The plant body of true fungi (Eumycota), the plant body is a thallus. It may be non-mycelial or mycelial. The non-mycelial forms are unicellular, however, they may form a pseudomycelium by budding. In mycelial forms, the plant body is made up of thread like structures called hyphae (sing. hypha). The mycelium may be aseptate (non-septate) or septate. When non-septate and multinucleate, the mycelium is described as coenocytic. In lower fungi the mycelium is non-septate e.g., Phycomycetae. In higher forms it is septate e.g., Ascomycotina, Basidiomycotina and Deuteromycotina. In some forms the plant body is unicelled at one stage and mycelial at the other. Their organization is sometimes described as dimorphic.
Holocarpic and Eucarpic : When the entire mycelium is converted into reproductive structure, the thallus is described as holocarpic. However, if only a part of it becomes reproductive, the thallus is called as eucarpic. The eucarpic forms may be monocentric (having a single sporangium) or polycentric (having many sporangia).

In higher forms the mycelium gets organised into loosely or compactly woven structure which looks like a tissue called plectenchyma. It is of two types :
(i) Prosenchyma : It comprises loosely woven hyphae lying almost parallel to each other.
(ii) Pseudoparenchyma : If the hyphae are closely interwoven, looking like parenchyma in a cross-section, it is called as pseudoparenchyma.
In addition to above, the fungal mycelium may form some specialized structures as under :
(a) Rhizomorphs : Its a 'root-like' or 'string-like' elongated structure of closely packed and interwoven hyphae. The rhizomorphs may have a compact growing point.
(b) Sclerotia : Here the hyphae gets interwoven forming pseudoparenchyma with external hyphae becoming thickened to save the inner ones from desiccation. They persist for several years.
(c) Stroma : It is thick mattress of compact hyphae associated with the fruiting bodies.

The cell wall of fungi is mainly made up of chitin and cellulose. While chitin is a polymer of N-acetyl glucosamine, the celulose is polymer of d-glucose. Precisely, the cell wall may be made up of cellulose-glucan (Oomycetes), chitin chitosan (Zygomycetes) mannan-glucan (Ascomycotina), chitin-mannan (Basidiomycotina) or chitin-glucan (some Ascomycotina, Basidiomycotina and Deuteromycotina). Besides, the cell wall may be made up of cellulose-glycogen, cellulose-chitin or polygalactosamine-galactan.
In higher fungi, where the mycelium is septate, the septa are of several types :
(i) Solid septum : It has no perforations.
(ii) Perforated septum : It has several perforations.
(iii) Acomycetean septum : It has a single large pore in the centre of the septum.
(iv) Bordered pit type septum : It has a perforation in the septum resembling the bordered pit of tracheary elements.
(v) Dolipore septum : It has a single barrel shaped pore in the septum due to thickened rim. The pore has a cap of ER called parenthosome.
The cell wall is closely associated with the inner layer, the plasma membrane. In fungi, specialized structure called lomasomes are also found associated to the plasma membrane. They appear to be as infoldings or invagination of the membrane. Almost similar structures called plasmalemmasomes are also found associated to the membrane. The cell contains one or more well defined eukaryotic nuclei. In fungi the nuclei show intranuclear mitosis which is sometimes referred to as karyochorisis. They also contains mitochondria, E.R., ribosomes, microbodies, lysosomes, vacuoles and crystals of reserve food particles (glycogen, lipid etc.). The cells lack golgi and chloroplast and therefore, chlorophyll and starch grains are also absent. However, a reddish pigment, neocercosporin has been isolated from the fungus Cercospora kikuchii. The vacuoles are bound by tonoplast. The genetic material is DNA.

