Microbes in Human WelfareClass 12 Biology NCERT Solutions
15 Solutions
Generated by KedovoAI
Solution 1 of 15
Q1EXERCISES
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 with the help of a microscope, which sample would you carry and why?
Solution
To demonstrate the presence of microbes, I would carry a sample of curd (or a starter for making curd) from home to the biology laboratory.
Reason:
The chapter states that curd is produced from milk by the action of micro-organisms such as Lactobacillus and other Lactic Acid Bacteria (LAB). A small amount of curd added to fresh milk as a starter or inoculum contains millions of these bacteria. Therefore, a drop of curd is a rich and concentrated source of bacteria, making them easy to observe under a microscope.
Q2EXERCISES
Give examples to prove that microbes release gases during metabolism.
Solution
There are several examples from the chapter that prove microbes release gases during metabolism:
-
Fermentation of Dough: The dough used for making foods like dosa, idli, and bread has a puffed-up appearance. This is due to the production of carbon dioxide () gas during fermentation by bacteria and yeast (Saccharomyces cerevisiae).
-
Cheese Making: The large holes observed in 'Swiss cheese' are a result of the production of a large amount of by a bacterium named Propionibacterium sharmanii.
-
Biogas Production: Certain anaerobic bacteria called methanogens, when grown on cellulosic material (like in cattle dung or sewage sludge), produce a large amount of methane () along with and . This mixture of gases is known as biogas.
Q3EXERCISES
In which food would you find lactic acid bacteria? Mention some of their useful applications.
Solution
Lactic acid bacteria (LAB) are found in curd.
Some of their useful applications are:
- Curd Production: LAB, such as Lactobacillus, grow in milk and convert it into curd. During their growth, they produce acids that coagulate and partially digest the milk proteins.
- Improved Nutrition: The conversion of milk to curd by LAB also improves its nutritional quality by increasing the content of vitamin .
- Beneficial Role in Stomach: In the human stomach, LAB play a very beneficial role by checking the growth of other disease-causing microbes.
Q4EXERCISES
Name some traditional Indian foods made of wheat, rice and Bengal gram (or their products) which involve use of microbes.
Solution
Based on the chapter, some traditional foods involving the use of microbes are:
- Made from Wheat: Bread is made from dough that is fermented using baker's yeast (Saccharomyces cerevisiae).
- Made from Rice: Dosa and idli are made from a dough of rice and lentils which is fermented by bacteria. The fermentation process causes the dough to puff up due to the production of gas.
- Made from Palms: 'Toddy' is a traditional drink from southern India made by fermenting sap from palms.
The chapter also mentions that microbes are used to ferment soyabean and bamboo shoots to make foods, but does not specify a traditional Indian food made from Bengal gram.
Q5EXERCISES
In which way have microbes played a major role in controlling diseases caused by harmful bacteria?
Solution
Microbes have played a major role in controlling diseases caused by harmful bacteria through the production of antibiotics.
Antibiotics are chemical substances produced by certain microbes that can kill or retard the growth of other disease-causing microbes. The discovery of Penicillin from the fungus Penicillium notatum was a significant milestone. Antibiotics have greatly improved our capacity to treat deadly infectious diseases such as plague, whooping cough (kali khansi), diphtheria (gal ghotu), and leprosy (kusht rog), which used to kill millions of people. The chapter states that antibiotics are one of the most significant discoveries of the twentieth century and that we cannot imagine a world without them today.
Q6EXERCISES
Name any two species of fungus, which are used in the production of the antibiotics.
Solution
Based on the provided chapter, one species of fungus used in the production of antibiotics is:
- Penicillium notatum: This mould was the original source from which the first antibiotic, Penicillin, was discovered by Alexander Fleming.
The chapter mentions that "After Penicillin, other antibiotics were also purified from other microbes," but it does not name a second species of fungus used for antibiotic production. It does, however, prompt the reader to find out about other antibiotics and their sources.
Q7EXERCISES
What is sewage? In which way can sewage be harmful to us?
Solution
Sewage is municipal wastewater generated every day in cities and towns. A major component of this wastewater is human excreta. It contains large amounts of organic matter and numerous microbes, many of which are pathogenic.
Sewage can be harmful to us in the following ways:
- Source of Pathogens: It contains many pathogenic (disease-causing) microbes. If untreated sewage is discharged into water bodies like rivers or streams, it can contaminate drinking water sources and lead to the spread of water-borne diseases such as cholera, typhoid, and dysentery.
- Environmental Pollution: The large amount of organic matter in sewage pollutes natural water bodies. The decomposition of this organic matter by microbes consumes a large amount of dissolved oxygen, which can kill fish and other aquatic organisms, disrupting the entire ecosystem.
