NCERT Solutions Class 12 Biology Chapter 10

NCERT Solutions Class 12 Biology Chapter 10

Biology is the branch of science concerned with studying living organisms and their activities. Biology is the science that studies all living things, including plants, animals, and microbes. Biology is essential because it allows us to understand how living things work and interact on several levels.

Microbes In Human Welfare is the 10th chapter of Class 12 Biology. This chapter discusses many concepts and theories linked to microorganisms’ common uses in our daily lives and their important role in industries and medications. The involvement of microorganisms in the synthesis of diverse products, sewage treatment, composting, and biogas generation, among other things, is the subject of this chapter. This chapter also covers the principles and methods that underpin these applications.

The 10th chapter of Class 12, Biology- Microbes in Human Welfare, is full of intricate details and concepts. To enhance understanding of these basic concepts, Extramarks introduces NCERT Solutions for Class 12 Biology Chapter 10. These Class 12 Biology Chapter 10 NCERT Solutions are made by subject experts so that students can grasp the concepts quickly. 

Extramarks are like the universe of excellent study material. Hence, along with Chapter 10 Biology Class 12 NCERT Solutions, students can use the Extramarks website to access several other study tools. For example, NCERT books, CBSE revision notes, CBSE sample papers, CBSE previous year question papers, and other materials are available to students.

Key Topics Covered NCERT Solutions Class 12 Biology Chapter 10

Listed below are the key topics that are covered in NCERT Solutions Class 12 Biology Chapter 10- Microbes in Human Welfare:

What are Microbes?
Microbes in vaccination, antibiotics and industrial products
Microbes in Household products
Microbes in Sewage treatment
Microbes in Gobar gas formation
Microbes as Biocontrol agents
Microbes in the Human Body
Microbes as Biofertilizers

Let us look at Extramarks in-depth information on each subtopic in NCERT Solutions Class 12 Biology Chapter 10.

What are Microbes?

NCERT Solutions Class 12 Biology Chapter 10 states that Microbes, often known as microorganisms, are essential to the earth’s biological processes. They’re everywhere — in the earth, all around us, in the water we drink, in the air we breathe, and in and on our bodies. Microbes can also be found in other animals and plants. They’re tiny, microscopic, and come in various shapes and sizes. They are only visible under a microscope. Microbes come in a variety of forms, including:

  • Virus
  • Algae
  • Bacteria
  • Protozoa
  • Fungi

Microbes in vaccination, antibiotics and industrial products

Microbes produce a variety of compounds that are beneficial to humans. Beverages and antibiotics are the most prevalent products derived from microorganisms. Fermenters are unique tanks used in industries for large-scale manufacture and usage of microorganisms.

The origin of wine, whiskey, brandy, and other fermented beverages dates back to the dawn of civilisation. The most common microorganism used for fermentation is Saccharomyces cerevisiae, often known as brewer’s yeast. It’s been used to make ethanol by fermenting malt-based cereals and fruit juices. Depending on the fermentation and the raw material employed, several alcoholic beverages are generated. For example, whisky, brandy, and rum are beverages made by distilling fermented broth, whereas wine and beer are produced through fermentation.

Antibiotics are chemical molecules created by microorganisms and are used to combat any disease-causing bacterium. For example, Penicillin, the first antibiotic discovered, is called Penicillium notatum after the mould derived from it. Antibiotics are essential for treating several diseases such as whooping cough, leprosy, diphtheria, plague, and others.

Microbes are utilised to make specific substances such as alcohols, enzymes, organic acids, etc. For example, acetic acid is produced by Acetobacter acetic, citric acid is produced by Aspergillus niger, and Lactobacillus produces lactic acid. During organ transplantation, an immunosuppressive drug called cyclosporin A is derived from the fungus Trichoderma polysporum.

In the above section, NCERT Solutions Class 12 Biology Chapter 10 describes the use of Microbes in antibiotics, vaccination and industrial products. These categories are highly significant, and to obtain more information on these topics, refer to the Extramarks website today.

Microbes in Household products

NCERT Solutions Class 12 Biology Chapter 10 states the different uses of Microbes in various household products. For example, Lactobacillus is a bacteria found in curd. It is essential to turn milk into curd. This bacterium produces lactic acid by partly digesting milk protein and thickening it into curd. A tiny inoculum of curd is necessary for curd development in milk.

