Free Man and His Environment MCQs with Answers

51. Which one of the following is an example of carrying out biological control of pests/diseases using microbes?

• A. Trichoderma sp. against certain plant pathogens
• B. Nucleopolyhedro virus against white rust in Brassica
• C. Bt­-cotton to increase cotton yield
• D. Lady bird beetle against aphids in mustard.

Explanation: A biological control being developed for use in the treatment of plant disease is the fungus Trichoderma. Trichoderma species are free living fungi that are very common in the root ecosystems. They are effective biocontrol agents of several plant pathogens.

52. In gobar gas, the maximum amount is that of

• A. Butane
• B. Methane
• C. Propane
• D. Carbon dioxide.

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%), carbon dioxide (30 ­-40%) with traces of nitrogen, hydrogen sulphide and hydrogen.

53. Read the following four statements (A­D). (A) Colostrum is recommended for the newborn because it is rich in antigens. (B) Chikungunya is caused by a Gram-negative bacterium. (C) Tissue culture has proved useful in obtaining virus-­free plants. (D) Beer is manufactured by distillation of fermented grape juice. How many of the above statements are wrong?

• A. Two
• B. Three
• C. Four
• D. One

Explanation: Chikungunya is caused by the Chikungunya virus. Colostrum is the first breast milk of a mother which contains antibodies (especially IgA) that protect the infant by the age of three months. Beer is manufactured by fermentation of barley malt by yeast species. Colostrum is a milky fluid that comes from the breasts of mammals the first few days after giving birth before true milk comes and is rich in proteins, carbohydrates, fats, vitamins, minerals, and antibodies (not antigens).

54. The domestic sewage in large cities

• A. Has a high BOD as it contains both aerobic and anaerobic bacteria
• B. Is processed by aerobic and then anaerobic bacteria in the secondary treatment in Sewage Treatment Plants (STPs)
• C. When treated in STPs does not really require the aeration step as the sewage contains adequate oxygen
• D. Has a very high amount of suspended solids and dissolved salts.

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.

55. Which one of the following is not a biofertilizer?

• A. Agrobacterium
• B. Rhizobium
• C. Nostoc
• D. Mycorrhiza

Explanation: Biofertilizers are organisms that enrich the nutrient quality of the soil. The main sources of biofertilizers are bacteria, fungi, and cyanobacteria. Rhizobium bacteria are found in the nodules on the roots of leguminous plants by symbiotic association. These bacteria fix atmospheric nitrogen into organic forms, which is used by the plants as a nutrient. Fungi are also known to form symbiotic associations with plants called mycorrhiza. Cyanobacteria are autotrophic microbes widely distributed in aquatic and terrestrial environments. Many of these can fix atmospheric nitrogen, e.g., Anabaena, Nostoc, Oscillatoria, etc. But Agrobacterium tumefaciens is a pathogen of several dicot plants. It causes gall tumors in the plants.

56. Which of the following is mainly produced by the activity of anaerobic bacteria in sewage?

• A. Laughing gas
• B. Propane
• C. Mustard gas
• D. Marsh gas

Explanation: Marsh gas or methane gas is mainly produced by the activities of anaerobic bacteria in sewage. Sewage contains large amounts of organic matter and microbes, many of which are pathogenic. These microbes (bacteria and fungi) are digested during the secondary treatment process of sewage by anaerobic bacteria. During digestion, bacteria produce a mixture of gases such as methane, hydrogen sulfide, and carbon dioxide. These gases are called biogas and can be easily used as a source of energy as it is inflammable.

57. An organism used as a biofertilizer for raising soyabean crop is

• A. Azotobacter
• B. Azospirillum
• C. Rhizobium
• D. Nostoc

Explanation: Rhizobium is used as a biofertilizer for raising crops. Rhizobium japonicum forms a symbiotic association in the roots of the leguminous plant, soybean.

58. Ethanol is commercially produced through a particular species of

• A. Saccharomyces
• B. Clostridium
• C. Trichoderma
• D. Aspergillus

Explanation: Ethanol is commercially produced through a particular species of yeast Saccharomyces (Saccharomyces cerevisiae).

59. Read the following statement having two blanks (A and B). A drug used for A patients is obtained from a species of the organism B. The one correct option for the two blanks is

• A. (a)
• B. (b)
• C. (c)
• D. (d)

Explanation: Cyclosporin A used as an immuno­ suppressive agent in organ-­transplant patients, is produced by the fungus Trichoderma polysporum.

60. Organisms called methanogens are most abundant in a

• A. Sulphur rock
• B. Cattle yard
• C. Polluted stream
• D. Hot spring.

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.