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| Name of Board | AHSEC |
| Class: | Assam Board Class 12 |
| Subject: | AHSEC Class 12 Biology |
| Number of Chapter: | 08 |
| Chapter Name | Microbes in Human Welfare |
| Content Type: | Text, Images and PDF Format |
| Academic Year: | 2024-25 |
| Medium: | English |
| Available Solution Link: | AHSEC Class Biology Notes |
AHSEC Class 12th Biology Chapter: 8 Microbes in Human Welfare
[A] SHORT ANSWER QUESTIONS: (1 MARK EACH)
1. What is biofertilizer? What are its sources?
Ans: Biofertilizers are organisms that enrich the nutrient quality of the soil. Its main sources are bacteria, fungi and cyanobacteria.
2. What do you mean by biopesticide? Name a biopesticide obtained from Neem.
Ans: Biopesticides are biological agents that are used for control of weeds, insects and pathogens. Azadirachtin is a biopesticide obtained from Neem.
3. What are bioreactors?
Ans: Bioreactors are vessels in which raw materials are biologically converted into specific products by microbes, plant and animal cells and their enzymes.
4. Which one is the first organic acid produced by microbial fermentation?
Ans: Lactic Acid.
5. Expand the term TPA.
Ans: Tissue Plasminogen Activator.
6. Name the blue green algae which is used as human food and its importance.
Ans: Spirulina. Its importance is that it is rich in protein.
7. Which one is the world’s problematic aquatic weed. At what condition it grows abundantly?
Ans: Water hyacinth. It grows in stagnant water rich in nutrients.
8. Name the group of organisms and the substrates they act on to produce biogas?
Ans: Methanogens and they act upon anaerobic sludge formed during sewage treatment to produce biogas.
9. Name the organism that fixes Nitrogen in symbiotic association with a water fern.
Ans: Anabaena.
10. What is mycorrhiza?
Ans: Mycorrhiza is the symbiotic association between fungi and roots of higher plants.
11. Name the curd forming bacteria. Mention at what temperature it can convert the milk to curd.
Ans: Lactobacillus acidophilus prepares curd at about 40°C or less.
12. What is SCP?
Ans: The biomass obtained from microorganisms can be treated or processed in industry to be used as food and is called single oil protein (SCP).
13. Why are pectinases and proteases added to fruit juices?
Ans: To clarify the bottle juices.
14. Define organic farming.
Ans: Organic farming is a cyclical, zero waste procedure. where waste products from one process are cycled in as nutrients for other processes, allowing maximum utilisation of resource and increasing the efficiency of production.
15. What is pesticides?
Ans. Pesticide is a substance used for destroying insects or other organisms harmful to cultivated plants.
16. Name the first organic acid produced by microbial fermentation.
Ans. Lactic acid
17. What is the scientific name of Baker’s yeast?
Ans. Saceharomyces cerevisiae
18. How do the differently written ‘Cry’ and ‘cry’ represent respectively?
Ans. Cry represents portion and cry represents gene.
19. Who coined the term antibiotic?
Ans. Selman waksman
[B] FILL UP THE BLANKS : (1 MARK EACH)
1. Yeast is used in preparation of______
Ans, Bread
2. Biogas mainly contains and is used for cooking.
Ans. Methane
3. Vinegar is prepared from alcohol with the help of oganism.
Ans. Yeast
4. The nutrient material for Wine and Brandy is______juice.
Ans. Fruit
5. Chemical fertilizers and_____ spread pollution. are the sources of wide
Ans. Pesticides
6. Single cell Protein (SCP) provides a valuable________ rich supplement in human diet.
Ans. Protein
7. The sewage water is treated till the BOD is found to be_______.
Ans. Reduced
8. _______and______are the two biotechnologically manufactured vitamins.
Ans. Riboflavin and Vitamin B12
9. ______is an antibiotic which is active against fungus.
