Free Man and His Environment MCQs with Answers

71. Probiotics are

• A. Cancer-inducing microbes
• B. New kind of food allergens
• C. Live microbial food supplement
• D. Safe antibiotics.

Explanation: Probiotics are dietary supplements containing potentially beneficial bacteria or yeast, with lactic acid bacteria (LAB) as the most common microbes used. LABs have been used in the food industry for many years because they are able to convert sugars (including lactose) and other carbohydrates into lactic acid. They not only provide the characteristic sour taste of fermented dairy foods such as yogurt but act as a preservative, by lowering the pH and creating fewer opportunities for spoilage organisms to grow.

72. The most thoroughly studied of the known bacteria-­plant interactions is the

• A. Cyanobacterial symbiosis with some aquatic ferns
• B. Gall formation on certain angiosperms by Agrobacterium
• C. Nodulation of Sesbania stems by nitrogen-fixing bacteria
• D. Plant growth stimulation by phosphate­ solubilizing bacteria.

Explanation: Agrobacterium tumefaciens is the causative agent of crown gall, an important disease of many commercial crops. This disease has come to be recognized in recent years as being caused by a DNA plasmid (Ti plasmid) carried by a bacterium and transferred to the plant cells.

73. A major component of gobar gas is

• A. Ammonia
• B. Methane
• C. Ethane
• D. Butane

Explanation: Biogas or gobar gas is a methane-rich fuel gas produced by anaerobic breakdown or digestion of biomass with the help of methanogenic bacteria. It is made up of methane (50 - ­70%), and carbon dioxide (30 - ­40%) with traces of nitrogen, hydrogen sulphide, and hydrogen.

74. During anaerobic digestion of organic waste, such as in producing biogas, which one of the following is left undegraded?

• A. Lipids
• B. Lignin
• C. Hemi­-cellulose
• D. Cellulose

Explanation: Lignin is a complex polymer of phenylpropane units, which are cross-linked to each other with a variety of different chemical bonds. This complexity has thus far proven as resistant to microbial degradation. Cellulose is a long chain of glucose molecules, linked to one another primarily with glycosidic bonds. The simplicity of the cellulosic structure, using repeated identical bonds, means that only a small number of enzymes are required to degrade this material. Hemicellulose are branched polymers of xylose, arabinose, galactose, mannose, and glucose. Hemicellulose binds bundles of cellulose fibrils to form microfibrils, which enhances the stability of the cell wall but these can be degraded by increasing the number of enzymes.

75. Which bacteria is utilized in gobar gas plant?

• A. Methanogens
• B. Nitrifying bacteria
• C. Ammonifying bacteria
• D. Denitrifying bacteria

Explanation: Methanogens are any of various archaebacteria that produce methane; they include genera such as Methanobacillus and Methanothrix. Methanogens are obligate anaerobes found in oxygen­ deficient environments, such as marshes, swamps, sludge, and the digestive systems of ruminants. They are also utilized in gobar gas plants.

76. During the formation of bread, it becomes porous due to the release of CO 2 by the action of

• A. Yeast
• B. Bacteria
• C. Virus
• D. Protozoans

Explanation: Saccharomyces converts starch or sugars to pyruvic acid through the EMP pathway. Then this pyruvic acid is converted to acetaldehyde and finally to ethyl alcohol in the absence of oxygen. This entire process is called fermentation. C 6 H 12 O 6 - 2CH 2 COCOOH - 2C 2 H 5 OH + 2CO 2 This released carbon dioxide makes the dough rise and gives a spongy nature to the bread.

77. The spoilage of oil can be detected by which fatty acid?

• A. Oleic acid
• B. Linolenic acid
• C. Linoleic acid
• D. Erucic acid

Explanation: Erucic acid is an unsaturated fatty acid belonging to the oleic acid series, occurring as glycerides in rapeseed oil and other vegetable oils. It is the cis-­isomer, the trans­-isomer being brassidic acid. Erucic acid is used as a binder for oil paints. It is useful in the manufacture of emulsions to coat photographic films and papers. Oleic acid is found in various animal and vegetable sources. It is widely used in industries including textile, chemical, medicine, leather, stationery, paper making, etc. Linolenic acids are used in making soaps, emulsifiers, and quick­-drying oils, in beauty products. It helps in acne reduction, moisture retention, etc. Linoleic acid is an important fatty acid, especially for the growth and development of infants. Commercially it is used in margarine, animal feeds, soaps, and drugs.

78. Which aquatic fern is used to increase the yield in paddy crop?

• A. Azolla
• B. Salvinia
• C. Marsilea
• D. Isoetes

Explanation: Azolla plays a very important role in rice production. Azolla and its nitrogen-fixing partner, Anabaena, have been used as green manure to fertilize rice paddies and increase production. With the help of Azolla, rice can be grown year after year, several crops a year, with little or no decline in productivity; hence no rotation of crops is necessary.

79. Which of the following is used to manufacture ethanol from starch?

• A. Penicillin
• B. Saccharomyces
• C. Azotobactor
• D. Lactobacillus

Explanation: Saccharomyces converts starch or sugars to pyruvic acid through the EMP pathway. Then this pyruvic acid is converted to acetaldehyde and finally to ethyl alcohol in the absence of oxygen. This entire process is called fermentation. C 6 H 12 O 6 - 2CH 2 COCOOH - 2C 2 H 5 OH + 2CO 2 This released carbon dioxide makes the dough rise and gives a spongy nature to the bread.

80. Which of the following ferns is an excellent biofertilizer?

• A. Marsilia
• B. Pteridium
• C. Azolla
• D. Salvinia

Explanation: Azolla plays a very important role in rice production. Azolla and its nitrogen-­fixing partner, Anabaena, have been used as green manure to fertilize rice paddies and increase production. With the help of Azolla, rice can be grown year after year, several crops a year, with little or no decline in productivity; hence no rotation of crops is necessary.