Detailed notes – 2-Chapter2-Biological Classification

2.3 KINGDOM FUNGI

1. Unique Kingdom:

   • Fungi constitute a unique kingdom of heterotrophic organisms with a diverse morphology and habitat.
   • They are commonly found on moist bread, rotten fruits, mushrooms, toadstools, and as parasitic organisms on plants like mustard leaves.

2. Uses and Impact:

   • Yeasts, a type of unicellular fungi, are used in the production of bread and beer.
   • Some fungi cause diseases in plants and animals, such as wheat rust caused by Puccinia.
   • Fungi like Penicillium are sources of antibiotics.

3. Distribution and Preference:

   • Fungi are cosmopolitan and can be found in air, water, soil, and on animals and plants.
   • They prefer warm and humid environments for growth.

4. Morphology:

   • Except for yeasts, fungi are filamentous organisms consisting of long, slender thread-like structures called hyphae.
   • The network of hyphae is known as mycelium.
   • Hyphae may be coenocytic (continuous tubes with multinucleated cytoplasm) or septate (with cross walls).

5. Nutrition:

   • Most fungi are heterotrophic and absorb soluble organic matter from dead substrates, making them saprophytes.
   • Some fungi are parasites, depending on living plants and animals for nutrition.
   • Fungi can also live as symbionts, such as in association with algae as lichens or with roots of higher plants as mycorrhiza.

6. Reproduction:

   • Fungi reproduce both vegetatively and sexually.
   • Asexual reproduction occurs by spores called conidia, sporangiospores, or zoospores.
   • Sexual reproduction involves the fusion of protoplasms (plasmogamy), fusion of nuclei (karyogamy), and meiosis resulting in haploid spores.
   • In some fungi, a dikaryotic stage occurs before diploid cells are formed, leading to the production of fruiting bodies and haploid spores.

7. Classification Basis:

   • The morphology of the mycelium, mode of spore formation, and fruiting bodies form the basis for the division of the kingdom into various classes.

2.3.1 Phycomycetes

1. Habitat:

   • Members of Phycomycetes are commonly found in aquatic habitats and on decaying wood in moist and damp places.
   • Some species also act as obligate parasites on plants.

2. Mycelium:

   • The mycelium of Phycomycetes is aseptate and coenocytic, meaning it lacks septa and consists of multinucleated hyphae.

3. Asexual Reproduction:

   • Asexual reproduction in Phycomycetes occurs through the production of zoospores or aplanospores.
   • Zoospores are motile, while aplanospores are non-motile.
   • These spores are endogenously produced within specialized structures called sporangia.

4. Sexual Reproduction:

   • Sexual reproduction involves the formation of a zygospore by the fusion of two gametes.
   • Gametes may be similar in morphology (isogamous) or dissimilar (anisogamous or oogamous).

5. Examples:

   • Common examples of Phycomycetes include Mucor, Rhizopus (commonly known as bread mold), and Albugo (a parasitic fungus found on mustard plants).

2.3.2 Ascomycetes

1. Common Name and Characteristics:

   • Ascomycetes are commonly known as sac-fungi.
   • They are mostly multicellular, such as Penicillium, or rarely unicellular, like yeast (Saccharomyces).
   • Ascomycetes exhibit various lifestyles, including saprophytic, decomposer, parasitic, or coprophilous (growing on dung).

2. Mycelium:

   • The mycelium of Ascomycetes is branched and septate, meaning it contains cross walls (septa) dividing the hyphae into compartments.

3. Asexual Reproduction:

   • Asexual spores in Ascomycetes are called conidia and are produced externally on specialized mycelium called conidiophores.
   • Conidia, upon germination, give rise to new mycelium.

4. Sexual Reproduction:

   • Sexual spores in Ascomycetes are called ascospores, which are produced internally within sac-like structures called asci (singular ascus).
   • These asci are arranged in various types of fruiting bodies called ascocarps.

5. Examples:

   • Common examples of Ascomycetes include Aspergillus, Claviceps, and Neurospora.
   • Neurospora is particularly notable for its extensive use in biochemical and genetic research.
   • Some members of Ascomycetes, such as morels and truffles, are edible and considered delicacies.

2.3.3 Basidiomycetes

1. Common Name and Characteristics:

   • Basidiomycetes are commonly known as club fungi.
   • Common forms of Basidiomycetes include mushrooms, bracket fungi, or puffballs.
   • They can be found growing in soil, on logs and tree stumps, and as parasites in living plant bodies, such as rusts and smuts.

2. Mycelium:

   • The mycelium of Basidiomycetes is branched and septate, similar to other fungal groups.

3. Asexual Reproduction:

   • Asexual spores are generally not found in Basidiomycetes.
   • Vegetative reproduction by fragmentation is common in these fungi.

4. Sexual Reproduction:

   • Basidiomycetes lack distinct sex organs.
   • Plasmogamy, the fusion of two vegetative or somatic cells of different strains or genotypes, leads to the formation of a dikaryotic structure.
   • The dikaryotic structure ultimately develops into a basidium.
   • Karyogamy and meiosis occur within the basidium, resulting in the production of four basidiospores.
   • Basidiospores are externally produced on specialized structures called basidia, which are arranged in fruiting bodies known as basidiocarps.

5. Examples:

   • Common examples of Basidiomycetes include Agaricus (mushroom), Ustilago (smut), and Puccinia (rust fungus).

2.3.4 Deuteromycetes

1. Common Name and Characteristics:

   • Deuteromycetes are commonly known as imperfect fungi because only their asexual or vegetative phases are known.
   • Historically, these fungi were classified as Deuteromycetes until the discovery of their sexual forms, after which they were moved to classes they rightly belong to.
   • It is possible that the asexual and vegetative stages were given one name (and placed under Deuteromycetes) and the sexual stage another (placed under another class).

2. Reproduction:

   • Deuteromycetes reproduce only by asexual spores known as conidia.

3. Mycelium:

   • The mycelium of Deuteromycetes is septate and branched, similar to other fungal groups.

4. Ecological Roles:

   • Some members of Deuteromycetes are saprophytes or parasites, while a large number of them are decomposers of litter, aiding in mineral cycling.

5. Examples:

   • Common examples of Deuteromycetes include Alternaria, Colletotrichum, and Trichoderma.