multi-cellular, some are also single-celled, such as yeast. Fungi are divided into many phyla, but the three most common are zygomycota, basidiomycota, and ascomycota. Fungi are usually classified based on structure and method of sexual reproduction. All fungi, however, are heterotrophic, deriving and absorbing their organic compounds from the environment around them. Fungi are key members of any habitat.

Key Terms

Fungi (singular, fungus): Kingdom in the domain Eukarya that includes molds, mushrooms, and yeasts.

Chitin: A polysaccharide found only in the cell walls of fungi.

Hyphae (singular, hypha): The filaments of multicellular fungi.

Mycelium (plural, mycelia): The body of a fungus comprised of a mass of hyphae.

Asexual Spores: Many multi-cellular fungi reproduce asexually by producing haploid spores by mitosis.

Budding: Type of asexual reproduction in yeasts in which an offspring cell pinches off from the parent cell.

Zygospore: Diploid spore in fungi that is produced by the fusion of two haploid parent cells.

Mycorrhiza: The symbiotic relationship formed between a fungus and a plant.

Lichen: The symbiotic association between a fungus and a photosynthetic organism.

General Characteristics

Fungi
Figure: Hyphae
image credit: Y_tambe,GNU-FDL 1.2
  • Fungi cells have cell walls made out of chitin, not cellulose.
  • Multicellular fungi have hyphae, which look like little threads.
  • A hypha consists of one or more cells surrounded by a tubular cell wall.
  • A network of hyphae called mycelium make up the body of the fungus.
  • Mycelium can be very small or very large.

Reproduction

Fungi can reproduce both asexually and sexually. They spend most of their life cycle as haploid. Diploid cells only form during sexual reproduction.
Asexual reproduction allows fungi to spread quickly.

  • Most fungi reproduce asexually by producing spores. Spores do not require fertilization and are genetically identical to the parent fungus.
  • Spores can be moved by water, wind, or other organ-isms.
  • Yeast reproduces by budding. In budding, the off-spring forms by pinching off the parent.

Sexual reproduction increases genetic variation.

  • Many multi-cellular fungi also undergo sexual reproduction.
  • In sexual reproduction, hyphae from two different mating types of the same species fuse, forming a zygospore, a diploid spore. Meiosis creates genetically different haploid cells that can develop into new hypahe.

Symbiotic Relationships

Parasitic fungi can cause illness and eventual death.

  • Major cause of disease in agricultural plants
  • Some types of fungi can grow as a parasite on animals
  • Athlete’s foot is a parasitic fungus that grows on humans

Fungi can also form mutualistic relationship.

  • In mycorrhiza, fungus grows in or on plant roots. The fungus has easy access to food, while the plant gets help in absorbing water and nutrients.
  • In lichen, fungus grows around the photosynthetic organism. The fungus gets a constant supply of food, while the photosynthetic organism gets help in absorbing water and nutrients.

Biology

Fungi Cont.

Role in the World

A common use of fungi in our society is as a source of food. For example, we eat many types of mushroom, the fruiting body of a fungus, and we use yeast to bake bread.

Fungi also play an important role in medicine, producing chemicals and antibiotics, such as penicillin, that have revolutionized treatment of human diseases and infections.

In the world at large, fungi, which are heterotrophs, serve as important decomposers in the environment, breaking down dead organic material from which they also derive nutrients. Fungi thus release important molecules back into the ecosystem.

However, fungi can also be harmful, causing certain diseases when they infect human tissue. Fungus is at the root of such diseases as athlete’s foot and ringworm.

Notes