The fungi are achlorophyllous organisms and hence they can not prepare their food. They live as heterotrophs i.e., as parasites and saprophytes. Some forms live symbiotically with other green forms.
(i) Parasites : They obtain their food from a living host. A parasite may be obligate or facultative. The obligate parasites thrive on a living host throughout their life. The facultative parasites are infact saprophytes which have secondarily become parasitic. While the above classification is based on the mode of nutrition, however, on the basis of their place of occurrence on the host, the parasites can be classified as ectoparasite, endoparasite and hemiendoparasite (or hemiectoparasite). The ectoparasites occur on the surface of the host tissue whereas the endoparasites are found within the host tissue. The forms belonging to the third category are partly ecto- and partly endoparasites. In parasitic forms. The mycelium may occur within the host cells (intracellular) or in between the host cells (intercellular).
Some forms produce rhizoids for absorbing food. The parasitic fungi produce appressoria for adhering to the host. For absorbing food, the obligate parasites produce haustoria. As a result, the plasma membrane of the host cell becomes convoluted but it does'nt break. The fungal cell wall also remains intact. The haustoria may be finger-like, knob-like or branched. Each haustorium is distinguishable into a base, stem and body.
(ii) Saprophytes : They derive their food from dead and decaying organic matter. The saprophytes may be obligate or facultative. An obligate saprophyte remains saprophytic throughout it's life. On the other hand, a facultative saprophyte is infact a parasite which has secondarily become saprophytic.
(iii) Symbionts : Some fungal forms grow in symbiotic association with the green or blue-green algae and constitute the lichen. Here the algal component is photosynthetic and the fungal is reproductive. A few fungal forms grow in association with the roots of higher plants. This association is called as mycorrhiza. They are two types – Ectotrophic mycorrhiza and Endotrophic mycorrhiza e.g., (VAM).

The fungi may reproduce vegetatively, asexually as well as sexually :

(i) Vegetative reproduction
(a) Fragmentation : Some forms belonging to Ascomycotina and Basidiomycotina multiply by breakage of the mycelium.
(b) Budding : Some unicelled forms multiply by budding. A bud arises as a papilla on the parent cell and then after its enlargement separates into a completely independent entity.
(c) Fission : A few unicelled forms like yeasts and slime molds multiply by this process.
(d) Oidia : In some mycelial forms the thallus breaks into its component cells. Each cell then rounds up into a structure called oidium (pl. oidia). They may germinate immediately to form the new mycelium.
(e) Chlamydospores : Some fungi produce chlamydospores which are thick walled cells. They are intercalary in position. They are capable of forming a new plant on approach of favourable conditions.

(ii) Asexual reproduction
(a) Sporangiospores : These are thin-walled, non-motile spores formed in a sporangium. They may be uni-or multinucleate. On account of their structure, they are also called as aplanospores.
(b) Zoospores : They are thin-walled, motile spores formed in a zoosporangium. The zoospores are of several types :
 Uniflagellate with whiplash type flagellum e.g., Allomyces.
 Uniflagellate with tinsel type flagellum e.g., Rhizidiomyces.
 Biflagellate with a tinsel type and a whiplash type flagella e.g., Saprolegnia.
 Biflagellate with two whiplash type flagella e.g., Plasmodiophora.
(c) Conidia : In some fungi the spores are not formed inside a sporangium. They are born freely on the tips of special branches called conidiophores. The spores thus formed are called as conidia. On the basis of development, two types of conidia are recognised namely thallospores and blastospores or true conidia.
Thallospores : In some forms the thallus itself forms spore like bodies called thallospores. The thallospore are of two types namely arthrospores and chlamydospores.
 Arthrospores : They are thinwalled spores formed in basipetal order e.g., Endomyces.
 Chlamydospores : Some of the hyphal cells are converted into thick walled chlamydospores. They may be terminal or intercalary e.g., Ustilago, Saprolegnia.
Blastospores : They develop on conidiophores in acropetal or basipetal succession. They are of two types –
 Porospores : When the blastospores develop by the balooning of the inner wall of conidiophore, it is called as porospore e.g., Alternaria.
 Phialospore : On the other hand, when the first conidium carries the broken parent wall of conidiophore and subsequent conidia possess a new wall, such basipetally formed conidia are called as phialospore e.g., Aspergillus.
Bi-celled conidia are formed in Trichothecium. In Fusarium it is possible to differentiate smaller microconidia from larger macroconidia. Sometimes the conidiophores form specialised structures as under :
Synnema or Coremium : Here the conidiophores get arranged in closely placed parallel plates.
Acervulus : It is a cushion-shaped mass of hyphae having closely packed conidiophores.
Sporodochium : It is also a cushion-shaped acervulus like structure having loosely arranged conidiophores.
Pycnidium : It is pitcher-shaped, embedded body which opens to exterior by a pore called ostiole. It is lined by conidiogenous hyphae. The conidia developing in pycnidia are often described as pycniospores.