Q8EXERCISES
What is the key difference between primary and secondary sewage treatment?
Solution
The key difference between primary and secondary sewage treatment lies in the method and purpose of the treatment.
-
Primary Treatment: This is a physical process. It involves the mechanical removal of large and small solid particles from the sewage. This is achieved through sequential filtration to remove floating debris and sedimentation to allow grit (soil and small pebbles) and other solids to settle down. It physically separates the solid waste (primary sludge) from the liquid waste (effluent).
-
Secondary Treatment: This is a biological process. The liquid effluent from the primary treatment is passed into aeration tanks where useful aerobic microbes are encouraged to grow. These microbes consume the dissolved organic matter present in the effluent, thereby significantly reducing its Biochemical Oxygen Demand (BOD) and polluting potential. This process uses living organisms to clean the water.
Q9EXERCISES
Do you think microbes can also be used as source of energy? If yes, how?
Solution
Yes, microbes can be used as a source of energy through the production of biogas.
How:
Certain types of anaerobic bacteria, collectively known as methanogens (e.g., Methanobacterium), are used in this process. These bacteria are commonly found in anaerobic sludge during sewage treatment and in the rumen of cattle.
In a biogas plant, organic waste such as cattle dung (gobar) and other bio-wastes are collected in a large concrete tank. The methanogens anaerobically digest the cellulosic material in this waste. During this digestion, the bacteria produce a mixture of gases, which includes methane (), carbon dioxide (), and hydrogen (). This gaseous mixture is called biogas. Since methane is highly inflammable, biogas can be used as a fuel for cooking and lighting, thus serving as a source of energy.
Q10EXERCISES
Microbes can be used to decrease the use of chemical fertilisers and pesticides. Explain how this can be accomplished.
Solution
Microbes can help decrease the dependence on chemical fertilisers and pesticides through their use as biofertilisers and biocontrol agents.
1. Decreasing the use of Chemical Fertilisers (using Biofertilisers):
Biofertilisers are organisms that enrich the nutrient quality of the soil. Instead of using chemical fertilisers, farmers can use these microbes:
- Nitrogen-fixing Bacteria: Bacteria like Rhizobium (in symbiosis with leguminous plants) and free-living bacteria like Azospirillum and Azotobacter fix atmospheric nitrogen into a usable form for plants, enriching the soil with nitrogen.
- Nitrogen-fixing Cyanobacteria: Cyanobacteria (blue-green algae) such as Anabaena and Nostoc also fix atmospheric nitrogen and add organic matter to the soil, increasing its fertility, especially in paddy fields.
- Phosphate-solubilising Fungi: Fungi from the genus Glomus form symbiotic associations with plant roots (mycorrhiza). They absorb phosphorus from the soil and transfer it to the plant.
2. Decreasing the use of Chemical Pesticides (using Biocontrol Agents):
Biocontrol is the use of biological methods to control pests and diseases, reducing the need for toxic chemical pesticides.
- Bacteria as Biocontrol Agents: The bacterium Bacillus thuringiensis (Bt) produces a toxin that kills specific insect larvae, such as butterfly caterpillars. Dried spores of Bt can be sprayed on plants, or the gene for the toxin can be incorporated into the plant itself (e.g., Bt-cotton).
- Fungi as Biocontrol Agents: Fungi like Trichoderma species, which are common in root ecosystems, are effective biocontrol agents against several plant pathogens.
- Viruses as Biocontrol Agents: Baculoviruses, particularly those of the genus Nucleopolyhedrovirus, are pathogens that attack insects and other arthropods. They are species-specific, narrow-spectrum insecticides that do not harm plants, birds, fish, or non-target insects.
Q11EXERCISES
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/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?
Solution
The Biochemical Oxygen Demand (BOD) is a measure of the amount of oxygen required by bacteria to break down the organic matter in a water sample. A higher BOD value indicates more organic waste and therefore, greater pollution.
Most Polluted Sample:
Comparing the BOD values:
- Sample A:
- Sample B:
- Sample C:
The highest BOD value is . Therefore, Sample C is the most polluted water sample.
Assigning Correct Labels:
- Untreated sewage water: This would have the highest amount of organic matter and therefore the highest BOD. Thus, Sample C () is the untreated sewage water.
- River water: Assuming it is relatively clean, it would have the lowest amount of organic pollutants and the lowest BOD. Thus, Sample B () is the river water.
- Secondary effluent: This is water from a sewage treatment plant after the biological treatment stage. Most of the organic matter has been removed, so its BOD is significantly reduced compared to untreated sewage, but it is still higher than clean river water. Thus, Sample A () is the secondary effluent.
