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

Reviewed by NCERT Help Editorial Team · Updated on 29 Jul 2026

NCERT Solutions PDF Class 12 PDF

CBSE Class 12 Biology Chapter 10, Microbes in Human Welfare, explores the essential roles microorganisms play in our lives and industries. These NCERT Solutions offer clear explanations on how microbes contribute to food production, including curd, bread, and fermented drinks. They also detail their vital applications in medicine, such as creating antibiotics and vaccines, and their significant use in sewage treatment and biogas generation. Understanding these applications helps students appreciate the beneficial aspects of microbes, moving beyond their association with diseases. The solutions are crafted to enhance comprehension of microbiology's core principles and practical uses, serving as a key resource for effective exam preparation and revision.

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Quick info

Board	CBSE
Class	Class 12
Subject	Biology
Session	2026
Language	English
Type	NCERT Solutions
Chapter	Chapter 10

Chapter summary

Chapter 10, Microbes in Human Welfare, focuses on the beneficial roles of microorganisms. The NCERT Solutions cover their applications in food processing (curd, idli, dosa, dhokla), industrial production (fermentation, biogas), and medicine (antibiotics, vaccines). It also touches upon their use in sewage treatment and as bio-control agents. These solutions clarify the scientific principles behind these applications, helping students understand the positive impact of microbes.

Learning outcomes

Understand the role of microbes in food production and fermentation.
Identify useful applications of lactic acid bacteria.
Explain how microbes are used to produce antibiotics.
Recognize the contribution of microbes in industrial processes like biogas generation.
Describe the use of microbes in sewage treatment.

Topics covered

Paper topics

Microbes in Household Products
Microbes in Industrial Production
Microbes in Sewage Treatment
Microbes in Production of Biogas
Microbes as Bio-control Agents
Microbes in Production of Antibiotics
Microbes in Production of Vaccines
Lactic Acid Bacteria
Fermentation
Traditional Indian Foods involving Microbes

Important topics

Microbes in Food Production (Curd, Bread, Idli, Dosa)
Antibiotic Production by Microbes
Role of Lactic Acid Bacteria (LAB)
Fermentation and Gas Production
Traditional Indian Fermented Foods

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Questions and Solutions

Question 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?

Solution: To demonstrate the presence of microbes, a sample of curd would be an excellent choice to carry from home to the biology laboratory. Curd is rich in Lactic Acid Bacteria (LAB), commonly known as Lactobacillus. These beneficial bacteria play a vital role in milk fermentation, producing lactic acid that coagulates milk proteins and gives curd its characteristic texture and taste. A small amount of curd contains millions of these bacteria, making them easily observable and identifiable under a microscope, thus effectively demonstrating the presence of living microorganisms.

Question 2

Give examples to prove that microbes release gases during metabolism.

Solution: Microbes release gases, primarily carbon dioxide, during their metabolic processes, especially fermentation. This phenomenon is evident in several applications:

Bread Making: Yeast, a type of fungus, ferments sugars in the dough, releasing carbon dioxide gas. This trapped CO2 causes the dough to rise, giving bread its spongy texture.
Idli and Dosa Preparation: The batter used for making South Indian dishes like idli and dosa is fermented by a mixture of bacteria and yeast. These microbes break down carbohydrates and release carbon dioxide. The gas bubbles get trapped within the batter, resulting in a puffed and airy final product.
Alcoholic Fermentation: In the production of alcoholic beverages, yeast ferments sugars into ethanol and carbon dioxide. The effervescence observed during this process is due to the release of CO2. The general equation for fermentation of glucose can be represented as: Glucose $\rightarrow$ Ethanol + Carbon dioxide + Energy.

Question 3

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

Solution: Lactic acid bacteria (LAB) are commonly found in fermented dairy products, most notably in curd. They are responsible for the conversion of milk into curd through the production of lactic acid. Useful applications of lactic acid bacteria include:

Food Production: They are essential for making curd, yogurt, and other fermented dairy products. They not only contribute to the texture and flavor but also enhance the nutritional value by increasing the content of certain vitamins, such as vitamin B12 in curd.
Gut Health: LAB reside in the human digestive tract and play a beneficial role by maintaining a healthy gut microflora. They help in checking the growth of potentially harmful pathogenic microorganisms, thus contributing to digestive health.
Fermentation: They are also involved in the fermentation of other food items, contributing to their preservation and unique characteristics.

