CBSE Questions for Class 12 Medical Biology Microbes In Human Welfare Quiz 3 - MCQExams.com

• The biological method is the technique in which there is the use of living microorganisms or their product for the control of pests. 
• This method uses the microbes which act as predators or enemies of the target pest species. 
• The biological control method is often relatively inexpensive because the method uses microorganisms that can be easily cultured. 
• They do not contribute the pollution. 
• If biocontrol agents are introduced in any area, they can survive for multiple years and are capable of continuing or renewing themselves indefinitely i.e. become self-perpetuating. 

• 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.

• Biogas/gobar gas is an alternate source of energy produced by the breakdown of organic matter in the absence of oxygen. 
• Biogas can be produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste, or food waste.
• Biogas can be produced by anaerobic digestion with anaerobic bacteria, which digest material inside a closed system, or fermentation of biodegradable materials. 
• Biogas or gobar gas is usually 50% to 80% methane and 20% to 50% carbon dioxide, with traces of gasses such as hydrogen, carbon monoxide, and nitrogen.

• There are four key biological and chemical stages of anaerobic digestion producing methane gas:

• Biogas typically refers to a mixture of different gases produced by the breakdown of many organic matters in the absence of oxygen. 
• Biogas can be produced from regionally available raw materials such as recycled waste. 
• It is a renewable energy source. It is primarily methane (CH$$_{4}$$) and carbon dioxide (CO$$_{2}$$) and may have small amounts of hydrogen sulphide (H$$_{2}$$S), moisture, and siloxanes.
• So, the correct answer is option D.

• Lactobacillus acts on the lactose of the milk and converts it into lactic acid. The increased acidity causes the milk proteins (casein) to coagulate and form the curd. 
• Vibrio cholerae bacterium causes cholera infection.
  
• Mycobacterium leprae is a bacterium that causes leprosy while tetanus is an infection caused by a bacterium called Clostridium tetani. 
  

• Antibiotics are chemical substances produced by microorganisms that can kill or inhibit the growth of other bacteria and fungi, thus used to treat bacterial and fungal infections. 
• Many antibiotics like penicillin target bacterial cell wall synthesis, while others inhibit protein synthesis by targeting prokaryotic ribosomes. The ribosome serves the cell as a protein-making machine.
  
• Viruses don't have cell walls or their own cellular machinery that can be attacked by antibiotics.

Correct option A

Explanation for correct option:

• Earthworms are commonly found living in the soil. They feed on dead organic matter. They help in the conversion of large pieces of organic matter into rich humus. This property helps to increase soil fertility. 
• Oscillatoria is the genus of blue-green algae. They are found in freshwater. Oscillatoria helps in nitrogen fixation and improves the quality and fertility of the soil. They are commonly used as a biofertilizer in paddy fields. 

• Glomus is the species that form the mycorrhizal association with the roots of the legumes and oilseed plants. These fungi help in the mineral uptake by the plants. 
  
  
• Snail is not used in organic farming.

• Biogas is an alternate source of energy produced by the anaerobic fermentation of domestic sewage, animal wastes, and agricultural wastes in the marshy environment by the microbes. 
• It is mainly comprised of carbon dioxide, methane, and hydrogen.