Fermentation is the process of turning sugar into alcohol. There is no need for oxygen in this procedure. As a result, the process is anaerobic. Bacteria also help make the dough needed to make idli, dosa, and other food items. Bacteria are responsible for the fermentation of the dough that results in the finished batter. The generation of carbon dioxide causes the dough to puff up. Saccharomyces cerevisiae is the yeast responsible for dough fermentation. Many beverages require the same fermentation process.

Propionibacterium shamanic, a fermenting bacterium, produces cheese. Different types of cheese are distinguished by their texture, flavour, and taste. These are the qualities that are based on the many microorganisms that are utilised.

Microbes in Sewage treatment

The wastewater contains a significant amount of human excreta. Sewage is another name for municipal sewage. It includes a large quantity of organic stuff as well as microorganisms. Wastes should be treated before being released to reduce contamination. Heterotrophic bacteria, naturally found in wastewater, are necessary to remediate the sewage. NCERT Solutions Class 12 Biology Chapter 10 explains that it happens in two stages:

  • Primary treatment
  • Secondary treatment

Primary treatment

The primary treatment process begins with manually removing small and large particles via filtration and sedimentation. Sequential filtration removes debris first. Sedimentation is then used to remove the dirt and tiny stones. Finally, the effluent (leftover) is collected for subsequent treatment.

Secondary treatment

The wastewater is passed via the aeration tanks by undertaking continuous aeration. The process of aeration that aids in the aerobic decomposition of organic materials allows aerobic microorganisms to develop rapidly. Aerobic bacteria form flocs. Once the sewage’s BOD has been lowered, it is pumped into a settling tank, where the bacterial flocs can settle. Activated sludge is the term for this type of sediment. A tiny amount of activated sludge is pumped back into the aeration tank to serve as inoculum. Carbon dioxide, methane, and hydrogen sulphide are among the gases produced. Furthermore, wastes can be dumped into rivers, streams, and other bodies of water.

Microbes in Gobar gas formation

NCERT Solutions Class 12 Biology Chapter 10 discusses that Biogas is a combination of gases with the most significant methane. When bacteria grow anaerobically on cellulose material, they create a lot of methane and CO2 and H2. The microorganisms that create methane because of anaerobic respiration are methanogens. Methanobacterium is an example of methanogenic bacteria.

Microbes as Biocontrol agents

NCERT Solutions Class 12 Biology Chapter 10 explains another important concept of Microbes as Biocontrol agents. The employment of biological approaches to manage plant diseases and pests is known as biocontrol. Pesticides and insecticides have traditionally been used to control illnesses and pests. Unfortunately, as a result, these compounds are exceedingly dangerous and poisonous.

Biological Control of Pests and Diseases

Bacillus thuringiensis is a bacterium used as a biocontrol agent against insects and pests (Bt). The endotoxin generated paralyses the intestines of the insect or pest that eats it. Bt cotton is an example of a plant that has been genetically modified. In addition, a fungus called Trichoderma is used to manage plant diseases. Baculoviruses are the pathogens of insects and other arthropods. The genus Nucleopolyhedrovirus is home to most baculoviruses utilised as biocontrol agents. They have been shown to have no harmful effects on other creatures, including plants, animals, birds, fish, and non-target insects. Microbes are also utilised as biofertilizers in some cases.

Microbes in the Human Body

NCERT Solutions Class 12 Biology Chapter 10 provides information about the Microbes in the human body; it is one such topic that everyone should know about.

Different bacteria colonise different regions of the human body, such as the skin, the stomach, the reproductive system, etc. However, the most significant bacteria in the human body are those located in the gut.

Streptococcus, Staphylococcus, and other bacteria populate the stomach microflora. These bacteria are always prepared to survive in the stomach’s acidic environment.

Enterobacteriaceae make up the intestinal flora. This flora is required for digestion and absorption to work correctly. As a result, the efficiency of the digestive process is improved, as is the gut’s usefulness.

The microorganisms are preventing the colonisation of another bacterium. However, they also release some chemicals that are necessary for food digestion.

Viruses are utilised as a vector to transfer a needed gene in recombinant DNA technology.

