CBSE Class 12 Biology Environmental Issues Worksheet Set B

MULTIPLE CHOICE QUESTIONS

Question. Drinking of mineral water with very low level of pesticides (about 0.02 ppm) for long periods may
(a) produce immunity against mosquito
(b) cause leukemia (blood cancer) in most people
(c) cause cancer of the intestine
(d) lead to accumulation of pesticide residues in body fat
Answer : D

Question. A lake near a village suffered heavy mortality of fishes within a few days. Consider the following reasons for this:
1. Lots of urea and phosphate fertilizer were used in the crops in the vicinity
2. The area was sprayed with DDT by an aircraft
3. The lake water turned green and stinky
4. Phytoplankton populations in the lake declined initially thereby greatly reducing photosynthesis.
Which two of the above were the main causes of fish mortality in the lake?
(a) 2 and 3
(b) 3 and 4
(c) 1 and 3
(d) 1 and 2
Answer : C

Question. Biological Oxygen Demand (BOD) is a measure of
(a) industrial wastes poured into water bodies
(b) extent to which water is polluted with organic compound
(c) amount of carbon monoxide inseparably combined with haemoglobin
(d) amount of oxygen needed by green plants during night
Answer : B

Question. A lake with an inflow of domestic sewage rich in organic waste may result in 
(a) drying of the lake very soon due to algal bloom
(b) an increased production of fish due to lot of nutrients
(c) death of fish due to lack of oxygen
(d) increased population of aquatic food web organisms
Answer : C

Question. Minimata disease is pollution related disease. It results from 
(a) oil spills in sea
(b) DDT pollution
(c) release of industrial waste containing mercury in fishing water
(d) accumulation of arsenic
Answer : C

Question. Which of the following is dissolved in water to make Bordeaux mixture ? 
(a) Calcium chloride
(b) Copper sulphate
(c) Sodium chloride
(d) None of these
Answer : B

Question. Acid rain is due to pollution of 
(a) dust
(b) pesticides
(c) SO₂ and NO₂
(d) carbon particle
Answer : C

Question. Which one of the following is an environmentrelated disorder with the correct main cause?
(a) Black lung disease (pneumoconiosis) found mainly in workers in stone quarries and crushers.
(b) Blue baby disease (methaemoglobinaemia) due to heavy use of nitrogen rich fertilizers in the area.
(c) Non-Hodgkin’s Lymphoma found mainly in workers involved in manufacture of neem based pesticides.
(d) Skin cancer mainly in people exposed to benzene and methane.
Answer : B

Question. Two lakes, A and B are identical in all aspects except that lake A has higher temperature. Which of the following is true ?
(a) A has higher rate of oxygen dissolution.
(b) B has higher rate of oxygen dissolution.
(c) Oxygen dissolution of both is the same.
(d) Both the lakes have same BOD. 28. Euro II norms stipulate that sulphur be controlled at _______ ppm in diesel and _______ ppm in petrol.
(a) 350; 150
(b) 150; 350
(c) 350; 250
(d) 150; 250
Answer : B

Question. Which of the following is biodegradable pollutant? 
(a) Plastic
(b) Asbestos
(c) Sewage
(d) Polythene
Answer : C

Question. Ozone in stratosphere extends 
(a) 10-20 km
(b) 20-25 km
(c) 15-30 km
(d) 25-40 km
Answer : B

Question. Green mufler is useful against 
(a) air pollution
(b) noise pollution
(c) soil pollution
(d) radioactive pollution
Answer : B

Question. In almost all Indian metropolitan cities like Delhi, the major atmospheric pollutant(s) is / are
(a) suspended particulate matter (SPM)
(b) oxides of sulphur
(c) carbon dioxide and carbon monoxide
(d) oxides of nitrogen
Answer : A

Question. Photochemical smog formed in congested metropolitan cities mainly consists of 
(a) ozone, peroxyacetyl nitrate and NOx
(b) smoke, peroxyacetyl nitrate and SO₂
(c) hydrocarbons, SO₂ and CO₂
(d) hydrocarbons, ozone and SOx
Answer : C

Question. Which one of the following pairs is mismatched?
(a) Fossil fuel burning - release of CO₂
(b) Nuclear power - radioactive wastes
(c) Solar energy - green house effect
(d) Biomass burning - release of CO₂
Answer : C

Question. Which one of the following organisms is likely to show the highest concentration of DDT, once it has been introduced into the ecosystem?
(a) Grasshopper
(b) Toad
(c) Snake
(d) Cattle
Answer : C

ASSERTION REASON QUESTIONS

Directions : These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following five responses.
(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
(b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
(c) If the Assertion is correct but Reason is incorrect.
(d) If both the Assertion and Reason are incorrect.
(e) If the Assertion is incorrect but the Reason is correct.