Question 4

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

Solution: Several traditional Indian foods utilize the metabolic activities of microbes, particularly bacteria and yeasts, for their preparation. Here are some examples based on the primary ingredients:

Wheat Products: While not explicitly listed in the source for wheat, microbial fermentation is crucial for products like bread, where yeast produces carbon dioxide to leaven the dough. Cakes and other baked goods also rely on microbial action or chemical leavening agents that mimic it.
Rice Products: Traditional South Indian dishes like Idli and Dosa are prepared from a fermented batter of rice and black gram. The fermentation process, carried out by lactic acid bacteria and yeasts, produces the characteristic texture and tangy flavor.
Bengal Gram (or its products): Popular Gujarati snacks like Dhokla and Khandvi are made from fermented batter, often involving rice flour and chickpea flour (Bengal gram). The fermentation step is critical for their soft, spongy texture and unique taste.

Question 5

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

Solution: Microbes have played a monumental role in controlling diseases caused by harmful bacteria primarily through the production of antibiotics. Antibiotics are chemical substances produced by certain microorganisms (like bacteria and fungi) that have the ability to kill or inhibit the growth of other disease-causing microorganisms, particularly bacteria. Key mechanisms include:

Inhibition of Bacterial Growth: Antibiotics work by interfering with essential processes in bacterial cells, such as cell wall synthesis, protein synthesis, or metabolic pathways. For example, penicillin, produced by the fungus Penicillium notatum, weakens the bacterial cell wall.
Bacterial Lysis: When the bacterial cell wall is weakened by antibiotics like penicillin, the internal osmotic pressure causes the cell to burst, a process known as lysis. This effectively destroys the bacteria.
Immune System Support: By eliminating or suppressing the growth of harmful bacteria, antibiotics allow the body's immune system, including white blood cells, to more effectively clear the infection.

Commonly used antibiotics like penicillin, streptomycin, and tetracycline are derived from microbial sources and have revolutionized the treatment of bacterial infections, saving countless lives.

Question 6

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

Solution: Fungi are a significant source for the production of life-saving antibiotics. Two important species of fungi used in antibiotic production are:

Penicillium notatum: This fungus is famously known for producing Penicillin, one of the earliest and most widely used antibiotics. Penicillin is effective against a range of Gram-positive bacteria.
Cephalosporium acremonium: This fungus is the source for the production of Cephalosporins. Cephalosporins are a broad class of antibiotics that are structurally related to penicillin and are used to treat various bacterial infections.

These fungal species are cultivated under controlled conditions to maximize the yield of these crucial antimicrobial compounds.

Common mistakes

Confusing beneficial microbes with disease-causing ones.
Not understanding the specific role of different microbes in fermentation.
Forgetting the names of specific antibiotics and their fungal sources.
Overlooking the importance of microbes in everyday food items.

Revision tips

Focus on the specific examples of food items and the microbes involved.
Memorize the key antibiotics and their fungal sources.
Understand the process of fermentation and gas production by microbes.
Relate the concepts to everyday life examples like curd and bread.

Practice MCQs

Q1. Which microbe is primarily responsible for the fermentation of milk into curd?

Q2. The puffed appearance of dough for idli and dosa is due to the release of which gas by microbes?

Q3. Which of the following is a common antibiotic derived from a fungus?

Q4. Lactic acid bacteria are beneficial in the human stomach because they:

Q5. Which traditional Indian food is made from Bengal gram and involves microbial fermentation?

Frequently asked questions

What is the primary role of microbes in human welfare?

Microbes play crucial roles in human welfare by being involved in food production (like curd, bread), industrial processes (fermentation, biogas), medicine production (antibiotics, vaccines), and waste management (sewage treatment).

Which microbes are responsible for making curd from milk?

Lactic Acid Bacteria (LAB), such as Lactobacillus, are responsible for converting milk into curd. They produce lactic acid which coagulates milk proteins.

How do microbes help in controlling diseases?

Certain microbes produce antibiotics, which are medicines that kill or inhibit the growth of disease-causing bacteria, thereby helping to control infectious diseases.

Can you give examples of traditional Indian foods made using microbes?

Yes, traditional Indian foods like idli, dosa, dhokla, and Khandvi are made using microbial fermentation processes involving bacteria and yeasts.

What is the significance of gas production by microbes in food?

Microbes like yeast and bacteria produce gases, primarily carbon dioxide, during fermentation. This gas gets trapped in doughs (like for bread, idli, dosa), causing them to rise and giving a puffed texture.

Which fungus is famously known for producing an antibiotic?

The fungus Penicillium notatum is famously known for producing the antibiotic penicillin.

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