CBSE Board 2015 Microbiology Practice Questions

1. Which antibiotic was extensively used to treat American soldiers wounded in World War II?
2. Name two growth regulators commonly used in plant tissue culture.
3. Give the scientific name of the plant from which cocaine is obtained.
4. Write down the following terms in expanded form
(i) ELISA (ii) MALT
5. Give one example each of exotic breed of cattle and exotic breed of fowl.
6. How does colostrum provide initial protection against diseases to new born infants?
7. Differentiate between the two different varieties of sugarcane i.e., Saccharum barberi and Saccharum officinarum.
8. Why is the excreta (dung) of cattle rich in bacteria?
9. What do you understand by MOET? How is it useful in cattle improvement?
What is meant by the term “inbreeding”? Write its disadvantages.
10. Riya, a 10 years old girl suffers from a bacterial disease.
She has rose coloured spots on her chest. She also suffers from adominal pain, light fever, low pulse rate and diarrhoea.
(i) From which disease does she suffer? Name the pathogen that infected her.
(ii) Which diagnostic test is used for its confirmation?
11. Draw a labelled diagram of a biogas plant, and explain its structure. How is biogas produced in the biogas plant?
12. Name the source of cyclosporin – A and streptokinase. Explain their importance in medical science.
13. (i) A farmer adds Azotobacter culture to the soil before sowing maize. How will it increase the yield of maize?
(ii) Explain the role of Lactobacillus in preparation of household products.
14. (i) Define the term ‘health’. When is “World Health Day” celebrated?
(ii) Describe the factors which affect our health.
15. What are baculoviruses? Why are they preferred as biological control agents?
16. What is mutation breeding? Explain its advantages over conventional methods of plant breeding?
17. What is biofortification? State its main objectives.
18. (i) How do plants develop insect resistance?
(ii) Name the resistant varieties of Brassica and flat bean and the related insect pests.
19. (i) Everyday humans are exposed to a large number of infectious agents in the environment, but only a few of these exposures result in disease. What is the reason for this?
(ii) Explain the different barriers of innate immunity.
20. (i) What will happen when a protoplast of tomato is fused with the protoplast of potato?
(ii) What is the role of micropropagation and somadones in improvement of crops?
Mili owns a dairy farm. In order to improve the quality and quantity of milk production, what measures should be taken by her?
21.Jane had gone to her grandparents home where she visited a park near by. Suddenly she showed strong unusual hypersensitive response like sneezing, running nose and watery eyes.
(i) What could be the possible reason for it?
(ii) What should be done to reduce the symptoms in Jane?
22. (i) Draw a well-labelled diagram of an antibody molecule.
(ii) Which type of antibody is produced during allergic reaction?
23. John, 14 years old teenager is good in academics. However, there are few boys in his class who go to pubs for late night parties, consume alcohol and also take drugs. From the last few days, John’s mother noticed his drop in academic performance, lack of interest in personal hygiene, aggressive and rebellious behaviour, his loss of interest in hobbies, and changed sleeping and eating habits.
(i) What do you think may be the possible reason for this attitude?
(ii) What are the different measures that should be taken by parents to protect their children from substance abuse?
24. (i) Define apiculture and mention any two economically important products or humans which are obtained from honey bees.
(ii) Which points should be kept in mind for successful bee keeping?
(iii) Name two common species of honey bee, which are used in apiculture.
(i) What is plant breeding?
(ii) Describe the major steps required for developing varieties of crops.
25. (i) How can microbes be useful in production of beverages?
(ii) Name a green manure crop? How does it help in increasing fertility of soil?
(i) Differentiate between primary sludge and activated sludge.
(ii) Three water samples were subjected to BOD test. The samples were labelled as A, B and C. The BOD values of the three samples. A, B and C were recorded as 20mg/L, 8mg/L and 400 mg/L, respectively. Which sample of the water is most polluted?
26. (i) Bob, a cab driver is in the habit of chewing tobacco throughout the day. Since a few days, he has not been able to eat his food, as there are many ulcers in his mouth, and he is also suffering from high blood pressure. What may be the possible reason for this?
(ii) How does morphine, an opioid drug affect the human body?
(i) What happens to a normal cell in a body when oncogenes the activated under certain conditions?
(ii) Which techniques are useful to detect cancer of internal organs?
(iii) Why are cancer patients often given a-interferon during their treatment?