Q12EXERCISES
Find out the name of the microbes from which Cyclosporin A (an immunosuppressive drug) and Statins (blood cholesterol lowering agents) are obtained.
Solution
The microbes that produce these bioactive molecules are:
-
Cyclosporin A: This immunosuppressive agent is produced by the fungus Trichoderma polysporum.
-
Statins: These blood-cholesterol lowering agents are produced by the yeast Monascus purpureus.
Q13EXERCISES
Find out the role of microbes in the following and discuss it with your teacher.
(a)
Single cell protein (SCP)
(b)
Soil
Solution
(a) Single cell protein (SCP): The provided chapter text on 'Microbes in Human Welfare' does not contain information about Single Cell Protein (SCP). This topic would require discussion with a teacher or research from other sources.
(b) Soil: Microbes play a crucial and multifaceted role in the soil ecosystem, as described in the chapter:
- Decomposers: Microbes are major components of biological systems and are present everywhere, including soil. They act as decomposers, breaking down dead organic matter and recycling essential nutrients.
- Enriching Soil Fertility (as Biofertilisers):
- Nitrogen Fixation: Bacteria like Rhizobium (symbiotically with legumes) and free-living bacteria like Azospirillum and Azotobacter fix atmospheric nitrogen into compounds that plants can absorb, thus enriching the soil's nitrogen content.
- Phosphorus Availability: Mycorrhizal fungi (e.g., Glomus) form a symbiotic association with plant roots. The fungus absorbs phosphorus from the soil and makes it available to the plant.
- Adding Organic Matter: Cyanobacteria (blue-green algae) not only fix nitrogen but also add organic matter to the soil, improving its overall fertility.
- Biocontrol Agents: Some soil microbes help control plant diseases. For example, the fungus Trichoderma is a free-living fungus in root ecosystems that acts as an effective biocontrol agent against several plant pathogens.
Q14EXERCISES
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
Solution
The arrangement in decreasing order of importance for the welfare of human society is:
Penicillin > Biogas > Curd > Citric acid
Reasons:
- Penicillin: As an antibiotic, penicillin revolutionized medicine. The chapter states that antibiotics are "one of the most significant discoveries of the twentieth century" and have saved millions of lives from deadly infectious diseases like plague, diphtheria, and whooping cough. Its impact on global human health and life expectancy is unparalleled.
- Biogas: Biogas provides a sustainable and renewable source of energy for cooking and lighting, especially in rural areas. It also helps in waste management (by digesting cattle dung and plant waste) and produces a nutrient-rich slurry that can be used as fertiliser. Its impact on environmental sustainability and improving rural life is immense.
- Curd: Curd is a widely consumed household food product with significant nutritional benefits, such as increased vitamin content. The Lactic Acid Bacteria (LAB) in curd also play a beneficial role in gut health. While important for daily nutrition and health, its impact is more at an individual or community level rather than a global life-saving scale like penicillin.
- Citric acid: Citric acid is mentioned as an example of an industrial chemical produced by a microbe (Aspergillus niger). While it has many uses in the food and other industries, its contribution to human welfare is more indirect and commercial compared to the direct health, energy, and nutritional benefits of the other three.
Q15EXERCISES
How do biofertilisers enrich the fertility of the soil?
Solution
Biofertilisers are organisms like bacteria, fungi, and cyanobacteria that enrich the nutrient quality of the soil, thereby increasing its fertility. They do this through several biological processes:
-
Nitrogen Fixation: The atmosphere contains a large amount of nitrogen gas (), which plants cannot use directly. Biofertilisers convert this atmospheric nitrogen into usable forms like ammonia, nitrates, and nitrites.
- Symbiotic Bacteria: Rhizobium bacteria live in the root nodules of leguminous plants and fix atmospheric nitrogen directly for the plant.
- Free-living Bacteria: Bacteria such as Azospirillum and Azotobacter live freely in the soil and enrich it with nitrogen compounds.
- Cyanobacteria: Autotrophic microbes like Anabaena, Nostoc, and Oscillatoria also fix atmospheric nitrogen. In paddy fields, they serve as an important biofertiliser.
-
Phosphorus Solubilisation and Uptake: Many fungi form a symbiotic association with the roots of higher plants, known as mycorrhiza (e.g., fungi of the genus Glomus). The fungal partner absorbs phosphorus from the soil and passes it to the plant. This is crucial as phosphorus is often a limiting nutrient in soil.
-
Addition of Organic Matter: Cyanobacteria (blue-green algae), apart from fixing nitrogen, also add organic matter to the soil upon their death and decomposition. This improves the soil structure, water-holding capacity, and overall fertility.