Day-254 | Daily MCQs | UPSC Prelims | ENVIRONMENT AND ECOLOGY

Answer: A
Explanation:
• An indicator species is an organism whose presence, absence or abundance reflects a specific environmental condition. Indicator species can signal a change in the biological condition of a particular ecosystem, and thus may be used as a proxy to diagnose the health of an ecosystem. For example, plants or lichens sensitive to heavy metals or acids in precipitation may be indicators of air pollution.
• Option (b) is a keystone species. Keystone species is a species that has a disproportionately large effect on the communities in which it occurs. Such species help to maintain local biodiversity within a community either by controlling populations of other species that would otherwise dominate the community or by providing critical resources for a wide range of species. The name keystone species, coined by American zoologist Robert T. Paine in 1969.
• Option (c) is an invasive species. Invasive species are plants, animals, or pathogens that are non-native (or alien) to the ecosystem under consideration and whose introduction causes or is likely to cause harm.

Answer: B
Explanation:
• Statement 1 is incorrect: The word smog is derived from smoke and fog. There are two types of smog: ∙ Classical smog occurs in cool humid climates. It is a mixture of smoke, fog and sulphur dioxide. Chemically it is a reducing mixture and so it is also called as reducing smog. ∙ Photochemical smog occurs in warm, dry and sunny climates. The main components of the photochemical smog result from the action of sunlight on unsaturated hydrocarbons and nitrogen oxides produced by automobiles and factories. (Statement 2 is correct.) Photochemical smog has high concentration of oxidizing agents and is, therefore, called as oxidizing smog.
• The common components of photochemical smog are ozone, nitric oxide, acrolein, formaldehyde and peroxyacetyl nitrate (PAN). Photochemical smog causes serious health problems. Both ozone and PAN act as powerful eye irritants. Ozone and nitric oxide irritate the nose and throat and their high concentration causes headache, chest pain, dryness of the throat, cough and difficulty in breathing. Photochemical smog leads to cracking of rubber and extensive damage to plant life. It also causes corrosion of metals, stones, building materials, rubber and painted surfaces. (Statement 3 is correct.)

Answer: D
Explanation:
• Statement 1 is correct:Bio-gas contains up to 65% methane and 35% CO2.
• Statement 2 is correct: Biogas is produced by the anaerobic digestion of organic materials in a sealed fermenter. This fermenter transforms organic materials into biogas by using methane-producing bacteria through a biologically complex process at approximately 38 – 55 degrees Celsius.
• Statement 3 is correct: It burns without smoke, leaves no residue like ash in wood, charcoal and coal burning. Its heating capacity is high. The large-scale utilization of bio-waste and sewage material provides a safe and efficient method of waste-disposal besides supplying energy and manure. Bio-gas is also used for lighting.

Answer: D
Explanation:
• Statement 1 is incorrect: Chemical oxygen demand (COD) is a measure of the capacity of water to consume oxygen during both the decomposition of organic matter and the oxidation of inorganic chemicals such as ammonia and nitrite. Biological oxygen demand (BOD) is the amount of dissolved oxygen needed by aerobic micro-organisms to break down organic material present in a given water sample.
• Statement 2 is incorrect: A highly polluted water will have high levels of both biological oxygen demand (BOD) and Chemical Oxygen Demand (COD).

Answer: B
Explanation:
• The xylem transports water and soluble mineral nutrients from the roots throughout the plant. It is also used to replace water lost during transpiration and photosynthesis. Phloem transports products of photosynthesis from the leaves to the other parts of the plant.