Ans. Griseofulvin
10. Trichoderma species are potentially useful as_______
Ans. Bioinsecticides
11. The biopesticides Axadirachtin obtained from______ plant.
Ans. Neem
12. _______a blue green algae used as human food.
Ans.: Spirulina
13. ______grow in milk and convert it to curd.
Ans. Lactid acid bacteria
14. Enzyme zymase convert the sugar into______during fermentation.
Ans. ethyl alcohol
[C] TRUE AND FALSE
1. Aquatic fern Marsilea is an excellent biofertilizer.
Ans. False
2. Extensive use of chemical fertilizers may lead to eutrophication of near by water bodies.
Ans. True
3. People recovering from long illness are often advised to take spirulina in their diet because it makes food easy to digest.
Ans. False
4. Dish washing powder contains an enzyme amylase.
Ans. False
5. Primary treatment of sewage is a biological process.
Ans. False
6. The free living fungus Trichoderma can be used for killing insects.
Ans. True
7. The most important role of microorganisms for the well being of human is sewage treatment.
Ans. False
8. Biogas is produced by the activity of aerobic bacteria on animal waste.
Ans. False
9. Saccharomyces cerevisiae is Bakers yeast.
Ans. True
10. DDT is the first commercially developed bioinsecticide.
Ans. False.
11. Biofertizers includes Blue green algae, Rhizobia and Mycorrhiza fungi.
Ans. True
12. Mycorrhiza is the association of Algae and Fungi.
Ans.: False
13. Methanobacterium is used in the production of biogas.
Ans.: True
14. Vit B content increases during the conversion of milk into curd by Lactobacilus bacteria.
Ans.: False
[II] SHORT QUESTIONS: (2 MARKS)
1. Explain how cyanobacteria serve as a main source of biofertilizer. Give the names of two cyanobacteria.
Ans: Cyanobacteria fix atmospheric nitrogen and increase the soil fertility by adding organic matter. e.g. Nostoc, Anabaena.
2. Identify the organisms.
(a) A microbe responsible for the preparation of alcohol from molasses.
(b) A soil microbe that forms symbiotic association with the roots of bean plants.
Ans: (a) Saccharomyces cerevisiae.
(b) Rhizobium.
3. What kind of microbes are present in our intestine? What are their role?
Ans: (i) Bifidobacterium Prevents colonization of potential pathogens.
(ii) Bacteroides initiates colon cancer.
(iii) E. coli pathogenic and produce vit B.
4. What are antibiotics? How they are able to prevent the growth of other microbes in media.
Ans: Antibiotics are chemical substances primarily produced by some micro organisms which in low concentration can kill or retard the growth of other disease causing microorganisms.
Antibiotics function either by killing the bacteria or inhibiting the growth of bacteria by acting on different metabolic pathways such as disruption of cell wall synthesis, disruption of plasmalemma repair and synthesis, inhibition of translation etc.
5. Discuss giving examples the statement ‘Legumes fertilize the soil but cereals do not’.
Ans: Leguminous plants possess root nodules where nitrogen is fixed by symbiotic nitrogen fixing bacteria Rhizobium whereas cereals do not possess nitrogen fixing bacteria in their root nodules, so they cannot fertilise the soil.
6. What is sewage? In which way can sewage be harmful?
Ans: Sewage is the municipal waste water containing large quantities of human excreta and other organic wastes. Sewage could be harmful to us as it contains many pathogenic microbes and produes foul smell. It is the cause of many water borne diseases. It is also the cause of eutrophication of water bodies thereby killing many aquatic organisms.
7. Write notes on:
(a) Baker’s yeast
Ans: Baker’s yeast is Saccharomyces cerevisiae which is added to the kneaded wheat flour. Yeast produces three types of enzymes- amylase, maltase and zymase complex. Amylase changes a small amount of starch into maltose. Maltase changes maltose to glucose and zymase complex acts on glucose to form bubbles of ethyl alcohol and CO2. The soft and spongy appearance is due to CO2.
(b) Brewer’s yeast.