1. Penicillin was extensively used to treat American soldiers wounded in World War II.
2. Two growth regulators used in plant tissue culture are:
(i) Auxins and
(ii) Cytokinins
3. Cocaine is obtained from coca plant, Erythroxylum coca, native to South America.
4. Expanded from of:
(i) ELISA -» Enzyme linked immuno-sorbent assay
(ii) MALT -» Mucosal associated lymphoid tissue.
5. Exotic breed of cattle is Jersey and exotic breed of fowl is White Leghorn.
6. Colostrum provides protection against diseases to new born babies because it is rich in antibodies e.g., IgA.
7. Differences between Saccharum barberi and Saccharum officinarum are as follows:

Saccharum barberi Saccharum officinarum
(i) Saccharum barberi grows
in north India.
It grows in south India.
(ii) It has poor sugar content and yield. It has thicker stems and high sugar content.

8. The dung of cattle is rich in bacteria called methanogens. These are present in the rumen (a part of stomach) of cattle, and help in the breakdown of cellulose. Thus, they play an important role in the nutrition of cattle.
9. MOET is Multiple Ovulation Embryo Transfer Technology. Yes, it has helped in increasing the herd size of the desired variety of cattle in a short time. High milk yielding breeds of females and high quality meat yielding bulls have been bred successfully to obtain hybrids by this method.
Inbreeding refers to the mating of more closely related individuals within the same breed for 4-6 generations. Disadvantages of inbreeding:
Continued inbreeding, especially close breeding, usually reduces fertility and even productivity. This is called inbreeding depression. This occurs due to homozygosity of recessive alleles.
10. (i) She suffers from typhoid fever. Salmonella typhi is the pathogenic bacterium that infected her.
(ii) Typhoid is confirmed by Widal Test.
11. The labelled diagram of a biogas plant is asfollows:-

