Q1. 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?
Answer: I would carry a small amount of curd (yogurt).
The reason for choosing curd contains millions of Lactic Acid Bacteria (LAB), which multiply at suitable temperatures and convert milk into curd. This high concentration makes it easy to collect a sample, prepare a slide, and demonstrate the presence of rod-shaped bacteria (like Lactobacillus) under a microscope.

Q2. Give examples to prove that microbes release gases during metabolism.
Answer: Microbes release various gases as end-products of their growth and metabolism:

Microbes release different gases during their metabolic activities.

1. Carbon dioxide (CO₂): Yeast (Saccharomyces cerevisiae) ferments sugar in dough, releasing CO₂, which makes the dough rise. Similarly, the large holes in Swiss cheese are formed due to CO₂ production by Propionibacterium sharmanii.
2. Methane (CH₄), carbon dioxide (CO₂), and hydrogen (H₂): Methanogenic bacteria such as Methanobacterium grow anaerobically on cellulosic material and release these gases, forming biogas.
3. Methane (CH₄) and hydrogen sulphide (H₂S): Anaerobic bacteria digest organic matter in sewage sludge during wastewater treatment, producing these gases as by-products.

Q3. In which food would you find lactic acid bacteria? Mention some of their useful applications.
Answer: Lactic Acid Bacteria (LAB) like Lactobacillus are found in curd (or yogurt).

Useful Applications of curd are:

1. Curd Production: LAB grow in milk and convert it to curd.
2. Nutritional Improvement: They improve the nutritional quality of milk by increasing Vitamin B₁₂.
3. Digestion/Immunity: They play a beneficial role in the stomach by checking disease-causing microbes.
4. Milk Digestion: They produce acids that coagulate and partially digest milk proteins.

Q4. Name some traditional Indian foods made of wheat, rice and Bengal gram (or their products) which involve use of microbes.
Answer:

Q5. In which way have microbes played a major role in controlling diseases caused by harmful bacteria?
Answer: Microbes help control bacterial diseases by producing antibiotics, which are chemical substances that kill or stop the growth of harmful bacteria. These antibiotics have been crucial in treating serious diseases such as plague, whooping cough, diphtheria, and leprosy. A well-known example is penicillin, the first antibiotic discovered, which was produced by the mould Penicillium notatum and has saved millions of lives worldwide.

Q6. Name any two species of fungus, which are used in the production of the antibiotics.
Answer: Two species of fungus, which are used in the production of the antibiotics are-

1. Penicillium notatum – for the antibiotic Penicillin.
2. Trichoderma polysporum – for the bioactive molecule Cyclosporin A (an immunosuppressive compound).

Q7. What is sewage? In which way can sewage be harmful to us?
Answer: Sewage is the municipal wastewater generated every day in cities and towns. A major component is human excreta.

Harmful Effects of sewage are:

1. Sewage contains large amounts of organic matter and microbes; discharging it into water bodies causes pollution.
2. Sewage contains pathogenic microbes, increasing the risk of water-borne diseases if untreated.

Q8. What is the key difference between primary and secondary sewage treatment?
Answer: The main difference between primary and secondary sewage treatment are-

1. Primary treatment is a physical process that removes large and small solid particles like grit and debris through filtration and sedimentation. It results in primary sludge (settled solids) and effluent (supernatant liquid).
2. Secondary treatment, on the other hand, is a biological process that uses heterotrophic microbes to break down organic matter present in the effluent. This reduces the Biochemical Oxygen Demand (BOD) and produces activated sludge (microbial flocs) and secondary effluent (partially purified water).

Q9. Do you think microbes can also be used as source of energy? If yes, how?
Answer: Yes, microbes can be used as a source of energy.
Certain microbes called methanogens (such as Methanobacterium) grow without oxygen on organic materials like cattle dung or plant waste. During this process, they release gases such as methane (CH₄), carbon dioxide (CO₂), and hydrogen (H₂). This mixture, known as biogas or gobar gas, is inflammable and can be used as an eco-friendly fuel for cooking, lighting, and generating electricity.