Question. Assertion : Inhabitants close to very busy airports are likely to experience health hazards.
Reason : Sound level of jet aeroplanes usually exceeds 160 dB. 
Answer : A

Question. Assertion : Organochlorine pesticides are organic compounds that have been chlorinated.
Reason : Fenitrothion is one of the organochlorine pesticides. 
Answer : C

Question. Assertion : Agricultural output increased several times after introduction of DDT.
Reason : DDT was the first insecticide used on a wide scale. 
Answer : A

Question. Assertion : A suspended particulate matter (SPM) is an important pollutant released by diesel vehicles.
Reason : Catalytic converters greatly reduce pollution caused by automobiles. 
Answer : B

Question. Assertion : Presently, the global atmosphere is warming up.
Reason : The depletion of stratospheric ozone layer has resulted in increase in ultraviolet radiations reaching the earth. 
Answer : B

Question. Assertion : Deforestation is one main factor contributing to global warming.
Reason : Besides CO₂, two other gases methane and CFCs are also included under green house gases.
Answer : B

Question. Assertion : UV radiation causes photodissociation of ozone into O₂ and O, thus causing damage to the stratospheric ozone layer.
Reason : Ozone hole is resulting in global warming and climate change. 
Answer : C

Question. Assertion : The concentration of methane in the atmosphere has more than doubled in the last 250 years.
Reason : Wetlands and rice fields are the major sources of methane. 
Answer : A

Question. Assertion (A) : Pollution is always caused by human activities.
Reason (R) : Pollution is not different from contamination.
Answer : D

Question. Assertion (A) : Chlorofluorocarbons are responsible for ozone depletion.
Reason (R) : Ozone level decreases by as much as 67% every year.
Answer : B

Very Short Answer Questions

Question. Name the greenhouse gases that contribute to total global warming. 
Answer. N2O, CFC, CH4, CO2.

Question. State the purpose of signing the Montreal Protocol. 
Answer. Montreal Protocol, was signed at Montreal, in 1987 to curb the emission of ozone depleting substances.

Question. Why are lichens regarded as pollution indicators? 
Answer. Lichens are regarded as pollution indicators because they do not grow in areas that are polluted.  So their presence indicates no pollution in that area and their absence indicates that the area is polluted.

Question. Write the unit used for measuring ozone thickness. 
Answer. Dobson unit.

Question. Mention the information that the health workers derive by measuring BOD of a water body.
Answer. By measuring BOD of a water body, health workers find the amount of dissolved oxygen in water. The lesser the amount of dissolved oxygen, the more polluted the water body will be.

Question. What is meant by ozone hole?
Answer. Depletion of ozone widely in the stratosphere, particularly over the Antarctic region result in formation of thinned ozone layer called ozone hole.

Question. Name two greenhouse gases produced by anaerobic microbes.
Answer. Carbon dioxide and methane.

Question. Name the gas which holds up ultraviolet rays.
Answer. Ozone

Short Answer Questions

Question. What is ozone shield and why is it important? Name the gases that cause stratospheric ozone depletion.
Answer. The thin layer of ozone around the atmosphere that prevents entry of harmful UV rays is called ozone shield. Ozone shield functions as a shield against strong UV radiations. The gases that cause ozone depletion are methane, nitrous oxide and chlorofluorocarbons.

Question. Mention how e-waste is produced and disposed off. Write the solution for its treatment.
OR 
Name any two sources of e-wastes and write two different ways for their disposal.
OR 
How e-wastes are being handled in our country? Write the correct solution for treating this waste. 
Answer. Irreparable computers and other electronic goods are the known sources of electronic wastes (e-wastes). E-wastes are buried in landfills or incinerated. Recycling is the only solution for the treatment of e-wastes.

Question. What initiatives were taken for reducing vehicular air pollution in Delhi? Has air quality improved in Delhi?
Answer. Delhi Government took following initiatives to reduce vehicular air pollution:
(i) Switching over to CNG for public transport vehicle.
(ii) Application of Euro II norms for vehicles.
(iii) Use of unleaded petrol.
(iv) Use of low-sulphur petrol and diesel.
(v) Use of catalytic converter in vehicles.
(vi) Phasing out of old vehicles.
In recent years, air quality of Delhi has improved with a substantial fall in pollutant gases like level between 1997 and 2005.

