Fungi are a diverse group of organisms that include molds, yeasts, mushrooms and bracket fungi. In class 8, students learn about the basic characteristics, structure, reproduction and importance of fungi. Fungi are classified as eukaryotes and have important differences from plants and animals. Understanding fungi helps students appreciate the biodiversity of life on Earth.
Characteristics of Fungi
Fungi have the following characteristics:
- They are eukaryotes – their cells contain nuclei and membrane-bound organelles.
- They have chitin in their cell walls, unlike plants that have cellulose.
- They lack chlorophyll and cannot prepare their own food through photosynthesis.
- They show absorptive nutrition, absorbing nutrients from dead and decaying organic matter.
- Their body consists of long, thread-like structures called hyphae.
- Their mode of nutrition is absorptive, saprophytic or parasitic.
Structure of Fungi
The basic structure of fungi consists of:
- Mycelium – This is a mesh-like structure made of thread-like hyphae. The network of hyphae forms the vegetative body of the fungus.
- Septa – Hyphae have cross walls or septa that divide them into cells. The septa have pores that allow cytoplasm and nutrients to flow between cells.
- Nucleus – Each cell contains one or more nuclei.
- Plasma Membrane – Hyphae have an outer plasma membrane covering the cell wall.
- Mitochondria – Provide energy to the fungus through cellular respiration.
- Vacuoles – Help maintain the turgor pressure in hyphae.
Types of Mycelium
Based on growth and division of nuclei, mycelium can be:
- Septate mycelium – Hyphae have septa dividing them into cells with one or more nuclei in each cell.
- Coenocytic mycelium – Hyphae lack septa and have several nuclei distributed throughout the cytoplasm.
- Apical growth – Growth occurs only at the tip or apex of the hyphae.
Reproduction in Fungi
Fungi show great diversity in their mode of reproduction. The common methods include:
1. Asexual Reproduction
This involves the production and dispersal of asexual spores like conidia, sporangiospores, zoospores, etc. Spores are haploid cells that can divide mitotically to form new hyphae. Common types of asexual spores include:
- Conidia – Produced exogenously at the tips of specialized hyphae called conidiophores.
- Sporangiospores – Formed endogenously inside a sac-like sporangium.
- Zoospores – Flagellated spores capable of movement.
- Chlamydospores – Thick-walled resting spores formed terminally or intercalarily.
2. Sexual Reproduction
Involves fusion of compatible hyphae and genetic recombination. Steps include:
- Plasmogamy – Cytoplasms of two parent hyphae fuse.
- Karyogamy – Nuclei of parents fuse to form diploid zygote.
- Meiosis – Zygote undergoes meiosis to form haploid recombinant nuclei.
- Mitosis – Nuclei divide mitotically forming haploid ascospores.
Based on the spore-bearing structure, sexual reproduction is classified into:
- Zygospore – Diploid spore formed within a thick-walled zygosporangium.
- Ascospore – Haploid spores contained within sac-like asci.
- Basidiospore – Haploid spores external to club-shaped basidia.
Importance of Fungi
Fungi play diverse roles in nature and human welfare:
1. Helpful Roles
- Decompose organic matter and help recycle nutrients.
- Form mutualistic mycorrhizal associations with plant roots.
- Provide food like mushrooms, morels and truffles.
- Help make cheese, bread, wine and beer.
- Provide antibiotics like penicillin.
- Source of industrial chemicals like citric acid.
2. Harmful Roles
- Cause diseases in plants, animals and humans.
- Cause food spoilage and decay.
- Produce toxins and allergens.
- Damage wood, paper, textiles, etc.
Examples of Major Fungal Groups
|Chytridiomycota||Chytrids, Allomyces||Aquatic fungi, produce zoospores|
|Zygomycota||Rhizopus, Mucor||Form zygospores sexually|
|Ascomycota||Yeasts, Penicillium, Aspergillus||Produce ascospores in sacs called asci|
|Basidiomycota||Mushrooms, smuts, rusts||Club-shaped basidia produce basidiospores|
|Deuteromycota||Alternaria, Colletotrichum||Asexual or imperfect fungi|
To summarize key points on fungi covered in class 8:
- Fungi are eukaryotic organisms with chitin cell walls and absorptive nutrition.
- The fungal body consists of thread-like hyphae forming a mycelium.
- They reproduce asexually by spores and sexually by plasmogamy and karyogamy.
- Fungi play vital roles in nutrient cycling, medicine, food industry and as pathogens.
- Major fungal phyla are Chytridiomycota, Zygomycota, Ascomycota, Basidiomycota and Deuteromycota.
Learning about fungi helps appreciate their ubiquity, diversity and significance in the living world. It builds foundations in biology needed for higher classes.