(iii) Sexual reproduction : With the exception of Deuteromycotina (Fungi imperfecti), the sexual reproduction is found in all groups of fungi. During sexual reproduction the compatible nuclei show a specific behaviour which is responsible for the onset of three distinct mycelial phases. The three phases of nuclear behaviour are as under :
Plasmogamy : Fusion of two protoplasts.
Karyogamy : Fusion of two nuclei.
Meiosis : The reduction division.
These three events are responsible for the arrival of the following three mycelial phases :
Haplophase : As a result of meiosis the haploid (n) or haplophase mycelium is formed.
Dikaryotic phase : The plasmogamy results in the formation of dikaryotic mycelium (n + n).
Diplophase : As a result of karyogamy the diplophase mycelium (2n) is formed.
In some fungi plasmogamy, karyogamy and meiosis do occur in a regular sequence but not at specified time or points in life cycle. Such a cycle is described as parasexual cycle and phenomena celled parasexuality recorded by Pontecorvo and Roper.
The fungi reproduce sexually by the following methods :
 Isogamy : It involves fusion of two morphologically similar flagellate gametes.
 Anisogamy : Here the two gametes are motile but morphologically dissimilar. The larger gamete may be called as female and the smaller one as male.
 Heterogamy : It involves fusion of a non-motile female gamete (egg) with the motile male gamete (antherozoid). While the male gamete is formed inside the antheridium, the female is produced inside the oogonium. Both the sex organs are unicelled structure.
 Gametangial contact : It involves fusion of two gametangia. In lower forms the female gametangium is called as oogonium. The male gametangium is termed as antheridium. A contact develops in between the two gametangia and then the male nucleus is transferred into the female directly or through a tube.
 Gametangial copulation : In this case the fusion occurs in between the two gametangia. When it occurs in some holocarpic forms where the entire thallus acts as gametangium, the phenomenon is called as hologamy. In others, dissolution of cell wall in between the two gametagial brings about gametangial copulation.
 Spermatization : Here the uninucleate male gametes called spermatia are formed in special structures called spermogonia or pycnidia. The female gametangium is called as ascogonium which has a long neck called trichogyne. The spermatium attaches itself with the trichogyne and transfers the male nucleus, thus bringing about dikaryotisation.
 Somatogamy : In higher fungi there is reduction of sexuality to the maximum level. Here two hyphae of opposite strains are involved in fusion thus bringing about dikaryotization.

In Basidiomycotina, the dikaryotic cells divide by clamp connections. They were first observed by Hoffman, (1856) who named it as 'Schnallenzellen' (buckle-joints). A lateral pouch like outgrowth arises which projects downward like a hook. This pouch or clamp becomes almost parallel to the parent cell. The two nuclei now undergo conjugate division in such a way that one spindle lies parallel to the long axis of the cell and the other somewhat obliquely. As a result, one daughter nucleus enters into the clamp. Now, septae appear separating the clamp and the lower hyphal cell. The upper cell has both the nuclei. The clamp with a nucleus now fuses with the lower cell. The septum between the pouch and the lower cell is dissolved and thus the lower cell now contains both the nuclei of opposite strains. The entire process takes some 23-45 minutes.

Blakeslee, (1904) while working with Mucor sp. observed that in some species sexual union was possible between two hyphae of the same mycelium, in others it occured between two hyphae derived from 'different' spores. He called the former phenomenon as homothallism and the latter as heterothallism. Thus, the homothallic species are self-fertile whereas the heterothallic are self sterile. In heterothallic species the two 'thalli' are sexually incompatible. They are said to belong to opposite strains. Blakeslee designated them as + and – i.e., belonging to opposite strains or mating types. Whitehouse, (1949) differentiated the phenomenon into two categories as under :
(i) Morphological heterothallism : When male and female sex organs are located on different 'thalli' the heterothallism is said to be morphological. Such species are generally described as dioecious.
(ii) Physiological heterothallism : In bisexual forms the two sex organs may be located on the same 'thallus' or on different 'thalli'. In some forms the two sexes even when present on the same 'thallus' are unable to mate, the heterothallism is said to be physiological. Such forms are self-sterile as they need genetically different nuclei. Such nuclei are absent when the same 'thallus' forms the two sex organs. Heterothallic fungi may be bipolar or tetrapolar.

