1 Microbes in Household Products

2 Microbes in Industrial Products

13 Microbes in Sewage Treatment

4 Microbes in Production of Biogas

5 Microbes as Biocontrol Agents

6 Microbes as Biofertilisers

Microbes are present everywhere –in soil, water, air, inside our bodies and that of other animals and plants. True or False

Ans. True

Microbes are present only in favorable conditions. Comment

Ans. NO. Microbes  are present even at places where no other life-form could possibly survive– 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 include

1. Protozoa
2. Bacteria
3. Fungi
4. Viruses, viroids and prions
5. All

Ans. 5) All

Draw a well labeled diagram of a bacteriophage.

Ans.

Adenovirus which causes

1. Respiratory infections
2. Skin infection
3. Circulatory problems
4. All

Ans. Respiratory infections

Mosaic Virus (TMV) is

1. Polyhedral
2. Spherical
3. Rod-shaped
4. Complex

Ans. 3) Rod-shaped

181 Rod-shaped Tobacco

Which of the following is FALSE?

1. Microbes cause a large number of diseases in human beings.
2. Microbes cause diseases in animals and plants. \
3. All microbes are harmful
4. Several microbes are useful to man

Ans. All microbes are harmful

What is the full form of LAB?

Ans. Lactic Acid Bacteria

Name the organism which converts milk into curd.

Ans. Micro-organisms such as Lactobacillus and others commonly called lactic acid bacteria (LAB)grow in milk and convert it to curd.

How curd is prepared?

Ans. To prepared curd, a small amount of curd added to the fresh milk as inoculum or starter containing millions of LAB, which at suitable temperatures multiply, thus converting milk to curd.

Mention some useful applications of LAB besides converting milk to curd.

Ans. Some useful applications of LAB are:

1. During growth, the LAB produce acids that coagulate and partially digest the milk proteins.
2. Improves nutritional quality by increasing vitamin B12.
3. In our stomach, the LAB play very beneficial role in checking disease causing microbes.

How dough, which is used for making foods such as dosa and idli, is prepared?

Ans. The dough, which is used for making foods such as dosa and idli is fermented by bacteria.

Mention the reason for the puffed-up appearance of dough.

Ans. The puffed-up appearance of dough is due to the production of CO2 gas.

How the dough, which is used for making bread, is prepared?

Ans. The dough, which is used for making bread, is fermented using baker’s yeast (Saccharomyces cerevisiae).

A number of traditional drinks and foods are made by _________________________.

Ans.fermentation by the microbes

What is “Toddy”?

Ans. ‘Toddy’ is a traditional drink of some parts of southern India.

How toddy is made?

Ans. ‘Toddy’ is made by fermenting sap from palms.

Microbes are also used to __________fish, soyabean and bambooshoots to make foods.

Ans. ferment

Why there are large holes in ‘Swiss cheese’?

Ans. The large holes in ‘Swiss cheese’ are due to production of a large amount of CO2 by a bacterium

Name the bacterium which produces  in ‘Swiss cheese’.

Ans. Propionibacterium sharmanii

How are ‘Roquefort cheese’ are ripened?

Ans. The ‘Roquefort cheese’ are ripened by growing a specific fungi on them, which gives them a particular flavour.

10.2 MICROBES IN INDUSTRIAL PRODUCTS

Give example of two products produced by microbes?

Ans. Beverages and antibiotics

What are fermentors?

Ans. Fermentors are very large vessels in which microbes are grown to produce valuable products on an industrial scale.

Name the yeast used for the production of beverages like wine, beer, whisky, brandy or rum.

Ans.  Saccharomyces cerevisiae, commonly called Brewer’s yeast

Which of the following is true?

1. Wine and beer are produced without distillation
2. Whisky, brandy and rum are produced by distillation
3. Whisky, brandy and rum are produced without distillation
4. Both (1) & (2)

Ans. 4) Both (1) & (2)

Write a short note on “Fermented Beverages”.

Ans. Microbes particularly yeasts have been used from time immemorial for the production of beverages like wine, beer, whisky, brandy or rum. The 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.

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.

What are antibiotics?

Ans. Antibiotics are chemical substances, which are produced by some microbes and can kill or retard the growth of other (disease-causing) microbes.

Antibiotics have significantly improved our ability to treat deadly diseases such as plague, whooping cough (kali khansi), diphtheria (gal ghotu) and leprosy (kusht rog).

Name the first antibiotic.

Ans. Penicillin.

Name the scientist who discovered Penicillin.

Ans. Alexander Fleming

How did Alexander Fleming discover Penicillin?

Ans. Discovery of  Penicillin is an example of chance discovery (serendipity). Alexander Fleming while working on Staphylococci bacteria, once observed that a mould growing in one of his unwashed culture plates around which Staphylococci could not grow. He found out that it was due to a chemical produced by the mould and he named it Penicillin after the mould Penicillium notatum.

Name the source of Penicillin.

Ans. Penicillium notatum (also known as Penicillium Chrysogenum)

Name the scientists who established full potential of penicillin as an effective antibiotic.

Ans. Ernest Chain and Howard Florey

Name some antibiotics and also mention their sources.

Ans. Some antibiotics with their sources:

10.2.3 Chemicals, Enzymes and other Bioactive Molecules

Microbes are also used for commercial and industrial production of certain chemicals like organic acids, alcohols and enzymes. True/ False

Ans. True

Which of the following are acid producers?

1. Aspergillus niger
2. Acetobacter aceti
3. Clostridium butylicum
4. Lactobacillus
5. All

Ans. 5) All

Name the microbe which produces citric acid.

