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.

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

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

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

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

Yeast is used in the production of alcohol, wine-making and in baking bread.

Ascomycetes are called sac fungi that live parasitically and in various habitats. They are responsible for a number of fungal diseases in plants.

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.

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

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

• 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

• 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. 
• Bt-cotton is one such example, which is being cultivated in some states of our country.

• 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.
  So the correct answer is 'A'.

• 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 highly flammable.
  Thus, the correct answer is option D.

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

• 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.

Escherichia coli is a gram-negative bacterium. The bacterium that does not retain the gram stain is called gram-negative bacteria.

• 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.

Rhizobium is a nitrogen-fixing bacteria found in the nodule of a leguminous plant's root. It increases the fertility of the soil.

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

• 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 yard where cow sheds are present. The methane gas produces a peculiar odour in these areas. Thus, the correct answer is 'Cattle yard.'

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

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

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

• 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.