CBSE Questions for Class 12 Medical Biology Microbes In Human Welfare Quiz 10 - MCQExams.com

• Glomus helps in the absorption of phosphorus from the soil by plants. It is an arbuscular mycorrhiza. Phosphorus is a major nutrient required for the growth of plants.
• Anabaena is a genus of nitrogen-fixing blue-green algae, with beadlike or barrel-like cells and interspersed enlarged spores (heterocysts), found as plankton in shallow water and on moist soil. There are both solitary and colonial forms, the latter resembling a closely related genus, Nostoc. In temperate latitudes during the summer months, Anabaena may form water blooms.
• Rhizobia are soil bacteria that fix nitrogen after becoming established inside root nodules of legumes. In order to express genes for nitrogen fixation, rhizobia require a plant host; they cannot independently fix nitrogen.
• Frankia is a genus of nitrogen-fixing, filamentous bacteria that live in symbiosis with actinorhizal plants, similar to the rhizobia bacteria that are found in the root nodules of legumes in the Fabaceae family.

Explanation for correction option: 

• Trichoderma is a genus of imperfect fungi that produce toxins that inhibit the growth of other fungi and thus protects the plant from fungal diseases.
  
• As it is a living organism used to control diseases, called a biocontrol agent.

• The sewage treatment process consists of primary and secondary treatment. 
• In primary treatment screening, filtration and sedimentation of sewage take place. 
• After primary treatment, the waste stream is brought to an aeration tank. Air is put in and/or there is mechanical stirring which provides aeration of the waste which allows the growth of useful aerobic microbes into flocs. 
• When effluent is passed into the settling tank the flocs sediment. This sediment is called activated sludge. 
• A portion of the settled sewage sludge is recycled and the remainder must be treated by composting or anaerobic digestion. 

• Yeast fermentation is the basis of baking as well as brewing industries.
  
• The strain of Saccharomyces cerevisiae fungus is commonly known as baker's yeast. 
• The organism is widely used in the baking industry. It has the ability to produce desirable flavor. 
• The organism is added to the dough of bread and cakes and allowed to perform fermentation. 
• The fermentation is brought by converting the fermentable sugars to alcohol and carbon dioxide. 
• The organisms are also cultured or grown on molasses. They bring about anaerobic fermentation and this helps in providing flavor to the substance. 

• Lignin is the most important factor affecting the hydrolysis of the cellulose component in lignocellulosic material. 
• The initial degradation step is difficult because the lignin-carbohydrate complexes create a barrier for microbial conversion due to the crystalline structure.