Ans. Aspergillus niger (a fungus)

Name the microbe which produces acetic acid.

Ans. Acetobacter aceti (a bacterium)

Name the microbe which produces acetic acid.

Ans. Clostridium butylicum (a bacterium)

Name the microbe which produces lactic acid.

Ans. Lactobacillus (a bacterium)

Name the yeast used for commercial production of ethanol.

Ans. Saccharomyces cerevisiae

Name the enzymes used in detergent formulations.

Ans. Lipases are used in detergent formulations and are helpful in removing oily stains from the laundry.

Bottled fruit juices bought from the market are clearer as compared to those made at home. Why?

Ans. This is because the bottled juices are clarified by the use of enzymes pectinases and proteases.

Name the bacterium which produces Streptokinase.

Ans. Streptococcus

Mention the function of Streptokinase.

Ans. Streptokinase is used as a ‘clot buster’ for removing clots from the blood vessels of patients who have undergone myocardial infaction leading to heart attack.

Name the organism which produces cyclosporin A.

Ans. Cyclosporin A is produced by the fungus Trichoderma polysporum.

What is cyclosporin A?

Ans. Cyclosporin A is bioactive molecule, which is used as an immunosuppressive agent in organ-transplant patients.

Name the organism which produces Statins.

Ans. Statins are produced by the yeast called Monascus.

What are Statins?

Ans. Statins are a class of drugs that acts as blood-cholesterol lowering agents. It acts by competitively inhibiting the enzyme responsible for synthesis of cholesterol.

10.3 MICROBES IN SEWAGE TREATMENT

Why is sewage treated before disposal?

Ans. Sewage also called municipal waste-water contains large amounts of organic matter, human excreta and microbes. Many microbes are pathogenic in nature. If sewage is discharged directly into natural water bodies like rivers and streams directly, it will cause pollution and health hazards. Therefore, sewage is treated in sewage treatment plants (STPs) to make it less polluting.

Treatment of waste water is done by the heterotrophic microbes naturally present in the sewage.  True/False

Ans. True

Name the two stages of sewage treatment.

Ans. Sewage treatment is carried out in two stages:

1. Primary Treatment
2. Secondary Treatment or Biological Treatment

Briefly describe primary treatment of sewage.

Ans. Primary treatment steps mainly involve physical removal of particles – large and small – from the sewage through filtration and sedimentation. Substances present in sewage are removed in stages; initially, floating debris is removed by sequential filtration. Then the grit (soil and small pebbles) are removed by sedimentation. All solids that settle form the primary sludge, and the supernatant forms the effluent. The effluent from the primary settling tank is taken for secondary treatment.

Describe secondary treatment of sewage.

Ans. Secondary treatment of sewage takes place as follows:

The primary effluent is passed into large aeration tanks where it is continuously agitated mechanically and air is pumped into it. This allows vigorous growth of useful aerobic microbes into flocs (masses of bacteria associated with fungal filaments to form mesh like structures). While growing, these microbes consume the major part of the organic matter in the effluent. This significantly reduces the BOD (biochemical oxygen demand) of the effluent. The sewage water is treated till the BOD is reduced.

Once the BOD of sewage or waste water is decreased significantly, the effluent is then passed into a settling tank where the bacterial ‘flocs’ are allowed to sediment. This sediment is called activated sludge.

A small part of the activated sludge is pumped back into the aeration tank to serve as the inoculum.  The remaining major part of the sludge is pumped into large tanks called anaerobic sludge digesters.

In anaerobic sludge digesters, other kinds of bacteria, which grow anaerobically, digest the bacteria and the fungi in the sludge.  During this digestion, bacteria produce a mixture of gases such as methane, hydrogen sulphide and carbon dioxide. These gases form biogas and can be used as source of energy as it is inflammable.

The effluent from the secondary treatment plant is generally released into natural water bodies like rivers and streams. In this way water is recycled in nature.

What is the full form of BOD?

Ans. Biochemical Oxygen Demand

Define BOD.

Ans. BOD refers to the amount of the oxygen that would be consumed if all the organic matter in one liter of water were oxidized by bacteria.

What is the significance of BOD Test?

Ans. BOD test measures the rate of uptake of oxygen by micro-organisms in a sample of water and thus, indirectly, BOD is a gauge of the organic matter present in the water. The greater the BOD of waste water, more is the organic matter present in waste water, more is its polluting potential.

What is activated sludge?

Ans. Activated sludge refers to aerated sewage containing aerobic microorganisms which helps to break it down.

What are the initiatives taken by the government of India to save major rivers from pollution?

Ans. The Ministry of Environment and Forests has initiated the following two plans to save our rivers from pollution:

1. Ganga Action Plan
2. Yamuna Action Plan

Under these plans, it has been proposed to build a large number of sewage treatment plants so that only treated sewage may be discharged in the rivers.

10.4 MICROBES IN PRODUCTION OF BIOGAS

What is biogas?

Ans. Biogas is a mixture of gases (containing mainly methane) produced by the microbial activity and which may be used as fuel.

What are the factors that determine the type of the gas produced by microbes?

Ans. Microbes produce different types of gaseous end-products during growth and metabolism.

The type of the gas produced depends upon

1. The microbes
2. The organic substrates

Name the main gas produce in fermentation of dough, cheese making and production of beverages?

Ans.

What are methanogens?

Ans. Methanogens are bacteria, which grow anaerobically on cellulosic material, produce large amount of methane along with and .

