CBSE Questions for Class 12 Medical Biology Environmental Issues Quiz 14 - MCQExams.com

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'.

Eutrophication is the buildup of biomass due to excessive inorganic nutrients in the water body. The dead biomass would then be subjected to the decomposition by the bacteria that would use the dissolved oxygen in the water body. The concentration of the oxygen would fall and this causes the death of the aquatic animals due to the suffocation. Hence, the correct answer is 'Non-availability of oxygen’.

• 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. 

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'.

The meltdown of the reactor core is the primary reason for the reactor mishap. The core is made up of the radioactive material. The core is subjected to the extremely high temperature and in the absence of the water, it melts. Its melting also breaks down the steel container and the radioactive waves leak from the reactor. The coolants are used to prevent this meltdown. Hence, the correct answer is 'Meltdown of reactor core'.

•  The UV region covers the wavelength range 100-400 nm and is divided into three bands: UVA (315-400 nm) UVB (280-315 nm)
• The most common form of UV radiation is sunlight, which produces three main types of UV rays: UVA, UVB, UVC.
• At certain wavelengths, UV is mutagenic to bacteria, viruses and other microorganisms. Particularly at wavelengths around 260–270 nm, UV breaks molecular bonds within microorganismal DNA, producing thymine dimers that can kill or disable the organisms.
• UVB, the chief cause of skin reddening and sunburn, tends to damage the skin's more superficial epidermal layers. It plays a key role in the development of skin cancer and a contributory role in tanning and photoaging.

• CFCs and other halogenated ozone depleting substances (ODS) are mainly responsible for manmade chemical ozone depletion.
• The total amount of effective halogen (Chlorine and bromine) in the stratosphere can be calculated and are known as the equivalent effective stratospheric chlorine.