Fungi Flashcards

The Evolution of Fungi

• Limited fossil evidence is available.
• Fungi are estimated to have emerged around 1 billion years ago.
• Fungal hyphae have been found in fossilized remains of ancient plants.
• Biochemical evidence supports fungal evolution.

Prototaxites

• Mention of Prototaxites, an ancient organism, possibly related to fungi.

Kingdom Fungi

• Initially categorized within the Plantae Kingdom until the late 20th century.
• Classification was based on:
  • Morphology of sexual organs.
  • Presence of septa (cross-walls) in hyphae.
  • Degree of chromosome repetition (ploidy).
• Recognized as a separate kingdom in the mid-20th century.
• Key distinguishing factor: method of nutrient acquisition.

Fungi Characteristics

• Heterotrophic: Obtain energy from organic compounds.
• Cell walls contain chitin (similar to arthropod exoskeletons).
• Produce various pigments, including melanin.
• Store carbohydrates as glycogen.
• Capable of absorbing nutrients from the environment directly through the cell surface.
• Act as decomposers.
• Share characteristics with both animals and bacteria.

Cell Structure and Function

• Complex cell structure, typical of eukaryotic cells.
  • Membrane-bound nucleus containing DNA.
  • DNA is wrapped around histones.
  • Presence of mitochondria.
  • Other membranous organelles: Golgi apparatus, endoplasmic reticulum.
  • Lack chloroplasts; color is derived from other cellular pigments.
  • Thick cell walls, similar to plants.

Anatomy of Fungi

• Mycelium: A network of hyphae that:
  • Obtains nutrients.
  • Produces the fruiting body.
  • Is primarily located underground.
• Reproductive Structure:
  • Fruiting body (e.g., mushroom) where spores are produced.
• Spores:
  • Involved in fungal reproduction.
  • Produced in the fruiting body.
  • Haploid (containing a single set of chromosomes).
  • Germinate when they land on damp soil.

Fungal Reproduction

• Undergo both sexual and asexual reproduction.
• Most produce haploid spores that undergo mitosis to form multicellular haploid organisms.
• Spores are dispersed from the parent organism by wind or animals.

Asexual Fungal Reproduction

• Budding: An expanded form of cytokinesis.
  • A bulge forms, and the nucleus divides via mitosis.
• Fragmentation:
  • Hyphae fragments can grow into new colonies.
• Spore Production:
  • Genetically identical spores are produced by the parental colony.
• Figure 24.8 illustrates the generalized fungal life cycle, highlighting both asexual and sexual reproduction stages.

Sexual Fungal Reproduction

• Introduces genetic variation.
• Typically occurs under adverse environmental conditions.
• Two mating types are produced:
  • Homothallic: Self-fertile; can reproduce sexually with itself.
  • Heterothallic: Requires two different but compatible mycelia for sexual reproduction.

Nutrition

• Fungi are heterotrophic, requiring organic molecules for energy.
• Digestion precedes ingestion (occurs externally).
  • Exoenzymes are secreted by hyphae to break down large organic molecules in the environment.
  • Smaller molecules are then absorbed across the cell membrane by the mycelium.
• Most fungi are saprobes, obtaining nutrients from decaying organic material.
• Some fungi are parasitic (e.g., athlete's foot), deriving nutrients from host tissues.

Fungal Growth

• Unicellular: Some exist as single cells (e.g., yeasts).
• Multicellular: Most form hyphae, the thread-like filaments.
• Dimorphous: Able to alternate between unicellular and multicellular forms.
• Thermal Dimorphism:
  • Observed in Sporothrix schenckii.
  • Sporothrix schenckii grown on Sabouraud Dextrose Agar at 30°C for 3 weeks.
  • Sporothrix schenckii grown on Brain-Heart Infusion (BHI) agar at 37°C for 10 days.

Amanita muscaria (fly agaric)

• Pigments are located in the cell wall.
• Provide protection against ultraviolet radiation.
• Some pigments are poisonous to humans.
• Figure 24.2 shows Amanita muscaria, a poisonous fungus native to temperate and boreal regions of North America.

Humongous Fungus

• Considered the largest organism on Earth.
• Covers approximately 2,000 acres and is about 2,500 years old.
• Reference to a science article: https://www.science.org/content/article/humongous-fungus-almost-big-mall-america

Ecology of Fungi

Fungal Habitat

• Moist environments.
• Slightly acidic conditions.
• Both dark and light environments.
• Varying oxygen requirements:
  • Most are obligate aerobes (require oxygen).
  • Some are obligate anaerobes (oxygen is toxic).
• Capable of living in diverse environments.

Decomposers & Recyclers

• Break down organic material, releasing essential molecules:
  • Nitrogen
  • Phosphorous
• Without fungal decomposers, these nutrients would remain trapped in decaying matter.
• This process relies on the digestion-before-ingestion model.
• Reference to a National Park Service article: https://www.nps.gov/mora/learn/nature/decomposing-fungi.htm

Mutualistic Relationships

• Plant/Fungi: Mycorrhizae
  • Present in about 90% of plant species.
  • Ectomycorrhizae: Wrap roots in a sheath of hyphae.
  • Endomycorrhizae: Fungi grow within roots.
  • Endophytes: Live within the plant and secrete toxins for protection against predation and environmental stress.

Mycorrhizae

• Fungi form mutualistic relationships with other organisms.
• Most terrestrial plant roots connect with fungi to form mycorrhizae.
• This relationship allows for the exchange of nutrients and water, benefiting both organisms.
• Reference to an ECHO Community article: https://www.echocommunity.org/resources/2494c049-7310-4773-ad49-fe2699331125

Mutualistic Relationships

• Lichen:
  • A fungus in a mutualistic relationship with a photosynthetic organism (algae or cyanobacteria).
  • Neither organism can survive independently.
  • Highly sensitive to air pollution, making them good indicator species.

Mutualistic Relationships - Animal/Fungus

• Mini Hercules: Example of an animal/fungus mutualistic relationship.

Fungivores

• Animals that disperse fungal spores through their diet without realizing it.

Importance of Fungi in Human Life

How Humans Benefit from Fungi

• Nutrient cycling in ecosystems.
• Pest control.
• Mycorrhizal relationships enhance plant growth for agriculture.
• Food for human consumption:
  • Mushrooms
  • Cheese
  • Alcohol
  • Bread
• Medication production.

Fungi in Industry

• Pulp, paper, and textile industries: Utilize enzymes such as amylases, proteases, cellulases, lipases, xylanases, laccase, tannase, pectinases, keratinases, maganeseperoxidase, ligninperoxidase.
• Food industry: Employs amylases, cellulases, xylanases, pectinases, β-galactosudase, tannases, lactase, and proteases.
• Beverage industry: Uses cellulases, xylanases, pectinases, and tannases.
• Household items: Applications include amylases, proteases, and lipases.
• Biofuel production: Involves amylases, ligninperoxidase, maganeseperoxidase, laccase, cellulases, and keratinases.
• Biocatalysts: Utilize amylases, proteases, cellulases, xylanases, and lipases.
• Animal feed: Enhanced with phytases, cellulases, lipases, and keratinases.
• Environmental management: Employs laccase, phenoloxidase, lipases, maganese peroxidase, phytases, lignin peroxidase, and keratinases.