Microbes in Human Welfare NEET Notes

Complete Microbes in Human Welfare Notes for Class 12 Biology | NEET Revision and NCERT Solutions

Microbes - Household and Industrial applications

Household Applications

Lactic acid bacteria (LAB)
- Milk Curd
- LAB produces acids that coagulate and partially digest milk proteins.
- Small amount of curd that is added to the milk for curdling acts as an inoculum containing thousands of LABS, which further multiply.
- LAB enhances the nutritional value of milk by increasing Vitamin B12.
- LAB present in stomach prevents infections.

Fermentation
- Dosaand idli dough is fermented by bacteria, which produces CO2gas and gives it a puffed-up appearance.
- Dough used for making breads is fermented by baker’s yeast (Saccharomyces cerevisiae).

‘Toddy’ (a traditional drink from South India made by fermenting sap from palm trees)

Cheese making
- The bacterium Propionibacterium sharmanii is used in ‘Swiss cheese’ to give it its characteristic holes by producing large amount of carbon dioxide.
- ‘Roquefort cheese’ is ripened by growing certain fungi on them to give them their specific flavour.

Industrial applications

For industrial purposes, microbes are grown in large vessels called fermentors.

On industrial scale, fermented beverages, antibiotics, enzymes, and other bioactive molecules are prepared using microbes.
Fermented beverages
Saccharomyces cerevisiae, also called brewer’s yeast, is used to prepare wine, beer, whisky, brandy, rum, etc. depending upon the type of raw material and processing.

If fermented broth is distilled, then brandy and rum are produced while wine and beer are produced without distillation.
Antibiotics
- Certain microorganisms inhibit the growth of other microorganisms wherever they grow.
- Antibiotics are chemical substances produced by certain microbes that kill or retard the growth of other microbes (disease-causing microbes).
- Penicillin discovered by Alexander Fleming was the first antibiotic to be discovered.
- Fleming discovered it by chance when he was working on the bacterium Staphylococcus. He discovered that growth of Staphylococcus ceases in the culture plates where Penicillium notatum was grown.
- Later on, its use as an effective antibiotic was established by Chain and Florey.

Chemicals, enzymes, and bioactive agents

Microorganism

Substance produced

Fungus Aspergillus niger

Citric acid

Bacterium Acetobacter aceti

Acetic acid

Bacterium Clostridium butylicum

Butyric acid

Bacterium Lactobacillus

Lactic acid

Yeast S.cerevisiae

Ethanol

Bacterium Streptococcus

Streptokinase (used as a clot buster for removing clots from blood vessels of patients with myocardial infarction)

Fungus Trichoderma polysporum

Cyclosporin A (used as immune-suppressive agent in organ transplantation)

Yeast Monascus purpureus

Statins (lower blood cholesterol levels)

Microbes: Applications in Sewage Treatment and Biogas Production

Microbes in Sewage Treatment

Sewage basically consists of human excreta. It may contain many microbes, which may be pathogenic also.
Sewage disposal is a huge problem. It cannot be directly disposed into rivers and streams. Hence, it has to be treated first in sewage treatment plants (STPs).
The heterotrophic microbes present in the sewage itself aid in its treatment.
Treatment of sewage includes two stages − primary treatment and secondary treatment.
Primary Treatment
− Involves physical removal of particles by filtration and sedimentation
- Initially, sequential filtration is used to remove floating debris.
- Then, grit (soil + small pebbles) are removed by sedimentation. Solids that settle down form the sludge while the supernatant forms the effluent.
- Effluent is taken for secondary treatment.

Secondary Treatment
- Effluent is passed to aeration tank → Constant agitation → Air pumped → Vigorous growth of bacteria → Floc formation → Consumption of organic matter by bacteria → Decrease in BOD
- BOD is the amount of oxygen required by bacteria to oxidise all the organic matter present in the effluent.
- Naturally, if organic matter decreases → BOD decreases → Pollution decreases

What is a floc?
Floc = Bacteria + Fungal filaments (in a mesh-like structure)
- When BOD and hence pollution is reduced, effluent is passed into a settling tank. Here, flocs settle down and it is known as Activated Sludge.
- In anaerobic sludge digesters, anaerobic bacteria act on the activated sludge to produce biogas (CH4, CO2, H2S).
- The effluent from secondary treatment plant is released into water bodies.
- Microbial technology for sewage treatment is so effective that no human technology has been able to beat it till date.