Give an example of methanogens.

Ans. Methanobacterium.

Which of the following statement is true about methanogens?

1. These bacteria are commonly found in the anaerobic sludge during sewage treatment.
2. These bacteria are also present in the rumen (a part of stomach) of cattle.
3. Both (1) & (2)
4. None

Ans. Both (1) & (2)

What is the role of methanogens in the rumen of cattle?

Ans. The food of cattle contains a large amount of cellulosic material. In rumen, these bacteria assist in the breakdown of cellulose and play an important role in the nutrition of cattle.

Are human beings able to digest the celluose present in our foods?

Ans.  Human beings cannot digest cellulose. This is because they lack the enzymes required  to breakdown cellulose.

Draw a well labelled diagram of biogas plant. Explain its working.

Ans. The excreta (dung) of cattle, gobar, is rich in methanogens. Dung can be used for production of biogas, commonly called gobar gas.

The biogas plant consists of a 10-15 feet deep concrete tank called digester. Bio-wastes are collected fed into the digester as slurry of dung. A floating cover, called gas-holder, is placed over the slurry, which keeps on rising as the gas is produced in the tank due to the microbial activity. The biogas plant has an outlet, which is connected to a pipe to supply biogas to nearby houses. The biogas so produced is used for cooking and lighting.

The spent slurry is removed through another outlet and may be used as fertiliser.

Name the institutions responsible for developing technology of biogas production in India?

Ans. The technology of biogas production was developed in India mainly due to the efforts of

1. Indian Agricultural Research Institute (IARI)
2. Khadi and Village Industries Commission (KVIC)

10.5 MICROBES AS BIOCONTROL AGENTS

What do you mean by Biocontrol?

Ans.Biocontrol refers to the use of biological methods and biological agents for controlling plant diseases and pests.

Biological control of pests and diseases:

• In agriculture, there is a method of controlling pests that relies on natural predation rather than introduced chemicals.

Which of the following is true?

1. Biodiversity fosters health of the ecosystem
2. The more variety a landscape has, the more sustainable it is.
3. Both (1) & (2)
4. None

Ans. 3) Both (1) & (2)

Write a short note on organic farming. How is it different from ‘conventional’ farming?

Ans. Organic farming is a form of agriculture that relies on techniques such as crop rotation, green manure, compost, and biological pest control.

In organic farming, the emphasis is on developing an understanding of the webs of interaction between the myriad of organisms that constitute the field fauna and flora; and creating a system where pests are not eradicated, but are kept at manageable levels by a complex system of checks and balances within a dynamic ecosystem.

The organic farming believes that the eradication of the creatures that are often described as pests is not only possible, but also undesirable, for without them the beneficial predatory and parasitic insects which depend upon them as food or hosts would not be able to survive.

In contrast, the ‘conventional’ farming practices use chemical methods to kill both useful and harmful life forms indiscriminately.

The use of biocontrol measures will greatly reduce our dependence on toxic chemicals and pesticides. True/False

Ans. True

Which of the following is true?

1. Ladybird is useful in controlling aphids
2. Dragonflies are useful to get rid of mosquitoes
3. Both (1) & (2)
4. None

Ans. 3) Both (1) & (2)

Give an example of microbial biocontrol agent that can be introduced in order to control butterfly caterpillars.

Ans. Bacillus thuringiensis (often written as Bt).

Write a short note on Bacillus thuringiensis.

Ans. Bacillus thuringiensis is an excellent example of microbial biocontrol agent. These are available in sachets as dried spores which are mixed with water and sprayed onto vulnerable plants such as brassicas and fruit trees, where these are eaten by the insect larvae. In the gut of the larvae, the toxin is released and the larvae get killed. The bacterial disease will kill the caterpillars, but leave other insects unharmed.

The development of methods of genetic engineering has allowed us to introduce B. thuringiensis toxin genes into plants, making them resistant to attack by insect pests.

Give one example of pest resistant plant.

Ans. Bt-cotton

Name the fungus which is used in treatment of plant diseases and serves as biocontrol agents of several plant pathogens.

Ans.Trichoderma.

Which of the following is true?

1. Trichoderma species are free-living fungi
2. They are very common in the root ecosystems
3. Both (1) & (2)
4. None

Ans. Both (1) & (2)

What are Baculoviruses?

Ans. Baculoviruses are pathogens that attack insects and other arthropods.

Name the genus that contains majority of baculoviruses used as biological control?

Ans. Nucleopolyhedrovirus.

What are the advantages of Baculoviruses?

Ans. Advantages of Baculoviruses are:

1. Baculoviruses are excellent agent for species-specific, narrow spectrum insecticidal applications.
2. They do not have negative effects on plants, mammals, birds, and fish or even on non-target insects.
3. They play an important role in integrated pest management (IPM) programme, especially when beneficial insects are to be conserved or when an ecologically sensitive area is being treated.

10.6 MICROBES AS BIOFERTILISERS

How can we deal with pollution caused by the use of chemical fertilisers?

Ans. Pollution caused by the use of chemical fertilisers can be dealt by switching to organicfarming – the use of biofertilisers.

What do you mean by Biofertilisers?

Ans. Biofertilisers refer to a substance which contains organisms that enrich the nutrient quality of the soil.

What are the main sources of biofertilisers?

Ans. The main sources of biofertilisers are bacteria, fungi and cyanobacteria.

 What are root nodules?

