Free Man and His Environment MCQs with Answers

231. Depletion of which gas in the atmosphere can lead to an increased incidence of skin cancers?

• A. Ammonia
• B. Methane
• C. Nitrous oxide
• D. Ozone

Explanation: Ozone layer or shield is present in stratosphere. It functions as a shield against strong UV radiations coming from sun. UV radiations are very harmful and may cause mutations in living organisms. Thinning of ozone layer increases the amount of UV radiations reaching the earth. The increase in UV radiation reaching the Earth's surface due to ozone layer depletion has raised concerns about a higher risk of skin cancers. Prolonged and frequent exposure to UV radiation, especially without proper sun protection, can increase the risk of skin cancers, including basal cell carcinoma, squamous cell carcinoma, and melanoma.

232. A river with an inflow of domestic sewage rich in organic waste may result in:

• A. An increased production of fish due to biodegradable nutrients.
• B. Death of fish due to lack of oxygen.
• C. Drying of the river very soon due to algal bloom.
• D. Increased population of aquatic food web organisms.

Explanation: High amount of organic waste in a lake will trigger and activate decomposer microbes which will decompose organic waste. Biochemical Oxygen Demand (BOD) of this lake will shoot up and decomposers will utilize most of the dissolved oxygen present in lake. Consequently, the level of dissolved oxygen will go down to alarming extent. Aquatic animals like fish which totally depend on the oxygen dissolved in water will ultimately die.

233. Acid rain is caused by increase in the atmospheric concentration of:

• A. CO2 and CO
• B. O3 and dust
• C. SO2 and NO2
• D. SO3 and CO

Explanation: Acid rain is rainfall and other forms of precipitation with a pH of less than 5. Acid rain is caused by the large scale emission of acidic gases into the atmosphere from thermal power plants, industries and automobiles. The common ones are sulphur dioxide, nitrogen oxides (NOx), volatile organic carbons (VOCs), and hydrogen chloride. Sulphur dioxide and nitrogen oxides are changed in the atmosphere into sulphuric acid and nitric acid by combining with oxygen and water, which then fall on the earth in the form of acid rain.

234. Eutrophication of water bodies leading to killing of fishes is mainly due to non-­availability of:

• A. Essential minerals
• B. Oxygen
• C. Food
• D. Light

Explanation: Eutrophication is the excessive growth of algae, plants and animals in water bodies due to the nutrient enrichment particularly with nitrogen and phosphate. Nutrients present in sewage, agricultural wastes and fertilizers cause dense growth of plants and planktonic algae. The excessive growth of planktonic algae that cause coloration of water is called algal bloom, which is toxic to animals and humans. Eutrophic water bodies also support excessive growth of floating plants. Algal blooms and floating plants cut off light form submerged plants, resulting in their death. There is drastic decrease in oxygen replenishment inside water. Non-­availability of oxygen results in the death of aquatic animals such as fish, which further adds to organic loading of water. Decomposition is replaced by putrefraction which is anaerobic, leading to absence of oxygen in water and death of aquatic animals.

235. Which of the following are most suitable indicators of SO2 pollution in the environment?

• A. Algae
• B. Fungi
• C. Lichens
• D. Conifers

Explanation: Lichens are very sensitive to SO2 pollution. They are completely destroyed at places where there is SO2 pollution in atmosphere. Therefore, they act as very good indicators of SO 2 pollution.

236. Increase in concentration of the toxicant at successive trophic levels is known as:

• A. Biotransformation
• B. Biogeochemical cycling
• C. Biomagnification
• D. Biodeterioration

Explanation: Biomagnification, also known as bioamplification or biological magnification, is a process that occurs in ecosystems where certain chemical substances or pollutants become increasingly concentrated in organisms at higher trophic levels in a food chain or food web. Heavy metals and persistent pesticides (e.g., chlorinated hydrocarbons like DDT) pass into food chain and increase in amount per unit weight of organisms with the rise in trophic level due to their accumulation in fat. The phenomenon is called biomagnification/ bioconcentration/biological amplification, e.g., 0.003 parts per billion of DDT in water becomes 0.003 ppm in phytoplankton, 0.04 ppm in zooplankton, 0.5 ppm in clams and small fish, 2.0 ppm in predator fish and 25 ppm in fish eating birds like seagulls.

237. Which of the following is not one of the prime health risks associated with greater UV radiations through the atmosphere due to depletion of the stratospheric ozone?

• A. Damage to eyes
• B. Increased liver cancer
• C. Increased skin cancer
• D. Reduced Immune System

Explanation: Ultraviolet radiations are of three types, i.e. ­UV-­C (100 ­- 280 nm), UV­-B (280 ­- 320nm) and UV­-A (320 ­- 390nm). Shorter ultraviolet radiations (UV­-C) are absorbed by the atmosphere. The longer ones (UV­-A) are not that harmful. The intermediate or UV­-B are harmful as well as capable of deep penetration. Thinning of the ozone layer increases the amount of UV­-B radiations reaching the earth. UV-­B radiations damage skin cells, cause ageing of the skin, skin cancer and eye damage. UV radiation can suppress the immune system, making it harder for the body to defend against infections and diseases.

238. High value of BOD (Biochemical Oxygen Demand) indicates that:

• A. Water is less polluted.
• B. Consumption of organic matter in the water is higher by the microbes.
• C. Water is pure.
• D. Water is highly polluted.

Explanation: Biochemical oxygen demand or BOD is the oxygen required for microbial decomposition of a unit mass of organic remains. The degree of impurity of water due to organic matter is measured in terms of BOD. A higher BOD of a river indicates that water is highly polluted .A high value of Biochemical Oxygen Demand (BOD) in water indicates that there is a substantial amount of organic material, such as sewage, wastewater, or other organic pollutants, present in the water. BOD is a measure of the amount of dissolved oxygen that is consumed by microorganisms while they decompose this organic material.

239. A location with luxuriant growth of lichens on the trees indicates that the:

• A. Trees are very healthy
• B. Trees are heavily infested
• C. Location is highly polluted
• D. Location is not polluted

Explanation: Lichens are very sensitive to SO2 and pollution and are completely destroyed at places with the presence of these substances. Therefore, they act as very good indicators of SO 2 and pollution. A location with luxuriant growth of lichens on the trees generally indicates that the air quality in that area is relatively clean and unpolluted. Lichens are highly sensitive to air pollution, including sulfur dioxide (SO2) and other pollutants. When lichens thrive on trees and other surfaces, it suggests that the atmosphere in the area has low levels of air pollutants.

240. The zone of atmosphere in which the ozone layer is present is called:

• A. Ionosphere
• B. Mesosphere
• C. Stratosphere
• D. Troposphere

Explanation: Ozone layer or shield is present in stratosphere. It functions as a shield against strong UV radiations coming from sun. UV radiations are very harmful and may cause mutations in living organisms. Thinning of ozone layer increases the amount of UV radiations reaching the earth. It would increase occurrence of cataract, skin cancers, dimming of eyesight, photoburning, deficient functioning of immune system, etc.