CBSE Class 12 Biology Microbes In Human Welfare Worksheet Set C

 

Very Short Answer Questions

Question. Mention the information that the health workers derive by measuring BOD of a water body.
Answer. (i) By measuring BOD of a water body, health workers find the amount of dissolved oxygen in water. The lesser the amount of dissolved oxygen, the more polluted the water body will be.
(ii) It is also measure of organic matter present in water and uptake of O2 by microbes.

Question. Write the scientific name of the microbe used for fermenting malted cereals and fruit juices.
Answer. Saccharomyces cerevisiae.

Question. The excreta of cattle does not contain any cellulose but human excreta may contain cellulose. Why?
Answer. The rumen of cattle contains methanogens which help in the digestion of cellulose but these bacteria are not present in human stomach so cellulose is not digested.

Question. Name the pests that ladybird, beetle and dragonflies help to get rid of.
Answer. Ladybird, beetle and dragonflies control aphids and mosquitoes respectively.

Question. 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 under a microscope, which sample would you carry and why? 
Answer. The most common household product that we would like to carry is curd which contains lactic acid bacteria (Lactobacillus sps.).

Short Answer Questions

Question. What is a broad spectrum antibiotic? Name one such antibiotic. 
Answer. A broad spectrum antibiotic is one which can inhibit the growth of both gram positive and gram negative bacteria. For example, tetracycline, which is obtained from Streptomyces aureofaciens.

Question. Name the source of streptokinase. How does this bioactive molecule function in our body?
Answer. Source: Streptococcus.
Streptokinase is a clot buster, i.e., it removes clot from the blood vessels of patients who had a heart attack.

Question. What is sewage? In which way can sewage be harmful to us?
Answer. 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 produces 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.

Question. Name the enzyme produced by Streptococcus bacterium. Explain its importance in medical sciences. 
Answer. Streptococcus bacterium produces streptokinase.
It is used for removing clots from the blood vessels in a patient suffering from myocardial infarction/or in a heart patient.

Question. (a) A patient who had an organ transplant was given cyclosporin A. Mention the microbial source and state the reason for administration of this bioactive molecule.
(b) Bottled fruit juices bought from the market are clearer as compared to those made at home.
Give reason. 
Answer. (a) Source: Trichoderma polysporum
Reason: It is an Immunosuppressive agent.
(b) Bottled fruit juices are clarified by pectinases and proteases which makes them clear.

Question. Describe how biogas is generated from activated sludge. List the components of biogas.
Answer. The activated sludge is pumped into large tanks called anaerobic sludge digesters. Here, bacteria which grow anaerobically digest the bacteria and the fungi in the sludge. During this digestion,bacteria produce a mixture of gases which form biogas. Biogas is made up of methane, hydrogen sulphide and carbon dioxide.

Question. 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. Sample C is most polluted (Highest BOD).
Sample A — River water
Sample B — Secondary effluent (Least BOD)
Sample C — Untreated sewage (Highest BOD)

Question. What are methanogens? Name the animals they are present in and the role they play there.
Answer. Methanogens are bacteria which grow anaerobically on cellulosic material.
They are present in the rumen of cattles.
These bacteria are responsible for the breakdown of cellulose, thus help in nutrition of animal.

Question. What is BOD? What does it mean if a water sample has more BOD?
Answer. BOD stands for biochemical oxygen demand which represents the amount of dissolved oxygen that would be consumed if all the organic matter in one litre of water were oxidised by microorganisms. More BOD value means the water sample is polluted by organic matter.

Question. Name the microbes that help production of the following products commercially:
(a) Statin (b) Citric acid
(c) Penicillin (d) Butyric acid
Answer. (a) Monascus purpureus (b) Aspergillus niger
(c) Penicillium notatum (d) Clostridium butylicum

Question. How do mycorrhizae help the plants to grow better? 
Answer. Mycorrhizae absorb phosphorus, provide resistance to root-borne pathogens and enhance the tolerance of the plants towards salinity and drought. (Any two)

Question. What is Chakravarthy bug? Give its scientific name and its application? 
Answer. Chakravarthy bug is a super bug of Pseudomonas with multiple plasmids. They are helpful in removing oil spills.

Long Answer Questions

Question. State the medicinal value and the bioactive molecules produced by Streptococcus, Monascus and Trichoderma. 
Answer. 

