Kingdom Fungi

The fungi constitute a unique kingdom of heterotrophic organisms. They show a great diversity in morphology and habitat. Fungi are seen on moist bread and rotten fruits; the common mushroom and toadstools are fungi; white spots on mustard leaves are due to a parasitic fungus; some unicellular fungi such as yeast are used to make bread and beer; others cause diseases in plants and animals — the wheat rust-causing Puccinia is an important example — and some, such as Penicillium, are a source of antibiotics. Fungi are cosmopolitan and occur in air, water, soil and on animals and plants. They prefer warm and humid places, which is why food is kept in the refrigerator to prevent fungal and bacterial spoilage.

With the exception of yeasts, which are unicellular, fungi are filamentous. Their bodies consist of long, slender thread-like structures called hyphae, and the network of hyphae is known as the mycelium. Some hyphae are continuous tubes filled with multinucleated cytoplasm — these are called coenocytic hyphae — while others have septae or cross walls. The cell walls of fungi are composed of chitin and polysaccharides.

Most fungi are heterotrophic and absorb soluble organic matter from dead substrates; hence they are called saprophytes. Those that depend on living plants and animals are called parasites. They can also live as symbionts — in association with algae as lichens, and with the roots of higher plants as mycorrhiza.

Reproduction in fungi takes place by:

• vegetative means — fragmentation, fission and budding
• asexual reproduction — by spores called conidia, sporangiospores or zoospores
• sexual reproduction — by oospores, ascospores and basidiospores

The various spores are produced in distinct structures called fruiting bodies. The sexual cycle involves three steps: plasmogamy (fusion of protoplasms between two motile or non-motile gametes), karyogamy (fusion of two nuclei), and meiosis in the zygote resulting in haploid spores. …