Test: Microbes in Human Welfare - 1

Microbes such as Lactobacillus and others commonly called lactic acid bacteria (LAB) grow in milk and convert it into curd.

Hence, the correct option is C.
NCERT Reference: Page no. 181 of topic “10.1 MICROBES IN HOUSEHOLD PRODUCTS” of chapter 10.

Saccharomyces is a yeast that is used to ferment sugar to produce ethanol in absence of oxygen or by anaerobic respiration.

Hence, the correct option is B.
NCERT Reference: Page no. 182 of topic “10.2.1 Fermented Beverages” of chapter 10.

• The puffed-up appearance of dough is due to the production of CO₂ gas.
• Baking soda (sodium hydrogen carbonate) on heating releases carbon dioxide gas along with sodium carbonate.

Hence, the correct option is B.
NCERT Reference: Page no. 181 of topic “10.1 MICROBES IN HOUSEHOLD PRODUCTS” of chapter 10.

• Clostridium butylicum is used to produce butyric acid.
• Butyric acid is an important industrial chemical used to process food items.

Hence, the correct option is A.
NCERT Reference: Page no. 183 of topic “10.2.3 Chemicals, Enzymes and other Bioactive Molecules” of chapter 10.

• Mycorrhiza is a symbiotic association between fungus and angiosperms.
• The most common fungal partners of mycorrhiza are the Glomus species.

Hence, the correct option is D.
NCERT Reference: Page no. 188 of topic “10.6 MICROBES AS BIOFERTILISERS” of chapter 10.

• Yeast is used in the production of alcohol, wine-making and in baking bread.
• Saccharomyces cerevisiae is known as baker's yeast and Saccharomyces ellipsoidens is called wine yeast. 

Hence, the correct  option is D.
NCERT Reference: Page no. 182 of topic “10.2.1 Fermented Beverages” of chapter 10.

• The biogas-producing bacteria are collectively known as methanogens and one such common bacterium is Methanobacterium.
• These bacteria are commonly found in the anaerobic sludge during sewage treatment and also in the rumen of cattle.

Hence, the correct option is D.

NCERT Reference: Page no. 185 of topic “10.4 MICROBES IN PRODUCTION OF BIOGAS” of chapter 10.

• The type of gas produced depends upon the microbes and the organic substrates they utilise.

Example: In the fermentation of dough, cheese making and production of beverages, the main gas produced is CO₂.

Hence, the correct option is C.
NCERT Reference: Page no. 185 of topic “10.4 MICROBES IN PRODUCTION OF BIOGAS” of chapter 10.

• The first organic acid produced by microbial fermentation was lactic acid.
• Lactic acid is produced by the anaerobic respiration of glucose.

Hence, the correct option is C.
NCERT Reference: Page no. 183 of topic “10.2.3 Chemicals, Enzymes and other Bioactive Molecules” of chapter 10.

Vinegar is chemically diluted acetic acid which is produced by fermentation molasses in presence of Yeast and Acetobacter.

Hence, the correct option is B.
NCERT Reference: Page no. 183 of topic “10.2.3 Chemicals, Enzymes and other Bioactive Molecules” of chapter 10.

• Treatment of wastewater is done by the heterotrophic microbes naturally present in the sewage.
• This treatment is carried out in two stages:
  (i) Primary Treatment  
  (ii) Secondary Treatment

Hence, the correct option is B.
NCERT Reference: Page no. 183 of topic “10.3 MICROBES IN SEWAGE TREATMENT” of chapter 10.

• Due to the development of various methods of genetic engineering, in the last decade or so, scientists have introduced Bacillus thuringiensis toxin genes into the plants. Such plants are resistant to attack by insect pests.
• These are available in sachets as dried spores which are mixed with water and sprayed onto vulnerable plants such as brassicas and fruit trees, where these are eaten by the insect larvae. In the gut of the larvae, the toxin is released and the larvae get killed. The bacterial disease will kill the caterpillars, but leave other insects unharmed.
• Bt-cotton is one such example, which is being cultivated in some states of our country.

Hence, the correct option is A.
NCERT Reference: Page no. 187 of topic “10.5 MICROBES AS BIOCONTROL AGENTS” of chapter 10.

• In primary treatment, initially floating debris is removed by sequential filtration.
• Then grit and small pebbles are removed by sedimentation.
• All solids that settle form the primary sludge while the supernatant forms the effluent.

Hence, the correct option is A.
NCERT Reference: Page no. 184 of topic “10.3 MICROBES IN SEWAGE TREATMENT” of chapter 10.

