The VIDYANKER team has thoughtfully prepared the NCERT Solutions for Class 12 Biology Chapter 10, "Microbes in Human Welfare" These solutions are designed to help you tackle the NCERT textbook questions with ease. We recommend going through the chapter's theory before diving into the solutions for a deeper understanding. Feel free to share these NCERT Solutions for Class 12 Biology with others—learning is always better when shared!
QUESTIONS FROM TEXTBOOK SOLVED
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?
Ans: Soil and water samples serve as the natural habitats for microorganisms, making them ideal for direct observation and study.
2. Give examples to prove that microbes release, gases during metabolism.
Ans: Yes! Microbes release gases during metabolism, and there are several examples to demonstrate this:
- The Role of Methanogens in Biogas Production: It thus becomes clear that Methanogenic bacteria such as Methanobacterium take an important role in the anaerobic decomposition of organic matter in biogas plants. Methane (CH₄) is a metabolic byproduct excreted during this process and is accompanied by other gases that include carbon dioxide (CO₂) and hydrogen (H₂). Methane forms the main component of biogas utilized as fuel.
- Yeast in Alcoholic Fermentation: Yeast (Saccharomyces cerevisiae), in its fermentative process, consumes sugars in the absence of air and produces ethanol (C₂H₅OH) along with carbon dioxide (CO₂). This form of CO₂ production can be seen as effervescence in dough fermentation or in beer brewing.
- In the nodules of roots of leguminous plants: Rhizobium and other free-living nitrogen-fixing bacteria reduce nitrogen gas to ammonia. In the process of these metabolic activities, small amounts of hydrogen gas are also produced during nitrogenase activity.
These are some examples illustrating how microbes emit gases in their metabolic process, which then find practical application in nature and industry.
3. In which food would you find lactic acid bacteria? Mention some of their useful applications.
Ans: Milk, Curd and Cheese are coagulated product. Lactic acid bacteria (LAB) convert lactose sugar into lactic acid. They also enhance the nutritional quality of curd by enhancing vitamin B12. Lactic acid bacteria also exist in the stomach where they check disease causing microbes.
4. Name some traditional Indian foods made of wheat, rice and Bengal gram (or their products) which involve use of microbes.
Ans: Some traditional Indian foods made from wheat, rice, and Bengal gram (or their products) that involve the use of microbes include:
- Idli and Dosa: These are made from fermented batter of rice and black gram (Urad dal). The fermentation process is carried out by lactic acid bacteria and yeast, which help in leavening the batter, making it soft and fluffy.
- Dhokla: A fermented snack made from Bengal gram flour (besan). The fermentation process involves lactic acid bacteria, which help in the rise of the batter, giving the dish a light and spongy texture.
- Bhatura: Made from fermented wheat flour (maida), microbes such as yeast are used to ferment the dough, causing it to rise and become fluffy when fried.
These examples illustrate how microbes are used in the preparation of various traditional Indian foods, contributing to their characteristic taste, texture, and nutritional value.
5. In which way have microbes played a major role in controlling diseases caused by harmful bacteria?
Ans: By production of antibiotics like penicillin, tetracyclin, by production of vaccines for herpes, TB, DPT, etc.
6. Name any two species of fungus, which are used in the production of the antibiotics.
Ans: Penicillium notatum and Streptomyces are two species offungus, which are used in the production of the antibiotics.
7. What is sewage? In which way can sewage be harmful to us?
Ans: Sewage means those collected municipal wastes that are carried away in sewers and drains.
It encompasses liquid and solid wastes full of organic matter and microbes. Many of these microbes are pathogenic in nature, which causes a number of diseases water-borne. Sewage water is the most common source through which drinking water is polluted. Therefore, unless one considers all aspects of collection, treatment, and disposal of the sewage water, the problem of drinking water pollution cannot be solved.
8. What is the key difference between primary and secondary sewage treatment?
Ans: The key difference between primary and secondary sewage treatment lies in the processes and the types of pollutants they target:
Primary Treatment:
- Objective: This is the first step of sewage treatment, focused on the physical removal of large solids and suspended particles.
- Process: Sewage is passed through screens, grit chambers, and sedimentation tanks where heavier solids settle at the bottom as sludge, and lighter materials like grease float to the top for removal.
- Pollutants Removed: Primarily removes physical contaminants such as debris, grit, and suspended solids but does not treat organic matter or pathogens.
Secondary Treatment:
- Objective: This stage involves the biological treatment of sewage, aimed at breaking down the dissolved and organic matter.
- Process: Microorganisms (mainly aerobic bacteria) decompose organic pollutants in the wastewater. The sewage is aerated in large tanks to enhance microbial activity, which converts organic matter into simpler, non-toxic compounds.
- Pollutants Removed: Primarily removes biodegradable organic matter and reduces the biological oxygen demand (BOD) of the water. It also reduces pathogens to some extent.
In summary, primary treatment is a physical process that removes large particles, while secondary treatment is a biological process that targets organic pollutants in the sewage.
9. Do you think microbes can also be used as source of energy? If yes, how?
Ans: Yes, anaerobic digestion of microbes present in the activated sludge produces a biogas that is a source of energy through the release of inflammable biogas from a biogas plant.
Microbial Culture Use for SCP:
- Biogas Production
- Bioethanol Production
- Biodiesel Production
- Microbial Fuel Cells (MFCs)
- Hydrogen Production
10. Microbes can be used to decrease the use of chemical fertilizers and pesticides. Explain how this can be accomplished.
