Kingdom Fungi | Biology Class 11 - NEET PDF Download

Introduction to Kingdom Fungi

• Fungi are a diverse group of heterotrophic organisms that vary greatly in their morphology and habitats. They are commonly found in places like moist bread, rotten fruits, and even in the form of mushrooms and toadstools.
• Yeast,. A type of unicellular fungus is used in making bread and beer. Other fungi, like Puccinia, cause diseases in plants. Some fungi, such as Penicillium, are sources of antibiotics.

Yeast

• Fungi are present all over the world, in the air, water, soil, and on plants and animals. They thrive in warm and humid conditions.
• Although fungi are often associated with food spoilage, they play a crucial role in decomposition and nutrient cycling in ecosystems.

Structure and Nutrition of Fungi

(i) Structure of Fungi

• Most fungi are filamentous, consisting of long, thread-like structures called hyphae. The network of hyphae forms the mycelium.
• Some hyphae are continuous tubes with multiple nuclei, known as coenocytic hyphae. Others have cross walls, called septae.
• The cell walls of fungi are made of chitin and polysaccharides.

(ii) Nutrition in Fungi

• Fungi are primarily heterotrophic and obtain their food by absorbing soluble organic matter. Most fungi are saprophytes, which means they feed on dead organic material.
• Some fungi are parasites and rely on living plants and animals for their nutrients. Others can live in a symbiotic relationship with other organisms, such as algae in lichens or with the roots of higher plants in mycorrhiza.

Reproduction in Fungi

• Vegetative Reproduction: Fungi can reproduce vegetatively through fragmentation, fission, and budding.
• Asexual Reproduction: Asexual reproduction occurs through the formation of spores such as conidia, sporangiospores, or zoospores.
• Sexual Reproduction: Sexual reproduction involves the formation of oospores, ascospores, and basidiospores. These spores are produced in specialised structures called fruiting bodies.

Sexual Cycle in Fungi

• The sexual cycle in fungi involves three main steps:
• Plasmogamy: This is the fusion of protoplasm between two gametes, which can be either motile or non-motile.
• Karyogamy: This is the fusion of two nuclei, resulting in a diploid cell.
• Meiosis: This occurs in the zygote, leading to the formation of haploid spores.

Mating Types and Dikaryotic Stage

• When fungi reproduce sexually, two haploid hyphae of compatible mating types come together and fuse. In some fungi, this fusion immediately results in diploid cells.
• In other fungi, such as ascomycetes and basidiomycetes, an intervening dikaryotic stage occurs, where two nuclei per cell are present. This stage is called the dikaryon, and the phase is known as the dikaryophase.

Formation of Fruiting Bodies

• Fungi form fruiting bodies where reduction division occurs, leading to the formation of haploid spores.

The morphology of the mycelium, mode of spore formation, and fruiting bodies are used to classify fungi into various groups.

Types of Fungi

1. Phycomycetes

• Members of phycomycetes are typically found in aquatic habitats and on decaying wood in moist and damp environments. They can also exist as obligate parasites on plants.
• The mycelium in phycomycetes is aseptate (lacking cross-walls) and coenocytic (multinucleated).
• Asexual reproduction occurs through the formation of zoospores (motile spores) or aplanospores (non-motile spores). These spores are produced endogenously within a sporangium.
•  A zygospore is formed by the fusion of two gametes, which can be similar in morphology (isogamous) or dissimilar (anisogamous or oogamous). 
•  Some common examples of phycomycetes include Mucor, Rhizopus (known as bread mould), and Albugo (a parasitic fungus on mustard).

Mucor

2. Ascomycetes

• Ascomycetes, commonly known as sac fungi, are primarily multicellular organisms, such as Penicillium, although some, like yeast (Saccharomyces ), are unicellular.
• They can be saprophytic, decomposers, parasitic, or coprophilous (growing on dung).
• Their mycelium is branched and septate.
• Asexual spores, known as conidia, are produced exogenously on specialised mycelium called conidiophores.
• Conidia germinate to form mycelium.
• Sexual spores, called ascospores, are produced endogenously in sac-like structures called asci.
• Asci are arranged in various types of fruiting bodies known as ascocarps.
• Examples of ascomycetes include Aspergillus, Claviceps, and Neurospora.
• Neurospora is widely used in biochemical and genetic research.
• Some ascomycetes, like morels and truffles, are edible and considered delicacies.

Asperguillus

3. Basidiomycetes

• Common Forms: Basidiomycetes are commonly known as mushrooms, bracket fungi, or puffballs.
• Habitat: They can be found growing in soil, on logs and tree stumps, and as parasites in living plant bodies. Examples of parasitic forms include rusts and smuts.
• Mycelium: The mycelium of basidiomycetes is branched and septate (divided by septa).
• Asexual Reproduction: Asexual spores are generally not found in basidiomycetes. Instead, they reproduce vegetatively by fragmentation.
• Sexual Reproduction: Basidiomycetes do not have sex organs. Plasmogamy (the fusion of cytoplasm) occurs when two vegetative or somatic cells of different strains or genotypes fuse. This fusion results in a dikaryotic structure, which eventually gives rise to a basidium.
• Karyogamy and Meiosis: These processes take place in the basidium, producing four basidiospores.
• Basidiospore Formation: Basidiospores are produced exogenously (on the outside) on the basidium.
• Basidia and Basidiocarps: The basidia are arranged in fruiting bodies called basidiocarps.
• Common Members: Some common members of basidiomycetes include Agaricus (mushroom), Ustilago (smut), and Puccinia (rust fungus).

Agaricus

4. Deuteromycetes

• Deuteromycetes, commonly referred to as imperfect fungi, are a group of fungi known only by their asexual or vegetative phases.
• When their sexual forms were discovered, these fungi were reclassified into the appropriate taxonomic groups.
• It is also possible that the asexual and vegetative stages were given one name and placed under Deuteromycetes, while the sexual stage was assigned a different name and placed under another class.
• Later, when the connections between these stages were established, the fungi were accurately identified and moved out of Deuteromycetes.
•  Once the perfect (sexual) stages of Deuteromycetes members were identified, they were often reclassified as Ascomycetes and Basidiomycetes. 
• Deuteromycetes reproduce exclusively through asexual spores called conidia. 
•  Their mycelium is septate (divided by septa) and branched. 
• Some members of Deuteromycetes are saprophytes or parasites, while many others play a crucial role as decomposers of organic litter and contribute to mineral cycling.
• Examples of Deuteromycetes include Alternaria, Colletotrichum, and Trichoderma.

Trichoderma

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