Biogas is a mixture of gases (containing predominantly methane) produced by the microbial activity and used as fuel for cooking and lighting.
The biogas plant consists of a concrete tank (10-15 feet deep) in which bio-wastes are collected and a slurry of dung is fed. A floating cover is placed over slurry, which keeps on rising as the gas is produced in the tank due to the microbial activity.
The biogas plant has an outlet, which is connected to a pipe to supply biogas to nearby houses. The spent slurry is removed through another outlet and may be used as fertiliser.
Cattle dung is available in large quantities in rural areas where cattle are used for a variety of purposes. So biogas plants are more often built in rural areas.
12. Cyclosporin A, that is used as an immunosuppressive agent in organ-transplant patients, is produced by the fungus Trichoderma polysporum.
Streptokinase produced by the bacterium Streptococcus and modified by genetic engineering is used as a ‘dot buster’ for removing clots from the blood vessels through dissolution of intravascular fibrin.
13. (i) Free-living nitrogen fixing bacteria fix atmospheric nitrogen in the soil and make it available for the higher plants. Azotobacter occurring in fields of cotton, maize, jowar and rice, not only increases yield but also saves about 10-25 kg/ha of nitrogen fertilizer.
(ii) Microorganisms commonly called Lactic acid bacteria (LAB) e.g., Lactobacillus are added to milk for production of curd. They convert lactose sugar of milk into lactic acid. Lactic acid causes coagulation and partial digestion of milk protein, casein, thereby changing milk into curd, yoghurt and cheese.
The starter or inoculum used in preparation of milk products actually contains millions of LAB. In this way, Lactobacillus plays an important role in preparation of household products.
14. (i) Health does not mean “absence of disease or physical fitness”. It may be defined as state of complete physical, mental and social well being and not only absence of disease.
World Health Day is celebrated on 7th April.
(ii) Our health is affected by different factors such as:
(a) genetic disorders – deficiencies with which a child is born and deficiencies/defects which the child inherits from parents from birth;
(b) infections and
(c) life style including food and water we take, rest and exercise we give to our bodies, habits that we have or lack etc.
15. Baculoviruses are pathogens that attack insects and other arthropods. The majority of baculoviruses used as biological control agents are in the genus Nucleopolyhedrovirus. These viruses are excellent candidates for species-specific, narrow spectrum insecticidal applications. They have been shown to have no negative impacts on plants, mammals, birds, fish or even on non-target insects. This is especially desirable when beneficial insects are being conserved to aid in an overall integrated pest management (IPM) programme, or when an ecologically sensitive area is being treated.
16. Use of induced mutations in plant breeding to develop improved varieties is called mutation breeding. Chemical mutagens (use of chemicals) and physical mutagens (like gamma-rays) induce changes in DNA and chromosomes, resulting in mutations. Conventional breeding is often constrained by the availability of limited number of disease resistance genes that are present and identified in various crop varieties or wild relatives. Inducing mutations in plants through diverse means and then screening the plant materials for resistance sometimes leads to desirable genes being identified. Therefore, mutation breeding is more beneficial than conventional breeding.
17. Biofortification means breeding crops with higher levels of vitamins and minerals, or higher protein and healthier fats. It is the most practical means to improve public health.
Breeding for improved nutritional quality is undertaken with the objectives of improving:
(i) Protein content and quality
(ii) Oil content and quality
(iii) Vitamin content and
(iv) Micronutrient and mineral content.
18. (i) Insect resistance in host crop plants may be due to morphological, biochemical or physiological characteristics. Hairy leaves in several plants are associated with resistance to insect pests, e.g., resistance to jassids in cotton and cereal leaf beetle in wheat. High aspartic acid, low nitrogen and sugar content in maize leads to resistance to maize stem borers.

Crop Variety Insect Pests
(rapeseed mustard)
 Pusa Gaurav  Aphids
Flat bean  Pusa Sem 2
Pusa Sem 3
 Jassids, aphids
and fruit borer

19. (i) Everyday we are exposed to a large number of infectious agents. However, only a few of these exposures result in disease. This is due to the fact that the body is able to defend itself from most of these foreign agents. This overall ability of the host to fight the disease-causing organisms, conferred by the immune system is called immunity.
(ii) Innate immunity consist of four types of barriers. These are-
fa) Physical barriers : The skin on our body is the main barrier which prevents entry of the microorganisms. Mucus coating of the epithelium lining the respiratory, gastrointestinal and urogenital tracts also help in trapping microbes entering our body.
(b) Physiological barriers: The acid in the stomach, saliva in the mouth, tears from eyes – all prevent microbial growth.
(c) Cellular barriers: Certain types of leukocytes of our body like polymorpho-nudear leukocytes (PMNL- neutrophils), monocytes and natural killer (type of lymphocytes) in the blood, as well as macrophages in tissues, can phagocytose and destroy microbes.
(d) Cytokine barriers: Virus-infected cells secrete proteins called interferons which protect non- infected cells from further viral infection.
20. (i) When a protoplast of tomato is fused with that of potato, a somatic hybrid named pomato is obtained, which is used to grow plants with characteristics of both tomato and potato.
(ii) Micropropagation and somadones have the following advantages:
1. Rapid multiplication of plants can be achieved i.e., larger number of plants can be produced in a short duration.
2. Progenies of sterile plants can be obtained.
3. Genetically similar plants can be produced, keeping desirable characters of the improved varieties constant for generations.
Mili should deal with processes and systems that increase yield and improve quality of milk.There are four essential methods for livestock improvement. These are ‘breeding, weeding, feeding and heeding,’ which not only increase the milk production, but also improve the health of farm animals.
1. Each animal should be fed on a balance ration. According to WHO ‘health’ is the state of complete physical, mental and social well being and not merely the absence of disease. A healthy animal eats, drinks and sleeps well regularly.
2. Adequate ventilation, suitable temperature, sufficient light, water, air and well-drained housing accommodation should be provided.
3. If the animal is well looked after, the resistance to diseases develops and animal is protected from the diseases.
4. Regular inspections, with proper record keeping and regular visits by veterinary doctor are necessary.
21. (i) Jane might have developed allergy as a result of which she started showing symptoms like running nose, sneezing and watery eyes. The exaggerated response
of the immune system to certain antigens present in the environment is called allergy. The substances to which such an immune response is produced are called allergens.
Common examples of allergens are mites, dust, pollens, etc.
Allergy is due to the release of chemicals like histamine and serotonin from the mast cells.
(ii) Jane could be treated with drugs like anti-histamine, adrenalin and steroids that will quickly reduce the symptoms of allergy.
22. (i) The labelled diagram of an antibody molecule is as follows:-