Ans. These are nodules found on the roots of leguminous plants formed by the symbiotic association of Rhizobium. These bacteria fix atmospheric nitrogen into organic forms, enriching the nitrogen content of the soil, which is used by the plant as nutrient,

Name two bacteria free-living in the soil that fix nitrogen.

Ans. Azospirillum and Azotobacter

Briefly explain mycorrhiza?

Ans. Mycorrhiza is a symbiotic association between fungi and roots of a vascular plant. Many members of the genus Glomus form mycorrhiza.

            In this mycorrhizal association, the fungal symbiont absorbs phosphorus from soil and passes it to the plant. Plants having such associations show other benefits also, such as resistance to root-borne pathogens, tolerance to salinity and drought, and an overall increase in plant growth and development.  

What advantage the fungus derives from mycorrhizal association?

Ans. In mycorrhizal association, the plants supply nutrients (carbohydrates, vitamins, etc), growth stimulators, etc for fungus.

Give examples of Cyanobacteria which fix atmospheric nitrogen.

Ans. Anabaena, Nostoc, Oscillatoria, etc

Briefly describe Cyanobacteria Biofertilizers.

Ans. Cyanobacteria are autotrophic microbes widely distributed in aquatic and terrestrial environments many of which can fix atmospheric nitrogen, e.g. Anabaena, Nostoc, Oscillatoria, etc.

In paddy fields, cyanobacteria serve as an important biofertiliser. Blue green algae also add organic matter to the soil and increase its fertility.

Microbes are an insignificant component of life on earth. True/False

Ans. False

All microbes are pathogenic. True/False

Ans. False

The dough, which is used to make bread, is fermented by yeast called ______________

Ans. Saccharomyces cerevisiae

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 microbes under 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.
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?
12. Find out the name of the microbes from which Cyclosporin A (an immunosuppressive drug) and Statins (blood cholesterol lowering agents) are obtained.
13. Find out the role of microbes in the following and discuss it with your teacher.

(a) Single cell protein (SCP)

(b) Soil

1.  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
2. How do biofertilisers enrich the fertility of the soil?

D’S

Here are CBSE Class 12 Biology (NCERT) Board Exam Answers for Chapter: Microbes in Human Welfare. These answers are written in the style expected in the CBSE board examination.

1. Which sample would you carry to demonstrate microbes under a microscope and why?

Answer:
I would carry a sample of curd because it contains a large number of lactic acid bacteria (LAB), especially Lactobacillus. These bacteria are easily visible under a microscope after proper staining and are present in large numbers due to fermentation.

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

Answer:
Examples are:

• Yeast produces carbon dioxide during fermentation of dough, causing bread and idli batter to rise.
• In biogas plants, methanogenic bacteria produce methane (CH₄) along with carbon dioxide and hydrogen sulphide.
• During the preparation of Swiss cheese, Propionibacterium shermanii releases carbon dioxide, forming large holes.

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

Answer:
Lactic acid bacteria are found in curd.

Applications:

• Convert milk into curd.
• Increase the nutritional value by increasing vitamin B₁₂.
• Improve digestion.
• Prevent the growth of harmful microbes in the stomach.

4. Name some traditional Indian foods made of wheat, rice and Bengal gram which involve the use of microbes.

Answer:
Examples include:

• Idli
• Dosa
• Dhokla
• Jalebi
• Bhatura

These foods are prepared by microbial fermentation, mainly involving lactic acid bacteria and yeast.

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

Answer:
Microbes produce antibiotics, which kill or inhibit the growth of disease-causing bacteria.
Example:

• Penicillin, produced by Penicillium notatum, is used to treat many bacterial infections.

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

Answer:

• Penicillium notatum
• Penicillium chrysogenum

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

Answer:
Sewage is municipal wastewater containing human excreta, domestic waste and industrial effluents.

Harmful effects:

• Contains disease-causing microorganisms.
• Pollutes water bodies.
• Reduces dissolved oxygen.
• Spreads water-borne diseases such as cholera, typhoid and dysentery.

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

Answer:

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

Answer:
Yes. Methanogenic bacteria convert cattle dung and organic waste into biogas, which mainly contains methane. Biogas is used as a clean and renewable source of energy for cooking, lighting and electricity generation.

10. How can microbes decrease the use of chemical fertilisers and pesticides?

Answer:
Microbes are used as biofertilisers and biopesticides.

• Biofertilisers such as Rhizobium, Azotobacter and cyanobacteria fix atmospheric nitrogen and improve soil fertility.
• Biopesticides such as Bacillus thuringiensis (Bt) control insect pests without polluting the environment.

11. Assign the correct labels to the water samples based on BOD values.

Answer:

• Most polluted sample: C (400 mg/L)
• Untreated sewage: C
• River water: B (8 mg/L)
• Secondary effluent: A (20 mg/L)

Higher BOD indicates greater organic pollution.

12. Name the microbes from which Cyclosporin A and Statins are obtained.

Answer:

• Cyclosporin A: Trichoderma polysporum
• Statins: Monascus purpureus

13. Role of microbes in:

(a) Single Cell Protein (SCP)

Answer:

• Microbes such as Spirulina, yeast and Methylophilus methylotrophus are used as SCP.
• They are rich in proteins, vitamins and minerals.
• Used as food supplements and animal feed.

(b) Soil

Answer:

• Decompose organic matter and recycle nutrients.
• Fix atmospheric nitrogen.
• Improve soil fertility.
• Help in nutrient cycling and humus formation.

