Important Questions for CBSE Class 12 Biology Chapter 8 - Microbes in Human Welfare 2024-25

Very Short Questions and Answers  (1 Mark Questions)

1. How does a small amount of curd added to fresh milk convert it into curd? Mention a nutritional quality that gets added to the curd.

Ans: In a small amount of curd, a huge number of lactic acid bacteria can be detected. By creating lactic acid, proliferate and turn the milk into curd. Increased Vitamin B12 enhances nutritional quality.

2. Why is the secondary treatment of water in sewage treatment plants called biological treatment?

Ans: Organic wastes from sewage water are digested by particular bacteria in this treatment In the presence of water, microorganisms.

3. An antibiotic called Wonder Drug was used to treat the wounded soldiers of America during World War II. Name the drug and the scientist who discovered it.

Ans: Alexander Fleming invented penicillin.

4. You have observed that fruit juice in bottles bought from the market is clearer as compared to those made at home. Give a reason.

Ans: Pectinase and proteases are used to clarify bottle juices.

5. Alexander Fleming discovered Penicillin, but its full potential as effective antibiotic was established by other scientists. Name the two scientists.

Ans: Howard Florey and Ernest Chain were the two scientists. 

6. Name the plant whose sap is used in making Toddy. Mention the process involved in this.

Ans: The sap of a palm tree is used in making Toddy and the process is called fermentation.

7. What is the medical use of cyclosporin A.

Ans: During organ transplantation, cyclosporin A is used as an immunosuppressive drug.

8. Name the pests that ladybird & dragonflies help to get rid of respectively?

Ans: Aphids are controlled by ladybird beetles, and mosquitoes are controlled by dragonflies.

9. Give an example to prove that microbes release gases during metabolism?

Ans: Bread and Puffed dough are suitable examples of bacteria releasing gases during metabolism.

10. What are interferons?

Ans: The Interferons are those proteins that are released by the cells in response to the viral infection and it helps in the fight against viral infection.

11. Name the enzyme which is used as a clot buster" to remove a blood clots from the blood vessels of patients.

Ans: Streptokinase is used. 

14. Expand LAB?

Ans: Lactic acid Bacteria is the full form of LAB.

15. Name any two free-living nitrogen-fixing bacteria.

Ans: Two free-living nitrogen bacteria are Azotobacter, Azospirillum

16. Name the organism used in the dough for making bread.

Ans: Saccharomyces cerevisiae.

17. Name the fungus used as a biocontrol of plant diseases.

Ans: The fungus used as a biocontrol of plant diseases is known as  Trichoderma.

18. Name any two gases produced during secondary treatment of Sewage?

Ans: Methane, Hydrogen sulphide & carbon dioxide.

Short Questions and Answers  (2 Marks Questions)

1. Name two alcoholic drinks produced in each of the following ways.

(i) by distillation and (ii) without distillation.

Ans:

(i) Distillation produces whisky, brandy, and rum.

(ii) Wine and beer that has not been distilled.

2. Lactic Acid Bacteria (LAB) is commonly used in the conversion of milk into curd. Mention any two other functions of LAB that are useful to humans.

Ans:

(i) Vitamin B12 is synthesised by LAB in the human gut.

(ii) The presence of LAB in the human stomach inhibits the growth of dangerous microorganisms.

3. How do mycorrhizae function as biofertilizers? Explain with examples.

Ans: Fungi connected with plant roots are known as mycorrhizae. Mycorrhizae are formed by many species of the Glomus genus. These fungal symbionts collect water and minerals such as phosphorus from the soil and pass them on to the plant.

Long Questions and Answers  (3 Mark Questions)

1. Fill in the blanks spaces a, b, c, d, e, and given in the following table:

Ans:

(a) to kill disease-causing bacteria

(b) Lactobacillus

(c) remove clots from blood vessels

(d) Cyclosporin A

(e) Beverage/medicines

(f) Propionibacterium Shermanii.

2. What is the biochemical oxygen demand (BOD) test? At what stage of Sewage treatment this test is performed? The BOD level of three samples of water labelled as A, B and C are 30 mg/L, 10mg/L and 500 mg/L respectively. Which sample of water is most polluted?

Ans:

• The BOD test determines how quickly microorganisms in a sample of water absorb oxygen.

• Secondary treatment or biological treatment.

• Sample C is the most polluted of the three water samples since it has the greatest BOD level.

3. Given below is the Flow chart of Sewage treatment. Fill in the blank spaces marked

'a' to f.

Ans:

(a) Primary treatment.

(b) Aeration

(c) Flocs 

(d) Biochemical Oxygen Demand (BOD)

(e) Activated sludge 

(f) Water bodies like river streams.

