Economic Importance of Fungi
ICSE Class 9 · Biology · Chapter 10
What this chapter covers
- Fungi: the kingdom behind bread, cheese and mushrooms
- Yeast: the fungus that ferments sugar
- Useful role of fungi in breweries
- Useful role of fungi in bakeries
- Useful role of fungi in cheese processing
- Mushroom cultivation
- Mushrooms as food and as a source of income
- Useful roles of fungi at a glance
Key definitions
Fungi are eukaryotic organisms that have a cell wall but no chlorophyll, and that obtain their food by absorbing it from dead or living organic matter around them.
A saprophyte is an organism that obtains its food from dead and decaying organic matter by secreting enzymes onto it and absorbing the dissolved products.
A hypha is a single thin, thread-like filament that makes up the body of most fungi.
A mycelium is the whole mass of interwoven hyphae that forms the body of a fungus.
Yeast is a microscopic, single-celled fungus that feeds on sugars and can break them down without oxygen into ethyl alcohol and carbon dioxide.
Budding is a method of asexual reproduction in which a small outgrowth, the bud, forms on the parent cell, receives a copy of the nucleus, grows and finally separates as a new individual.
Fermentation is the anaerobic breakdown of sugar by micro-organisms such as yeast and some bacteria, producing alcohol or an acid together with carbon dioxide.
Alcoholic fermentation is the kind of fermentation, carried out mainly by yeast, in which glucose is broken down in the absence of oxygen into ethyl alcohol (ethanol) and carbon dioxide, with the release of a small amount of energy.
Brewing is the production of alcoholic drinks, such as beer, by fermenting a sugary liquid made from grain with yeast.
Malt is grain, usually barley, that has been soaked and allowed to begin germinating and then dried.
Baker's yeast is a specially selected strain of the yeast Saccharomyces cerevisiae that is grown in large quantities on molasses and sold to bakeries and households to make dough rise.
Leavening is the process of making dough or batter light and porous by producing a gas inside it, and a leavening agent is the substance that produces the gas.
Key points
- Fungi are eukaryotic, non-green organisms with chitin cell walls that absorb food from organic matter; most are saprophytes, built of hyphae forming a mycelium, and they reproduce by spores.
- Yeast (Saccharomyces cerevisiae) is a single-celled fungus that reproduces by budding and, in the absence of oxygen, carries out alcoholic fermentation: C6H12O6 → 2C2H5OH + 2CO2 + energy, aided by the enzymes zymase and invertase.
- Yeast works best at about 25 °C to 35 °C, is killed above about 50 °C to 60 °C, and stops fermenting when alcohol reaches about 12 to 15 per cent.
- In breweries, yeast ferments the sugar of malted barley, grape juice, palm sap, rice or molasses into ethyl alcohol; the industry also supplies industrial alcohol, fuel ethanol, carbon dioxide and spent yeast.
- In bakeries, baker's yeast ferments sugars in dough; the carbon dioxide, trapped by gluten, leavens the dough, the oven kills the yeast and drives off the alcohol, and the bread is left soft and porous.
- In cheese processing, moulds such as Rhizomucor miehei supply rennet to curdle milk, Penicillium roqueforti ripens blue cheeses and Penicillium camemberti ripens soft white-rind cheeses.
- A mushroom is the fleshy fruiting body of a fungus; button (Agaricus bisporus), oyster (Pleurotus), paddy straw (Volvariella volvacea) and milky (Calocybe indica) mushrooms are cultivated in India.
- Mushroom cultivation in brief: prepare and pasteurise the substrate, mix in spawn, allow the spawn run, add casing for button mushrooms, then keep cool, humid and ventilated for fruiting and harvest.
- Mushrooms are rich in protein, B vitamins, minerals and fibre and low in fat; growing them turns farm waste into food and income, and the spent substrate becomes manure.
- Wild mushrooms may be deadly poisonous and must never be eaten unless identified by an expert.