		Bioactive Molecule Produced	Medicinal Value
(i)	Streptococcus	Streptokinase	Removes clot from the blood vessels
(ii)	Monascus purpureus	Statin	Inhibits enzymes responsible for synthesis of cholesterol. So is used as cholesterol lowering agent.
(iii)	Trichoderma polysporum	Cyclosporin A	Immunosuppressive agents used in organ transplantation.

Question. What are the harmful effects of chemical pesticides?
Answer. The harmful effects of chemical pesticides are:
(i) They pollute the soil and water.
(ii) They kill many useful organisms in the soil.
(iii) They enter the food chain and cause disease at various trophic levels (Biological magnification).
(iv) They affect the salinity of the soil.

Question. What are the advantages of using biofertilisers in agriculture?
Answer. Following are the advantages of using biofertilisers in agriculture:
(i) Biofertilisers do not cause any pollution.
(ii) These are cheap and economical.
(iii) Some of them act as biopesticides also.
(iv) In ill-irrigated conditions few biofertilisers can enhance the crop yield.
(v) They improve soil structure and function.
(vi) They make available vitamins and other growth promoting biochemicals.

Question. Identify a, b, c, d, e and f in the table given below:

S. No.	Organism	Bioactive molecule	Use
(i)	Monascus purpureus (yeast)	a	b
(ii)	c	d	Antibiotic
(iii)	c	Cyclosporin A	f

Answer. (a) Statins
(b) Blood cholesterol lowering agent
(c) Penicillium notatum
(d) Penicillin
(e) Trichoderma polysporum
(f) Immunosuppressant

Question. An organic farmer relies on natural predation for controlling plant pests and diseases. Justify giving reasons why this is considered to be a holistic approach.
Answer. Besides acting as ‘conduits’ for energy transfer across trophic levels, predators are used in biological control of plant pests. This ability of the predator is based on its regulating the prey population.
The natural predators reduce interspecific competition and does not harm the crop plants. For example, in an area the invasive cactus can be brought under control by cactus-feeding predator (a moth).
Using natural predation, the ecosystem is kept stable without harming any of the trophic levels.

Question. Identify ‘a’, ‘b’, ‘c’, ‘d’, ‘e’ and ‘f’ in the table given below: (table 388)
Answer. (a) Bioactive molecule used to remove blood clot
(b) Trichoderma polysporum
(c) Immunosuppressant
(d) Statin
(e) Blood cholesterol lowering agent
(f) Lactic acid

Question. Name the blank spaces a, b, c and d in the table given below :

Type of Microbe	Scientific Name	Commercial Product
Bacterium	a	Clot buster enzyme
b	Aspergillus niger	Citric acid
Fungus	Trichoderma polysporum	c
Bacterium	d	Butyric acid

Answer. a - Streptococcus
b - Fungus
c - Cyclosporin - A
d - Clostridium acetobutylicum

Question. Name the blank spaces a, b, c and d in the table given below :

Type of Microbe	Scientific Name	Commercial Product
Bacterium	a	Lactic acid
Fungus	b	Cyclosporin A
c	Monascus purpureus	Statin
Fungus	Penicillium notatum	d

Answer. a - Streptococcus lactis, Lactobacillus
b - Trichoderma polysporum
c - Fungus
d - Penicillin

Question. Identify a, b, c, d, e and f in the table given below:

Scientic name of the organism	Product produced	Use in human welfare
Streptococcus	Streptokinase that was later modied	a
b	Cyclosporin A	c
Monascus purpureus	d	e
Lactobacillus	f	sets milk into curd

Answer. a - Helps in clearing blood clots inside the blood vessels through dissolution of intravascular fibrin.
b - Trichoderma polysporum
c - Antifungal, anti-inflammatory and immuno- suppressive prevents rejection reactions in organ transplantation.
d - Statins
e - Help in lowering blood cholesterol level f - Lactic acid 

Question. Identify a, b, c, d, e and f in the table given below :

Organism	Bioactive molecule	Use
Monascus purpureus (yeast)	a	b
c	d	Antibiotic
e	Cyclosporin A	f

Answer. a - Statins
b - Used in lowering blood cholesterol c - Penicillium notatum
d - Penicillin
e - Trichoderma polysporum
f - Prevents rejection reactions in organ transplantation

Question. What are the properties of an antibiotic?
Answer. Antibiotics are chemical substances produced by some microbes which in small concentration can kill or retard the growth of harmful microbes without adversely affecting the host. Broad spectrum antibiotic can kill or destroy a number of pathogens that belong to different groups with different structures and wall compositions. Specific antibiotics are effective only against one type of pathogen. Good antibiotics should be harmless to host with no side effects. They should be harmless to beneficial microorganism of alimentary canal and should be effective against all strains of pathogen. They should also be quick in action.