(i) Phycomycetes (Oomycetes/Egg fungi) : It is also called lower fungi, mycelium is coenocytic. Hyphal wall may contain chitin or cellulose (e.g., Phytophthora). Asexual reproduction occurs with the help of conidio-sporangia. Under wet conditions they produce zoospores. Under dry conditions, the sporangia directly function as conidia. Zoospores have heterokont flagellation (one smooth, other tinsel). Sexual reproduction is oogamous. It occurs by gametangial contact where male nucleus enters the oogonium through a conjugation tube. The fertilized oogonium forms oospore. e.g., Sapolegnia, Albugo (Cystopus), Phytophthora, Phythium, Sclerospora.
(ii) Zygomycetes (Conjugation fungi) : Mycelium is coenocytic. Hyphal wall contains chitin or fungal cellulose. Motile stage is absent. Spores (Sporangiospores/aplanospores) are born inside sporangia. Sexual reproduction involve fusion of coenogametes through conjugation (Gametangial copulation). It produces a resting diploid Zygospore. On germination, each zygospore forms a germ sporangium at the tip of a hypha called promycelium e.g., Mucor, Rhizopus.
(iii) Ascomycetes (Ascus : sac, mycete : fungus) : These are unicellular as well as multicellular fungi. In the latter, mycelium is septate. The asexual spores formed in chains are called conidia. The spores are formed exogenously, i.e. outside sporangium. They detach from the parent and form new mycelia. Sexual reproduction is through ascospores, which are formed endogenously (within the mycelium) in a sac like structure called ascus (pl. asci). The gametes involved in sexual reproduction are nonmotile compatible and are generally represented as + and –. The fusion of gametes is followed by reductional division that produces haploid ascospores. The fruiting body called ascocarp.
The ascocarp are of four types :
(a) Cleistothecium : It is an ovoid or spherical fruiting body which remains completely closed e.g., Aspergillus.
(b) Perithecium : It is a flask shaped fruiting body which opens by a single pore called ostiole. It is lined by sterile hyphae called paraphyses. The asci are also mixed with paraphysis e.g., Cleviceps.
(c) Apothecium : It is a saucer-shaped fruiting body. The asci constitute the fertile zone called hymenium e.g., Peziza.
(d) Ascostroma : It is not a distinct fruiting body. It lacks its own well defined wall. The asci arise directly with a cavity (locule) of stroma. It is also called as pseudothecium e.g., Mycosphaerella.
(iv) Basidiomycetes : They are the most advanced fungi and best decomposers of wood. These are called club fungi because of a club shaped end of mycelium known as basidium. They have septate multinucleated mycelium. Septa possess central dolipores and Lateral clamp connections. The sexual spores called basidiospores are generally four in number. They are produced outside the body (exogenuous) unlike ascomycetes where they are endogenous. Two compatible nuclei fuse to form zygote, which undergoes meiosis and forms four basidiospores. The fruiting body containing basidia is a multicelular structure called basidiocarp. The common members are edible mushrooms (Agaricus). Smut and Rust.
(v) Deuteromycetes (Fungi inperfecti) : The group include all those fungi in which sexual or perfect stage is not known. Mycelium is made of septate hyphae. Asexual reproduction commonly occur by means of conidia.

Harmful aspects :

The antibiotics are chemicals produced by living organisms that kill other living organisms. The first known antibiotic is penicillin that was extracted from Penicillium notatum by A. Fleming, (1944). Raper (1952) also extracted the same antibiotic from P. chrysogenum. Besides, several other antibiotics have been extracted since then.

Various vitamins have been obtained from different kind of fungi.