Microbes in Human Welfare: Introduction and MCQs

Ans. c. lactic acid bacteria

Explanation: Bacteria that grow in milk and convert milk to curd are commonly called lactic acid bacteria. They are a group of Gram-positive bacteria that produce lactic acid as the result of the fermentation of carbohydrates. They enhance lactose digestion, stimulate the immune system, and are useful in the prevention and treatment of diarrhea.

Ans. b. Saccharomyces

Explanation: Saccharomyces is the name of the yeast through which ethanol is commercially produced. It is called brewer’s yeast or baker’s yeast and is a genus of fungi that includes many genera of yeasts. It is instrumental in wine-making, baking, and brewing. It is a single cell-celled eukaryote that is frequently used in scientific research.

Ans. b. Carbon dioxide

Explanation: The gas that causes the puffed-up appearance of dough is carbon dioxide. During the preparation of the dough, yeast or bacteria is added to it. Carbon dioxide is released by bacteria during fermentation. A prominent ingredient used in baking is baking soda also known as sodium hydrogen carbonate. It releases carbon dioxide and sodium carbonate on heating.

Ans. a. Clostridium butylicum

Explanation: The bacterium that produced butyric acid is called Clostridium butylicum. It is an anaerobe, mesophilic bacterium also called "Weizmann Organism". It is commercially valuable because it is used for the industrial-scale production of the organic solvents acetone, n-butanol, and ethanol, collectively called ABE. The process is called known ABE fermentation.

Ans. d. Glomus

Explanation: Mycorrhiza is defined as the symbiotic association between a green plant and a fungus. The fungus is supplied with organic molecules like sugar by the plants. The plants are supplied water and mineral nutrients by the fungus. Glomus species are the common fungal partners of mycorrhiza. All species of Glomus form symbiotic relationships with plant roots.

Ans. a. Beer and bread

Explanation: The main use of yeast is in the production of fermented products like cake, bread, and alcohol. Yeast converts the fermentable sugars in the substrate into carbon dioxide and ethanol. The carbon dioxide makes the dough used to make bread and cake soft and fluffy. The pores in the bread and cake are made from the carbon dioxide bubbles that are trapped during the process of baking.

Ans. a. Ascomycetes

Explanation: Ascomycetes are known as sac fungi. They are the members of kingdom Fungi and subkingdom Dikarya along with Basidiomycota. They are of particular use for humans because they are used in the production of medicinal components like antibiotics, baking bread, for making alcoholic beverages and cheese. But many Ascomycetes are also pathogens. Several of them are also used in biological research.

Ans. b. Substrate

Explanation: The type of gas produced depends on two factors – the microbes and the organic substrates they utilize. For example, consider the cases of production of beverages, cheese making, and the fermentation of dough. The gas produced in all three cases is carbon dioxide. In the case of fermentation of dough, carbon dioxide is produced and trapped in tiny air pockets within the dough. This causes the dough to rise.

Ans. d. Lactic acid

Explanation: Lactic acid was the first acid produced using microbial fermentation. It is mainly produced in muscle cells and red blood cells of the human body when the body breaks down carbohydrates in the case of low oxygen levels. When Lactococcus lactis is added to milk, it uses the enzymes to produce energy from lactose, and lactic acid is formed as a byproduct. Lactic acid curdles milk that then separates to form curds. Cheese and whey are made from the curds.

Ans. a. Yeast and acetobacter

Explanation: Vinegar is simply a sour-tasting aqueous solution of acetic acid. The first step in the production of vinegar is the conversion of fermentable sugar of molasses into ethanol and carbon dioxide by yeast. Then, the acetic acid bacteria convert ethanol into acetic acid and water. Finally, centrifugation is used for the separation of the product.

Ans. b. Heterotopic microbes.

