Question 2

Forest versus desert ecosystem; primary versus secondary air pollutants

10 marks

Question

Question 2 · 10 marks

Differentiate between each of the following pairs (attempt any two): 2×5=10

Reworded from the university paper; the task is the same. The original paper belongs to the University of Delhi. See DU's question bank.

Read off the question and its marks

20 minfor 10 marks

any twoAnswer any 2 of the 3, 5 marks each. Only 2 are marked: a third earns nothing.
Differentiate betweenSet the differences out in a table, basis by basis, not as two separate essays.

The parts stand alone: start with the one you are surest of.

Short on time? A few lines on every part beat a full answer to one: each part is capped at its own marks.

Try it first. About 20 minutes for 10 marks. Write it out, then open the solution.

Hover or tap a marked figure, like 72,000, to see how it is made and where else it appears.

The question asks for any two of the three pairs. Pairs (i) and (iii) are answered.

(i) Forest ecosystem versus desert ecosystem

Both are terrestrial ecosystems, but they lie at the two ends of the scale of water supply.

Basis	Forest ecosystem	Desert ecosystem
Rainfall	Moderate to high; evergreen forests grow where the monsoon lasts several months, as in the Western Ghats and the North-East	Very low and irregular; in parts of the Thar it may rain only once in several years
Vegetation	Dense trees forming a canopy, with shrubs and herbs below in layers (stratification)	Sparse grasses and a few shrubs after rain; thorny trees such as kher and babul in the semi-arid fringe
Light at the floor	Little light reaches the floor under a closed evergreen canopy	Open ground, full sunlight, high daytime heat
Animal life	Very rich, especially in insects; large herbivores and carnivores	Specialised insects and reptiles; wolf, desert cat, desert fox, Great Indian Bustard
Productivity	High biomass and productivity	Low productivity, limited by water
Indian examples	Sal forests of central India, evergreen forests of the Western Ghats	Thar desert of Rajasthan; cold desert of Ladakh
Main threats	Felling for timber and fuel, conversion to farms	Canal irrigation that makes the land saline, and overuse of groundwater

(iii) Primary versus secondary air pollutants

Basis	Primary air pollutants	Secondary air pollutants
Meaning	Pollutants released directly into the air from a source that can be identified	Pollutants that form in the atmosphere through chemical reactions among primary pollutants
Sources	Natural events such as dust storms and volcanoes, and human activities such as vehicle and factory emissions	No direct source; they arise from sunlight, moisture and the mixing of primary pollutants
Examples	Carbon oxides, nitrogen oxides, sulphur oxides, volatile organic compounds and suspended particulate matter; together these five make up about 90 per cent of global air pollution	Sulphuric acid, nitric acid and carbonic acid; ground-level ozone, formed with the help of nitrogen oxides
Control	Controlled at the source: cleaner fuels, catalytic converters, filters on chimneys	Controlled only indirectly, by cutting the primary pollutants that produce them
Indian example	Exhaust from diesel vehicles and smoke from brick kilns	Ozone building up over a city on a hot, sunny afternoon; acid rain near coal-burning plants

Thus the difference lies in origin: primary pollutants come straight from a source, secondary pollutants are made in the air itself.

#	Component	Marks
1	(i) Forest versus desert ecosystem	5
2	(iii) Primary versus secondary air pollutants	5
	Total	10

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