• Methane is also called marsh gas because it is produced by the anaerobic bacterial decomposition of vegetable matter underwater or in a marshy area. 
• The decomposition of sludge by anaerobic bacteria in sewage-treatment processes also produces a gas rich in methane. This gas has a pungent smell and is highly flammable.

Hence, the correct option is D.
NCERT Reference: Page no. 184 of topic “10.3 MICROBES IN SEWAGE TREATMENT” of chapter 10.

Secondary treatment of sewage is also called biological treatment because in this treatment aeration of sewage water is done that increases the microbes that decompose the organic materials in sewage water.

Hence, the correct option is A.
NCERT Reference: Page no. 184 of topic “10.3 MICROBES IN SEWAGE TREATMENT” of chapter 10.

• Biological oxygen demand is the amount of oxygen required to completely decompose the organic waste present in one litre of water by bacteria.
• A high value of BOD shows that water is highly polluted.

Hence, the correct option is A.
NCERT Reference: Page no. 184 of topic “10.3 MICROBES IN SEWAGE TREATMENT” of chapter 10.

• Some of the aerobic nitrogen-fixing bacteria are Azotobacter and Beijerinckia.
• Some of the anaerobic nitrogen-fixing bacteria are Clostridium, Rhodospirillum and Rhodopseudomonas.
• Soil is enriched through exudation and the formation of nitrates after their death and decay.

Hence, the correct option is A.
NCERT Reference: Page no. 188 of topic “10.6 MICROBES AS BIOFERTILISERS” of chapter 10.

• Atmospheric nitrogen is not available to plants. There are certain nitrogen-fixing bacteria that convert atmospheric nitrogen into ammonium compounds and make them available to the plants.
  Examples: Azotobacter, Frankia, Rhizobium, Azospirillum.
• Out of these, Azospirillum is widely used as a nitrogen fixer organism in paddy fields. It is used as a biofertilizer in rice fields. It promotes plant growth.

Hence, the correct option is D.
NCERT Reference: Page no. 188 of topic “10.6 MICROBES AS BIOFERTILIZERS” of chapter 10.

• Rhizobium is a nitrogen-fixing bacteria found in the nodule of a leguminous plant's root.
• These bacteria fix atmospheric nitrogen into organic forms, which is used by the plant as nutrient.
• It increases the fertility of the soil.

Hence, the correct option is D.
NCERT Reference: Page no. 188 of topic “10.6 MICROBES AS BIOFERTILIZERS” of chapter 10.

• Spirogyra is a filamentous alga. This alga does not fix atmospheric nitrogen.
• Anabaena, Nostoc and Oscillatoria can fix atmospheric nitrogen.

Hence, the correct option is B.
NCERT Reference: Page no. 188 of topic “10.6 MICROBES AS BIOFERTILIZERS” of chapter 10.

• Methanogen belongs to the Archaebacteria group. They are capable of producing methane gas or marshy gas or biogas.
• They produce methane gas in marshy areas. They are most abundant in marshy areas and cattle yards where cow sheds are present. The methane gas produces a peculiar odour in these areas. Thus, the correct answer is 'Cattle yard.'

Hence, the correct option is B.
NCERT Reference: Page no. 185 of topic “10.4 MICROBES IN PRODUCTION OF BIOGAS” of chapter 10.

• Baculoviruses are pathogens that attack insects and other arthropods.
• The majority of baculoviruses used as biological control agents fall under the genus Nucleopolyhedrovirus.

Hence, the correct option is C.
NCERT Reference: Page no. 187 of topic “10.5 MICROBES AS BIOCONTROL AGENTS” of chapter 10.

Both assertion and reason are correct statements but the reason is not the correct explanation of the assertion. 

Hence, the correct option is D.
NCERT Reference: Page no. 187 of topic “10.6 MICROBES AS BIOFERTILISERS” of chapter 10.

Bio-fertilizer enriches the nutrient in the soil. The main sources of bio-fertilizers are bacteria, fungi and cyanobacteria.

Hence, the correct option is D.
NCERT Reference: Page no. 187 of topic “10.6 MICROBES AS BIOFERTILISERS” of chapter 10.

• Microbes are not used in the production of antiviral drugs and the production of inorganic fertilizers.
• Although, microbes are used in converting milk into curd, antibiotic production, sewage treatment, bread and cheese industry etc.

Hence, the correct option is C.
NCERT Reference: Refer topics “10.3 MICROBES IN SEWAGE TREATMENT” and “10.2 MICROBES IN INDUSTRIAL PRODUCTS” of chapter 10.