Question. Why is sewage water treated until the BOD is reduced ? Give a reason. 
Answer. Sewage water is highly polluted and contains high amount of organic waste hence biochemical oxygen demand (BOD) of sewage water is high. Sewage is treated in sewage treatment plants to remove polluntants with the reduction in pollution BOD of the water decreases. Hence BOD is the indicator of decrease of pollutants present in sewage. Sewage water is therefore treated till the BOD is reduced to minimal value which ensures that water is free of organic pollutants.

Question. BOD of two samples of water A and B were 120 mg/L and 400 mg/L respectively. Which sample is more polluted? 
Answer. Water body having high BOD is more polluted as compared to water body having low BOD. Hence water sample having BOD 400 mg/L is more polluted as compared to water sample having BOD,120 mg/L.

Question. Given below are a few impurities in urban waste water. Select two colloidal impurities : ammonia, faecal matter, silt, bacteria, calcium.
Answer. Two colloidal impurities in urban waste water are faecal matter and bacteria.

Question. List the events that reduce the Biological Oxygen Demand (BOD) of a primary effluent during sewage treatment. 
Answer. Secondary treatment or biological treatment of sewage considerably reduces the biological oxygen demand (BOD) of primary effiuent during sewage treatment. The organic matter present in the effiuent is decomposed with the help of microbial flora called as sewage fungus. The effiuent is constantly agitated or aerated. This causes the growth of various aerobic microorganisms and sewage fungi. These microbes digest the organic matter thereby reducing the BOD of original sewage by 10-15%.

Question. Distinguish between the roles of flocs and anaerobic sludge digesters in sewage treatments.
Answer. Flocs are masses of aerobic bacteria held together by slime and fungal filaments to form mesh like structures. These microbes digest a lot of organic matter converting it into microbial biomass and releasing a lot of minerals. This reduces biochemical oxygen demand or BOD.
In anaerobic sludge digesters, aerobic microbes present in the sludge get killed. Anaerobic microbes digest the organic mass as well as aerobic microbes of the sludge. During this digestion, bacteria produce a mixture of gases such as methane, hydrogen sulphide and carbon dioxide. These gases form biogas which can be used as source of energy as it is inflammable. The spent sludge of anaerobic sludge digester can be used as manure or part of compost.

Question. Explain the different steps involved during primary treatment phase of sewage. 
Answer. Primary treatment phase of sewage treatment removes floating and suspended solids from sewage through two processes of filtration and sedimentation. First floating matter is removed through sequential filtration. The filtrate is kept in large open settling tanks where grit settles down. Aluminium or iron sulphate is added in certain places to flocculation and settling down of solids. The sediment is called primary sludge while the supernatant is called effiuent. The primary sludge traps a lot of microbes and debris. It is subjected to composting or land fill where anaerobic digestion removes the organic matter.  

Question. Explain the process of secondary treatment given to the primary effluent up to the point it shows significant change in the level of biological oxygen demand (BOD) in it.
Answer. During secondary treatment, the primary effluent is taken to aeration tanks. A large number of aerobic heterotrophic microbes grow in the aeration tank. They form flocs which are masses of bacteria held together by slime and fungal filaments to form mesh like structures. The microbes digest a lot of organic matter, converting it into microbial biomass and releasing a lot of minerals. As a result the BOD of the waste matter is reduced to 10-15% of raw sewage, it is passed into settling tank.

Question. Name the two different categories of microbes naturally occurring in sewage water. Explain their role in cleaning sewage water into usable water. 
Answer. Aerobic heterotrophs like bacteria and fungi occur in sewage water. They are natural decomposers and digiest a lot of organic matter present in the polluted water thereby releasing minerals and reducing organic waste. Hence, they play an important role in cleaning water and making it fit for various domestic uses.

