Environmental Issues | Class 12 Botany| Previous Years Questions and Answers (2018 to 2020)


2020 SAY

1.  One of the effects of water pollution is algal bloom. (2)

(a)    Define algal bloom.

(b)   Write two effects of algal bloom in aquatic ecosystem.

ü Answer:

(a) Algal bloom is the presence of large amount of nutrients in water resulting in excess growth of planktonic algae.

(b) i) imparts a distinct colour to the water bodies.

ii) cause deterioration of water quality and fish mortality.

2.  Write the uses of scrubber and electrostatic precipitator. (2)

ü Answer:

Scrubber: Removes gases like sulphur dioxide from exhaust.

Electrostatic precipitator: Removes particulate matter present in the exhaust.

3.   The concentration of toxicants like DDT increase in successive trophic levels. (2)

(a)    Name this phenomenon.

(b)   How does this phenomenon affect the fish-eating birds in an aquatic food chain? (2)

ü Answer:

(a) Biomagnification.

(b) High concentrations of DDT disturb calcium metabolism in birds that causes thinning of eggshell.

2020 MARCH

1.   What are the main consequences of Global warming? (2)

ü Answer:

Climatic changes, El Nino Effect, Melting of polar ice etc.

2.   Suggest any two methods for the disposal of solid wastes. (2)

ü Answer:

1. Sanitary landfills,     2. Recycle,           3. Incineration etc.

3.   Ozone depletion in stratosphere is a serious environmental issue. (3)

a.  What is good ozone?

b.  How do CFCs degrade ozone molecules in stratosphere?

ü Answer:

(a) Good ozone: It is the ozone found in the stratosphere which prevents harmful UV rays.

(b) When CFCs reach stratosphere, UV rays act on them releasing Cl atoms. In presence of Cl (catalyst), ozone degrades to O2. This causes ozone depletion

2019 SAY June

1.   Expand CNG. (1)

ü Answer:

Compressed Natural Gas.

2.   Water bodies around us are getting polluted due to various reasons. Write any four consequences of water pollution. (2)

ü Answer:

BOD of water increases.

Algal bloom.


Water borne diseases.


3.   Observe the figure showing the relative contribution of various greenhouse gases to global warming. (3)

a.  Identify A, B.

b.  Write any two consequences of global warming.

ü Answer:

(a) A= Methane           B= CO2

(b) Odd climatic change.

Melting of polar ice and rise in sea level.

2019 MARCH

1.   The Government of India has introduced the concept of ......................., so as to work closely with the local communities for protecting and managing forests. (1)

ü Answer:

Joint Forest Management (JFM).

2.   Which among the following is not a greenhouse gas? (1)

a.  N2O

b.  Methane

c.  Carbon dioxide

d.  Ozone

ü Answer:

(d) Ozone

3.   Deforestation is a serious issue in the present scenario. Write any two major consequences of deforestation. (2)

ü Answer:

Increase in atmospheric CO2 concentration causing Global warming, Loss of habitat and biodiversity, Desertification.

4.   Given below is a flow chart showing the accumulation of DDT in different trophic levels: (2)

a.  Name the phenomenon.

b.  How does it affect bird population?

ü Answer:

(a) Biomagnification

(b) In birds, it disturbs calcium metabolism resulting in thinning of egg shells.

2018 SAY June

1.   Catalytic converters are used in automobiles to control air pollution. Briefly comment on its role. (2)

ü Answer:

Ÿ Unburnt hydrocarbons are converted into CO2 and water.

Ÿ Carbon monoxide is changed to CO2.

2.   Domestic sewage and industrial effluents contain large amount of nutrients. What are the probable effects of these nutrients on water bodies? (2)

ü Answer:

Ÿ Algal bloom.

Ÿ Eutrophication.

Ÿ Biomagnification.

Ÿ Deterioration of water quality.

2018 MARCH

1.   Ozone acts as a shield for absorbing ultraviolet radiations from the Sun. (2)

a.    Name the region of atmosphere where Ozone is seen.

b.   Write the unit used to measure ozone layer.

ü Answer:

(a) Stratosphere or Troposphere.

(b) Dobson (Db).

2.   In 1990s, Delhi ranked 4th among the most polluted cities of the world. What are the parallel steps taken to reduce vehicular pollution? (2)

ü Answer:

Ÿ Use of lead-free petrol or diesel.

Ÿ Use of catalytic converters.

Ÿ Phasing out of old vehicles.

Ÿ Use of low-sulphur petrol and diesel.

Ÿ Use of compressed natural gas (CNG) etc.

3.   Increase in the level of greenhouse gases leads to global warming. How can it be controlled? (2)

ü Answer:

Ÿ Reduce the use of fossil fuel.

Ÿ Improve efficiency of energy usage.

Ÿ Reduce deforestation and plant trees.

Ÿ Slowing down the growth of human population.

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