Question. Name any one of the green house gases and its possible source of production on a large scale. What are the harmful effects of it? 
Answer. CO2 and Methane. CO2 levels are increasing due to burning of fossil fuel leading to global warming.

Question. How does an algal bloom cause eutrophication of a water body? Name the weed that can grow in such a eutrophic lake. 
Answer. Algal bloom in the lake or any other water body forms a scum. The scum depletes the oxygen in the water leading to foul smelling of the water body. The oxygen depletion affects the aquatic life adversely resulting in the death of fish and ultimately the eutrophic lake itself dies. Water hyacinth grows in such a eutrophic lake.

Question. How do chlorofluorocarbons destroy ozone layer?
Answer. Chlorofluorocarbons (CFCs) break down in the presence of UV rays and produce active chlorine.
The chlorine atoms break down ozone into molecular O2, thereby depleting ozone layer.

Question. What is joint forest management? How can it help in conservation of forests?
Answer. Joint Forest Management (JFM) is a programme initiated by the Government of India in 1980 where government works closely with the local communities for protecting and managing forests.
By this programme forests are conserved by locals in a sustainable manner as locals are also benefited with forest products like fruits, gum, rubber, medicines, etc.

Question. Write what was the percentage of forest cover of India at the beginning and at the end of the twentieth century. How different is it from the one recommended by the National Forest Policy of our country? 
Answer. At the beginning of the twentieth century, forests covered about 30 % of the land of India. By the end of the century, it shrunk to 19.4 %, whereas the National Forest Policy (1988) of India has recommended 33 % forest cover for the plains and 67 % for the hills.

Question. Justify the need for signing of ‘Montreal Protocol’ by the participating nations in 1987.
Answer. Montreal Protocol has been signed to control the emission of ozone depleting substances which results in thinning of ozone layer and allows the UV rays to penetrate the earths surface. These harmful UV rays cause deleterious effects (cataract/skin cancer/ageing of skin.)

Long Answer Questions

Question. What are the various constituents of domestic sewage? Discuss the effects of sewage discharge on a river.
Answer. The various constituents of domestic sewage are:
(i) Suspended solids: Grit made up of sand, silt and clay.
(ii) Colloidal materials: Including faecal matter, bacteria, paper fibres, cloth fibres, etc.
(iii) Dissolved solids: They are inorganic nutrients (e.g., nitrates, ammonium salts, calcium salts), toxic metal ions and organic compounds.
(iv) Pathogens: A number of pathogens cause various diseases like typhoid, cholera, dysentery, etc.
Effect of sewage discharge on a river:
Domestic sewage mainly contains biodegradable organic wastes which are decomposed by decomposers like bacteria and other micro-organisms. Decomposers require oxygen for their activity and hence BOD (Biochemical Oxygen Demand) increases. Many aquatic organisms die due to lack of dissolved oxygen. Domestic sewage contains nitrogen and phosphorus which favour the excess growth of algae called algal bloom. Excessive growth of water hyacinth causes imbalance in water ecosystem and thus aquatic animals die.

Question. Discuss the following:
(i) Chipko Movement
(ii) Scrubber
(iii) Radioactive wastes.
Answer. (i) Chipko Movement: Chipko movement (Hug the Trees Movement) was an organised resistance to the destruction of forests. It started in 1974 in Reni village of Garhwal. A contractor was allowed to cut trees in a forest near the village. When the contractor’s workers appeared, the women of the village reached the forest quickly and clasped the tree trunks with their arms, preventing the workers from cutting down the trees. Mr. Sunder Lal Bahuguna, a Gandhian activist and philosopher was the leader of Chipko Movement.
(ii) Scrubber:
• It is used to remove gases like sulphur dioxide from industrial exhaust.
• The exhaust is passed through a spray of water or lime.
• Water dissolves gases and lime reacts with sulphur dioxide to form a precipitate of calcium sulphate and sulphide.