Ans: They have an important role in organic farming, which is carried out without applying chemical fertilizers and pesticides. Bio-fertilizer is the living organisms to increase soil fertility. It applies the choice of those benevolent micro-organisms that assist in improving the growth of plants by providing plant nutrients. Bio-fertilizers are applied to seeds, roots, or soil with the objective of mobilizing nutrient availability. Thus, they are highly useful in enrichment of soil with organic nutrients. Many species of bacteria and cyanobacteria are able to fix free atmospheric nitrogen. Rhizobium is a symbiotic bacteria existing in root nodules of leguminous plants. Azospirillium and Azotobocter are free living nitrogen-fixing bacteria, whereas Anabena, Nostoc and Oscillitoria are examples of nitrogen-fixing cyanobacteria. Bio-fertilizers are cost effective and eco-friendly. Bio-pesticides are used to control insect pests present in plants. Microbes can also be used as bio-pesticides.
Bacillus thuringiensis is another type of bio-pesticides, where this produces a toxin that kills the insect pest. The bacterial spores are dried and mixed with water and sprayed in agricultural fields. Once the larvae of insects feed on crops, these bacterial spores come into the gut of the larvae and release toxins, thereby killing it. Similarly, Trichoderma are free living fungi. They live in the roots of higher plants and protect them against many pathogens. Another bio-pesticide, this time used as a biological control agent, is Baculoviruses in fight against insects and some other arthropods.
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 20 mg/L, 8 mg/Land 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?
Ans: Sample A (BOD 20mg/L) is secondary effluent discharged from a sewage treatment plant.
Sample B (BOD 8mg/L) is river water.
Sample C (BOD 400mg/L) is the untreated sewage water.
As BOD is the direct measure of the organic matter present in water, higher the BOD, more polluted the water.
12. Find out the name of the microbes from which cyclosporin A (an immuno suppressive drug) and statins (blood cholesterol lowering agents) are obtained.
Ans: Cyclosporin A (an immuno suppressive drug) is obtained from fungus Trichoderma polysporum while statins (blood cholesterol lowering agent) is obtained from yeast Monascus purpureus.
13. Find out the role of microbes in the following and discuss it with your teacher.
(a) Single cell protein (SCP)
(b) Soil
Ans: a) Single Cell Protein (SCP) : safe microbial cells which can be taken as alternative source of good protein. Similarly, mushrooms (a fungus) is being consumed by thousands of people and yeast is being taken by sportsmen as a protein supplement; in the same way, other forms of microbial cells can also be used as a source of nutrition rich in proteins, minerals, fats, carbohydrates, and vitamins. Such microbes as Spirulina and Methylophilus methylotrophus are being grown on industrial scale on starch containing materials like water from potato starch processing units, straw, molasses, animal manure, and even sewage. These single cell microorganisms can be used as source.
b) Soil; Microbes play a very important role in soil fertility. Decomposition is one of the contributions toward the formation of nutrient-rich humus. Many species of bacteria and cyanobacteria have the ability to fix atmospheric nitrogen into usable form. Rhizobium is symbiotic bacteria found in the root nodules of leguminous plants. Azospirillium and Azotobocter are free living nitrogen-fixing bacteria, whereas Anabena, Nostoc, and Oscillitoria are examples of nitrogen-fixing cyanobacteria.
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.
Ans: Here’s the arrangement of the given items in decreasing order of their importance for human welfare, along with reasons:
Penicillin > Biogas > Curd > Citric acid
- Penicillin: Penicillin, the first antibiotic discovered by Alexander Fleming, revolutionized medicine by effectively treating bacterial infections. Its significance lies in saving countless lives by fighting infections such as pneumonia, strep throat, and syphilis. Antibiotics are essential in healthcare and their impact on human welfare is immense.
- Biogas: Biogas is a renewable energy source that plays a crucial role in sustainable development. It helps reduce reliance on fossil fuels, decreases greenhouse gas emissions, and provides a clean, efficient form of energy for cooking, heating, and electricity generation, especially in rural areas. Biogas also helps manage organic waste, making it important for both environmental and human welfare.
- Curd: Curd is a probiotic food that promotes gut health by aiding digestion and boosting immunity. It is a staple in many cultures and provides essential nutrients like calcium and proteins. Though vital for daily health and nutrition, its impact is more localized compared to antibiotics or renewable energy.
- Citric Acid: Citric acid is widely used in the food and beverage industry as a preservative and flavoring agent. It also has applications in pharmaceuticals and cosmetics. While important in industrial processes, its contribution to human welfare is relatively lower compared to life-saving medicines, renewable energy, or probiotics.
Penicillin ranks highest due to its critical role in healthcare, followed by biogas for its environmental and energy benefits. Curd's nutritional value makes it third, and citric acid, while industrially useful, is ranked fourth.
15. How do biofertilizers enrich the fertility of the soil?
Ans: Bio-fertilizers are living organisms that enhance the fertility of soil. It encompasses selection of positive microorganisms that assist in the improvement of plant growth by providing plant nutrients. These are applied to seeds, roots, or soil, and their biological activity mobilizes the availability of nutrients. So, they are very useful in enriching the soil with organic nutrients. Many species of bacteria and cyanobacteria fix free atmospheric nitrogen. Rhizobium are symbiotic bacteria present in the root nodules of leguminous plants. Azospirillium and Azotobocter are free living nitrogen-fixing bacteria, whereas Anabena, Nostoc, and Oscillitoria are examples of nitrogen-fixing cyanobacteria. Bio-fertilizers are cost effective and eco-friendly.