Ans: Brewer’s yeastccharomyces cerevisiae. It has the property of alcoholic fermentation for which it is used for fermenting malted cereals and fruit juices to produce ethanol. Depending on the type of the raw material used for fermentation and the type of processing different types of alcoholic drinks are obtained.
8. What is mycorrhiza? How does it help as a biofertilizer?
Ans: Mycorrhiza is the symbiotic association between fungi and roots of higher plants.
The fungal hyphae of the mycorrhizal association take part in solubilisation and absorption of nutrients like phosphorus, nitrogen etc. from organic matter and passes it to the plant.
9. Are microbes can be used as a source of energy? If yes how?
Ans: Yes, microbes can be used as a source of energy indirectly. Methanogens like Methanobacterium found in the anaerobic sludge during sewage treatment and also present in the rumen of cattle is involved in the production of biogas which is used as a source of energy.
10.Discuss the biological significance of Azolla pinnata in agriculture.
Ans. Azolla always remains in symbiotic association with a blue green algae, anabaena. Azolla anabaena association is of great importance to agriculture. It fixes nitrogen so it is provided in the rice fields. The decaying azolla release the nitrogen for utilization of the rice plants when field is dried at the time of harvesting the fern functions as the green manure decomposing and enriching the field for the next crop.
11. What is the chemical nature of bio-gas? Name an organism involved in biogas production.
Ans. Biogas is mode up of methane (50-70%) carbondioxide (30-40%) with traces of nitrogen, hydrogen sulphide and hydrogen. Methanobacterium is involved in biogas production
12. Name the microbes used for the production of following- (a) Citric acid
(b) Acetic acid
(c) Butyric acid
(d) Lactic acid
Ans. (a) Aspergillus niger
(b) Acetobacter aceti
(c) Clostridium butylicum
(d) Lactobacillus sp.
[III] SHORT QUESTIONS: (3 MARKS EACH)
1. What do you mean by organic farming? Why it is suggested to switch over to organic farming from other types?
Ans: The non use of artificial fertilizers and chemical pesticides and use of biopesticides as well as biofertilizers in agriculture is called organic farming.
It is suggested to switch over to organic farming because-
(i) Use of excess chemical fertilisers make the soil unsuitable for cultivation.
(ii) Natural resources get depleted due to manufacturing of chemical fertilisers.
2. What are biogas? Give its composition why is biogas preferred to other conventional energy fuels.
Ans: The gas produced by the anaerobic action of bacteria on biomass is known as biogas.
It consists of methane, hydrogen sulphide and CO2. It is preferred over other conventional energy fuels because it is a cleaner fuel, has no foul smell and can be used as a source of energy as it is inflammable.
3. Lactic acid bacteria inhibit in what kind of food. Mention some of its useful applications.
Ans: Lactic acid bacteria inhibits in milk and convert it to curd. Its useful applications are-
(i) Convert the lactose sugar of milk into lactic acid.
(ii) Improves the nutritional quality of milk by increasing vitamin B12.
(iii) Checks disease causing microbes in stomach.
4. How are biofertilizers different from fertilizers such as NPK sold in the market. Discuss the role of Rhizobium as a biofertilizer .
Ans:- Biofertilizer
1. They are microorganisms
2. They do not cause pollution.
3. They improve soil structure and function.
4. Biofertilizers are unable to meet the deficiency of micronutrients present in the soil
Chemical fertilizer
1. They are chemical formulation
2. Causes water as well as soil pollution.
3. They deteriorate soil structure and function.
4. They are able to meet all type of nutrient defiencies of the soil.
Rhizobium lives in symbiotic relationship in the root modules of leguminous plants. These bacteria fix atmospheric nitrogen into organic forms, which is used by the plant as nutrient.
5. What are flocs? State their role in effluent treatment and their fate in sewage treatment tank?
Ans: Flocs are masses of bacteria associated with fungal filaments to form mesh like structures.
