Environmental Issues Test - 82

Methyl bromide, halon, nitrogen oxides and chlorofluorocarbons are the potent ozone-depleting substances. These accumulate in the stratosphere and undergo photodissociation when exposed to the UV rays. The reactive chlorine and bromine react with ozone to form diatomic oxygen and molecular oxygen.

Among the five layers of the earth's surface ozone is present in the stratosphere which absorbs UV radiation before it reaches the ground. The main cause of ozone depletion is manufactured chemicals especially CFCs, these compounds reach the stratosphere by winds, where they release halogen atoms through photodissociation and cause the breakdown of ozone into oxygen. The ozone hole formed due to this increase the exposure of direct UV rays on earth carrying the potential risk of skin cancer and other negative effects. Direct exposure of harmful UV rays that penetrates skin can damage the genetic material I.e., DNA in skin cells and if the body is unable to recover the damage the cells stars to divide and grow uncontrollably which eventually leads to a tumour.

Ozone is found in high concentration in the stratosphere of the earth's surface in the form of ozone blanket or commonly known as the ozone layer. The vital function of ozone is to absorb the sun's ultraviolet radiation before it reaches the ground hence protecting the earth from its harmful effect. But the ozone-depleting substance such as Chlorofluorocarbons, nitrous oxides, etc that reacting with the ozone layer by releasing the reactive chlorine and cause depletion of it forming ozone hole. The concentration of ozone is less than 220 DU in the hole.

Plants are categorised into three groups based on their uptake of heavy metals - indicator, excluder and hyperaccumulator. Hyperaccumulator is a plant capable of growing in soils with high concentration of metals. They absorb through their roots and concentrate them in their tissues. The concentration is toxic to other species not adapted to grow on such soil. Arabidopsis belonging to the family Brassicaceae is a hyperaccumulator. Hence, the correct answer is 'Arabidopsis'.

Carbon dioxide is a greenhouse gas. It absorbs the long wavelength infrared radiations. The chemical bond between carbon and oxygen absorb infrared light very well and traps the heat from escaping, so they are considered to be opaque to the infra-red rays as these cannot pass across the carbon dioxide. Carbon dioxide molecules vibrate on receiving energy from the photon and allows molecules to capture the infrared photons (radiation). 

• BOD is the Biological Oxygen Demand that is created when there is an excessive quantity of the organic matter in the water body and its decomposition is initiated by the decomposing bacteria. More the amount of organic waste, the higher will be the BOD and so more will be pollution in the water body. 
• This causes an extreme reduction in the dissolved oxygen and suffocates the aquatic animals. 
• Distillery effluent is rich in organic waste left from alcoholic fermentation and it has the highest BOD. 

Sugar mill effluent follows the distillery effluent in the concentration of organic content. The sewage water contains the excreta and detergents mixed with it. 

Global warming refers to the overall increase in the tropospheric temperature reflected on the earth's surface. Developing substitutes for chloroform will not allow the build of chloroforms in the atmosphere. Minimal use of nitrogen fertilizers will not allow nitrogen oxides to cause secondary pollutants. Increase in vegetation like forests will make sure that carbon dioxide is used and so it will not cause the greenhouse effect. Limited use of fossil fuels will not add carbon dioxide, methane, oxides of sulphur etc and thus environment can be saved from their deleterious effects. On the other hand increase use of ACs, refrigerators, production of plastic forms and aerosol spray can propellants are harmful to the environment in a great deal because they cause ozone hole as well as global warming.

Polychlorinated biphenyls (PCBs)  are synthetic chemicals that are extremely resistant to the high temperature and pressure. These are used in capacitors and transformers, cable insulation, switches, regulators etc. These are light in colour and do not have any smell or taste. However, they have known to cause skin irritation, acne, eye problems etc. They are also carcinogenic in nature and cause liver and gallbladder cancer. Hence, the correct answer is 'Polychlorinated biphenyls'.

Chlorinated hydrocarbons are not soluble in water. They tend to combine with the adipose or the fatty tissues in the body of animals, including the humans. DDT is a type of such hydrocarbons and these are responsible for showing biomagnification as the food chain goes up because of increased consumption by the consumers and their tendency to accumulate in the fats. From the fatty tissues, these can be localised to the myelin sheath of neurons, connective tissues etc. and cause various diseases.