Class 12 Biology Chapter 8 Microbes in Human Welfare Solutions. Explore Class 12 Biology Chapter 8 Microbes in Human Welfare Solutions with easy-to-understand answers, important questions, and exam-focused explanations to master key concepts, revise effectively, and prepare confidently for exams. Continue reading: Class 12 Biology Chapter 8 Microbes in Human Welfare Solution

Class 12 Biology Chapter 8 Microbes in Human Welfare Solutions

A. Very Short-Answer Questions (Microbes in Human Welfare Solutions)

1. Which bacterium converts milk into curd?

Ans: Lactobacillus, or lactic acid bacteria (LAB).

2. Which vitamin is increased in curd?

Ans: Vitamin B12.

3. What is used to ferment dough made from flour?

Ans: Baker’s yeast, a fungus.

4. What are bioreactors?

Ans: Bioreactors are vessels in which microorganisms or cells are cultured to obtain useful products. They maintain suitable conditions such as nutrients, temperature, pH and aeration or moisture as required.

5. What is mycorrhiza?

Ans: Mycorrhiza is a mutually beneficial association between a fungus and the roots of a plant.

6. What is a fermenter?

Ans: A fermenter is a large vessel in which microorganisms are grown under controlled conditions for industrial production.

7. What raw materials are used to produce ethanol?

Ans: Cereal grains such as malted grains, rice and wheat, as well as fruit juices, may be used.

8. What was the first widely recognised antibiotic discovered?

Ans: Penicillin.

9. Name the microorganisms used to produce citric acid, acetic acid and butyric acid.

Ans: Citric acid — Aspergillus niger; acetic acid — Acetobacter aceti; butyric acid — Clostridium butylicum.

10. Which enzyme is used to dissolve blood clots in patients with certain heart conditions?

Ans: Streptokinase, an enzyme used as a clot-dissolving agent in selected medical situations.

11. What is the first organic acid produced during microbial fermentation?

Ans: Lactic acid, according to the source text.

12. What is BOD?

Ans: Biochemical oxygen demand (BOD) is the amount of dissolved oxygen required by microorganisms to break down biodegradable organic matter in a water sample under specified conditions.

13. Who introduced the term “antibiotic”?

Ans: The source gives Alexander Fleming. Note: the term “antibiotic” is generally credited to Selman Waksman, while Fleming discovered penicillin.

14. Which two institutions promoted the development and use of biogas technology in India?

Ans: The source names the Indian Council of Agricultural Research (ICAR) and the Khadi and Village Industries Commission (KVIC).

15. Which microorganism is used to control caterpillar larvae?

Ans: Bacillus thuringiensis (Bt).

16. Name a blue-green microorganism used as human food.

Ans: Spirulina, a cyanobacterium.

17. Name a fungus used in plant disease control.

Ans: Trichoderma.

Fill in the blanks (Microbes in Human Welfare Solutions)

18. Biogas mainly contains __________ and is used as a cooking fuel.

Ans: Methane.

19. During fermentation, the enzyme zymase converts sugar into __________.

Ans: Alcohol (ethanol).

20. The biopesticide azadirachtin is obtained from the __________ tree.

Ans: Neem.

21. The association between a fungus and plant roots is called __________.

Ans: Mycorrhiza.

22. The microorganism grown on molasses and sold for food-related uses is __________.

Ans: Baker’s yeast.

23. Chemical fertilisers and __________ are responsible for widespread pollution.

Ans: Pesticides.

24. The source refers to a “flavonoid process” for protecting crops from __________. The term appears corrupted or unclear in the source.

Ans: Insect pests (intended answer based on the surrounding wording; verify the original textbook term).

25. Chemicals used to destroy weeds in crop fields are called __________.

Ans: Herbicides.

B. Short-Answer Questions (Microbes in Human Welfare Solutions)

26. State some important uses of lactic acid bacteria (LAB).

Ans: LAB convert milk into curd by producing lactic acid, which coagulates milk proteins. They can improve the nutritional quality of curd, including increasing vitamin B12 content. Beneficial lactic acid bacteria in the digestive tract may also help limit the growth of some disease-causing microorganisms.

27. What are antibiotics? How do they prevent the growth of other microorganisms in a culture medium?

Ans: Antibiotics are substances produced by certain microorganisms that inhibit or kill other microorganisms, often at concentrations that do not seriously harm the host. In culture media, an appropriate antibiotic may be added to suppress unwanted bacteria, although the antibiotic must be selected for the intended organism and purpose.

28. What role do microorganisms play in preparing fermented beverages?

Ans: Yeast is important in producing wine, beer, whisky, brandy and rum. It ferments sugars in fruit juice or materials such as malted grains, rice and wheat to produce ethanol. Wine and beer are generally produced without distillation, whereas whisky, brandy and rum are made by distilling fermented mixtures.

29. What is sewage? How can it be harmful?

Ans: Sewage is wastewater from homes and urban areas that contains human waste and other contaminants. It may carry disease-causing microorganisms; if released untreated into rivers, streams or other water bodies, it can pollute the water, harm aquatic life and create risks to human health.

30. “Leguminous crops enrich the soil, whereas rice crops do not.” Why?

Ans: Leguminous plants have root nodules containing symbiotic Rhizobium bacteria, which fix atmospheric nitrogen into forms that contribute to soil fertility. Rice plants do not normally have these Rhizobium-containing root nodules, so they do not enrich soil through this same mechanism.