14. Arrange the following in decreasing order of importance for the welfare of human society and give reasons.

Answer:

Penicillin > Curd > Biogas > Citric acid

Reasons:

• Penicillin: Saves millions of lives by treating bacterial diseases.
• Curd: Nutritious food with beneficial bacteria that improve digestion.
• Biogas: Renewable, eco-friendly source of energy and helps in waste management.
• Citric acid: Mainly used as a food preservative and flavouring agent in industries.

15. How do biofertilisers enrich soil fertility?

Answer:
Biofertilisers improve soil fertility by:

• Fixing atmospheric nitrogen (Rhizobium, Azotobacter, cyanobacteria).
• Solubilising phosphate.
• Increasing nutrient availability.
• Improving soil texture and microbial activity.
• Reducing the need for chemical fertilisers.

Important Board Exam Keywords

• Lactic Acid Bacteria (LAB)
• Fermentation
• Antibiotics
• Penicillin
• Biofertilisers
• Biopesticides
• Methanogens
• Biogas
• Biological Oxygen Demand (BOD)
• Activated sludge
• Rhizobium
• Lactobacillus
• Trichoderma polysporum
• Monascus purpureus
• Bacillus thuringiensis (Bt)

These answers are concise, NCERT-based, and suitable for CBSE Class 12 Board examinations (2–5 marks).

MICROBES IN HUMAN WELFARE:: TOPIC 4NEET & CBSE Class 12 Biology

What is Sewage?

• Sewage = Municipal wastewater containing:
  • Human excreta
  • Organic matter
  • Microorganisms
  • Disease-causing (pathogenic) microbes

Why is sewage treated?

Untreated sewage:

• Pollutes rivers and lakes.
• Decreases dissolved oxygen.
• Spreads water-borne diseases.
• Harms aquatic organisms.

Therefore, sewage is treated in Sewage Treatment Plants (STPs).

Sewage Treatment – Flow Chart

Sewage
   ↓
Primary Treatment (Physical)
   ↓
Primary Effluent
   ↓
Secondary Treatment (Biological)
   ↓
Activated Sludge
   ↓
Anaerobic Sludge Digester
   ↓
Biogas Produced
   ↓
Treated Water Released into Rivers

STEP 1 : Primary Treatment (Physical Treatment)

Purpose

Removes large and small solid particles.

Processes

(A) Filtration

Removes:

• Plastic
• Cloth
• Wood pieces
• Floating debris

↓

(B) Sedimentation

Heavy particles settle down.

Removes:

• Sand
• Soil
• Pebbles
• Grit

Products formed

Settled solids
→ Primary Sludge

Upper liquid
→ Primary Effluent

Primary effluent is sent for biological treatment.

STEP 2 : Secondary Treatment (Biological Treatment)

This is the most important NEET topic.

The primary effluent enters large aeration tanks.

What happens?

✔ Air is continuously pumped.

✔ Mechanical agitation is done.

This provides oxygen.

↓

Useful aerobic bacteria multiply rapidly.

Formation of Flocs

Bacteria combine with fungal filaments.

They form mesh-like structures called

Flocs

Definition

Flocs are masses of bacteria associated with fungal filaments.

Function of Flocs

The microbes consume organic matter present in sewage.

As organic matter decreases,

↓

BOD decreases.

What is BOD?

BOD = Biochemical Oxygen Demand

Definition

Amount of oxygen required by bacteria to oxidize organic matter present in 1 litre of water.

Important Points

High BOD

More organic matter

More pollution

Low BOD

Cleaner water

Less pollution

NEET Line

Greater the BOD, greater the pollution.

Activated Sludge

After BOD decreases,

The sewage enters a settling tank.

Flocs settle at the bottom.

This settled material is called

Activated Sludge

What happens to Activated Sludge?

Small Portion

Sent back into aeration tank.

Purpose:

Acts as inoculum (starter culture).

Remaining Portion

Transferred to

Anaerobic Sludge Digester

STEP 3 : Anaerobic Digestion

Inside sludge digester,

Anaerobic bacteria digest

• Dead bacteria
• Fungi
• Organic matter

Gases Produced

During digestion,

Biogas is produced.

Contains:

• Methane (CH₄)
• Hydrogen sulphide (H₂S)
• Carbon dioxide (CO₂)

Uses of Biogas

• Fuel
• Electricity
• Cooking
• Heating

STEP 4 : Final Effluent

After treatment,

Water becomes much cleaner.

It is discharged into

• Rivers
• Lakes
• Streams

Importance of Sewage Treatment

✔ Reduces pollution

✔ Removes pathogens

✔ Reduces BOD

✔ Produces biogas

✔ Protects aquatic life

✔ Prevents water-borne diseases

Ganga Action Plan (GAP)

Purpose:

Clean River Ganga.

Method:

Construction of Sewage Treatment Plants (STPs).

Yamuna Action Plan (YAP)

Purpose:

Reduce pollution in River Yamuna.

Method:

Treat sewage before discharge.

Complete Process (Easy Flow)

Raw Sewage
      ↓
Filtration
      ↓
Sedimentation
      ↓
Primary Sludge + Primary Effluent
                     ↓
              Aeration Tank
                     ↓
     Aerobic bacteria + Fungi
                     ↓
                Flocs formed
                     ↓
     Organic matter consumed
                     ↓
             BOD decreases
                     ↓
            Settling Tank
                     ↓
           Activated Sludge
            ↙             ↘
 Small part          Large part
 (Inoculum)              ↓
                    Anaerobic
                 Sludge Digester
                        ↓
              Methane + CO₂ + H₂S
                        ↓
                     Biogas
                        ↓
               Treated Water Released

NEET Important Definitions

Sewage

Municipal wastewater containing human excreta, organic matter, and microbes.