Question. Explain the different steps involved in sewage treatment before it can be released into natural water bodies. 
Answer. Sewage water can be purified by passing it through sewage treatment plants with the action of microorganisms. A sewage treatment plant separates solids from liquids by physical processes and purifies the liquid by biological processes. There are three stages of this treatment; primary, secondary and tertiary. Primary treatment is physical, secondary biological and tertiary chemical.
Primary treatment phase of sewage treatment removes floating and suspended solids from sewage through two processes of filtration and sedimentation. First floating matter is removed through sequential filtration. The filtrate is kept in large open settling tanks where grit settles down. Aluminium or iron sulphate is added in certain places to flocculation and settling down of solids. The sediment is called primary sludge while the supernatant is called effiuent. The primary sludge traps a lot of microbes and debris. It is subjected to composting or land fill where anaerobic digestion removes the organic matter.
During secondary treatment, the primary effiuent is taken to aeration tanks. A large number of aerobic heterotrophic microbes grow in the aeration tank. They form flocs are masses of bacteria held together by slime and fungal filaments to form mesh like structures. The microbes digest a lot of organic matter, converting it into microbial biomass and releasing a lot of minerals. As a result the BOD of the waste matter is reduced to 10-15% of raw sewage, it is passed into settling tank. In settling tank, the bacterial flocs are allowed to undergo sedimentation. The effiuent or spernatant is generally passed into natural water bodies and sediment of settling tank is called activated sludge.

Question. This sludge can be used as an inoculum or as a source of biogas. Explain.
Answer. A small part of the activated sludge is pumped back into the aeration tank to serve as the inoculum. The remaining major part of the activated sludge is pumped into large tanks called anaerobic sludge digesters. The anaerobic bacteria digest the bacteria and fungi in a sludge and produce mixture of gases like methane, hydrogen sulphide and CO2 which constitute biogas.

Question. Name the group of organisms and the substrate they act on to produce biogas.  
Answer. Methanogenic bacteria or methanogens are the group of anaerobic microbes which digest organic mass as well as aerobic microbes of the sludge to produce a mixture of gases containing methane, H₂S and CO₂ called biogas.

Question. What are methanogens? How do they help to generate biogas?  
Answer. Methanogens are a group of anaerobic bacteria which obtain their energy by reducing carbondioxide and oxidising hydrogen with the production of methane. They are found in oxygen deficient environment such as marshes, swamps, sludge and digestive systems of ruminant animals like cow, buffalo etc. These microorganims are present in anaerobic sludge digester where they digest organic mass as well as aerobic microbes of the sludge to produce mixture of gases containing methane, H2S and CO2 called biogas.

Question. What makes the Nucleopolyhedrovirus a desirable biological control agent? 
Answer. Nucleopolyhedrovirus a genus of baculoriviruses are useful in controlling many insects and other arthropods. They are species specific narrow spectrum bioinsecticides with no side effects on plants, mammals, birds, fish and non-target insects. Therefore, they serve as an important component of integrated pest management programme in dealing with ecological sensitive areas. These properties are useful in organic farming .

Question. Given below is a list of six microorganisms.
State their usefulness to humans.
(a) Nucleopolyhedrovirus
(b) Saccharomyces cerevisiae
(c) Monascus purpureus
(d) Trichoderma polysporum
(e) Penicillium notatum
(f) Propionibacterium sharmanii
Answer. (a) Nucleopolyhedrovirus : It is a baculovirus which is an effective biocontrol agent as it is useful in controlling many insects and other arthropods. It serves as species specific narrow spectrum bioinsecticide.
(b) Saccharomyces cerevisiae : It is used to ferment dough, in order to make bread. It is also used for the preparation of ethanol.
(c) Monascus purpureus : Its fermentation activity produces statins which inhibits cholesterol synthesis and is therefore used in lowering blood cholesterol.
(d) Trichoderma polysporum : It is a fungus that produces cyclosporin–A, which is used as immunosuppressive agent in organ-transplantation.
(e) Pencillium notatum : It secretes the antibiotic, penicillin.
(f ) Propionibacterium sharmanii : It is used in processing of ‘Swiss cheese’. The large holes in Swiss cheese are due to production of a large amount of CO₂ by this bacterium.

Question. (a) How do organic farmers control pests? Give two examples.
(b) State the difference in their approach from that of conventional pest control methods.
Answer. (a) Organic farming involves the use of biopesticides, i.e., biocontrol agents to control weeds, insects and pathogen. These biocontrol agents include viruses, bacteria, protozoa, fungi and mites. Example : Baculovirus heliothis can control cotton bollworm (Helicoverpa zea) whereas Bacillus thuringeinsis is effective against cabbage looper (Trichoplusia ni).
(b) Conventional pest control involves the use of chemical pesticides to control pests in crop-field. Pesticides are toxic and harmful to crop plants. Other crop field animals and humans. On the other hand organic farmers use biopesticides to control field pests. This approach is environment friendly, exercises specific control over pests and is harmless to humans.