31. What is biological control? What may be the consequences of using chemical pesticides and herbicides?

Ans: Biological control uses living organisms or their products to manage plant diseases and pests. Excessive or inappropriate use of chemical pesticides and herbicides can harm humans and other organisms, contaminate soil and water, leave residues on crops, and damage non-target species and ecosystems.

32. What is the main difference between primary and secondary sewage treatment?

Ans: Primary treatment mainly removes suspended solids by screening, sedimentation and related physical processes. Secondary treatment uses microorganisms to break down dissolved and fine organic matter, commonly in aerated biological treatment systems followed by settling.

33. State the chemical composition of biogas and name one organism involved in its production.

Ans: Biogas consists mainly of methane and carbon dioxide, with small amounts of other gases such as hydrogen sulphide and water vapour. Methanogenic archaea, for example Methanobacterium, are involved in methane production.

34. What is cyclosporin A? From which organism is it obtained?

Ans: Cyclosporin A is an immunosuppressive drug used to help prevent rejection after organ transplantation. The source gives “Trichoderma polysporum”; the commonly cited organism in biology texts is the fungus Tolypocladium inflatum (formerly classified under other names).

35. State some uses or advantages of biofuels.

Ans: Biofuels can be produced from renewable biological materials and may reduce reliance on fossil fuels. Their environmental impact varies with the feedstock, production method and use; they are not necessarily pollution-free and may still produce emissions.

C. Descriptive Questions (Microbes in Human Welfare Solutions)

36. Explain the role of microorganisms in biogas production.

Ans: Biogas is a fuel mixture produced when microorganisms break down organic matter in the absence of oxygen. Methanogenic archaea produce methane during anaerobic digestion. These organisms occur in anaerobic digesters and in the rumen of ruminants such as cattle. In a biogas plant, dung and other biodegradable waste are mixed with water and placed in an airtight digester. Microbial activity produces gas that collects under a movable or fixed gas holder and is carried through pipes for use as fuel.

37. Describe the role of microorganisms as biofertilisers.

Ans: Biofertilisers are living microorganisms that improve the availability of nutrients to plants. Rhizobium bacteria in legume root nodules fix atmospheric nitrogen. Free-living or associative nitrogen-fixing bacteria such as Azotobacter and Azospirillum can also contribute nitrogen to soil systems. Cyanobacteria can fix nitrogen in suitable environments and are useful in paddy fields. Mycorrhizal fungi, including species of Glomus, help plants absorb phosphorus and may improve tolerance to drought, salinity and some root pathogens. These organisms can reduce dependence on some chemical fertilisers when used appropriately.

38. Explain the role and importance of baculoviruses as biological-control agents.

Ans: Baculoviruses infect particular insect pests and can be used as biological-control agents. Their narrow host range makes them useful for targeting selected pests while minimising harm to many beneficial insects, plants and vertebrates. They can be valuable in integrated pest management and organic farming because they may reduce the need for broad-spectrum chemical insecticides.

39. Why can microorganisms help reduce the use of chemical fertilisers and pesticides? Explain.

Ans: Some microorganisms improve nutrient availability and plant growth, reducing the need for certain chemical fertilisers. Nitrogen-fixing bacteria convert atmospheric nitrogen into biologically usable forms. Mycorrhizal fungi help plants absorb phosphorus and can improve tolerance to environmental stresses. Other beneficial microorganisms can suppress plant pathogens or pests. Cyanobacteria can contribute nitrogen to some agricultural systems, especially paddy fields. Their effectiveness depends on the crop, soil, climate and management, so they complement rather than universally replace all fertilisers and pesticides.

D. Additional Questions and Answers (Microbes in Human Welfare Solutions)

1. What are antibiotics?

Ans: Antibiotics are substances produced by certain microorganisms, or derived from them, that kill or inhibit the growth of other microorganisms. Their safe and effective use depends on the type of infection and the specific medicine.

2. Name two microorganisms used to produce acids.

Ans: Acetic acid — Acetobacter aceti; butyric acid — Clostridium butylicum. (The source’s wording is unclear about whether it asks for organisms or acids.)

3. Name an enzyme used to dissolve blood clots.

Ans: Streptokinase.

4. How does primary treatment of sewage differ from secondary treatment?

Ans: Primary treatment removes physical solids through screening and sedimentation. Secondary treatment uses microorganisms to degrade organic matter; it is a biological process, not simply the addition of anaerobic bacteria to remove all pathogens.

5. How do ruminants such as cattle digest their food?

Ans: Ruminants host communities of microorganisms in their rumen that help break down cellulose and other plant material. Anaerobic microbes, including methanogens, contribute to fermentation and may produce methane and carbon dioxide as by-products.

6. Name two free-living nitrogen-fixing bacteria.

Ans: Azotobacter and Azospirillum are commonly cited examples, although Azospirillum is often described as associative rather than strictly free-living.

7. What is floc?

Ans: A floc is an aggregate of bacteria associated with fungal filaments or other material, forming a mesh-like structure during biological sewage treatment.

8. Give an example showing that microorganisms produce gases during metabolism.

Ans: During alcoholic fermentation, yeast converts sugars into ethanol and carbon dioxide. The carbon dioxide makes bread dough rise. Microorganisms also produce carbon dioxide during fermentation of batter used to prepare foods such as idli and dosa, helping the batter become aerated. 0 0 0

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