Describe various classes of Kingdom Fungi.

(N/A) The morphology of the mycelium,mode of spore formation,and fruiting bodies form the basis for the division of the kingdom into various classes.
$(A)$ Phycomycetes:
- Habitats: Members of Phycomycetes are found in aquatic habitats and on decaying wood in moist and damp places or as obligate parasites on plants.
- Body organization: The mycelium is aseptate and coenocytic.
- Hyphal wall contains microfibrils of cellulose,chitin,or both.
- Reproduction: Asexual reproduction takes place by zoospores (motile) or by aplanospores (non-motile). These spores are endogenously produced in a sporangium. $A$ zygospore is formed by the fusion of two gametes. These gametes are similar in morphology (isogamous) or dissimilar (anisogamous or oogamous).
- Examples: Mucor,Rhizopus (the bread mould),and Albugo (the parasitic fungi on mustard). Diseases caused include white rust (Albugo),late blight of potato (Phytophthora infestans),and downy mildew (Peronospora parasitica).
$(B)$ Ascomycetes:
- Commonly known as sac-fungi,they are mostly multicellular (e.g.,Penicillium) or rarely unicellular (e.g.,yeast,Saccharomyces).
- Mode of nutrition: They are saprophytic,decomposers,parasitic,or coprophilous (growing on dung).
- Body organization: Mycelium is branched and septate.
- Reproduction: Asexual spores are conidia produced exogenously on special mycelium called conidiophores. Sexual spores are called ascospores,which are produced endogenously in sac-like asci. These asci are arranged in different types of fruiting bodies called ascocarps.
- Examples: Aspergillus,Claviceps,and Neurospora.
$(C)$ Basidiomycetes:
- Commonly known as club fungi. They grow in soil,on logs and tree stumps,and in living plant bodies as parasites (rusts and smuts).
- Body organization: Mycelium is branched and septate.
- Reproduction: Asexual spores are generally not found,but vegetative reproduction by fragmentation is common. Sex organs are absent,but plasmogamy is brought about by fusion of two vegetative or somatic cells of different strains or genotypes. The resulting structure is dikaryotic which ultimately gives rise to basidium. Karyogamy and meiosis take place in the basidium producing four basidiospores exogenously.
- Examples: Agaricus (mushroom),Ustilago (smut),and Puccinia (rust fungus).
$(D)$ Deuteromycetes:
- Commonly known as imperfect fungi because only the asexual or vegetative phases of these fungi are known.
- Body organization: Mycelium is septate and branched.
- Nutrition: Some are saprophytes or parasites,while a large number of them are decomposers of litter and help in mineral cycling.
- Examples: Alternaria,Colletotrichum,and Trichoderma.