Microbes in Production of Biogas

Microbes produce many gases during their metabolism.
The type of gas produced depends upon the substrate they grow on and the type of microbe.
Anaerobic bacteria usually produce methane along with CO2 and H2. Such bacteria are called methanogens.Example - Methanobacterium

Methanogens are commonly found in anaerobic sludge (as in sewage treatment) and in the rumen of cattle. In the rumen of cattle, these bacteria help in cellulose digestion.
Hence, excreta of cattle (gobar) are rich in methanogens. Biogas is also called gobar gas.
Biogas Plant − Components of biogas plant:
- Concrete tank− Here, slurry of dung is fed. It is a 10 − 15 feet deep tank.
- Floating cover− Placed on slurry; rises as the gas is produced
- utlet − It is connected to the pipe.
- Pipe − It supplies the biogas to nearby houses.
- Outlet for spent slurry − Spent slurry can be used as a fertiliser.

Biogas plant is usually set up in rural areas since cow dung is available in abundance there.
Biogas is used for cooking and lighting.
Biogas technology in India is due to the efforts of:
- IARI (Indian Agricultural Research Institute)
- KVCI (Khadi and Village Industries Commission)

Microbes: Bio control Agents and Biofertilizers

Microbes as Bio control Agents

Chemical insecticides and pesticides are harmful as:
- They kill the useful and harmful life forms indiscriminately.
- They are toxic to human beings as well as in the long run.
- If all insects of a particular species are killed, then the natural predator-prey relationship and food chains will get distorted.

Hence, biological means to eradicate pests can be used. This requires knowledge of the life forms (predator + prey) that inhabit a particular area, their life cycles, and patterns of feeding and preferred habitats.

Example − Ladybirds and dragonflies are used to get rid of aphids and mosquitoes.

Microbes can also act in the same manner. Bacillus thuringiensis (Bt) is used to control butterfly caterpillars.
This bacterium is available in sachets as dried spores, which are sprayed on the crops. The spores get into the gut of the larvae and kill it while the other insects remain unperturbed.
By methods of genetic engineering, the genes of B. thuringiensis responsible for killing the larvae have been incorporated into the plants.
Cotton plant with Bt gene incorporated is called Bt-cotton.
The fungus Trichoderma living in roots of plants acts as a bio control agent against several plant pathogens.
Baculoviruses, particularly genus Nucleopolyhedrovirus,are also used as narrow spectrum insecticidal agents.
Bio control agents are particularly useful when useful insects are required to be conserved under IPM (integrated pest management programmes).

Microbes as bio-fertilizers

Chemical fertilizers contribute to the pollution.
Bio-fertilizers are organisms that enrich the nutrient quality of the soil.
Many bacteria, fungi, and cyanobacteria act as biofertilizers.
They act as bio-fertilizers by living in symbiotic association with root nodules of leguminous plants such as Rhizobuim.
These bacteria fix atmospheric nitrogen and enrich the nitrogen content of soil.
Fungi also form symbiotic associations with plants (Mycorrhiza) such as Glomus. They absorb phosphorus and pass it to plants.
Cyanobacteria such as Nostoc, Anabaena, etc. also fix atmospheric nitrogen and act as bio-fertilizers especially in paddy fields.

NCERT Solutions

Microbes, in addition to macroscopic plants and animals, are the most important components of biological systems on Earth. In Class XI, students studied the diversity of living organisms. Protozoa, bacteria, fungi, and microscopic animal and plant viruses, viroids, and prions, which are proteinaceous infectious agents, are all examples of microbes. Bacteria and many fungi can be grown on nutritive media to form colonies visible with the naked eye. These cultures are useful in microorganism research. Microbes in Household Products, Microbes in Industrial Products, Microbes in Sewage Treatment, Microbes in Biogas Production, Microbes as Biocontrol Agents, and Microbes as Biofertilizers are a few of the subtopics. Microbes in Human Welfare discusses microbes in food processing, industrial production, and sewage.