Microbes as Biofertilizers

Farmers have been obliged to move to organic farming due to the excessive usage of pesticides and their detrimental effects. Bio fertilisers are organisms that are needed to enhance the soil with nutrients. Bacteria, fungus, and cyanobacteria are all found in bio-fertilisers. Leguminous plants, such as peas and beans, contain Rhizobium bacteria. Plants in the nitrogen absorption process require this bacteria. Azospirillum and Azotobacter are the other bacteria that fix nitrogen. Mycorrhiza is a fungus that forms a symbiotic association with the roots of higher plants. The fungus absorbs phosphorus from the earth and then transfers it to the plant. Autotrophic microorganisms are cyanobacteria. They may be found both in aquatic and terrestrial habitats. Microbes such as Anabaena, Nostoc, Oscillatoria, and others may fix atmospheric nitrogen. As a result, cyanobacteria, an essential bio fertiliser, is necessary, particularly in paddy fields. Blue-green algae provide organic materials to the soil to boost its fertility.

NCERT Solutions Class 12 Biology Chapter 10 Exercise and Solutions

Extramarks is a platform containing unlimited quality study material for all classes. Students can access materials like past year’s question papers, questions and solutions, revision notes, additional questions, and tons of other stuff. Click on the below links to view NCERT Solutions Class 12 Biology Chapter 10:

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By getting access to NCERT Solutions Class 12 Biology Chapter 10, students can easily understand all the concepts of Microbes in human welfare.

Key Features of NCERT Solutions Class 12 Biology Chapter 10

Students are often advised to go through NCERT questions while preparing for the examinations. These NCERT questions are a perfect blend of all the chapter’s concepts. NCERT Solutions by Extramarks have been designed to make it easy for students to grasp every concept of any challenging chapter. Here, we give you reasons to choose Extramarks:

  • Extramarks subject experts have prepared these solutions so that students can easily comprehend all the concepts of a chapter.
  • These solutions have proven to be time-saving for the students.
  • These solutions help students clear all their doubts and practise the exam writing pattern appropriately.

Q.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?


I would carry some fresh homemade yogurt/ curd because ‘Lactic acid bacteria’ (LAB) for example Lactobacillus grows in milk and converts it into curd. A small amount of curd contains millions of LAB and these can be easily observed under a microscope.

Method to observe LAB under the microscope:

  1. Make a thin smear of curd on a glass slide.
  2. Stain the smear according to the procedure for the Gram stain or with methylene blue.
  3. View the stained smear at 400x to determine the characteristic features of Lactobacillus like rod-shaped cells.
  4. Observe the morphology. LABs the rod- shaped bacteria will stain blue.

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


Microbes produce different types of gaseous end-products during growth and metabolism. The type of gas produced depends upon the microbes and the organic substrates they utilise.

  1. Microbes found in the dough of idli, dosa or for making bread release CO2 during fermentation. The idli batter after being kept overnight becomes very fluffy with small bubbles. If the batter is mixed hard it flattens down because the entrapped air (carbon dioxide) escapes.
  2. Some microbes which grow anaerobically on cellulosic material produce a large amount of methane along with CO2 and H2. These bacteria are collectively called methanogens, and one such common bacterium is Methanobacterium. These bacteria reside in the stomach of cattle and help these animals to digest the cellulose. Cattle dung is rich in these bacteria and is used in the production of biogas, which can be used for cooking food and generating electricity.

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


Lactic Acid Bacteria (LAB) can be found in curd. LAB converts milk into curd. Lactobacillus (LAB) is also used for commercial and industrial production of lactic acid. Casein, an important milk protein, is soluble at a neutral pH, but insoluble in acid. When milk turns sour, casein precipitates leading to the thickening of the product.

Lactose (milk sugar) + Lactobacillus → Lactic acid

This lactic acid causes casein to curdle and form the curd.

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


Wheat: Bread, kulchas and bhaturas

Rice: Dosa and idli

Bengal Gram: Dhokla and khandvi

Explanation: The microbes that ferment these batters are found naturally on urad dal which is used for making the batter hence, no inoculums are required to start the fermentation unlike in bread where yeast inoculum is used to initiate fermentation.