These microbes consume the major part of the organic matter in the effluent and reduces the BOD of the effluent. The sewage water is treated till the BOD is reduced. Once the BOD of waste water is reduced significantly the effluent is then passed into a settling tank where the bacterial flocs are allowed to sediment. This sediment is called activated sludge. A small part of the activated sludge is pumped back into the aeration tank to serve as inoculum and the remaining part is pumped into anaerobic sludge digesters for production of biogas.
6. What is the full form of VAM? What is its role? Give at least two examples each of endo and ecto mycorrhiza.
Ans: The full form of VAM is vesicular arbuscular mycorrhiza. They help in obtaining nourishment.
1. e.g. of ectomycorrhiza Boletus, Rhizopogon.
2. e.g. of endomycorrhiza Glomus, Endogone.
7. Explain the role of baculoviruses as a biological control agents. Mention their importance in organic farming.
Ans. Baculovisuses are pathogens that attack insects and other orthropods, so it acts as a biocontrol agent.
Importance:
1. These viruses are excellent candidates for species specific, narrow spectrum insecticidal applications.
2. They have no negative impact on plants, mammals birds, fish or over on non target insects. This is especially desirable when beneficial insects are being conserved to aid in an overall integrated pest management programme, or when an ecological sensitive ova is being treated.
8. Discuss the role of microbes in sewage treatment.
Ans. In sewage heterotrophic microbes are naturally present which carry out the process of decomposition. The primary effluent collected from primary treatment is mechanically agitated and aerated in large aeration tables to alloes growth of useful aerobic microbes into floes (masses of bacteria associated with fungal filaments). While growing these microbes consume the major art of the organic matter in the effluent, thus reducing BOD of the effluent. The sewage water is treated till the BOD is reduced, so that the polluting potential of the waste water is reduced. Once the BOD of waste water is reduced due to the activity of microbes, it is send for further treatment.
9. What are antibiotics? Name any two micro organisms with their products used in the production of antibiotics.
Ans. Antibiotics are chemical subtances produced by some microbes which in small concentration can kill or retard the growth of harmful microbes without adversely affecting the host.
Two microorganisms are-
(i) Penicillium notatum produces penicillin
(ii) Streptomyces grises produces Streptomycin.
IV. LONG QUESTIONS (5 MARKS)
1. What is sustainable agriculture? Discuss the role of biopesticides and biofertilizers in sustainable agriculture.
Ans: Sustainable agriculture is an agricultural practice which uses renewable resources, causes minimum pollution and maintains optimum field level.
Role of biofertilisers :
(i) Biofertilisers do not cause any pollution.
(ii) They are cheap and economical.
(iii) Biofertilisers enhance the crop yield.
(iv) Decreases the requirement of chemical fertilisers.
(v) They improve soil structure and function.
Role of biopesticides :
(i) Biopesticides like smoother crops eliminate weeds through chemical secreted by them without any risk.
(ii) Destructive insects or plant pests can be brought under control through introduction of their natural predators.
(iii) Some natural insecticides and related pesticides obtained from microbes and plants are used which kills only the susceptible insect without harming others.
Thus biofertilisers and biopesticides play very important role in sustainable agriculture.
2. What are organic acids? Give an account on different kinds of organic acids manufactured in the industry with the help of respective microbes.
Ans: The acids which are produced from microbes by various microbial metabolic actions are called organic acids.
Different types of organic acids are
Organic acid
1. Acetic acid
2. Citric acid
3. Butyric acid
4. Lactic acid
Microbe
Aspergillus niger
Acetobacter aceti
Lactobacillus sp.
3. Draw a diagrammatic sketch of a biogas plant and label its components. Gas
Ans.
4. Describe the main idea behind biological control of pests and diseases. Give at least two examples each from biopesticides and bioinsecticides.