Primary Sludge

Solid particles settled during primary treatment.

Primary Effluent

Liquid remaining after primary treatment.

Flocs

Masses of aerobic bacteria associated with fungal filaments.

Activated Sludge

Settled bacterial flocs obtained after secondary treatment.

BOD

Amount of oxygen required by bacteria to oxidize organic matter present in 1 litre of water.

Biogas

Mixture of methane, carbon dioxide, and hydrogen sulphide produced during anaerobic digestion.

NCERT-Based NEET Questions

1. Primary treatment is: Physical treatment.
2. Secondary treatment is: Biological treatment.
3. Flocs are formed by: Bacteria + fungal filaments.
4. Activated sludge contains: Settled bacterial flocs.
5. BOD stands for: Biochemical Oxygen Demand.
6. High BOD indicates: High pollution.
7. Biogas mainly contains: Methane.
8. Biogas is produced in: Anaerobic sludge digester.
9. Small amount of activated sludge is used as: Inoculum.
10. Large amount of activated sludge is sent to: Anaerobic sludge digester.

Memory Trick

“Filter → Settle → Air → Flocs → BOD ↓ → Activated Sludge → Biogas → River”

This sequence is the complete sewage treatment process and is one of the most frequently tested NCERT topics in NEET Biology.

MICROBES IN HUMAN WELFARE TOPIC 3

1. Industrial Chemicals Produced by Microbes

2. Industrial Enzymes

Lipase

• Breaks down fats (lipids).
• Used in detergents.
• Removes oil and grease stains from clothes.

Pectinase

• Breaks down pectin in fruits.
• Used to clarify fruit juices.

Protease

• Breaks down proteins.
• Also used for juice clarification.

Result: Market fruit juices are clearer than homemade juices.

3. Streptokinase

• Produced by Streptococcus bacteria.
• Modified using genetic engineering.
• Called a Clot Buster.
• Dissolves blood clots.
• Used after myocardial infarction (heart attack).

4. Cyclosporin A

• Produced by Trichoderma polysporum (Fungus).
• Functions as an Immunosuppressant.
• Used in organ transplantation.
• Prevents organ rejection by suppressing the immune system.

5. Statins

• Produced by Monascus purpureus (Yeast).
• Used to lower blood cholesterol.
• Works by competitively inhibiting the enzyme responsible for cholesterol synthesis.

One-Line Revision

• Aspergillus niger → Citric acid
• Acetobacter aceti → Acetic acid
• Clostridium butylicum → Butyric acid
• Lactobacillus → Lactic acid
• Saccharomyces cerevisiae → Ethanol
• Lipase → Detergents (oil stain removal)
• Pectinase + Protease → Fruit juice clarification
• Streptokinase → Clot buster (heart attack patients)
• Trichoderma polysporum → Cyclosporin A (Immunosuppressant)
• Monascus purpureus → Statins (Lower cholesterol)

NEET Most Important Table

NEET Memory Trick

“AACLuS Makes Life Pretty Smart”

• A → Aspergillus → Citric acid
• A → Acetobacter → Acetic acid
• C → Clostridium → Butyric acid
• L → Lactobacillus → Lactic acid
• S → Saccharomyces → Ethanol
• P → Pectinase + Protease → Clear juice
• S → Streptococcus → Streptokinase (Clot buster)
• T → Trichoderma → Cyclosporin A
• M → Monascus → Statins (Cholesterol lowering)

NEET Tip: The microbe–product pairs (Aspergillus–Citric acid, Trichoderma–Cyclosporin A, Monascus–Statins, Streptococcus–Streptokinase) are among the most frequently tested facts from this chapter.

MICROBES IN HUMAN WELFARE class 12 biology

1. Industrial Use of Microbes

• Microbes are used to produce many commercially valuable products.
• Major industrial products include:
  • Fermented beverages
  • Antibiotics
• Industrial-scale production is carried out in large vessels called fermentors (bioreactors).

2. Fermented Beverages

Microorganism Used

• Yeast: Saccharomyces cerevisiae
• Also called Brewer’s yeast.

Raw Materials

• Malted cereals
• Fruit juices

Main Product

• Ethanol (Alcohol)

Metabolic Pathway

• Alcoholic fermentation (Anaerobic respiration)

Alcohol Produced

Important Points

• Yeast converts sugars into:
  • Ethanol
  • CO₂
• Type of alcoholic beverage depends on:
  • Raw material used
  • Distillation process

3. Antibiotics

Definition

• Antibiotics are chemical substances produced by certain microbes.
• They kill or inhibit the growth of disease-causing microorganisms.

Meaning

• Anti = Against
• Bio = Life
• Together means “Against life” (against disease-causing microbes).

Importance

• One of the greatest discoveries of the 20th century.
• Revolutionized the treatment of bacterial diseases.

4. Penicillin

First Antibiotic

• Penicillin was the first antibiotic discovered.

Discovery

• Discovered accidentally (chance discovery).

Discovered By

• Alexander Fleming

Year of Nobel Prize

• 1945

Source Organism

• Penicillium notatum (mould)

Discovery Story

• Fleming observed that a mould was growing on an unwashed culture plate containing Staphylococci.
• Around the mould, bacteria failed to grow.
• The mould produced a chemical called Penicillin.

Full Potential Established By

• Ernest Chain
• Howard Florey

Major Use

• Widely used to treat American soldiers during World War II.