(iii) Radioactive wastes: Radioactive wastes such as uranium, are used as fuel in the atomic power plant. The accidental leakage and disposal of radioactive wastes are the most serious problems. All safety measures for this purpose should be strictly enforced. Highlevel radioactive wastes generate a lot of heat and thus require cooling, as well as special protective shield during handling and transport. Radiation, that is given off by nuclear wastes is extremely harmful to the organisms, because it causes mutation at a very high rate.
At high doses, nuclear radiation is lethal but at lower doses, it creates various disorders, the most frequent of all being cancer. Therefore, nuclear waste is an extremely potent pollutant
and has to be dealt with utmost caution.

Question. Explain the ways by which solid waste can be disposed.
Answer. (i) Open burning: Municipal waste is reduced by burning in open dumps but the unburnt waste serve as the breeding ground for rats and flies.
(ii) Sanitary landfills: Wastes are dumped in a depression or trench after compaction and covered with dirt. But seepage of chemicals from these landfills can pollute underground water resources. Landfills are also getting filled.
(iii) Rag-pickers and kabadiwallahs: Wastes are collected and separated out into reusable or recyclable categories.
(iv) Natural breakdown: The biodegradable materials are kept into deep pits in the ground for natural breakdown.
(v) Recycling: E-wastes can be recycled in specifically built factories or manually to recover important metals like copper, iron, silicon, nickel and gold but in eco-friendly manner. Recycling in developing countries involve manual participation, exposing workers to toxic substances present in e-waste.

Question. Explain biomagnification. How does biomagnification of DDT affect the population of fisheating birds? 
Answer. Unknowingly some harmful chemicals enter our bodies through the food chain. We use several pesticides and other chemicals to protect our crops from diseases and pests. These chemicals are either washed down into the soil or into the water bodies. From the soil, these are absorbed by the plants along with water and minerals, and from the water bodies these are taken up by aquatic plants and animals. This is one of the ways in which they enter the food chain. As these chemicals are not degradable, these get accumulated progressively at each trophic level. As human beings occupy the topmost level in any food chain, the maximum concentration of these chemicals get accumulated in our bodies. This phenomenon is known as biological magnification. The population of fish-eating birds living on the bank of a contaminated lake differs from those living on the bank of another lake free from such insecticides (DDT). DDT being highly poisonous caused the thinning of their egg-shells and population of birds declined. The phenomenon is known as biological magnification.

Question. (a) What depletes ozone in the stratosphere? How does this affect human life?
(b) Explain biomagnification of DDT in an aquatic food chain. How does it affect the bird population? 
Answer. (a) Chlorofluorocarbons (CFCs) deplete ozone in the stratosphere.
UV(B) damages DNA causing mutation, skin cancer, inflammation of cornea, cataract, aging of skin, snow blindness.
(b) If DDT reaches from the agricultural field, it gets into the water body (the concentration is 0.0003 ppm) and enters the food chain: zooplanktons (0.04 ppm) → small fish (0.05 ppm) → large fish (2 ppm) → any fish eating bird (5 ppm). Concentration of DDT increases along the food chain, reaching a high level in the top carnivore bird.
DDT concentration disturbs Ca++ metabolism, egg shells become thin, premature breaking resulting in decline in bird population.

Question. (a) What is El Nino effect? Explain how it accounts for biodiversity loss.
(b) Explain any three measures that you as an individual would take, to reduce environmental pollution. 
Answer. (a) El Nino effect refers to the odd climatic changes in pacific ocean due to rise in temperature.
It leads to increased melting of polar ice caps as well as other places like the Himalayan snow caps. This will result in a rise in sea level that can submerge many coastal areas. Thus, resulting in biodiversity loss, it can also result in intense storms in some places and droughts or more rains in others.
(b) Measures to reduce environmental pollution
(i) Use of renewable energy resources.
(ii) Use of television and other gadgets at low pitch.
(iii) Minimum use of fossil fuel.
(iv) No tobacco smoking.
(v) Planting more trees.

Question. Why ozone hole forms over Antarctica? How will enhanced ultraviolet radiation affect us?
Answer. In Antarctica, winter months receive no sunlight and thus the temperature is extremely low (–85°C). It facilitates the formation of ice clouds which provide the catalytic surface on which thechlorine atoms react with ozone and degrade it. This happens with the return of sun to Antarctica in spring (September and October). Therefore, an ozone hole appears in Antarctica in spring.
Enhanced ultraviolet radiation will cause the following effects:
(i) Damage skin cells, ultimately leading to skin cancer.
(ii) Mutation will result due to damage of DNA.
(iii) Malfunctioning of immune system.

Please click on below link to download CBSE Class 12 Biology Environmental Issues Worksheet Set B