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

Reviewed by · Updated on

NCERT Solutions PDF Class 12 PDF

This chapter, "Microbes in Human Welfare," delves into the significant roles microorganisms play in various aspects of human life. The NCERT Solutions for Class 12 Biology Exemplar cover key concepts such as the beneficial uses of microbes in food production (like curd and bread), industrial processes (fermentation for beverages and organic acids), and medicine (antibiotics and vaccines). It also explores the application of microbes in sewage treatment, biogas production, and as biofertilizers. The solutions provide clear explanations and step-by-step answers to multiple-choice questions, helping students understand the diverse and crucial contributions of microbes to our ecosystem and well-being. These solutions are designed to aid students in grasping the fundamental principles and applications of microbiology, reinforcing their understanding for effective exam revision.

Home

Quick info

BoardCBSE
ClassClass 12
SubjectBiology Exemplar
Session2026
LanguageEnglish
TypeNCERT Solutions
ChapterChapter 10

Chapter summary

Chapter 10 of the CBSE Class 12 Biology Exemplar focuses on the indispensable role of microbes in human welfare. The NCERT Solutions cover their applications in food processing, such as the production of curd and bread, and their use in industrial fermentation for producing organic acids, enzymes, and antibiotics. The solutions also explain the significance of microbes in sewage treatment, biogas generation, and as biofertilizers, highlighting their ecological importance. This chapter emphasizes how understanding and utilizing microorganisms benefits human society in numerous ways.

Learning outcomes

  • Understand the role of Lactic Acid Bacteria (LAB) in milk fermentation and vitamin production.
  • Identify the process of wastewater treatment and the function of anaerobic digesters.
  • Recognize the habitat and function of methanogenic bacteria.
  • Match various bacteria with their commercially important products.
  • Associate bioactive substances with their specific roles in medicine and industry.
  • Explain the contribution of microbes to human welfare in food, industry, and medicine.

Topics covered

Paper topics

  • Microbes in Household Products
  • Microbes in Industrial Products
  • Microbes in Sewage Treatment
  • Microbes in Biogas Production
  • Microbes as Biofertilizers
  • Microbes as Biocontrol Agents
  • Lactic Acid Bacteria (LAB)
  • Methanogens
  • Wastewater Treatment
  • Biogas
  • Bioactive Substances
  • Fermentation

Important topics

  • Microbes in Food and Industry
  • Wastewater Treatment Process
  • Biogas Production
  • Biofertilizers and Biocontrol Agents
  • Key Bioactive Substances (Statins, Cyclosporin A, Streptokinase)

PDF preview

Read page by page below. PDF is streamed from the official NCERT website — no download button on this page.

Loading document …
Page of
Loading page …

Questions and Solutions

MCQ 1

The vitamin whose content increases following the conversion of milk into curd by lactic acid bacteria is:
  1. Vitamin C
  2. Vitamin D
  3. Vitamin B12
  4. Vitamin E
Solution: Lactic Acid Bacteria (LAB), such as Lactobacillus, are crucial in the fermentation of milk into curd. During this process, these bacteria produce acids that help in coagulating milk proteins. Importantly, the metabolic activities of LAB also enhance the nutritional value of the curd by increasing the concentration of Vitamin B12. The other vitamins listed are not directly increased by this process. Therefore, Vitamin B12 content is elevated in curd compared to fresh milk.

Answer: (c) Vitamin B12

MCQ 2

Wastewater treatment generates a large quantity of sludge, which can be treated by:
  1. Anaerobic digesters
  2. Flocculants
  3. Chemical precipitation
  4. Oxidation ponds
Solution: Wastewater treatment involves several stages. The sludge produced, which is a semi-solid residue, requires further treatment. A common and effective method for treating sludge is using anaerobic digesters. These are large, often heated, tanks where anaerobic microorganisms break down the organic matter in the sludge in the absence of oxygen. This process reduces the volume of the sludge and produces biogas, primarily methane and carbon dioxide. While oxidation ponds are used for treating the liquid effluent, and flocculants/chemicals might be used in primary treatment, anaerobic digestion is specifically employed for sludge treatment.

Answer: (a) Anaerobic digesters

MCQ 3

Methanogenic bacteria are not found in:
  1. Rumen of cattle
  2. Gobar gas plant
  3. Bottom of water-logged paddy fields
  4. Activated sludge
Solution: Methanogenic bacteria are a group of archaea that produce methane as a metabolic byproduct in anaerobic conditions. They are commonly found in environments rich in organic matter and lacking oxygen, such as the rumen of herbivorous animals (like cattle), where they help digest cellulose; gobar gas plants, where biogas is produced; and the anaerobic mud at the bottom of water-logged paddy fields. Activated sludge, however, primarily consists of aerobic bacteria and fungi that thrive in the presence of oxygen during the secondary treatment of wastewater. Therefore, methanogens are generally not found in activated sludge.

Answer: (d) Activated sludge

MCQ 4

Match the following column of bacteria and their commercially important products.