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 microbes with the help of a microscope, which sample would you carry and why?

Solution:

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 which coagulate and digest the milk proteins. One drop of bacteria can consists of millions of bacteria. These can be observed easily under a microscope.

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

Solution:

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

Methano bacterium observed in anaerobic sludge releases methane along with hydrogen gas and carbon dioxide
The process of fermentation of cheese, dough and production of beverages releases carbon dioxide. The microbes involved in the process are Propionibacterium, lactic acid bacteria and Saccharomyces.

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

Solution:

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

It causes an increase in the Vitamin B12 level of curd, thus increasing the nutritional value of curd
It can be used to ferment or culture food
They check the health of the gut

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

Solution:

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

Idli/Dosa traditional south Indian dishes are made from rice and Bengal gram. It is fermented by the action of bacteria
Vada, an Indian dish is a popular snack or breakfast recipe made of Bengal gram. It is fermented by the action of bacteria
One of the other food item that is extensively used is bread which is formed by the action of Saccharomyces cerevisiae, Baker’s yeast.

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

Solution:

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

Microbes are known to produce antibiotics which can be used to treat harmful diseases such as leprosy, diphtheria etc
Microbes produce antitoxins or antisera which acts against a specific pathogen. Antisera is known to be widely used against lock jaw tetanus, diphtheria etc
They produce antibodies which contain antitoxins and opsonins that check the occurrence of diseases namely, cholera, typhoid, small pox etc
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 cell lysis is where cells such as blood cells are destructed by bacteria.
Penicillium notatum, a fungus, produces 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 the antibiotics.

Solution:

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

Penicillin, fungal source is Penicillium notatum
Cephalosporin, fungal source is Cephalosporium acremonium

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

Solution:

The term sewage refers to the municipal waste material which is carried in drains and sewers. Sewage includes both solid and liquid wastes that is 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 to contaminate drinking water. Therefore, it is vital to treat sewage water, by collecting and disposing it.

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

Solution:

The key differences are as follows:

Primary sewage treatment

Secondary sewage treatment

It is the mechanical or physical removal of small and large substances from sewage

It includes the removal of organic matter by microbes

The process deployed is through sedimentation and filtration

The process used is Biological digestion of wastes

Less complicated and relatively low-priced method of treatment

It is a complicated process and is expensive.

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

Solution:

Yes, microbes can certainly be a source of energy. Some bacteria such as the Methane bacterium can be used to generate biogas or gobar gas. In a biogas plant, under anaerobic conditions, biogas can be generated. The biogas plant consists of a concrete tank, with a depth of nearly 10-15 feet, comprising of adequate outlets and inlets. The gathered dung is mixed with water for the formation of slurry and flung into the tank. The tank consists of a digester, which is filled with plenty of anaerobic methane-producing bacteria. This produces biogas from the slurry. Biogas can be extracted through a pipe which can be used as a source of energy. The slurry that is used, is removed from the outlet and used as a fertilizer.

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

Solution:

Organic farming is carried out without the use of any pesticides and chemical fertilizers. Microbes play a major role in organic farming. Bio-fertilizers involves picking advantageous microbes to help improve plant growth, by supplying nutrients as bio-fertilizers are living entities that are known to increase soil fertility. These are introduced into roots, seeds and soil in order to make nutrients available, thus enriching it with organic and soil nutrients. Some species of cyanobacteria and bacteria have the potential to fix the free atmospheric nitrogen.

A symbiotic bacteria, Rhizobium, is found in the root nodules of leguminous plants. Some free living nitrogen-fixing bacteria are Azotobacter and Azospirillium, while Nostoc, Oscillitoria, Anabena are some nitrogen-fixing cyanobacteria. These bio fertilizers are eco-friendly and cost effective.

On the other hand, microbes can also serve as bio-pesticides to check insect pests in plants. The Bacillus thuringiensis, a bio-pesticide, produces a toxin which kills the insect pests.

Withered bacterial spores are mixed with water and sprinkled in fields. These spores enter the gut of the larvae to release toxins, when larvae of various insects feed on the crops. Likewise, a free living fungi, Trichoderma, are found in the roots of higher plants, safeguarding them from pathogens. Another bio-pesticide, Baculovirus, is used as a biological control agent against many arthropods and insects.

