CBSE Questions for Class 12 Medical Biology Environmental Issues Quiz 12 - MCQExams.com

A) Correct Option – D

B) Explanation for correct option -

• Forest serves many functions in our daily life from tiny matchsticks to large constructions.
• It helps in improving the water holding capacity of soil as the roots hold water.
• It is the major source of habitat, food, and protection for the wildlife in there.
• It maintains the balance of oxygen and carbon dioxide in the atmosphere due to the respiration and photosynthesis process. 

• Degradation of organic matter by microbes requires oxygen. 
• Degree of impurity of water due to organic matter is measured in terms of biochemical oxygen demand or BOD. 
• It is the oxygen required for the microorganisms to completely metabolize organic wastes. 
• BOD is maximum for the distilleries and sugar industry. 
  
  

Solution

Correct answer is option C.

Explanation for correct option:

• Eutrophication is an enrichment of water by nutrient salts that causes structural changes to the ecosystem.
• Discharge of untreated domestic sewage and surface runoff water, having residues of phosphate, nitrate fertilizers, from agricultural fields etc is main reason of eutrophication.
• Water pollution leads to eutrophication. Eutrophication in turn causes increase in turbidity and reduces levels of dissolved oxygen, thus killing aquatic animals.

$$\textbf{Correct option: }$$ C

$$\textbf{Solution: }$$ 

$$\textbf{Option (C) }$$

$$\bullet$$BOD stands for Biological Oxygen Demand. 

$$\bullet$$The BOD represents the amount of oxygen consumed by bacteria and other microorganisms suspended in the water body which is required for the decomposition of organic matter under aerobic conditions. 

$$\bullet$$BOD level indicates the quantity of organic wastes present in the water body by the health workers. 

$$\bullet$$The survey depicts that instead of the efforts being made to clean Yamuna river, the pollution is still on an increase in Delhi. 

Hence, the correct option is (C)

• Incineration is a waste treatment process that involves the combustion of organic substances contained in waste materials.
•  Incineration and other high temperature waste treatment systems are described as "thermal treatment".
•  Incineration of waste materials converts the waste into ash, flue gas and heat.
• Hence, Incinerator is not a device used to control a particulate matter.

A.Correct option D

B.Explanation for correct option:

• Global warming is the phenomenon of a gradual increase in the temperature near the earth’s surface. 
• Air conditioners, refrigeration units, production of plastic foams and propellants in aerosol spray release chlorofluorocarbons into the atmosphere. 
• These CFCs deplete the ozone layer that contributes to global warming. 

$$\textbf{Correct option: }$$ D

$$\textbf{Solution: }$$ 

$$\textbf{Option (D) }$$

$$\bullet$$The addition of sewage in the water body bring in the constant supply of nutrients encourages the growth of aquatic organisms such as algae that increases their productivity.  

$$\bullet$$The presence of algal bloom increases the rate of oxygen depletion as the population of phytoplankton is very high.

$$\bullet$$This possesses a drastic negative effect on aquatic life such as fishes and its survival.

$$\bullet$$This process is known to be eutrophication that is depicted to be the natural aging of a lake by nutrient enrichment of its water, especially by nitrates and phosphates.

• Coal burning results in the generation of large quantities of coal residues, which contains very fine particles that tend to become airborne and which contribute to the formation of suspended particulate matter (SPM). 
  
  
• An electrostatic precipitator (ESP) is a filtration method that removes fine particles, like dust and smoke, from a flowing gas using the force of an induced electrostatic charge minimally impeding the flow of gases through the unit.
  
  Hence, option D is correct.

$$\textbf{Correct option: }$$ D

$$\textbf{ Solution: }$$

$$\textbf{ Option (A): }$$

$$\bullet$$Mechanised agriculture  is the process of using all kinds of agricultural machinery by the farmer in order to increase agricultural productivity. 

$$\textbf{ Option (B): }$$

$$\bullet$$The increase in irrigation efficiency can step up the productivity of the agricultural crops. 

$$\bullet$$This irrigation efficiency can be improved through altering farming practices, such as crop rotation and conservation tillage. 

$$\bullet$$This increases the moisture content in the soil which naturally increases the production of agriculture. 

$$\textbf{ Option (C): }$$

$$\bullet$$The chemical fertilizer whether be its natural or artificial substance can improve the productivity of agriculture. 

$$\textbf{ Option (D): }$$

$$\bullet$$Deforestation increases the chances of soil erosion. 

$$\bullet$$This increases the chances of floods and drought. The occurrence of floods causes siltation.

$$\bullet$$Decreased benefits of wildlife and the action of deforestation can result in the lose of their habitat.  

$$\bullet$$The human activity of deforestation can lead to the scarcity of timber, fuelwood, etc, and also leads to the adverse or drastic effects of the climatic conditions. 

Hence, the correct option is (D). 

Ozone is an inorganic molecule. It is a pale blue gas with a distinctively pungent smell. In the environment ozone is known for its both harmful and useful effects.
Ozone present in stratosphere is useful as it act like shield and protect the earth from harmful UV-rays which can cause serious problems like skin cancer and decrease in level of photosynthesis. Ozone present in troposphere act as pollutant and have many deleterious effects. 

Therefore, the correct answer is option C.