Column I (Bacterium)

A. Aspergillus niger

B. Acetobacter aceti

C. Clostridium butylicum

D. Lactobacillus

Column II (Product)

1. Lactic acid

2. Butyric acid

3. Acetic acid

4. Citric acid

Codes:

A B C D

  1. 4 3 2 1
  2. 2 4 3 1
  3. 4 3 1 2
  4. 2 1 4 3
Solution: This question requires matching specific bacteria with the commercially important products they yield through fermentation or other metabolic processes.
  • Aspergillus niger is a fungus widely used for the large-scale production of citric acid.
  • Acetobacter aceti is a bacterium known for its ability to convert ethanol into acetic acid, commonly used in vinegar production.
  • Clostridium butylicum is a bacterium capable of producing butyric acid through fermentation.
  • Lactobacillus species are well-known for fermenting lactose into lactic acid, a key process in dairy product manufacturing.
Based on these associations, the correct matching is A-4, B-3, C-2, and D-1.

Answer: (a) 4 3 2 1

MCQ 5

Match the following column of bioactive substances and their roles.

Column I (Bioactive Substance)

A. Statin

B. Cyclosporin A

C. Streptokinase

D. Lipase

Column II (Role)

1. Removal of oil stains

2. Removal of clots from blood vessels

3. Lowering of blood cholesterol

4. Immuno-suppressive agent

Codes:

A B C D

  1. 3 4 2 1
  2. 4 2 1 3
  3. 2 1 3 4
  4. 1 2 3 4
Solution: This question involves matching bioactive substances, often produced by microorganisms, with their specific therapeutic or industrial applications.
  • Statin: These are a class of drugs that inhibit the enzyme HMG-CoA reductase, thereby lowering the production of cholesterol in the liver. Thus, Statins are used for lowering blood cholesterol.
  • Cyclosporin A: This is a potent immunosuppressive drug produced by the fungus *Tolypocladium inflatum*. It is widely used to prevent organ transplant rejection by suppressing the immune system.
  • Streptokinase: This enzyme is produced by certain strains of *Streptococcus*. It acts as a plasminogen activator, converting plasminogen into plasmin, which breaks down blood clots. It is used to treat conditions like myocardial infarction (heart attack).
  • Lipase: Lipases are enzymes that break down fats (lipids). They are used in various applications, including laundry detergents to remove oil and grease stains from fabrics.
Therefore, the correct matching is A-3, B-4, C-2, and D-1.

Answer: (a) 3 4 2 1

Common mistakes

  • Confusing the specific vitamins produced during milk fermentation.
  • Misidentifying the primary treatment methods for sludge in wastewater.
  • Incorrectly associating methanogenic bacteria with aerobic environments.
  • Errors in matching bacteria or bioactive substances with their correct products or roles.

Revision tips

  • Focus on the specific roles of different microbes mentioned in the solutions.
  • Pay close attention to the matching exercises to memorize associations between microbes and their products.
  • Review the wastewater treatment process and the function of anaerobic digesters.
  • Understand the nutritional enhancement of food products due to microbial activity.

Practice MCQs

Q1. Which vitamin's content increases significantly when milk is converted into curd by lactic acid bacteria?

Q2. What is the primary method for treating the large quantity of sludge generated during wastewater treatment?

Q3. Methanogenic bacteria, which produce methane, are typically NOT found in which of the following environments?

Q4. Which bacterium is correctly matched with its commercially important product?

Q5. Match the bioactive substance with its correct role:

Frequently asked questions

What is the main benefit of using Lactic Acid Bacteria (LAB) in making curd?

LAB not only convert milk into curd by producing lactic acid but also improve its nutritional quality by increasing the content of Vitamin B12.

How are microbes used in wastewater treatment?

Microbes, particularly aerobic and anaerobic bacteria, are used in secondary treatment to break down organic matter in sewage. Anaerobic digesters treat sludge, producing biogas.

Where are methanogenic bacteria found, and what do they produce?

Methanogenic bacteria are found in anaerobic environments like the rumen of cattle, gobar gas plants, and water-logged paddy fields. They produce methane gas, a key component of biogas.

Can you name some commercially important products derived from microbes?

Yes, microbes are used to produce various products like lactic acid (Lactobacillus), acetic acid (Acetobacter aceti), citric acid (Aspergillus niger), and butyric acid (Clostridium butylicum).

What are some important bioactive substances produced by microbes and their uses?

Key bioactive substances include Statins (lower blood cholesterol), Cyclosporin A (immunosuppressant), and Streptokinase (clot remover). Lipase is used for stain removal.

How do these NCERT Solutions help in preparing for exams?

These solutions provide clear, rewritten answers to all questions, explaining the concepts and methods thoroughly. They help in understanding the applications of microbes and revising key facts for exams.

Important links

Content reviewed by the NCERT Help team. Editorial Team and update policy

NCERT Solutions PDF PDF on NCERT Help. URL unchanged for search indexing.