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Chapter 31: FungiLearning Objectives

• Describe the structure of the fungal body.

• Compare and contrast sexual and asexual reproduction in fungi.

• Explain the evolutionary origins of fungi from a single-celled protist.

• Identify and characterize major phylogenetic groups of fungi.

• Explore interactions between fungi and other organisms.Suggested: Complete crossword for terminology review.

Concept 31.1: Nutrition and Feeding in Fungi

Heterotrophic Nature

• Fungi are heterotrophs that obtain organic compounds mainly by absorption from their environment, playing a crucial role in nutrient cycling.

Feeding Mechanism

• Fungi secrete enzymes that break down complex organic materials, such as carbohydrates, proteins, and lipids, into simpler organic compounds that can be absorbed.

Ecological Roles

• Decomposers: Fungi are vital decomposers in ecosystems, breaking down nonliving organic material like dead plants and animals, thus recycling nutrients.

• Parasitic Fungi: Some fungi act as parasites, absorbing nutrients from living hosts, which can lead to diseases in plants and animals.

• Mutualistic Fungi: Mutualistic fungi enter into symbiotic relationships with hosts, particularly in mycorrhizal associations with plant roots, which enhance nutrient uptake for both partners.

Structure of Fungal Body

Common Structures

• Fungal bodies typically consist of multicellular filaments known as hyphae and single-celled forms known as yeasts.

Morphology

• The structure of fungi enhances their ability to absorb nutrients through a vast network of branched filaments called hyphae, which collectively form the mycelium.

Hyphal Structure

• Hyphae have tubular cell walls that are strengthened with chitin, a tough polysaccharide.

Hyphae and Mycelium

Septic and Coenocytic Hyphae

• Most hyphae are divided into cells by septa, which have pores that allow organelles and cytoplasm to move between cells.

• Coenocytic fungi, on the other hand, lack septa and consist of a single cytoplasmic mass with multiple nuclei, allowing for rapid growth.

Mycelium

• The mycelium is an intricate, interwoven mass of hyphae, which maximizes the surface area to volume ratio, enabling effective nutrient absorption.

Specialization in Mycorrhizal Fungi

Feeding Structures

• Mycorrhizal fungi develop specialized hyphae for nutrient extraction from plant roots.

• Haustoria: These are specialized hyphae that penetrate plant cells and facilitate nutrient exchanges between the fungus and plant.

• Ectomycorrhizal Fungi: These fungi form sheaths of hyphae around root systems and grow into the extracellular spaces of roots. (wraps on outside of cell)

• Arbuscular Mycorrhizal Fungi: They extend arbuscules into plant cells, which are critical for nutrient exchange, particularly phosphorus. (penetrates inside cell)

Concept 31.2: Fertilization and Reproduction

Spores

• Fungi reproduce by producing spores, which can be formed either sexually or asexually.

• Spores are produced in large quantities, are typically dispersed by wind or water, and can germinate in suitable environmental conditions, leading to the growth of new fungal organisms.

Sexual Reproduction in Fungi

Nuclear Arrangement

• Fungal nuclei are commonly haploid, containing a single set of chromosomes.

Mating

• Hyphae of different mating types can fuse, facilitated by chemical signals known as pheromones.

Plasmogamy

• This is the process by which the cytoplasm of two parent mycelia fuses before the nuclei undergo fusion (karyogamy).

Diploid Phase

• The resulting diploid phase is typically short-lived and usually undergoes meiosis to produce haploid spores, thus introducing genetic variation in the population.

Asexual Reproduction in Fungi

• Many fungi reproduce asexually through methods such as mitotic spore production.

• Molds: These fungi produce visible mycelium that generates haploid spores.

• Yeasts: Single-celled fungi typically reproduce by budding, a process where a new organism develops from an outgrowth of the parent cell instead of producing spores.

Classification and Phylogenetic Relationships

• Deuteromycetes: This group includes fungi with unknown sexual states that were often reclassified once their sexual reproduction methods were discovered.

• Opisthokonts Clade: Fungi are more closely related to animals than to plants, sharing a common ancestor within the Opisthokonts clade, which diverged from a unicellular flagellated protist.

Concept 31.4: Diversity of Fungi

Phylogenetic Groups

• Fungi are classified into five major phyla:

  • Chytrids (Chytridiomycota): Characteristic of aquatic habitats, they are among the earliest diversifiers and possess flagellated spores (zoospores).

  • Zygomycetes (Zygomycota): Recognized for their rapid growth, these molds, like black bread mold, display coenocytic hyphae.

  • Glomeromycetes (Glomeromycota): These fungi are known for forming arbuscular mycorrhizae, previously classified alongside zygomycetes.

  • Ascomycetes (Ascomycota): Known as sac fungi, they occupy diverse habitats and play significant roles in various symbiotic associations.

  • Basidiomycetes (Basidiomycota): This group includes mushrooms and shelf fungi and is characterized by the production of basidiospores.

Concept 31.5: Ecological Roles of Fungi

Nutrient Cycling

• As decomposers, fungi play a vital role in recycling chemical elements between living and nonliving components of ecosystems.

Mutualism

• Fungi also form beneficial partnerships with plants and animals, such as mycorrhizal relationships, increasing nutrient uptake for plants while providing carbohydrates to fungi.

Fungal-Animal Interactions

• Certain fungi are important for the digestion of plant materials in grazing mammals, while others, such as the fungi cultivated by certain ant species, exemplify mutualistic symbiosis.

Lichens

Symbiotic Association

• Lichens are symbiotic associations between fungi and photosynthetic organisms, typically green algae or cyanobacteria.

Pioneers

• Lichens are crucial for colonizing bare substrates and contribute significantly to soil formation processes.

Practical Uses of Fungi

Human Consumption

• Many fungi are consumed directly by humans as food and are also crucial in the production of bread and alcoholic beverages.

Medicinal Uses

• Fungi, such as Penicillium, are significant for their medicinal properties, particularly in the production of antibiotics and other pharmaceuticals.

Genetic Research

• Fungi have become essential in biotechnology, contributing to genetic research, gene therapy for various diseases, and biofuel production, highlighting their diverse impacts on science and medicine.