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Class 12 VBQs Biology Environmental Issues

Very Short Answer Type Questions

Question. State the purpose of signing the Montreal Protocol. 
Answer :
To control the emission of ozone depleting substances. 

Question. Where is good ozone present? Why is it called so ? 
Answer :
Good ozone is present in the upper part of atmosphere called stratosphere. It is called as good ozone because it absorbs the ultra-violet radiation of the sun and acts as a shield which does not allow the harmful UV-radiations to enter the earth’s atmosphere. 

Question. Mention the cause of thinning of ozone layer.
Answer :
Thinning in the ozone layer is caused by increasing concentrations of ozone-depleting chemicals like chlorofluorocarbons or CFCs. 

Question. How is snow blindness caused in humans ?
Answer :
Snow blindness (inflammation of cornea) is caused by absorption of UV-B radiations. 

Short Answer Type Questions

Question. Explain the relationship between CFC’s and ozone in the stratosphere. 
Answer :
UV rays act on CFC’s, release Cl atom, which act on ozone to release O2 resulting in ozone layer depletion/ causing ozone hole. 
Detailed Answer :
The ozone layer is getting depleted by the action of CFCs (Chlorofluorocarbons) used as coolant in refrigerators.
UV rays act on CFCs releasing Cl atoms. In presence of Cl (catalyst), ozone degrades releasing molecular oxygen (O2). This causes ozone depletion. 

Question. Why are the environmentalists worried about the considerable increase in the level of green house gases? List the different greenhouse gases other than carbon dioxide.
Answer :
Increase in the level of green house gases has led to heating of earth leading to global warming/ melting of glaciers/ rise in sea level that can flood the coastal areas. (Any two) Greenhouse gases other than CO2 are:
Methane (CH4), Chlorofluorocarbon(CFCs), Nitrous oxide (N2O). 


Class 12 VBQs Biology Environmental Issues

(i) What are the after effects of the degradation of ozone ?
(ii) How does it affect human health.
Answer :
(i) Thinning of Ozone / Ozone depletion / UV-B penetrates Ozone-forms hole-reaches earth. 
(ii) UV-B damages DNA causes mutation, ageing of skin / damage of skin cells / skin cancer / inflammation of cornea (snow blindness, cataract) 

Question. (i) State the cause of depletion of ozone layer.
(ii) Specify any two ill–effects that it can cause in the human body.
Answer : (i) UV radiations acts upon CFCs (chlorofluorocarbons), releasing Cl atoms (in the stratosphere), the Cl atoms degrade ozone.
(ii) Ageing of skin / skin cancer, inflammation of cornea / snow blindness / cataract / permanently damaged cornea.
Detailed Answer :
(i) The main cause of depletion of ozone layer is the increase in ozone degradation by chlorofluoro carbons (CFCs)
(ii) Its effects on human body are :
(a) It allows/UV B radiation to enter the atmosphere.
(b) Causes inflammation of cornea (snow blindness) cataract. etc.
(c) Causes ageing of skin, damage the skin cell and may even cause cancer.

Question. Why are the there regular reminders to reduce the use of CFCs in the production of industrial and household appliances ? Explain.
Answer :
(i) CFC adds to degradation of ozone layer in the stratosphere
(ii) Ozone shields the earth by absorbing UV radiation from sun
(iii) UV rays are highly injurious to organisms
(iv) To prevent degradation of ozone layer (in stratosphere) / to maintain a balance between production and degradation of ozone in stratosphere 

Question. Explain the relationship between green house gases and global warming. 
Answer :
Green house gases absorb a major fraction of infra red radiation, emitted by earth, and do not allow it to escape into space and reflects it back to earth, leading to considerable heating of earth and its atmosphere causing global warming. 

Question. How have human activities caused desertification? Explain. 
Answer :
Desertification is a type of land degradation in which relatively dry land region becomes increasingly arid.
Human activities responsible for desertification are as follows :
(i) Deforestation (slash and burn and destruction of plants that retain water and shade land).
(ii) Introduction of invasive species.
(iii) Cattle grazing or overgrazing.
(iv) Improper farming practices.
(v) Excessive ploughing of land may also cause soil erosion. 

Question. (i) Expand CFCs.
(ii) CFCs are a part of greenhouse gases. Name the other gases.
(iii) Explain the major harms caused by these gases.
(iv) Mention the consequences of the degradation of O3
Answer :
(i) Chlorofluorocarbons.
(ii) CO2, CH4, N2O
(iii) These gases absorb radiations that come to earth’s surface and heat it.
(iv) Degradation of ozone layer is very harmful to the mankind. It damages the human skin cells.
It may reduce breaks in the chemical bond of DNA molecules and cause mutation.

Long Answer Type Questions 

Question. (i) What is El Nino effect ? Explain how it accounts for biodiversity loss.
(ii) Explain any three measures that you as an individual would take to reduce environmental pollution.
Answer : (i) El Nino effect :
El Nino is a severe atmospheric and oceanic disturbance in the Pacific Ocean that occurs every seven to fourteen years. It is called El Nino, meaning ‘the Christ Child’, because it usually appears near the Christmas season. Warm surface waters flow from the central Pacific towards eastern Pacific.
El Nino effects are actually thought to be potentially more damaging on global scale, as they may cause floods and mudslides in Latin America.
(ii) The three measures that we as an individual would take to reduce environmental pollution are :
(a) Turning off the air conditioners when not in use.
(b) Planting more and more trees.
(c) Reducing the use of plastics.
(d) Composting biodegradable kitchen waste.

Question. (i) Why is the ozone layer required in the stratosphere ? How does it get degraded ? Explain.
(ii) Why is the ozone depletion a threat to mankind ? 
Answer :
(i) The ozone formed in the stratosphere is called ‘good’ ozone, as it acts as a shield and absorbs the ultraviolet radiation from the sun.
The major ozone-depleting substances are chlorofluorocarbons, which release active chlorine in the presence of UV. The chlorine atoms degrade ozone into molecular oxygen.

Class 12 VBQs Biology Environmental Issues

(ii) (a) The thinning of the ozone layer results in an increase in the UV radiation reaching the earth’s surface. 5% loss of ozone results in a 10% increase in UV radiation.
(b) In humans, the increased UV radiation increases the incidence of cataract and skin cancer (including melanoma) and diminishes the functioning of the immune system.
(c) Elevated levels of UV radiation affect photosynthesis as well as damage nucleic acids in living organisms. UV radiation inhibits photosynthesis in most phytoplankton as it penetrates through the clear open ocean water.
(d) This, in turn, can affect the whole food chain of organisms that depends on the phytoplankton. 

Question. People living in the coastal areas are forced to evict their dwelling units as the sea has inundated into the land areas. State the possible reasons and suggest measures that could be taken to reduce the deleterious changes in the environment.
Answer :
Increase in the level of greenhouse gases has led to considerable heating of Earth leading to global warming; the temperature of Earth has increased by 0.6 °C most of it during the last three decades.
El Nino effect is leading to increased melting of polar ice caps as well as of other snow caps. This has resulted in a rise in sea level that can submerge many coastal areas. 
The measures include
(a) Cutting down use of fossil fuel,
(b) Improving efficiency of energy usage
(c) Reducing deforestation and planting trees.
(d) Slowing down the growth of human population.
(e) Reduce the emission of greenhouse gases into the atmosphere.

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