Question. How are baculoviruses and Bacillus thuringiensis used as bio-control agents? Why are they preferred over readily available chemical pesticides?
Answer. Nucleopolyhedrovirus a genus of baculoriviruses are useful in controlling many insects and other arthropods. They are species specific narrow spectrum bioinsecticides with no side effects on Bacillus thuringiensis is a soil bacterium. The spores of this bacterium possess insecticidal cry protein, hence, kill larvae of certain insects. This bacterium was first biopesticide to be used on commercial scale. The commercial preparations of B. thuringiensis contain a mixture of spores, cry protein and inert carrier.
Chemical pesticides used in agricultural fields are toxic and biocides. They kill even useful organisms along with harmful ones, harm human beings and animals, pollute soil and water and crop plants. It is estimated that despite the use of chemical pesticides 30% of the agricultural produces is lost to pathogens and pests because these continue to develop resistance against various pesticides. On the other hand biopesticides are the biological agents that control the growth of weeds, insects and pathogens in an agricultural field. They have targeted actions and are harmless to the crop plants, other beneficial field animals and humans. Therefore, nowadays biopesticides are preferred over chemical pesticides.

Question. What are biopesticides? Give the scientific name and the use of the first commercially used biopesticide in the world. 
Answer. Biopesticides are those biological agents that are used for control of weeds, insects and pathogens. The microorganisms used as biopesticides are viruses, bacteria, protozoa, fungi etc. 

Question. State one reason for adding blue-green algae to the agricultural soil. 
Answer. A number of free living and symbiotic blue green algae or cyanobacteria have the property of nitrogen fixation and are photosynthetic. Therefore, they add organic matter as well as extra nitrogen to the soil. Hence, blue green algae serve as biofertilisers and are added to agricultural fields such as cotton, maize, jowar, rice, etc.

Question. Name any one symbiont which serves as a biofertiliser. Mention its specific role.
Answer. Rhizobium is the symbiotic nitrogen fixing bacteria which forms nodules on the roots of legume plants. Hence, it help the plants in obtaining their nitrogen nutrition.

Question. Which of the following is a free living bacteria that can fix nitrogen in the soil?
Spirulina, Azospirillum, Sonalika 
Answer. Azospirillum is a free living nitrogen fixing bacteria.

Question. Which of the following is cynobacterium that can fix atmospheric nitrogen?
Azospirillum, Oscillatoria, Spirulina.
Answer. Oscillatoria is a nitrogen fixing cyanobacterium.

Question. How does a small amount of curd added to fresh milk convert it into curd? Mention a nutritionalquality that gets added to the curd.
Answer. A large number of lactic acid bacteria are found in small amount of curd which  multiply and convert the milk into curd by producing the lactic acid,
The nutritional quality improves by increasing Vitamin B12

Question. Why is secondary treatment of water in sewage treatment plant called biological treatment?
Answer. In this treatment Organic wastes of sewage water are decomposed by certain  microorganisms in presence of water

Question. 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.
Answer. Penicillin, Alexander Fleming 

Question. You have observed that fruit juice in bottles bought from the market is clearer as compared to those made at home. Give reason.
Answer. Bottle juices are clarified by the use of pectinase and proteases 

Question. Alexander Fleming discovered .Penicillin, but its full potential as an effective antibiotic was established by other scientists. Name the two scientists.
Answer. Ernest chain and Howard Florey

Question. Name the plant whose sap is used in making .Toddy.. Mention the process involved in it.
Answer. Palm tree, by fermentation

Question. Name two alcoholic drinks produced in each of the following ways. (i) by distillation and (ii) without distillation.
Answer. (i) Whisky, brandy, rum . by distillation
(ii) Wine, beer . without distillation

Question. 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.
Answer.  (i) LAB in human intestine synthesizes Vitamin B12. 
(ii) LAB in human stomach checks the growth of harmful microbes

Question. How do mycorrhizae function as biofertilisers? Explain with example.
Answer. Mycorrhiza are fungi associated with the roots of plants. Many members  of genus Glomus form mycorrhiza. These fungal symbiont absorbs water and minerals like phosphorus from the soil and provide them to the plant

Question. Cyanobacteria (Nostoc, Anabaena) are used as bio fertilisers in certain crop fields. Name such one crop. Also, mention the names of two other microorganisms which perform the same function.
Answer.  Paddy (Rice Crop), Rhizobium and Azotobacter 

