Fungi

1. Origin and Basic Characteristics of Fungi

General Features

  • Kingdom separate from plants and animals.

  • Eukaryotic → membrane-bound nucleus.

  • Cell walls made of chitin (not cellulose like plants).

  • Heterotrophs → obtain food from other organisms.

  • First organisms with adaptations for life on land.

  • Reproduce using airborne spores.

Nutrition

  • External digestion:

    • Secrete enzymes → digest food outside body.

    • Absorb nutrients afterward.

  • Different from animals (animals ingest food first).

Types of Nutrition

  • Decomposers (saprophytes) → feed on dead matter.

  • Parasites → feed on living hosts.

Examples

  • Mushrooms

  • Molds

  • Yeasts

  • Rusts

  • Smuts

  • Truffles

  • Morels

2. Structure of Fungi

Hyphae

  • Thin branching filaments.

  • One cell thick.

  • Perform digestion and reproduction.

Mycelium

  • Mass/network of hyphae.

  • Main body of fungus.

  • Usually underground.

  • Function: nutrient absorption and digestion.

Fruiting Body

  • Reproductive structure (visible part like mushroom).

  • Contains structures that produce spores.

Sporangium

  • Spore-producing structure at hypha tip.

Spores

  • Reproductive cells.

  • Function like seeds.

  • Dispersed by wind or water.

3. Reproduction in Fungi

Asexual Reproduction (Most Common)

Fragmentation

  • Hypha breaks → each piece grows into new fungus.

Fission

  • One cell splits into two.

  • Common in yeast.

Budding

  • New cell grows from parent cell.

  • Common in yeast.

Spore Formation (Most Important)

  • Spores produced by mitosis.

  • Spread by air/water.

  • Germinate into new fungi.

Sexual Reproduction

Mating Types

  • No male/female sexes.

  • Two types: + and −.

Process

  1. Hyphae of opposite types fuse.

  2. Nuclei combine → diploid zygote.

  3. Meiosis occurs.

  4. Haploid spores produced.

Key Terms

  • Diploid (2n) → two chromosome sets.

  • Haploid (n) → one chromosome set.

4. Example — Black Bread Mold (Rhizopus stolonifer)

Asexual Cycle

  • Haploid hyphae form sporangia.

  • Sporangia release haploid spores.

  • Spores germinate into new fungus.

Sexual Cycle

  • and − hyphae fuse.

  • Form gametangia (sexual structures).

  • Fusion produces zygosporangium (dormant structure).

  • Under good conditions → meiosis → spores.

Life Cycle Pattern

  • Alternates between sexual and asexual reproduction.

5. Four Phyla of Fungi

1. Zygomycota (Common Mold)

  • Example: black bread mold.

  • Found in soil and decaying matter.

  • Reproduce:

    • Asexual → sporangia.

    • Sexual → fused hyphae.

  • Hyphae often multinucleate.

2. Ascomycota (Sac Fungi)

  • Largest group.

  • Sexual reproduction in asci (spore sacs).

  • Fruiting body = ascocarp.

  • Asexual spores = conidia.

Examples

  • Yeast (Saccharomyces cerevisiae)

  • Morels

  • Candida albicans

  • Aspergillus flavus

3. Basidiomycota (Club Fungi)

  • Includes mushrooms, puffballs, shelf fungi.

  • Sexual reproduction in basidium.

  • Produce basidiospores.

  • Important decomposers and plant symbionts.

  • Some parasites (rusts, smuts).

4. Deuteromycota (Imperfect Fungi)

  • No known sexual stage.

  • Temporary classification.

  • Many parasites or decomposers.

  • Example: Penicillium (source of penicillin).

6. Ecological Importance of Fungi

Decomposers

  • Break down organic matter.

  • Recycle nutrients (carbon, nitrogen).

  • Essential for ecosystem energy flow.

Symbiotic Relationships

Lichens

  • Fungus + photosynthetic organism.

  • Fungus → protection, water, minerals.

  • Alga/cyanobacteria → energy.

  • Indicators of air pollution.

Mycorrhizae

  • Fungus + plant roots.

  • Fungus increases nutrient absorption.

  • Plant provides sugars.

7. Harmful Effects of Fungi

Plant Diseases

  • Destroy crops.

  • Examples:

    • Corn smut

    • Mildew

    • Wheat rust

Animal Diseases

  • Example: Cordyceps infects insects.

Human Diseases

  • Athlete’s foot.

  • Ringworm.

  • Thrush (Candida).

  • Yeast infections.

  • Mycotoxicosis (toxins from molds).

AP Biology High-Yield Concepts

  • Fungi = eukaryotic heterotrophs with chitin cell walls.

  • Nutrition by external digestion and absorption.

  • Body structure: hyphae → mycelium.

  • Spores = major reproductive strategy.

  • Alternation of sexual and asexual reproduction.

  • Major ecological role: decomposition and symbiosis.

  • Four phyla distinguished mainly by reproductive structures.