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


Microbes such as fungi and bacteria produce antibiotics which are chemical substances that can kill or retard the growth of other (disease-causing) microbes. Antibiotics can be used to treat potentially life threatening diseases like pneumonia to relatively mild conditions such as acne. Antibiotics have greatly improved our ability to treat deadly diseases such as plague, whooping cough (kali khansi), diphtheria (gal ghotu) and leprosy (kusht rog), which used to kill millions of people all over the world.

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


Fungus Antibiotic
Penicillium notatum Penicillin
Streptomyces griseus Streptomycin

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


Municipal wastewater that contains human excreta and effluent from the kitchen and bathrooms is collectively called sewage. Sewage contains large amounts of organic matter and also microbes some of which can be harmful to humans and other living beings. Sewage water is a major source of water pollution. Therefore, it is important and mandatory to collect, treat and dispose of sewage responsibly.

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


Primary Sewage Treatment Secondary Sewage Treatment
Mechanical, inexpensive and simple process Biological, expensive and complicated process
Involves simple filtration and sedimentation of sewage for the removal of debris Involves the use of microbes to breakdown the organic matter in the sewage

Explanation: Before being drained into water bodies like rivers and lakes, sewage needs to be treated to remove the organic matter. This is carried out in two stages:

Primary Sewage Treatment: The initial phase of sewage treatment involves physical removal of particles. These are removed in two stages;

  1. Sequential filtration for removing floating debris
  2. Sedimentation for removing grit (soil and small pebbles)

All the 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.

Secondary sewage treatment or Biological treatment: This is also carried out in stages before the water can be returned to natural water sources.

  1. Aeration tank: The primary effluent is passed into large aeration tanks where it is constantly 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. BOD refers to the amount of the oxygen that would be consumed if all the organic matter in one litre of water is oxidised by bacteria. The sewage water is treated till the BOD is sufficiently reduced after which the effluent is then passed into a settling tank.
  2. Settling tank: Here 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.

Anaerobic sludge digesters: Here anaerobic bacteria digests the bacteria and fungi in the sludge. The effluent from the secondary treatment plant is generally released into natural water bodies like rivers and streams.

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


Yes, microbes can be used as a source of energy. One of the most common examples of microorganisms being used for obtaining energy is biogas.

Biogas: Methanogens are anaerobic bacteria that breakdown cellulosic material producing large amounts of methane along with carbon dioxide and hydrogen. These bacteria reside in the stomach of cattle and help the animal to digest the cellulose. Cattle dung is rich in these bacteria and is used in the production of biogas. The biogas plant consists of a concrete tank (10-15 feet deep) into which biowastes are collected and the slurry of dung is fed. A floating cover 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.

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


The chemical fertilisers and pesticides used in agricultural practices these days pose several health hazards to humans and also create an imbalance in the natural ecosystem. To decrease the use of these chemicals, microbes have been employed through various methods like:

Biopesticides: Biological control of pests and diseases relies on using the natural pest-predator relationship to control diseases. Some microbes have proven to be effective biological control agents and have shown to have no impact on other useful plants or animals. For examples:

  • Trichoderma species is a fungus that is commonly found in the root ecosystem. They are effective biocontrol agents of several plant pathogens.
  • Bacillus thuringiensis is the most widely used species of bacteria for biological control of insects.
  • Baculoviruses are pathogens that attack insects and other arthropods.

Biofertilisers: They add nutrients through the natural processes of nitrogen fixation, solubilising phosphorus, and stimulating plant growth through the synthesis of growth-promoting substances. They can be applied to seed, plant surfaces, or soil. They colonise the interior of the plant and promote growth by increasing the supply or availability of primary nutrients to the host plant. For examples:

  • Azotobacter can be used with crops like wheat, maize, mustard, cotton, potato, and other vegetable crops.
  • Azospirillum inoculations are recommended mainly for sorghum, millets, maize, sugarcane, and wheat.
  • Blue-green algae fix atmospheric nitrogen and are used as inoculations for paddy crop.

Q.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 labeled 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 20 mg/L, 8 mg/L and 400 mg/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?


BOD refers to the amount of the oxygen that would be consumed if all the organic matter in one litre of water is oxidised by bacteria. The BOD test measures the rate of uptake of oxygen by micro-organisms in a sample of water and thus, indirectly, BOD is the measure of the organic matter present in the water. The greater the BOD of waste water more is its polluting potential.

