Lecture_12_-_Fungi_2024

Kingdom Fungi (Fungi)

Overview

• Focus on the basic characteristics of fungi, energy and nutrient acquisition, ATP production, reproduction, and their importance.

Basic Characteristics of Fungi

1. Cell Structure

   • Eukaryotic cells, distinguishing them from prokaryotes.

2. Cell Walls

   • Composed of chitin, unlike plant cell walls which are made of cellulose.

3. Body Plans

   • Two main forms:

     • Single-celled (e.g., yeast)

     • Multicellular (e.g., mycelium, which consists of filamentous hyphae).

Fungal Nutrition

1. Energy and Nutrient Acquisition

   • Fungi are heterotrophs:

     • Obtain energy (carbohydrates) and nutrients (nitrogen, phosphorus) from other organisms.

   • Types of Fungi:

     • Decomposers (Saprophytes): Break down dead organic matter.

     • Parasites: Infect living organisms (plant and animal parasites).

     • Mutualistic Associations: Collaborate with other taxa (e.g., plants via mycorrhiza).

   • Mechanism:

     • Release digestive enzymes into the environment to break down complex substances, absorbing simpler nutrients through hyphae.

2. ATP Production

   • Primarily through aerobic cellular respiration.

   • Some taxa can also undergo anaerobic cellular respiration:

     • Facultative anaerobes (e.g., brewer's yeast): Can switch between aerobic and anaerobic methods.

     • Obligate anaerobes (e.g., some soil or gut fungi): Only produce ATP via anaerobic respiration.

Fungi Reproduction

1. Asexual Reproduction

   • Commonly seen in bread molds:

     • Sporangium development: A haploid (n) mycelium produces haploid spores via mitosis.

     • Germination: Haploid spores germinate by mitosis to form a new haploid mycelium.

     • Spore production continues: New mycelium can produce more spores.

   • Each daughter cell is genetically identical to the parent.

2. Sexual Reproduction

   • Involves fusion of haploid hyphae from two different mating types:

     • Formation of a diploid zygote (2n).

   • Meiosis followed by mitosis results in haploid spores within the sporangium.

     • Each spore has 50% of the DNA of the zygote.

     • Germination leads to a new haploid mycelium.

Importance of Fungi in Ecosystems

1. Ecosystem Inhabitants

   • Fungi are present in various aquatic and terrestrial ecosystems.

   • Form symbiotic relationships with prokaryotes, protists, plants, and animals.

2. Saprophytic Fungi

   • Improve biological production and biodiversity by decomposing:

     • Digest lignin and cellulose, releasing nutrients locked in dead organisms.

     • Provide available energy and nutrients (e.g., nitrogen, phosphorus) to primary producers via biomass and excretion.

3. Mutualistic Associations

   • Mycorrhizal fungi facilitate the transfer of nutrients (N, P, water) to plants.

   • Fungi gain carbohydrates from plants produced through photosynthesis.

4. Parasitic Fungi Impact

   • Can decrease host population sizes and affect biodiversity (e.g., chytridiomycosis in amphibians).

   • White-nose syndrome is impacting bat populations in North America.

Importance of Fungi to Human Welfare

1. Health Impacts

   • Mycotoxins and infections:

     • Internal organ infections (e.g., Candida sp.), respiratory issues (e.g., black mold), and poisonous mushrooms.

2. Agricultural Diseases

   • Fungal parasites (smuts, rusts) contribute to crop losses.

   • Decomposition processes can spoil stored food items.

   • Historical impact on forests (e.g., Dutch elm disease, chestnut blight).

3. Pharmaceutical Applications

   • Source of antibiotics (e.g., Penicillium).

   • Psilocybin's potential in neurological illness treatment is under research.

4. Biological Control Agents

   • Use of fungi to manage pests (e.g., arthropod parasites).

5. Food Production

   • Essential for plant growth, especially mycorrhizal associations.

   • Yeast is critical for bread production through fermentation.

6. Climate Change Mitigation

   • Soil fungi help sequester carbon, promoting plant growth and reducing CO2 levels in the atmosphere.