Notes on the important Features Of Fungi

1. The fungi arc achlorophyllous eukaryotic thallophytic.

2. They grow in habitats where organic material is present. They prefer to grow in darkness or dim light in moist habitat.

3. The plant body is a thallus and haploid (gametophyte). The thallus consists either a single cell or a number of thinly cylindrical, delicate threads like filaments known as hyphae (singular hypha). Collectively the hyphae comprise the vegetative body of a fungus known as mycelium. The hyphae may be septa or aseptate.

4. All fungi are heterotrophs. The mode of nutrition is either saprophytic, pan or symbiotic.

When fungi live as saprobes, they grow on dead organisms or decaying organic materials. As parasites, they attack living protoplasm of plants, animals including human beings and draw their nutrition. Some fungi live in lichen thallus along with algae as a symbiont for mutual benefit.

5. Cell wall is composed of chitin or cellulose or both.

6. Food is stored in the form of glycogen, oil drops and lipid globules. There are no starch grains.

7. Majority of fungi are eucarpic i.e. a small part of the thallus is concerned with reproduction and rest of it remains vegetative. The lower group of fungi having uni cellular thallus is holocarpic i.e. they either remain in vegetative reproductive phase at a time.

8. Reproduction is of three types – Vegetative, asexual and sexual. Vegetative reproduction takes place by fragmentation of thallus, budding or fission. Asexual reproduction takes place by the formation of spores or conidia. Usually spores are uni nucleate, single celled propagules, may be motile, endogenously borne called zoospores. Exogenously borne unicellular non-motile asexual spores are called condia. Multinucleate conidia are produced by certain fungi.

Sexual reproduction is variable but comprises of plasmogamy, karyogamy and meiosis:

(i) In lower fungi, two similar gametes fuse and form a zygospore which is known as isogamy.

(ii) In oogamy, the female gamete (egg) is inactive and immobile. The male gamete is active and mobile. Their fusion is known as oogamy. Here, the gametes are morphologically and physiologically quite dissimilar.

(iii) In fungi belonging to Ascomycetes, the sex organs are known as antheridum and ascogonium. In Basidiomycetes, there are no sexual organs at all. The mycelial cells of one strain fuse with the cells of opposite strain and produce diploid structures. Thus, on the basis of sex, fungi may be monoecious (male and female sex organs borne by same mycelium) or dioecious (male and female sex organs are borne on separate mycelia).

Plasmogamy is the mechanism which brings two compatible nuclei together into a single protoplast. Karyogamy is the actual fusion of the two nuclei following plasmogamy which results in the formation zygote (2n). Zygote undergoes meiotic division and forms haploid spores.

9. Sexually produced spores are genetically different; some are + strain and others – strain.

10. Spores on germination produce new mycelia.

SACCHAROMYCES (YEAST)

Systematic Position

Kingdom – Plantae

Division – Thallophyta

Class – Ascomycetes

Sub- Class – Protoascomycetes

Order – Endomycetales

Family – Saccharomycctaceae

Genus – Saccharomyces

(About 30 species)

Occurrence

Species of Sacchciromyces arc commonly known as the yeasts. They occur mostly as saprophytes in substrata which contain sugars such as sugar solution, surface of ripe fruits, nectar of flowers etc. These are called sugar fungi because of their love for sugar. They are also found in soil, milk, animal excreta and decaying vegetables. Some occur as parasites in plants and animals including man.