Microbes In Human Welfare Solutions Class 12 Biology NCERT PDF

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Microbes in Human Welfare Solutions

Chapter 10: Microbes in Human Welfare Solutions

10.1 Microbes In Household Products

You would be surprised to know that we use microbes or products derived from them every day. 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 produces acids that coagulate and partially digest the milk proteins. A small amount of curd added to the fresh milk as inoculum or starter contains 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 stomachs too, the LAB plays a very beneficial role in checking disease-causing 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 microbes. ‘Toddy’, a traditional drink in some parts of southern India is made by fermenting sap from palms.

Microbes are also used to ferment fish, soybean, and bamboo shoots 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, flavor, and taste, the specificity coming from the microbes used.

For example, the large holes in ‘Swiss cheese’ are due to the production of a large amount of CO2 by a bacterium named Propionibacterium shamanic.

The ‘Roquefort cheese’ is ripened by growing specific fungi on them, which gives them a particular flavor.


Even in industry, microbes are used to synthesize 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

10.2.1 Fermented Beverages

Microbes especially yeasts have been used from time immemorial for the production of beverages
like 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, to produce 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
Figure 10.5.

10.2.2 Antibiotics

Antibiotics produced by microbes are regarded as one of the most significant discoveries of the twentieth century and have greatly contributed to the welfare of 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 it. Antibiotics are chemical substances, which are produced by some microbes and can kill or retard the growth of other (disease-causing) microbes.

Language English
No. of Pages12
PDF Size11.1 MB

NCERT Solutions Class 12 Biology Chapter 10 Microbes in Human Welfare Solutions

1. Bacteria cannot be seen with 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 microbes with the help of a microscope, which sample would you carry and why?


To demonstrate the presence of microbes with the help of a microscope, Curd is apt. It can be used as a sample as it contains plenty of Lactobacillus or lactic acid bacteria. These are the bacteria that produce acids that coagulate and digest the milk proteins. A small drop of curd consists of millions of bacteria. These can be observed easily under a microscope.

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


Microbes release gases during metabolism, some examples are as follows:

(i) Methano bacterium observed in anaerobic sludge releases a large amount of methane along with hydrogen gas and carbon dioxide

(ii) The process of fermentation of cheese, dough, and the production of beverages releases carbon dioxide. The microbes involved in the process are Propionibacterium sharmanii, lactic acid bacteria and Saccharomyces cerevisiae.

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


We can find lactic acid bacteria in curd. Some of the useful applications of these bacteria are:

(i) It causes an increase in the Vitamin B12 level of curd, thus increasing the nutritional value of curd

(ii) It can be used to ferment or culture food

(iii) They check the health of the gut

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


Some Indian food made of wheat, rice, and Bengal gram are:

(i) Wheat: Bread, Bhatura, and Cake are made of Wheat

(ii) Rice: Idli, Dosa, and Uttapam are made of Rice

(iii) Bengal gram: Dhokla and Khandvi are made of Bengal gram

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


Microbes play an important role in controlling diseases caused by harmful bacteria, some are:

(i) Microbes are known to produce antibiotics that can be used to treat harmful diseases such as leprosy, diphtheria, etc

(ii) Microbes produce antitoxins or antisera which act against a specific pathogen. Antisera is known to be widely used against lockjaw tetanus, diphtheria, etc

(iii) They produce antibodies that contain antitoxins and opsonins that check the occurrence of diseases namely, cholera, typhoid, smallpox etc

(iv) The design of antibiotics is such that they destroy bacteria by weakening their cell walls. This in turn weakens several immune cells (white blood cells) that enter the bacterial cell causing cell lysis. The process of destructing cells such as blood cells by bacteria is known as cell lysis.

(v) Penicillium notatum, a fungus, produces the chemical penicillin. It inhibits the growth of bacteria named Staphylococci in the body

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


Several microbes produce antibiotics, that kill other microbes which cause diseases. These medicines, and antibiotics are typically acquired from fungi and bacteria. Two species of fungus that are used in the production of antibiotics are:

(i) Penicillin, the fungal source is Penicillium notatum

(ii) Cephalosporin, the fungal source is Cephalosporium acremonium

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


The term sewage refers to the municipal waste material which is carried away in drains and sewers. Sewage includes both solid and liquid wastes that are rich in microbes and organic matter.

Most of these microbes are pathogenic, i.e., they are capable of causing diseases such as water-borne diseases. This sewage water is one of the major causes of contamination in drinking water. Therefore, it is vital to treat sewage water, by collecting and disposing of it.

Microbes in Human Welfare Solutions NCERT Textbook With Solutions PDF Free Download

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