Explanation: Heterotopic microbes are used for the treatment of wastewater. They are naturally present in the sewage. Aerobic bacteria are used to digest the waste from the biological degradation and purification process. It is the most widespread wastewater treatment method used throughout the world. Compared to aerobic digestion, anaerobic digestion is complex. Anaerobic digestion is involved in carrying out many biochemical reactions that involve many microorganisms.

Ans. a. Bt-cotton

Explanation: Bt-cotton is produced by the insertion of one or more genes from a common soil bacterium, Bacillus thuringiensis. It is a genetically modified pest-resistant cotton that produces an insecticide to control bollworms. India has produced many Bt-cotton varieties such as Bikaneri Nerma and hybrids such as NHH-44.

Ans. a. First, any floating debris is removed through distillation.

Explanation: Initially, during the primary treatment of wastewater, any floating debris is removed by the means of sequential filtration through wire or mesh screens. The next step is the removal of grit and pebbles through sedimentation. The sediment is referred to as primary sludge and the supernatant is referred to as effluent. After primary treatment, the effluent is sent for secondary treatment.

Ans. b. Biological treatment

Explanation: Another name for secondary sewage treatment is biological treatment. It is called so because secondary treatment degrades pollutants dissolved in effluents using microbes. The microbes use the pollutants to live and reproduce. In other words, the pollutants are used as nutrients by the microbes. It is effective because wastewater contains a lot of organic matter like garbage, partially digested food, etc.

Ans. b. High pollution rate of water

Explanation: BOD or Biological Oxygen Demand means the amount of oxygen bacteria and other microorganisms use while they decompose organic matter under aerobic conditions. Sewage with a high BOD can decrease the oxygen levels of the receiving waters, causing the death of some of the aerobic organisms. High BOD is usually caused by a high level of organic pollution.

Ans. b. Escherichia coli

Explanation: Escherichia coli, a type of bacteria that lives in the human intestines, is an example of a Gram-negative bacterium. Gram-negative bacteria can be defined as bacteria that stain red when the Gram staining method of bacterial differentiation is used on them. Other examples of Gram-negative bacteria are Pseudomonas, Klebsiella, Proteus, Salmonella, Providencia, Morganella, Aeromonas, and Citrobacter. They are harder to kill because they have a harder cell wall.

Ans. d. Azospirillum

Explanation: Nitrogen-fixing bacteria are microorganisms that transform atmospheric nitrogen into fixed nitrogen (inorganic compounds usable by plants). They are essential because plants do not have access to atmospheric nitrogen. 

Examples of nitrogen-fixing bacteria are Rhizobium (formerly Agrobacterium), Frankia, Azospirillum, Azoarcus, Herbaspirillum, Cyanobacteria, Rhodobacter, Klebsiella, etc. There are many heterotrophic bacteria in the soil that fix nitrogen without interacting with other organisms. Azospirillum, a Gram-negative microaerophilic, non-fermentative, and nitrogen-fixing bacterial genus, is the common nitrogen-fixer in paddy fields.

Ans. d. Rhizobium

Explanation: Rhizobium is a bacteria present in the soil that fix nitrogen in legume plants. They colonize cells within root nodules where they convert atmospheric nitrogen to ammonia. Their cells lack membrane-bound organelles and they are unique in the sense that they are the only nitrogen-fixing bacteria that have a symbiotic relationship with legumes.

Ans. a. Spirogyra

Explanation: Spirogyra is a genus of free-floating green algae commonly found in freshwater environments. They are filamentous algae consisting of thin unbranched chains of cylindrical cells. They are used as a source of food around the world because they are rich in vitamins and minerals. Since they are photosynthetic, they are also an important part of aquatic systems.

Ans. a. Cattle yards

Explanation. Methanogens are microorganisms that produce methane under hypoxic conditions during the decomposition of organic matter. The methane produced is a metabolic byproduct. All known methanogens are euryarchaeote Archaea. Methanogens are strict anaerobes and, hence, their growth is limited to anaerobic environments. They are widely distributed in oxygen-free environments and participate actively in the carbon cycle. They are abundant in marshy areas and in cattle yards where cows are present.