11. Three water samples namely river water, untreated sewage water and secondary effluent discharged from a sewage treatment plant were subjected to BOD test. The samples were labelled A, B and C; but the laboratory attendant did not note which was which. The BOD values of the three samples A, B and C were recorded as 20mg/L, 8mg/L and 400mg/L, respectively. Which sample of the water is most polluted? Can you assign the correct label to each assuming the river water is relatively clean?

Solution:

BOD or the biochemical oxygen demand refers to the amount of oxygen which would be consumed if all the organic matter in one liter of water were to be oxidized by bacteria. This BOD test measures the rate of uptake of oxygen by microbes in a sample of water, hence BOD is said to be a measure of the organic matter found in water. Therefore, greater the BOD of waste water, the greater is the polluting potential.

Sample A with BOD 20mg/L can be assigned as the secondary effluent discharged from a sewage treatment plant.

Sample B with BOD 8mg/L can be assigned as river water

Sample C with BOD 400mg/L can be assigned as untreated sewage water.

This assignment in on the basis that the highest BOD value is the sample carrying the most polluted water.

12. Find out the name of the microbes from which Cyclosporin A (an immunosuppressive drug) and Statins (blood cholesterol lowering agents) are obtained.

Solution:

Cyclosporin A, an immunosuppressive drug is obtained from the fungus Trichoderma polysporum. Statins, a blood cholesterol lowering agent, is obtained from Monascus purpureus.

13. Find out the role of microbes in the following and discuss it with your teacher.

(a) Single cell protein (SCP)

(b) Soil

Solution:

The role of microbes in the following are as follows:

(a) Single cell protein (SCP)

It refers to the harmless microbial cells that can be substituted for good proteins.
Some forms of microbial cells can be consumed as food enriched in minerals, proteins, fats, vitamins and carbohydrates like how mushrooms are consumed and yeast is eaten by athletes as a source of protein.
Methylophilus methylotrophus, Spirulina are cultivated on large scale on materials comprising starch-like waste water from potato processing plants, molasses, straw, animal manure and sewage

(b) Soil

The role of microbes is crucial in preserving the fertility of soil
It helps in forming nutrient-rich humus by the phenomena of decomposition
Several bacteria and cyanobacteria species have the potential to fix atmospheric nitrogen to a form that can be used by plants
A symbiotic bacteria, Rhizobium, is found in the root nodules of leguminous plants
Some free living nitrogen-fixing bacteria, Azotobacter and Azospirillium, and some nitrogen-fixing cyanobacteria – Nostoc, Oscillitoria, and Anabena are found here.

14. Arrange the following in the decreasing order (most important first) of their importance, for the welfare of human society. Give reasons for your answer. Biogas, Citric acid, Penicillin and Curd.

Solution:

The following are arranged in decreasing order of importance, the first being most important for welfare of human society.

Penicillin > Biogas > Curd > Citric acid

Reason:

Penicillin is an antibiotic that kills pathogens which causes harmful diseases and infections hence saving lives. Therefore, it is the most important
Biogas is the next in line as it serves as a non-polluting clean fuel which is generated as a byproduct of sewage treatment. It can be used to cook food, and as a source of lighting homes in remote areas
Next is curd. It has a high nutritional value supplying vitamin B12. It helps maintain the health of the gut, and replaces harmful bacteria of the stomach with the beneficial ones.
The last in order is citric acid. It is used as a food preservative.

15. How do biofertilisers enrich the fertility of the soil?

Solution:

Bio-fertilizers are living entities that are known to increase soil fertility, involving picking advantageous microbes to help improve plant growth, by supplying nutrients. These are introduced into roots, seeds and soil in order to make nutrients available, thus enriching it with organic and soil nutrients. Some species of cyanobacteria and bacteria have the potential to fix the free atmospheric nitrogen. A symbiotic bacteria, Rhizobium, is found in the root nodules of leguminous plants. Some free living nitrogen-fixing bacteria are Azotobacter and Azospirillium, while Nostoc, Oscillitoria, Anabena are some nitrogen-fixing cyanobacteria. These bio fertilizers are eco-friendly and cost effective.