4. What are biofertilizers? A farmer is advised to add a culture of bacterium in the soil before sowing the crop. Name the bacterium in the culture. How is this bacterium useful to the crop?

Ans: Some points on biofertilizers are: 

•  Biofertilizers are organisms that improve the soil's nutrient quality.

• Azotobacter/Azospirillum is a bacteria found in the bacterium Azotobacter/Azospirillum (free living)

• This bacterium converts atmospheric nitrogen into organic molecules that are used as a fertiliser by plants.

5. What are statins? Name the microorganism that produces this substance. How is it medically important?

Ans: The Monascuspurpureus produces statins, which are cholesterol-lowering drugs (Yeast). They operate as blood cholesterol-lowering drugs by competitively blocking the enzymes involved in cholesterol production.

6. Describe the procedure involved in Sewage treatment?

Ans: The following technique is performed for the treatment of sewage waste:

i) Primary Treatment- This entails physically separating suspended materials in settling tanks in order to reduce BOD. The raw sewage is routed into massive open tanks where it is subjected to anaerobic digestion to remove the solid fraction.

ii) Secondary Therapy- Secondary treatment relies on microbial activity, either aerobic or anaerobic. Secondary treatment techniques include:

1. Sand filters for filtration

2. Process of aeration

3. Application of oxidation ponds:

After drying, the sludge that collects after secondary treatment is disposed of, and the efferent is allowed to be used for tertiary treatment.

7. What is Biogas? How is it produced & Name the microbes invaded in Biogas production?

Ans: Biogas is the gas produced by anaerobic fermentation of waste biomass. It is made up of methane, CO₂, hydrogen, nitrogen, oxygen, and hydrogen sulphide, among other things. Microbes that are often employed in the production of biogas-

i) Hydrolytic Bacteria, such as cellulosomes, clostridium, etc.

ii) Bacteria that produce hydrogen sulphide, such as Syntrophomonas wolfei

iii) Methanobacterium Omelianskii is an example of a methanogenic bacteria.

The biogas plant is fed by a concrete tank. The slurry is covered with a floating cover, which continues to rise when gas is created in the tank owing to microbial activity. The biogas plant includes an output that connects to a pipe that distributes biogas to surrounding residences. Microbes transform the organic part of biodegradable organic solid waste and trash into energy in the form of biogas and humus during biogas production.

$ CO + H_2O \to CO_2 + H_2 $

$ CO_2 + 4H_2 \to CH_4 + 2H_2O $

$ CH_3OH \to CH_4 + O_2 $

8. Microbes can be used to decrease the use of chemical fertilizers & pesticides. Explain how this can be accomplished?

Ans: Below are some of the ways that microbes can be used to decrease the use of chemical fertilizers & pesticides:

• Chemicals are commonly used to control plant diseases and pests in modern society.

• However, these chemicals can be harmful to humans and the environment due to their toxicity.

• In agriculture, natural predation can be used as a form of pest control instead of pesticides.

• Bacillus thuringiensis (Bt) is a type of bacteria that can be used to control butterflies, caterpillars, and other insects.

• Dried spores of Bt are mixed with water and sprayed onto sensitive plants such as brassicas.

• The toxin released by Bt in the intestines of larvae kills them, but it does not harm other insects.

• This natural form of pest control can help to reduce the use of harmful chemicals in agriculture and minimize their impact on the environment.

9. How do Bio fertilisers enrich the fertility of soil? How do cyanobacteria act as biofertilizers?

Ans: Microorganisms employ biological channels to improve soil fertility for optimal crop development, and they are referred to as "BIOFERTILIZERS." These microorganisms can boost crop output in one of two ways.

i) By removing nitrogen from the atmosphere

ii) Insoluble fertiliser solubilization

iii) By promoting the growth of plants.

iv) Through phosphorus absorption.

v) By allowing plant remnants to decompose.

Anabaena, a cyanobacterium found in the leaf cavity of the water fern Azolla, fixes nitrogen from the air and excretes nitrogenous compounds into the leaf cavity.

10. How does primary sludge differ from activated sludge? What type of changes in the sludge is carried out in an anaerobic sludge digester? Give the composition of biogas produced in the sewage treatment plant.

Ans: 

• Primary sludge consists of all solids, such as soil and small stones, that settle in the settling tank during sewage treatment.

• Activated sludge is the sediment of bacterial flocs that settle in the settling tank after biological treatment during sewage treatment.

• Bacteria, slime and fungal filaments bind together to form flocs in the activated sludge.

• A portion of the activated sludge is used as inoculum in the aeration tank and the remaining is sent to the anaerobic sludge digester.

• In the anaerobic sludge digester, bacteria that grow anaerobically consume the bacteria, fungus and cellulose in the sludge.

• Biogas is a mixture of methane, hydrogen and carbon dioxide that is produced in sewage treatment plants.

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