CBSE Questions for Class 12 Medical Biology Microbes In Human Welfare Quiz 5 - MCQExams.com

• Lactobacillus belongs to the group of bacteria which through fermentation converts the sugars into lactic acid in the absence of oxygen. 
• This bacterium is added to the milk in the form of an already synthesized curd where they multiply and convert lactose sugar into lactic acid. 
• The lactic acid which is produced gives a sour taste and the milk is converted to curd. 

• Fermentation is the process of anaerobic respiration in which organisms utilize food in the absence of oxygen. 
• Penicillin is produced by the fungus Penicillium chrysogenum which requires lactose, other minerals, and a source of nitrogen (in this case a yeast extract) in the medium to grow well.
  
• So, the main fermentable source in the culture to produce penicillin is lactose.
• Other minerals include amino acids and mineral salts. 
• The pH of the culture is maintained at 5 and 6 and temperature is maintained at 26$$^o$$C.

• The production of biogas is performed in anaerobic reactors. There are bacteria that perform anaerobic fermentation which means without the use of oxygen. 
• These bacteria perform anaerobic digestion of the waste matter from plants and animals. The decomposition of the organic matter results in the formation of biogas. 
• Biogas is commonly used as clean and non-polluting fuel. 

Biogas consists primarily of methane (the source of energy within the fuel) and carbon dioxide. It also may contain small amounts of nitrogen or hydrogen. Contaminants in the biogas can include sulphur or siloxanes but this will depend upon the digester feedstock.

• Aspergillus produces citric acid through fermentation process.
• Streptococcus  produces lactic acid through fermentation.
• Acetobacter produces acetic acid through fermentation.
• Streptomyces produces antibiotics.
• So, the correct answer is 'Aspergillus'.

• Biogas is a mixture of mostly methane and carbon dioxide with trace amounts of other gases and is considered as a valuable renewable energy source.
• Methane comprises of 45-70% of biogas and thus biogas is inflammable. It produces a deep blue flame and can be used as an energy source.

$$\textbf{Correct option: }$$ A

$$\textbf{Solution: }$$ 

$$\textbf{Option (A) }$$

$$\bullet$$The sewage effluent is pumped into an aeration or oxidation tank which contains sludge.

$$\bullet$$A part of activated sludge is pumped back into an aeration tank to act as inoculum while a major part of it is pumped into an anaerobic sludge digester for anaerobic microbial decomposition and production of biogas. 

$$\bullet$$The bacteria are able to decompose most of the organic matter while algae provide oxygen to these decomposers. 

$$\bullet$$The other organism along with bacteria are archaebacteria, fungi, and protists.

Hence, the correct option is (A)

• Biogas is the mixture of gases that is mainly produced by anaerobic digestion of biodegradable waste.
• It usually contains from 45 to 70% methane and from 30 to 45% carbon dioxide. Biogas can also contain nitrogen, hydrogen sulfide, halogenated compounds, and organic silicon compounds in traces.

• Spirulina is a cyanobacterium. This is a spiral shaped alga. The algae are considered as a source of many elements like iron, manganese and chromium. 
• There are many essential amino acids. The algae is a source of vitamins like vitamin A, K$$_1$$, K$$_2$$, B$$_{12}$$, C, D and E.
•  Due to the presence of vitamins, the algae is used for the preparation of the tablets which are enriched with the vitamins and are used as supplements.
• Thus, the correct answer is option D. 

• Primary treatment removes material that will either float or readily settle out by gravity. It includes the physical processes of screening, comminution, grit removal, and sedimentation. Screens are made of long, closely spaced, narrow metal bars. They block floating debris such as wood, rags, and other bulky objects that could clog pipes or pumps. In modern plants, the screens are cleaned mechanically, and the material is promptly disposed of by burial on the plant grounds. A comminutor may be used to grind and shred debris that passes through the screens. The shredded material is removed later by sedimentation or flotation processes.
• Secondary treatment removes the soluble organic matter that escapes primary treatment usually accomplished by biological processes in which microbes consume the organic impurities as food, converting them into carbon dioxide, water, and energy for their own growth and reproduction. The sewage treatment plant provides a suitable environment, albeit of steel and concrete, for this natural biological process. Removal of soluble organic matter at the treatment plant helps to protect the dissolved oxygen balance of a receiving stream, river, or lake.
• Hence, the correct answer is 'Primary treatment'.

• Ethanol can be produced from agricultural wastes with the help of a bacterial or fungal activity. 
• The bacteria or fungi can perform anaerobic fermentation to produce ethanol. 
• It can be produced at relatively less cost and acts as a cheap and clean-burning fuel. 
• This liquid can be used as an alternative source of energy in place of LPG. 

• The National Environmental Engineering Research Institute (NEERI) has developed a technology to treat wastewater generated from industries and sewage. 
• This technology has proved to be extremely effective in removing organic pollutants in the case of chemical industries.

• Biogas is a gaseous fuel that is a mixture of different gasses produced by the breakdown of organic matter such as domestic and animal waste anaerobically. 
• This fuel mainly consists of methane, carbon dioxide, sulfide, and hydrogen. The composition of carbon dioxide is around 35%. 
  Thus the correct answer is option B.