Biology: Characteristics of Fungi

Heterotrophic by Absorption

• Fungi obtain their carbon from organic sources
• Hyphal tips release enzymes to break down the substrate
• Products of enzymatic breakdown are absorbed back into the hyphae

The Characteristics of Fungi

• Body forms
  • Unicellular
  • Filamentous (strands called hyphae)
  • Mycelium (aggregate of hyphae)
  • Sclerotium (hardened mass of mycelium for overwintering)
  • Multicellular (mycelial cords, rhizomorphs, fruit bodies)
• Yeasts: Single-celled fungi
  • Candida
  • Saccharomyces
• Heterotrophy
  • Saprophytes or saprobes: Feed on dead tissues or organic waste
  • Symbionts: Mutually beneficial relationship with another organism
  • Parasites: Feed on living tissue, pathogens cause disease
• Cell wall: Composed of cellulose and/or chitin
• Food storage: Primarily lipids and glycogen
• Eukaryotes: True nucleus
• Water & Oxygen requirements: All fungi require both
• Habitat: Fungi grow in various habitats, requiring organic matter and non-extreme environments.
• Hyphae:
  • Tubular
  • Hard wall of chitin
  • Multinucleate
  • Grow at tips

Fungi as Saprobes and Decomposers

• Important role in recycling nutrients and carbon

Fungi as Symbionts (Mutualism)

• Mycorrhizae: "Fungus roots" beneficial to both organisms
  • Fungus: Increased nutrient and water uptake for the plant
  • Plant: Carbohydrate supply for the fungus
• Mycorrhizae are ecologically significant
  • Improve nutrient uptake by plants
  • Enhance plant growth and survival
  • Increase drought and stress tolerance

Lichens

• “Mutualistic” relationship involving:
  • Fungus: Provides structure
  • Alga or cyanobacterium: Provides food

Fungi as Parasites

• Fungi can infect plants and animals, including humans.
• Plant infections can cause various symptoms:
  • Smuts
  • Rusts
  • Spots
  • Blights
  • Root rots
  • Seedling blights
  • Seed discoloration
  • Wilts
  • Stem rots
• Fungi can cause a variety of symptoms in animals and humans
• Hyphae can absorb water and nutrients, and secrete enzymes, toxins, and other substances that contribute to disease development and symptoms.

HUMAN-FUNGUS INTERACTIONS

• Beneficial Effects of Fungi:
  • Decomposition: Nutrient and carbon recycling
  • Biosynthetic factories: Used to produce drugs, antibiotics, alcohol, acids, foods (fermented products, mushrooms)
  • Model organisms: Biochemical and genetic studies
• Harmful Effects of Fungi:
  • Destruction of food, lumber, paper, and cloth
  • Animal and human diseases: Allergies
  • Toxins: Poisonous mushrooms and food contamination
  • Plant diseases

Generalized Life Cycle of a Fungus

• Typically involves both sexual and asexual stages.
• Sexual reproduction:
  • Production of spores
  • Fusion of gametes
  • Formation of a zygote
• Asexual reproduction:
  • Budding, fragmentation, spore formation
  • Results in genetically identical offspring

Terminology

• Teleomorph: The sexual reproductive stage
  • Often a fruiting body (e.g. Morchella esculenta, Agaricus brunescens)
• Anamorph: The asexual reproductive stage
  • Often mold-like (e.g. Aspergillus flavus, Fusarium solani)
• Holomorph: The entire fungus, including all anamorphs and teleomorphs

Course Information

• Course Code: BMD-322
• Midterm Exam: Week 6
• Assessment percentages:
  • Midterm exam: 10%
  • Oral exam: 10%
  • Exercise-activities: 20%
  • Practical exam: 20%
  • Final exam: 40%

Systematics in Biology:

• Concerned with classification systems and nomenclature of organisms
• Studies the distinctive characteristics of species and their relationships through time

Classification:

• The process of grouping things based on their similarities

The word "fungus"

• Latin origin
• "Mycology" comes from the Greek word "mukēs," meaning "fungi"

KINGDOM FUNGI

• Over 100,000 species of fungi discovered
• Estimated to be over one million undiscovered species.
• Mycologists: People who study fungi
• Fungi are saprotrophs: They live on dead organic matter
• Fungi secrete digestive enzymes: Degrade organic material externally
• Degraded compounds are absorbed by the mycelium.

“Ecto”mycorrhizae

• Fungal hyphae:
  • Surround the root
  • Extend between the root cells

Lichen Internal Structure

• Example: Lobaria
• Symbiotic structure

Hyphal growth from spore germination:

• Spore germinates
• Forms mycelium
• The mycelium has a large surface area