Q10. Microbes can be used to decrease the use of chemical fertilisers and pesticides. Explain how this can be accomplished.
Answer: Microbes can reduce the need for chemical fertilisers and pesticides by acting as biofertilisers and biocontrol agents.

As Biofertilisers:

1. They enrich the soil with essential nutrients and promote plant growth naturally.
2. Rhizobium (in legume root nodules) and Azospirillum/Azotobacter (free-living) help in nitrogen fixation.
3. Cyanobacteria also fix nitrogen, especially in paddy fields.
4. Mycorrhizal fungi such as Glomus increase phosphorus absorption and supply it to plants.

As Biocontrol Agents:

1. Bacillus thuringiensis (Bt) produces toxins that kill harmful insect larvae while being safe for other organisms.
2. Trichoderma, a free-living fungus, protects plants by fighting disease-causing pathogens.
3. Baculoviruses (like Nucleopolyhedrovirus) act as natural, species-specific pest controllers, reducing chemical pesticide use.

Q11. 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?
Answer:
Pollution and BOD: Biochemical Oxygen Demand (BOD) measures the organic matter present in water. Greater BOD indicates more pollution.

Most Polluted Sample: Sample C (400 mg/L) — most polluted.

Assigning Labels:

1. Sample C (400 mg/L) = Untreated Sewage Water
2. Sample A (20 mg/L) = Secondary Effluent
3. Sample B (8 mg/L) = River Water

Q12. Find out the name of the microbes from which Cyclosporin A (an immunosuppressive drug) and Statins (blood cholesterol lowering agents) are obtained.
Answer:

1. Cyclosporin A: Obtained from the fungus Trichoderma polysporum.
2. Statins: Obtained from the yeast Monascus purpureus.

Q13. Find out the role of microbes in the following and discuss it with your teacher.
Answer: Microbes play an important role in many areas that support human life and the environment. Some key examples include:

(a) Single Cell Protein (SCP): Microbes such as Spirulina and yeast are cultivated in large quantities to produce Single Cell Protein (SCP), a rich source of proteins, vitamins, and minerals. It serves as a nutritious and sustainable food supplement, helping to overcome global protein shortages.

(b) Soil: In soil, microbes are essential for maintaining fertility and nutrient balance. They decompose organic matter, fix atmospheric nitrogen (e.g., Rhizobium, Cyanobacteria), and form mycorrhizal associations (e.g., Glomus) that improve nutrient absorption and enhance soil quality.

Q14. Arrange the following in the decreasing order (most important first) of their importance, for the welfare of human society. Give reasons for your answer.
Answer:
Order of Importance:

1. Penicillin
2. Biogas
3. Curd
4. Citric acid

Reasons:

1. Penicillin: Saved millions of lives by controlling bacterial diseases like plague and diphtheria.
2. Biogas: Provides a clean, renewable source of energy, reduces waste, and yields useful fertilizer.
3. Curd: Improves nutritional quality and gut health.
4. Citric Acid: Industrially important but less directly significant to human welfare.

Q15. How do biofertilisers enrich the fertility of the soil?
Answer: Biofertilisers help enrich soil fertility and promote healthy plant growth in the following ways:

1. Nitrogen Fixation: Microbes such as Rhizobium (symbiotic), Azospirillum, and Azotobacter (free-living) convert atmospheric nitrogen into usable organic forms for plants.
2. Phosphate Mobilisation: Mycorrhizal fungi like Glomus absorb phosphorus from the soil and make it available to plants.
3. Organic Matter Addition: Cyanobacteria add organic matter to the soil, improving its fertility and texture.
4. Plant Growth Promotion: Biofertilisers enhance plant growth, increase resistance to diseases, and improve tolerance to salinity and drought.