CBSE Questions for Class 12 Medical Biology Microbes In Human Welfare Quiz 4 - MCQExams.com

• Pasteurization is the process of heating a liquid or food to kill pathogenic bacteria. 
• The use of pasteurization has helped to reduce the transmission of many diseases. 
• The heating of the food and liquid products helps in the destruction of harmful bacteria and other pathogenic microorganisms. 
• This process ensures that the food is treated and the food is safe to be consumed. 

• Bacillus thuringiensis (Bt) is a species of bacteria that can infect and kill insects and thus, it is used as an insecticide. 
• It is used to control pests like butterfly caterpillars.
• So, the correct answer is option B.

• Antibiotics is discovered by Alexander Fleming in 1928. But in 1943, American microbiologist Selman Waksman (1888–1973) made the drug streptomycin from soil bacteria, the first of a new class of drugs called aminoglycosides. 
• The term 'antibiotic' was coined by Waksman to describe a substance derived from naturally occurring microorganisms and possessing antimicrobial activity in high dilution.

• Green manure acts mainly as soil acidifying matter to decrease the alkalinity/pH of alkali soils by generating humic acid and acetic acid. 
• The root systems of some varieties of green manure grow deep in the soil and bring up nutrient resources unavailable to shallower-rooted crops.
• Green manure also can help prevent soil erosion in areas with sandy soil, and help keep weeds from growing. 

A.Correct option: D
B. Explanation for correct option:

• Xanthomonas campestris is not used as a biopesticide because it is a plant pathogen.
• Thus, it is not a biopesticide. 
  
  

• There are spores of Rhizopus are present in the atmosphere. The spores germinate when they obtain a favourable climate and substratum. In the presence of moisture and nutrients on the surface of bread, the spores germinate and form the hyphae. Thus, these fungi are commonly called as bread mould.
• Lactobacillus is the bacterium present in raw milk which performs fermentation. The bacterium converts the lactose sugar in the milk to lactic acid by the process of fermentation. Thus, the activity of the bacterium is responsible for curd formation. 
• Yeast cells are added to the batter of idli and dosa. The cells perform anaerobic fermentation by utilizing the fermentable sugars and converting them to ethanol and carbon dioxide. The carbon dioxide gas makes the products soft, porous and fluffy.
• Protozoa known as Plasmodium is the organism which is responsible for causing malaria in humans. The organism grows in mosquitoes and are transmitted to humans while feeding on human blood. 

• Rhizobium is the symbiotic soil bacteria that fix nitrogen in leguminous plants. They form a symbiotic relationship with legume and resides in the root nodules of legumes. 
• They cannot independently fix nitrogen. 

• Yeast is a eukaryotic and single-celled fungus. The commonly used species of yeast is Saccharomyces cerevisiae. It is also known as baker's yeast. 
• The yeast is used in the production of fermented products like cakes, bread, and alcohol. 
• The organism converts the fermentable sugars present in the substrate into carbon dioxide and ethanol. 
• The carbon dioxide gas makes the dough of bread and cake soft and fluffy. There are pores in the bread and cakes which is due to the carbon dioxide gas bubbles which get trapped during the process of baking. 

• Milk is converted into curd by the action of the bacteria Lactobacillus. 
• It multiplies and promotes the formation of curd in milk by converting milk protein casein into lactic acid.