Nobel Prize (1945)

Awarded jointly to:

• Alexander Fleming
• Ernest Chain
• Howard Florey

5. Diseases Controlled by Antibiotics

Antibiotics have greatly reduced deaths due to:

• Plague
• Whooping cough (Pertussis)
• Diphtheria
• Leprosy

NEET Important Table

Scientists to Remember

NEET One-Liners

• Industrial production of microbes is carried out in fermentors.
• Brewer’s yeast = Saccharomyces cerevisiae.
• Yeast converts sugars into ethanol and CO₂.
• Wine and beer are produced without distillation.
• Whisky, brandy, and rum are produced after distillation.
• Penicillin is the first antibiotic discovered.
• Source of penicillin: Penicillium notatum.
• Penicillin was discovered accidentally by Alexander Fleming.
• Chain and Florey established its therapeutic use.
• Fleming, Chain, and Florey received the Nobel Prize in 1945.
• Antibiotics kill or inhibit the growth of disease-causing microorganisms.

🎯 Most Important NCERT Facts for NEET

• Fermentor = Large vessel used for industrial-scale microbial growth.
• Brewer’s yeast = Saccharomyces cerevisiae.
• Metabolic pathway for alcohol production = Alcoholic fermentation (anaerobic respiration).
• First antibiotic = Penicillin.
• Source = Penicillium notatum.
• Discovered by = Alexander Fleming.
• Nobel Prize = 1945 (Fleming, Chain, and Florey).

MICROBES IN HUMAN WELFARE CLASS 12 BIOLOGY TOPIC 2

1. Curd Formation

• Microbe involved: Lactobacillus and other Lactic Acid Bacteria (LAB).
• LAB convert milk into curd.
• They produce lactic acid, which:
  • Coagulates (curdles) milk proteins.
  • Partially digests milk proteins.
• A small amount of curd is used as a starter (inoculum).
• Starter contains millions of LAB.
• At suitable temperature, LAB multiply rapidly and convert milk into curd.
• LAB increase the nutritional value of curd by increasing Vitamin B₁₂.
• LAB in the human intestine help prevent the growth of disease-causing microbes (probiotics).

2. Idli and Dosa Batter

• Batter is fermented by bacteria (mainly LAB).
• Fermentation produces CO₂ gas.
• CO₂ makes the batter soft, fluffy, and puffed up.
• Metabolic pathway involved: Fermentation (Anaerobic respiration).
• The bacteria usually come from:
  • Previous fermented batter (starter)
  • Rice and urad dal surfaces
  • Surrounding environment

3. Bread Making

• Microbe used: Baker’s yeast (Saccharomyces cerevisiae).
• Yeast ferments sugars and produces:
  • CO₂
  • Ethanol
• CO₂ causes the dough to rise and become soft.

4. Traditional Fermented Foods and Drinks

• Toddy
  • Traditional drink of southern India.
  • Produced by fermenting palm sap.
• Microbes are also used to ferment:
  • Fish
  • Soybean
  • Bamboo shoots

5. Cheese Production

• Cheese is one of the oldest fermented foods.
• Different microbes produce different:
  • Texture
  • Flavour
  • Taste

(a) Swiss Cheese

• Microbe: Propionibacterium sharmanii
• Produces large amounts of CO₂.
• CO₂ forms the large holes (eyes) in Swiss cheese.

(b) Roquefort Cheese

• Ripened using a specific fungus.
• The fungus gives the cheese its characteristic flavour.

NEET Important Microbes Table

NEET One-Liners

• LAB = Lactic Acid Bacteria.
• Lactobacillus converts milk into curd.
• LAB increase Vitamin B₁₂ content in curd.
• LAB suppress harmful microbes in the gut (probiotic effect).
• Baker’s yeast = Saccharomyces cerevisiae.
• CO₂ causes bread dough and idli batter to rise.
• Swiss cheese holes are due to Propionibacterium sharmanii.
• Roquefort cheese is ripened by a specific fungus.
• Toddy is prepared by fermentation of palm sap.

🎯 NCERT Facts Frequently Asked in NEET

• Starter used in curd making: Inoculum containing millions of LAB.
• Gas responsible for puffing of idli/dosa batter: CO₂.
• Metabolic pathway: Fermentation (anaerobic respiration).
• Vitamin increased in curd: Vitamin B₁₂.

Microbes – Key Points

1. Microbes are microscopic organisms found everywhere on Earth.
2. Besides plants and animals, microbes are the major components of biological systems.
3. Microorganisms mainly belong to:
   • Monera (Bacteria)
   • Protista (Protozoa)
   • Fungi (Yeasts, moulds)
   • Viruses, viroids, and prions (acellular infectious agents)
4. Only microscopic organisms include:
   • Bacteria
   • Protozoa
   • Many fungi (e.g., yeast)
   • Viruses
   • Viroids
   • Prions
5. Microbes are found in:
   • Soil
   • Water
   • Air
   • Inside plants and animals
   • Human body
6. Microbes survive even in extreme environments, such as:
   • Thermal vents (up to 100°C)
   • Deep underground
   • Beneath thick layers of snow
   • Highly acidic environments
7. Major groups of microbes:
   • Bacteria
   • Fungi
   • Protozoa
   • Viruses
   • Viroids
   • Prions
8. Bacteria and many fungi can be grown on nutritive media.
9. They form colonies that are visible to the naked eye.
10. Colony formation helps in the isolation, identification, and study of microorganisms.