IgE Antibody -

(ii) IgE type of antibody is produced during allergic reaction.
23. (i) John is under the constant peer pressure from his friends, who go to late night parties, consume alcohol and take drugs, might have also forced him to take do the same. The adverse effects of drugs and alcohol abuse are seen in the form of reckless behaviour, vandalism and violence. His drop in academics performance may be the warning signs of drug and alcohol abuse.
(ii) The following are the measures that should be taken by parents to protect their children from substance abuse:-
(a) Education and counselling: Education and counselling to face problems and stresses, and to accept disappointments and failures as a part of life.
(b) Seeking help from parents and peers: Help from parents and peers should be sought immediately by children, so, that they can be guided appropriately. Besides getting proper advise to sort out their problems, this would help young children to vent out their feelings of anxiety and guilt.
(c) Looking for danger signs: Appropriate measures should be taken to diagnose the problem and the underlying causes. This would help in initiating proper remedial steps or treatment.
(d) Seeking professional and medical help: A lot of help is available in the form of highly qualified psychologists, psychiatrists, de-addiction and rehabilitation programmes to help individuals who have unfortunately got in the habit of drug/alcohol abuse. With such help, the affected individual with sufficient efforts and will power, can get rid of the problem completely and lead a perfectly normal and healthy life.
24. (i) Rearing of honey bees for obtaining honey and bee wax is called apiculture. Honey and bee wax are obtained from honey bees.
(ii) The following points are important for successful bee keeping:
(a) Knowledge of the nature and habits of honey bees.
(b) Selection of suitable location for keeping the beehives.
(c) Catching and hiving of swarms (groups of bees).
(d) Management of beehives during seasons.
(e) Handling and collection of honey and bees wax.
(iii) Apis mellifera and Apis indica are most common species of honey bees which are reared.
(i) Plant breeding is the purposeful manipulation of plant species in order to create desired plant types that are better suited for cultivation, give better yields and are disease resistant.
(ii) The main steps in breeding a new genetic variety of a crop are
(a) Collection of variability: Genetic variability is important for any breeding programme. In many crops, pre-existing genetic variability is available from wild relatives of the crop. The entire collection (of plants/seeds) having all the diverse alleles for
all genes in a given crop is called germplasm collection.
(b) Evaluation and selection of parents: The germplasm is evaluated, so as to identify plants with desirable combination of characters. The selected plants are multiplied and used in the process of hybridisation. Purelines are created wherever desirable and possible.
(c) Cross hybridisation among the selected parents: The desired characters have very often to be combined from two different parents plants, for example high protein quality of one parent combined with disease resistance from another parent. This is possible by cross hybridizing the two parents to produce hybrids that genetically combine the desired characters in one plant.
(d) Selection and testing of superior recombinants: The selection process is crucial to the success of the breeding objective and requires careful scientific evaluation of the progeny. This step yields plants that are superior to both of the parents (very often more than one superior progeny plant may become available). These are self-pollinated for several generations till they reach a state of uniformity (homozygosity), so that the characters will not segregate in the progeny.
(e) Testing, release and commercialisation of new cultivars: The newly selected lines are evaluated for their yield and other agronomic traits of quality, disease resistance, etc. This evaluation is done by growing these in the research fields, and recording their performance, under ideal fertiliser application, irrigation, and other crop management practices.
25. (i) Microbes especially yeasts, have been used from time immemorial for the production of beverages like wine, beer, whisky, brandy or rum. Yeast Saccharomyces cerevisiae used for bread-making and commonly called brewer’s yeast, 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 (with or without distillation) different types of alcoholic drinks are obtained. Wine and beer are produced without distillation, whereas whisky, brandy and rum are produced by distillation of the fermented broth.
(ii) A green manure crop is Crotolaria juncea. The plants are leguminous which possess root nodules where atmospheric nitrogen is fixed by Rhizobium bacteria. Therefore, these plants enrich the soil by supplying fixed nitrogen, organic matter and other nutrients.
(i) Difference between primary sludge and activated sludge:

Primary sludge Activated sludge
1 It is the sludge formed during primary sewage treatment. It is the sludge formed during secondary sewage treatment.
2 It does not possess floes of decomposer microbes. It possess floes of decomposer microbes
3 It does not require aeration. Formation of activated : sludge requires aeration.
4 Little decomposition has occurred during formation of primary sludge. A lot of decomposition has occurred during formation of activated sludge.

(ii) BOD refers to the amount of the oxygen that would be consumed if all the organic matter in one liter of water is oxidized by bacteria. The sewage water is treated till the BOD is reduced. The BOD test measures the rate of uptake of oxygen by microorganisms in a sample of water and thus, indirectly, BOD is a measure of the organic matter present in the water. The greater the BOD of waste water, more is its polluting potential. In the given problem BOD values of the three samples A, B and C are 20 mg/L, 8 mg/L and 400 mg/L, respectively.
Here the sample B has least BOD value as compared to sample A and C, while, sample C has the greatest BOD value, hence it is the most polluted.
26. (i) Chewing tobacco throughout the day is affecting of Bob’s health day by day, because tobacco contains a large number of harmful chemical substances including nicotine, an alkaloid. Nicotine stimulates adrenal gland to release adrenaline and nor-adrenaline into blood circulation, both of which raise blood pressure and increase heart rate. Tobacco chewing is associated with increased risk of cancer of the oral cavity, and that is the reason for Bob’s mouth ulcers.
(ii) Morphine is the active principle of opium, that causes addiction. It is an alkaloid that depresses respiratory centre, leads to the fall in blood pressure and causes bradycardia (slow heart beat). Morphine also causes release of ADH, reduces urine output, causes constipation and also mild hyperglycaemia. However, morphine is a very effective sedative and painkiller.
(i) When cellular oncogenes or proto oncogens are activated under certain conditions in normal cells in a body, they could lead to oncogenic transformation of the cells. Transformation of normal cells into cancerous neoplastic cells may be induced by physical, chemical or biological agents also.
(ii) Techniques like radiography (use of X-rays), CT (computed tomography) and MRI (magnetic resonance imaging) are very useful to detect cancers of the internal organs. Computed tomography uses X-rays to generate a three-dimensional image of the internals of an object. MRI uses strong magnetic fields and nonionising radiations to accurately detect pathological and physiological changes in the living tissue.
(iii) Cancer patients are often given oc-interferon during their treatment, because these biological response modifiers activate the immune system, and help in destroying the tumour.

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