Question. Which Ministry of Govt. of India had initiated Ganga Action Plan and Yamuna Action Plan? What are the objectives of these plans?
Answer. The Ministry of Environment and Forests. The objective of Ganga Action Plan and Yamuna Action Plan is to save these rivers from pollution. It was proposed to build a large number of sewage treatment plants. So that only treated sewage may be discharged into these rivers

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

 Name of Organism      Commercial Product      Application
Penicillium notatum         Penicillium                          (a)
(b)                                    Lactic acid Making            Curd
Streptococcus                 Clot buster enzyme            (c)
Trichoderma                       (d)                                Immuno 
polysporum                                                             suppressive agent
Saccharomyces              Ethanol                               (e)
cerevisiae
(f)                                   Swiss cheese                  Food Product
Answer. a) to kill disease causing bacteria
(b) Lactobacillus
(c) remove clots from blood vessels
(d) Cyclosporin A
(e) Beverage/medicines
(f) Propionibacterium sharmanii

Question. What is biochemical oxygen demand (BOD) test? At what stage of Sewage treatment this test is performed? 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?
Answer. The BOD test measures the rate of uptake of oxygen by microorganisms in a  sample of water.Biological treatment or Secondary treatment Sample .
C. is most polluted because it has highest BOD level among the three samples of water.

Question. Given below is the Flow chart of Sewage treatment. Fill in the blank spaces marked .a. to .f..
Answer. a) Primary treatment (b) Aeration (c) Flocs (d) Biochemical Oxygen  Demand (BOD)
(e) Activated sludge (f) Water bodies like river stream.

Question. What are biofertilisers? 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?
Answer. Biofertilisers are organisms that enrich the nutrient quality of the soil.Azotobacter/Azospirillum (free living) This bacterium fixes atmospheric nitrogen into organic forms, which is used by the plants as nutrient.

Question. What are statins? Name the microorganism that produces this substance. How is it medically important?
Answer. Statins are cholesterol reducing agents. They are produced by Monascus purpureus (Yeast) They act by Competitively inhibiting the enzymes responsible for synthesis of cholesterol and are used as blood cholesterol lowering agents.

Question. How does primary sludge differ from activated sludge? What type of changes in the sludge is carried out in anaerobic sludge digester? Give the composition of biogas produced in the sewage treatment plant.
Answer. Primary sludge is all solids like soil, small pebbles that settle down in settling tank during primary treatment of sewage. Activated sluge is the sediment of bacterial .flocs. in settling tank during biological treatment. Flocs are masses of bacteria held together by slime and fungal filaments. A part of activated sluge is used asinoculum in aeration tank and remaining is passed into a large tank called anaerobic sluge digester. In this tank, other kind of bacteria which grow anaerobically, digest the bacteria, fungi and biomass in the sludge. Biogas that produced in Sewage treatment plant is a mixture of metnane,hydrogen and Carbon dioxide

Question.Tina went to a supermarket with her mother to buy rice. They saw that two types of products are available.one is organically grown & second is conventionally grown. The organically grown crops are costlier so Tina's mother does not want to purchase it.
(I ) Which rice should be purchased? Why/
(ii)What values are exhibited by Tina?
Answer. Organically grown rice, since bio fertilisers & bio pesticide are used, which are not harmful to health. sensitivity & awareness about use of harmful chemicals, Decision making, c) critical thinking

Question. After a rainy day Shruti found many dragonflies flying over stagnant water.She thinks these flies come to drink ater.
i) Is Shruti,s explanation correct? Give your views.
ii) What values are shown by Shruti?
Answer. No, dragonflies come to eat mosquito larvae & act as bio control agents Awareness about environment, critical thinking

Question. Manoj was going home from school. On his way he saw a 'panipuri' vendor cleaning the dishes with bare hands & then serving the customers with the same hands without washing hands with a soap or wearing plastic gloves. Manoj went to the vendor & told him the need for washing
hands before touching any eatables. The vendor hushes him away & tells him there is no harm as he has rinsed his hands with water
(a)In the given solution, whom do you think has the correct prospective? Justify your answer by giving reasons Suggest few ways by which cleanliness can be promoted.
Answer. (a) Concern for everyone's health is correct. Tiny microbes do not get cleaned up by just water & most of the microbes are disease causing.
(b) By pasting posters in public places regarding importance of cleanliness.
Educating people about the harms of uncleanliness, With advertisements in media like television, newspapers etc. 

 

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