NCERT Book Class 12 Biology Microbes In Human Welfare

MICROBES IN HUMAN WELFARE

Besides macroscopic plants and animals, microbes are the major components of biological systems on this earth. You have studied about the diversity of living organisms in Class XI. Do you remember which Kingdoms among the living organisms contain micro-organisms? Which are the ones that are only microscopic? Microbes are present everywhere – in soil, water, air, inside our bodies and that of other animals and plants. They are present even at sites where no other life-form could possibly exist–sites such as deep inside the geysers (thermal vents) where the temperature may be as high as 1000C, deep in the soil, under the layers of snow several metres thick, and in highly acidic environments.

Microbes are diverse–protozoa,bacteria, fungi and microscopic plants viruses, viroids and also prions that are proteinacious infectious agents. Someof the microbes are shown in Figures 10.1 and 10.2.  Microbes like bacteria and many fungi can be grownon nutritive media to form colonies (Figure 10.3), that can be seen with the naked eyes. Such cultures are useful in studies on micro-organisms.

10.1 MICROBES IN HOUSEHOLD PRODUCTS

You would be surprised to know that we use microbes or products derived from them everyday. A common example is the production of curd from milk. Micro-organisms such as Lactobacillus and others commonly called lactic acid bacteria (LAB) grow in milk and convert it to curd. During growth, the LAB produce acids that coagulate and partially digest the milk proteins. A small amount of curd added to the fresh milk as inoculum or starter contain millions of LAB, which at suitable temperatures multiply, thus converting milk to curd, which also improves its nutritional quality by increasing vitamin B12. In our stomach too, the LAB play very beneficial role in checking diseasecausing microbes. 

The dough, which is used for making foods such as dosa and idli is also fermented by bacteria. The puffed-up appearance of dough is due to the production of CO2 gas. Can you tell which metabolic pathway is taking place resulting in the formation of CO2? Where do you think the bacteria for these fermentations came from? Similarly the dough, which is used for making bread, is fermented using baker’s yeast (Saccharomyces cerevisiae).

A number of traditional drinks and foods are also made by fermentation by the microbes. ‘Toddy’, a traditionaldrink of some parts of southern India is made by fermenting sap from palms. Microbes are also used to ferment fish, soyabean and bambooshoots to make foods. Cheese, is one of the oldest food items in which microbes were used. Different varieties of cheese are known by their characteristic texture, flavour and taste, the specificity coming from the microbes used. For example, the large holes in ‘Swiss cheese’ are due to production of a large amount of CO2 by a bacterium named Propionibacterium sharmanii. The ‘Roquefort cheese’ are ripened by growing a specific fungi on them, which gives them a particular flavour.

10.2 MICROBES IN INDUSTRIAL PRODUCTS

Even in industry, microbes are used to synthesise a number of products valuable to human beings. Beverages and antibiotics are some examples. Production on an industrial scale, requires growing microbes in very large vessels called fermentors (Figure 10.4).10.2.1 Fermented Beverages Microbes especially yeasts have been used fromtime immemorial for the production of beverageslike wine, beer, whisky, brandy or rum. For this purpose the same yeast Saccharomyces cerevisiae used for bread-making and commonly called brewer’s yeast, is used for fermenting malted cereals and fruit juices, toproduce ethanol.

Do you recollect the metabolic reactions, which result in the production of ethanol by yeast? Depending on the type of the raw material used for fermentation and the type of processing (with or without distillation) different types of alcoholic drinks are obtained. Wine and beer are produced without distillation whereas whisky, brandy and rum are produced by distillation of the fermented broth. The photograph of a fermentation plant is shown in Antibiotics produced by microbes are regarded as one of the most significant discoveries of the twentieth century and have greatly contributed towards the welfare of the human society. Anti is a Greek word that means ‘against’, and bio means ‘life’, together they mean ‘against life’ (in the context of disease causing organisms); whereas with reference to human beings, they are ‘pro life’ and not against. Antibiotics are chemical substances, which are produced by some microbes and can kill or retard the growth of other (disease-causing) microbes.

EXERCISES

1. Bacteria cannot be seen with the naked eyes, but these can be seen with the help of a microscope. If you have to carry a sample from your home to your biology laboratory to demonstrate the presence of microbesunder a microscope, which sample would you carry and why?

2. Give examples to prove that microbes release gases during metabolism. 

3. In which food would you find lactic acid bacteria? Mention some of their useful applications.

4. Name some traditional Indian foods made of wheat, rice and Bengal gram (or their products) which involve use of microbes.

5. In which way have microbes played a major role in controlling diseases caused by harmful bacteria?

6. Name any two species of fungus, which are used in the production of the antibiotics.

7. What is sewage? In which way can sewage be harmful to us?

8. What is the key difference between primary and secondary sewage treatment?

9. Do you think microbes can also be used as source of energy? If yes, how?

10. Microbes can be used to decrease the use of chemical fertilisers and pesticides. Explain how this can be accomplished.

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