Additional NCERT Points (Included from the Next Paragraph)

11. Many microbes are disease-causing (pathogenic).
12. Microbes cause diseases in:

• Humans
• Animals
• Plants

13. Not all microbes are harmful.
14. Many microbes are beneficial and play an important role in human welfare.
15. Microbes have diverse useful applications in daily life and industry.
16. This chapter discusses the important contributions of microbes to human welfare.

NEET One-Liner Facts

• Microbes are ubiquitous (present everywhere).
• Pathogenic microbes cause diseases in humans, animals, and plants.
• Beneficial microbes are used in food production, industry, medicine, agriculture, and environmental management.
• Prions are infectious proteins.
• Viroids are infectious RNA molecules without a protein coat.
• Viruses are obligate intracellular parasites.
• Colonies are visible masses of microorganisms formed on solid nutritive media.

Quick Revision

• 1870 → Crookes discovered cathode rays.
• 1879 → Crookes proposed negatively charged particles.
• 1895 → Roentgen discovered X-rays.
• 1897 → J. J. Thomson discovered electron and measured e/m ratio.

Cathode Rays and Electron Discovery – Key Points

1. Cathode ray particles travel at speeds of about 0.1–0.2 times the speed of light.
2. The accepted value of the charge-to-mass ratio (e/m) is:
   1.76×1011 C kg⁻¹
3. The value of e/m is independent of:
   • The cathode material used.
   • The gas present in the discharge tube.
4. This showed that cathode ray particles are universal in nature.
5. In 1887, it was observed that some metals emit negatively charged particles when exposed to ultraviolet light (photoelectric effect).
6. Certain metals also emit negatively charged particles when heated to high temperatures (thermionic emission).
7. The e/m value of these particles was found to be the same as that of cathode ray particles.
8. Therefore, all these particles were concluded to be identical in nature.
9. In 1897, J. J. Thomson named these particles electrons.
10. Thomson proposed that electrons are fundamental constituents of matter.
11. For his work on conduction of electricity through gases and discovery of the electron, Thomson received the Nobel Prize in Physics (1906).
12. In 1913, Robert A. Millikan performed the famous oil-drop experiment.
13. Millikan measured the charge of an electron as:
    e=1.602×10−19 C
    
14. He found that the charge on oil drops was always an integral multiple of the elementary charge.
15. This established that electric charge is quantized.
16. Using the values of e and e/m, the mass of an electron was calculated:
    m=9.11×10⁻³¹ kg

Important Years for NEET/JEE

• 1887 → Photoelectric emission observed.
• 1897 → J. J. Thomson discovered and named the electron.
• 1906 → Thomson received Nobel Prize.
• 1913 → Millikan’s oil-drop experiment.
• (e = 1.602 \times 10^{-19}) C
• (e/m = 1.76 \times 10^{11}) C kg⁻¹
• (m = 9.11 \times 10^{-31}) kg.

48. Given below are two statements:

Statement-I: Heating NaCl with concentrated H₂SO₄ and MnO₂ results in oxidation of Mn.

Statement-II: Heating NaI with concentrated H₂SO₄ and MnO₂ results in reduction of Mn.

In light of the above statements, choose the most appropriate answer from the options given below:

1. Statement-I is correct but Statement-II is incorrect.
2. Statement-I is incorrect but Statement-II is correct.
3. Both Statement-I and Statement-II are correct.
4. Both Statement-I and Statement-II are incorrect.

Answer: (2) Statement-I is incorrect but Statement-II is correct.

Reactions of Halide Salts with MnO₂ and Concentrated H₂SO₄

These are important for Salt Analysis, p-Block (Halogens), and Redox Reactions.

1. NaCl + MnO₂ + Conc. H₂SO₄

Step 1: Formation of HCl

$$2NaCl + H_2SO_4 \rightarrow Na_2SO_4 + 2HCl$$

Step 2: Oxidation of HCl by MnO₂

$$MnO_2 + 4HCl \rightarrow MnCl_2 + Cl_2 + 2H_2O$$

Overall Reaction

$$2NaCl + MnO_2 + 2H_2SO_4 \rightarrow Cl_2 + MnSO_4 + Na_2SO_4 + 2H_2O$$

Observation: Greenish-yellow chlorine gas evolved.

2. NaBr + MnO₂ + Conc. H₂SO₄

Step 1: Formation of HBr

$$2NaBr + H_2SO_4 \rightarrow Na_2SO_4 + 2HBr$$

Step 2: Oxidation of HBr

$$MnO_2 + 4HBr \rightarrow MnBr_2 + Br_2 + 2H_2O$$

Overall Reaction

$$2NaBr + MnO_2 + 2H_2SO_4 \rightarrow Br_2 + MnSO_4 + Na_2SO_4 + 2H_2O$$

Observation: Reddish-brown bromine vapours evolved.

Step 1: Formation of HI

$$2NaI + H_2SO_4 \rightarrow Na_2SO_4 + 2HI$$

Step 2: Oxidation of HI

$$MnO_2 + 4HI \rightarrow MnI_2 + I_2 + 2H_2O$$

Overall Reaction

$$2NaI + MnO_2 + 2H_2SO_4 \rightarrow I_2 + MnSO_4 + Na_2SO_4 + 2H_2O$$

Observation: Violet iodine vapours evolved.

Reactions of Halide Salts with MnO₂ and Concentrated H₂SO₄

These are important for Salt Analysis, p-Block (Halogens), and Redox Reactions.

Memory Trick

Cl → Green, Br → Brown, I → Viole

NEET Shortcut

Memory Trick:

Cl → Green, Br → Brown, I → Violet