Ans: Biological control of pests and diseases believes in creating a system where the pests are not eradicated but are kept at manageable levels by a complex system of checks and balances within a living and vibrant ecosystem. If the pests are completely eradicated then the beneficial predatory and parasitic insects which depend upon them as food or hosts would not be able to survive. Thus biocontrol measures will greatly reduce our dependence on toxic chemicals and pesticides. It also make familiar with the various life forms that inhabit the field, predators as well as pests, and also their life cycles, patterns of feeding and the habitats that they prefer.
Two examples of biopesticides are
(i) Dried spores of Bacillus thuringiensis
(ii) Use of ladybirds and dragonflies to get rid of aphids and mosquito
Two examples of bioinsecticides are –
(i) Azadirachtin obtained from Neem plant
(ii) Baculoviruses are pathogens that atack insects.
5. In which way sewage can be harmful to us? Mention the principle of sewage treatment. Write the key differences found in between primary and secondary sewage treatment.
Ans: Sewage can be harmful to us in the following ways- (i) It contains many pathogenic microbes and produces foul smell.
(ii) It is the cause of many water borne diseases.
(iii) It is the cause of eutrophication of water bodies thereby killing many aquatic organisms.
Sewage treatment is based on the principle that treatment of waste water is done by the heterotrophic microbes naturally present in the sewage.
Primary Treatment
1. It is a physical process.
2. It involves filtration and sedimentation.
3. It does not require aeration
Secondary Treatment
1. It is a biological process.
2. It involves microbial digestion of organic matter, formation of flocs sludge and sludge digestion.
3. Aeration is required.
6. What are enzymes? Name some major enzymes used in industry and explain their importance.
Ans. Enzymes re proteinaceous substances of biological origin which are capable of catalysing biochemical reactions without themselves undergoing any change.
Some major enzymes used in industry are-
(i) Protease: Used in clearing bottled juices, manufacture of detergents capable of removing proteinaceous stains and manufacture of liquid glue.
(ii) Amylase: Used in production of alcoholic beverages from starchy materials separation and desizing of textile febris.
(iii) Pectinase: Used for clarifying bottled juices. Also used in retting of fibres and preparation of green coffee.
(iv) Lipase: Used in detergent formulations Helps in removing oily stains from laundry.
7. Microbes can be used to decrease the use of chemical fertilizers and pesticides. Explain how this can be accoplished.
Ans. Microbes can be used both as fertilizers and pesticides called biofertilisers and biopesticides respectively. This can be accomplished in the following ways-
1. Microbes are used as biofertilisers to enrich the soil nutrient eg. Rhizobium, Azotobacter, Azospirillum etc. fix atmospheric nitrogen in the soil.
2. Bacillus thuringrinsis bacteria act as biopesticides to control the growth of insect pest.
3. Trichoderma, a fungal species, is effective biocontrol agent of several plant pathogens.
4. Baculoviruses are excellent for species specific, narrow spectrum insecticidal applications without negative impact on non target insects.
5. Fungi form symbiotic associations with plant called mycorrliza. The fungal symbiont in these associations absorbs phosphorus from the soil and passes if to the plant.
8. Discuss briefly what would happen if a a large volume of untreated sewage is discharged into a river?
Ans. If large amounts of untreated sewage is discharged into a river following consequences may arise :
1. Discharge of domestic sewage into a river will result in rise of BOD because decomposer organisms consume a lot of oxygen.
If sewage quantity is large, the whole of dissolved oxygen may be consumed leaving nothing for respiration of fish and other clean water organisms. They therefore get killed.
2. Sewage is the source of various water borne diseases such as Typhoid Jaundice, Cholera etc.
3. Organic loadings produces brown coloration, foul smell and bad taste due to formation of secondary pollutants like methane, ammonia and hydrogen sulphide.
4. Hydrogen sulphide reacts with various metallic ions to found sulfides. They produce scum and sludge alongwth organic matter.
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Last Words on AHSEC Class 12 Biology Chapter: 8 Microbes in Human Welfare
The Chapter 8 of AHSEC Class 12 Biology deals with Microbes in Human Welfare for a brief understanding. You can Download this HS 2nd Year Biology Notes in PDF 2025.
