Free Man and His Environment MCQs with Answers

81. Farmers have reported over 50% higher yields of rice by using which of the following biofertilizer?

• A. Cyanobacteria
• B. legume-­Rhizobium symbiosis
• C. Mycorrhiza
• D. Azolla pinnata

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.

82. The biological control component is central to advanced agricultural production. Which of the following is used as a third-generation pesticide?

• A. Insect repellants
• B. Organophosphate and carbamates
• C. Pathogens
• D. Pheromones

Explanation: Pheromones are volatile chemicals produced by a given species to communicate with other individuals of the same species to change their behavior. The synthetic versions of lepidopteran pheromones can be used as pesticides. Sometimes the relative amount of several pheromone chemicals in a pesticide product determines which specific pests are controlled when the pesticide product releases pheromone into the air where males are looking for females, the males become confused and cannot easily locate the females. As a result, many of the females do not mate and lay eggs and there are many fewer offspring than usual. These insect pheromones are third-generation pesticides. Other third-generation pesticides are insect growth regulators, chitin synthesis inhibitors, and juvenile hormones.

83. The biofertilizers are

• A. Anabaena and Azolla
• B. Cow dung, manure, and farmyard waste
• C. Quick growing crop plowed under soil
• D. None of these

Explanation: Biofertilizers are organisms that bring about nutrient enrichment of the soil. Azotobacter is a free-living, aerobic, nitrogen-fixing bacteria. Anabena is a nitrogen-fixing cyanobacteria that occurs in both free-living and symbiotic associations with Azolla, Cycas roots, etc. Rhizobium lives symbiotically in root nodules of legumes and non­ legumes. Vesicular­-arbuscular mycorrhiza (VAM) is an example of endomycorrhiza in which fungal hyphae penetrate the cortical cells of grasses to form vesicles.

84. Gobar gas contains mainly:

• A. CO 2 + H 2
• B. CO 2 + H 2 O
• C. CH 4 only
• D. CH 4 + CO 2

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.

85. When a natural predator (living being) is applied on the other pathogen organism to control them, this process is called:

• A. Artificial control
• B. Confusion technique
• C. Biological control
• D. Genetic engineering

Explanation: The control of insect pests by the introduction, encouragment and artificial increase of biological agencies like predaceous and parasitic insects, other animals and diseases is termed as biological control. It is basically a natural control in which man plays significant role of making the biological agencies more effective. Of these agencies, insect enemies play important role in nature for managing the phytophagous insect pests and keep a balance e.g., lady bugs or praying mantis, frog, toads, lizard and birds are employed by man to eat up the insect pests like aphids. It is a self perpetuating method.

86. The rotenone is:

• A. A natural herbicide
• B. A natural insecticide
• C. An insect hormone
• D. A bioherbicide

Explanation: Natural insecticides are those which are obtained from microorganisms and plants. The first natural insecticide used by man is azadirachtin obtained from Azadirachta indica. Rotenone is another natural insecticide which is obtained from the roots of Derris and Lonchocarpers. It is harmless to warm blooded animals.

87. Biological control of agricultural pests, unlike chemical control, is:

• A. Self perpetuating
• B. Polluting
• C. Very expensive
• D. Toxic

Explanation: The control of insect pests by the introduction, encouragment and artificial increase of biological agencies like predaceous and parasitic insects, other animals and diseases is termed as biological control. It is basically a natural control in which man plays significant role of making the biological agencies more effective. Of these agencies, insect enemies play important role in nature for managing the phytophagous insect pests and keep a balance e.g., lady bugs or praying mantis, frog, toads, lizard and birds are employed by man to eat up the insect pests like aphids. It is a self perpetuating method.

88. Which of the following species does not have the ability to fix atmospheric nitrogen?

• A. Azotobacter
• B. Anabaena
• C. Nostoc
• D. Spirogyra

Explanation: Members of Kingdom Monera -­ bacteria and cyanobacteria (blue-green algae)- have the ability to fix nitrogen. Azotobacter is an N2 ­fixing bacteria. Anabaena and Nostoc are heterocystous blue­-green algae. The heterocysts are the sites of N2 fixation. Spirogyra is one of the commonest green algae. It has no function in nitrogen fixation.

89. Asymptote in a logistic growth curve is obtained when

• A. K = N
• B. K > N
• C. K < N
• D. The value of 'r' approaches zero.

Explanation: Asymptote in a logistic growth curve is obtained when population density (N) reaches the carrying capacity (K) i.e., N = K.

90. Mycorrhizae are the example of:

• A. Amensalism
• B. Antibiosis
• C. Symbiosis
• D. Fungistasis

Explanation: Mycorrhizae is an association between the roots of plants growing in acid soil and certain fungi. The host is pine, beech or heather and it provides the fungus with an enzyme to digest carbohydrates in leaf litter. In return, the fungus symbiont passes mineral ions from the soil to the host.