Biology & Human Welfare Test - 3

• 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:  Topic- MICROBES IN SEWAGE TREATMENT ”of chapter  "Microbes in Human Welfare "  of NCERT.  

• 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: Topic-  MICROBES AS BIOCONTROL AGENTS ”of chapter  "Microbes in Human Welfare "  of NCERT.  

• 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:  Topic- MICROBES IN SEWAGE TREATMENT ”of chapter  "Microbes in Human Welfare "  of NCERT.  

• 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: Topic-  MICROBES IN SEWAGE TREATMENT ”of chapter  "Microbes in Human Welfare "  of NCERT.  

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:  Topic- MICROBES IN SEWAGE TREATMENT ”of chapter  "Microbes in Human Welfare "  of NCERT.  

• 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:  Topic- MICROBES IN SEWAGE TREATMENT ”of chapter  "Microbes in Human Welfare "  of NCERT.  

• 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: Topic-  MICROBES AS BIOFERTILISERS ”of chapter  "Microbes in Human Welfare "  of NCERT.  

• 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 inpaddy fields . It is used as a biofertilizer in rice fields. It promotes plant growth.

Hence, the correct option is D.
NCERT Reference:  Topic- MICROBES AS BIOFERTILIZERS ”of chapter  "Microbes in Human Welfare "  of NCERT.  

• 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:  Topic: MICROBES AS BIOFERTILIZERS ”of chapter  "Microbes in Human Welfare "  of NCERT.  

• 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: Topic:  MICROBES AS BIOFERTILIZERS ”of chapter  "Microbes in Human Welfare "  of NCERT. 

• 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 apeculiar odour in these areas. Thus, the correct answer is 'Cattle yard.'

Hence, the correct option is B.
NCERT Reference:  Topic- MICROBES IN PRODUCTION OF BIOGAS ”of chapter "Microbes in Human Welfare "  of NCERT.

• 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:  Topic- MICROBES AS BIOCONTROL AGENTS ”of chapter  "Microbes in Human Welfare "  of NCERT.  

Explanation of Assertion: Biofertilizers are living microorganisms that, when applied to seeds, plant surfaces, or soil, colonize the rhizosphere or the interior of the plant and promote growth by increasing the supply or availability of primary nutrients to the host plant. They are a natural and environmentally friendly way to provide essential nutrients to plants, which in turn boosts soil fertility and productivity.

Explanation of Reason: Organic farming is an agricultural system that seeks to provide the consumer with fresh, tasty, and authentic food while respecting natural life-cycle systems. It involves the use of natural fertilizers, such as compost, manure, and green manure, instead of synthetic fertilizers. It also relies on natural pest control methods, such as biological control, crop rotation, and the use of resistant plant varieties, instead of chemical pesticides.

While both the assertion and reason are correct statements, the reason does not directly explain the assertion. The assertion is about the role of biofertilizers in enriching soil nutrients, while the reason is about the principles of organic farming, which is a broader concept that encompasses not only the use of biofertilizers but also other natural and sustainable practices.

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

Hence, the correct option is D.
NCERT Reference: Topic-  MICROBES AS BIOFERTILISERS ”of chapter  "Microbes in Human Welfare "  of NCERT.  

• 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: Topic-  MICROBES IN SEWAGE TREATMENT ”and  MICROBES IN INDUSTRIAL PRODUCTS ”of chapter  "Microbes in Human Welfare "  of NCERT.