Free Man and His Environment MCQs with Answers

61. Which one of the following is a wrong matching of a microbe and its industrial product, while the remaining three are correct?

• A. Yeast - statins
• B. Acetobacter aceti - acetic acid
• C. Clostridium butylicum - lactic acid
• D. Aspergillus niger - citric acid

Explanation: Microbes are used for commercial and industrial production of certain chemicals like organic acids, alcohols, and enzymes. Examples of acid producers are Aspergillus niger (a fungus) of citric acid, Acetobacter aceti (a bacterium) of acetic acid; Clostridium butylicum (a bacterium) of butyric acid and Lactobacillus (a bacterium) of lactic acid.

62. Select the correct statement from the following.

• A. Biogas is produced by the activity of aerobic bacteria on animal waste
• B. Methanobacterium is an aerobic bacterium found in the rumen of cattle
• C. Biogas, commonly called gobar gas, is pure methane
• D. Activated sludge­-sediment in settlement tanks of sewage treatment plant is a rich source of aerobic bacteria.

Explanation: Sewage water can be purified by passing it through sewage treatment plants with the action of heterotrophic microorganisms. There are three stages of this treatment - primary, secondary, and tertiary. Primary treatment removes floating and suspended solids from sewage through two processes filtration and sedimentation. First, the floating matter is removed through sequential filtration. The filtrate is kept in large open settling tanks where grit settles down. The sediment is called primary sludge while the supernatant is called effluent. The primary sludge traps a lot of microbes and debris. In secondary treatment, the primary effluent is taken to aeration tanks. A large number of aerobic heterotrophic microbes grow in the aeration tank. They form flocs. Flocs are masses of bacteria held together by slime and fungal filaments to form mesh-like structures. The microbes digest a lot of organic matter, converting it into microbial biomass and releasing a lot of minerals. As the BOD of the waste matter is reduced to 10-­15% of raw sewage, it is passed into the settling tank. Thus secondary treatment is more or less biological. The sediment of the settling tank is called activated sludge. The remaining is passed into a large tank called an anaerobic sludge digester. It is designed for continuous operation. The aerobic microbes present in the sludge get killed. Anaerobic microbes digest the organic mass as well as aerobic microbes of the sludge. They are of two types, nonmethanogenic and methanogenic. Methanogenic bacteria produce a mixture of gases containing methane, H2S, and CO2.

63. A common biocontrol agent for the control of plant diseases is

• A. Baculovirus
• B. Bacillus thuringiensis
• C. Glomus
• D. Trichoderma.

Explanation: The natural method of pest and pathogen control involving the use of viruses, bacteria, and other insects (which are their natural predators and pests) is called biocontrol or biological control. For example, the free-living fungus Trichoderma exerts biocontrol over several plant pathogens for the control of plant diseases. Baculoviruses (mostly of genus Nucleo­ polyhedrovirus) are also used as biocontrol agents but they are used for the control of insects and arthropods. Bacillus thuringiensis is a soil bacterium which is used as a biopesticide. Glomus species are the most common fungal partners of mycorrhiza residing in the roots of higher plants.

64. The common nitrogen­ fixer in paddy fields is

• A. Rhizobium
• B. Azospirillum
• C. Oscillatoria
• D. Frankia

Explanation: Azospirillum is an anaerobic nitrogen-fixing bacteria that forms loose associations with the roots of some plants. Inoculation of paddy fields with these bacteria helps in increasing yield and saving nitrogen fertilizers

65. Which one of the following is not used in organic farming?

• A. Glomus
• B. Earthworm
• C. Oscillatoria
• D. Snail

Explanation: Organic farming is a method of farming that primarily aims to keep the soil alive and in good health by the use of organic wastes and other biological material along with beneficial microbes (biofertilizers) to release nutrients to crops for increased sustainable production in an eco-friendly, pollution-free environment.

66. Which one of the following pairs is wrongly matched?

• A. Alcohol ­- Nitrogenase
• B. Fruit juice ­- Pectinase
• C. Textile -­ Amylase
• D. Detergents ­- Lipase

Explanation: Yeast species are used in alcoholic fermentation due to the presence of the zymase enzyme. It was known that the yeast extract contained an enzyme zymase, which is nondialyzable, and a coenzyme that is dialyzable. It is now well known that zymase is a complex mixture of many enzymes and that several coenzymes are necessary for their function. The activity of this enzyme was lost because the main enzyme was separated from its coenzyme during dialyzation. Thus, it was established later that the extracellular enzyme zymase, secreted by yeast cells, carries out the process of fermentation.

67. Which of the following is not used as a biopesticide?

• A. Trichoderma harzianum
• B. Nucleopolyhedrovirus (NPV)
• C. Xanthomonas campestris
• D. Bacillus thuringiensis

Explanation: The natural method of pest and pathogen control involving the use of viruses, bacteria, and other insects (which are their natural predators and pests) is called biocontrol or biological control. For example, the free-living fungus Trichoderma exerts biocontrol over several plant pathogens for the control of plant diseases. Baculoviruses (mostly of genus Nucleo­ polyhedrovirus) are also used as biocontrol agents but they are used for the control of insects and arthropods. Bacillus thuringiensis is a soil bacterium which is used as a biopesticide. Glomus species are the most common fungal partners of mycorrhiza residing in the roots of higher plants.

68. Trichoderma harzianum has proved a useful microorganism for

• A. Gene transfer in higher plants
• B. Biological control of soil­-borne plant pathogens
• C. Bioremediation of contaminated soils
• D. Reclamation of wastelands.

Explanation: The natural method of pest and pathogen control involving the use of viruses, bacteria, and other insects (which are their natural predators and pests) is called biocontrol or biological control. For example, the free-living fungus Trichoderma exerts biocontrol over several plant pathogens for the control of plant diseases. Baculoviruses (mostly of genus Nucleo­ polyhedrovirus) are also used as biocontrol agents but they are used for the control of insects and arthropods. Bacillus thuringiensis is a soil bacterium which is used as a biopesticide. Glomus species are the most common fungal partners of mycorrhiza residing in the roots of higher plants.

69. Nitrogen fixation in root nodules of Alnus is brought about by

• A. Frankia
• B. Azorhizobium
• C. Bradyrhizobium
• D. Clostridium

Explanation: The most common symbiotic association of legumes and bacteria on roots is as nodules, which are small outgrowths on the roots. The microbe Frankia is symbiont in root nodules of several non­-legume plants like Casurina and Ausln. Both Rhizobium and Frankia are free living in soil but as symbionts they can fix atmospheric nitrogen.

70. Which one of the following proved effective for the biological control of nematode diseases in plants?

• A. Gliocladium virens
• B. Paecilomyces lilacinus
• C. Pisolithus tinctorius
• D. Pseudomonas cepacia

Explanation: Paecilomyces lilacinus proved effective for the biological control of nematode diseases in plants.