Sample BOD values Water sample types
A 20 mg/L Secondary effluent This is the effluent that has been treated before disposing into the natural water bodies.
B 8 mg/L River water This sample has the least amount of organic matter. Therefore, it can be considered the river water.
C 400 mg/L Untreated sewage water This is the municipal sewage that is collected for treatment in the STP.

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


Cyclosporin A An immunosuppressive drug Tolypocladium inflatum (fungus)



Blood cholesterol lowering agents Monascus purpureus (fungus)

Aspergillus terreus (fungus)

Q.13 Find out the role of microbes in the following and discuss it with your teacher.
(a) Single cell protein (SCP)
(b) Soil


(a) Single Cell Protein (SCP)

SCP refers to the dried microbial cells or total protein extracted from pure microbial cell culture (algae, bacteria, filamentous fungi, yeasts), which can be used as food supplement for humans (food grade) or animals (feed grade). SCP, a non-conventional protein source can help solve the problem of malnutrition, food and feed shortage in the developing countries. The production of ‘Single Cell Protein’ can be done using waste materials as the substrate, specifically agricultural wastes such as wood shavings, sawdust, corn cobs, etc. and culturing yeast, bacteria, algae or fungi. Spirulina algae, is a good resource as it can be mass cultivated easily and is fast growing with high nutritional content.

(b) Soil

Microorganisms in soil are important because they affect the structure and fertility of different soils. Soil microorganisms can be classified as bacteria, actinomycetes, fungi, algae, and protozoa. Each of these groups has different functions in the soil they inhabit. Some examples of microbes, which are beneficial for soil quality are as follows:

Microorganisms Species Function
Bacteria Nitrobacter Turns nitrite into nitrate, which results in the gain of oxygen and is also known as oxidation
Pseudomonas Metabolises a wide range of chemicals and fertilisers
Anabaena, Nostoc, Oscillatoria Nitrogen fixation
Azospirillum and Azotobacter Fixes atmospheric nitrogen
Algae Blue-green algae Nitrogen fixation
Fungi Glomus Absorption of phosphorus

Q.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


Entity Importance in society
1 Penicillin The first antibiotic and is used for the treatment of several life-threatening bacterial infections.
2 Biogas A clean, environmentally friendly, sustainable source of energy made of biological waste product. Biogas production can be carried out by unskilled people and is not expensive. It provides energy for cooking and generating electricity in the areas with limited resources.
3 Citric Acid The dominant use of citric acid is as a flavouring agent and preservative in food and beverages. Industrial-scale production of citric acid began during world war I.
4 Curd Curd has many health benefits for humans. It is a natural probiotic which keeps the microflora of the gut healthy and balanced. Curd is also a source of nutrients like calcium, vitamin-B12, etc.

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


Biofertilisers are organisms that enrich the nutrient quality of the soil. The main sources of biofertilisers are bacteria, fungi, and cyanobacteria. Biofertilisers can enrich the fertility of the soil in the following ways:

  1. Nitrogen enrichment – Bacteria like Azospirillum and Azotobacter are free-living in the soil and can fix atmospheric nitrogen thus increasing the nitrogen content of the soil. Rhizobium another nitrogen-fixing bacteria forms nodules on the plant roots and lives symbiotically. Cyanobacteria are 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.
  2. Phosphorous enrichment – Fungus like Glomus form Mycorrhiza live symbiotically with a plant and help in absorbing phosphorus for the plant.

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FAQs (Frequently Asked Questions)

1. How important is the chapter' Microbes in Human Welfare' for the NEET examination?

Students will learn about the many significant functions of microorganisms in Chapter 10. Microbes are employed for human benefit in various home goods, businesses, and procedures. This chapter covers several key ideas that are frequently tested in NEET exams. As a result, students should learn this chapter well. Furthermore, it is a concise chapter compared to other Class 12 Biology chapters. As a result, it has the potential to be a high-scoring chapter.

2. What are the Microbes that are helpful for Humans?

Antibiotics produced by microbes support the body in killing the disease-causing microorganism. However, only a few microorganisms are beneficial to our bodies. Bacteria, Fungi, and Protozoa are their names. These bacteria contribute to human well-being. They improve digestion and defend the body against illnesses. Refer to Extramarks NCERT Solutions Class 12 Biology Chapter 10 to gain more information.