NCERT Class-9 Science Solutions: Chapter 14-Natural Resources Part 7 (For CBSE, ICSE, IAS, NET, NRA 2022)

Doorsteptutor material for CBSE/Class-9 Science is prepared by world's top subject experts: fully solved questions with step-by-step explanation- practice your way to success.

Question 42:

Why does Mathura refinery pose problems to the Taj Mahal?


Environmental pollution is damaging the monument Taj Mahal and discoloring its once translucent white marble. Mathura refinery is a biggest culprit in damaging Taj Mahal.

Sulphur dioxide emission from industry have reached levels ten times above the prescribed level. Combined with oxygen and moisture, Sulphur dioxide settles on the surface of the tomb and corrodes the marble, farming a fungus that experts call as ‘marble cancer;’ The environmentalists analysed that the refinery is creating high levels of suspended particulate matter, dust and exhaust. These are causing the Taj Mahal to change colour.

Question 43:

Why do not lichens occur in Delhi whereas they commonly grow in Manali or Darjeeling?


Lichens are also called the bio-indicators of the pollution. They are found only in the non-polluted areas. Lichens are highly susceptible towards Sulphur dioxide. A compound in them reacts with Sulphur dioxide to form a poisonous chemical that kills the plant itself. This is because lichens grow in areas where Sulphur dioxide pollution is very less, e. g. , in Manali and Darjeeling. Delhi is highly polluted place where lichens cannot grow and survive.

Question 44:

Why does water need conservation even though large oceans surround the land masses?


Marine water is not useful for human and plant life directly. Uneven distribution of limited fresh water resources need conservation to cater to the demands.

Water need to be conserved even though large ocean surrounded the land masses because the water which is present in the oceans are very salty and are not suitable for our daily use.

We need fresh water . Without fresh water we will die in just a few days

Question 45:

There is mass mortality of fishes in a pond. What may be the reasons?


  1. Thermal pollution
  2. Addition of poisonous (mercury) compounds in water
  3. Due to blockage of gills with any pollutant.
Image Mass Mortality of Fishes in a Pond

Question 46:

Lichens are called pioneer colonisers of bare rock. How can they help in formation of soil?


They enrich the soil by trapping water, dust and slit . When lichens die they contribute in organic matter to the soil improving the soil so that so that other plants can grow there.

Question 47:

“Soil is formed by water.” If you agree to this statement then give reasons


Water helps in formation of soil in following ways

  1. Water causes ‘wear off’ of rocks over a long period of time.
  2. It also causes the rocks to rub against other rocks creating small particles which are taken away downstream and deposited as soil.
  3. Water expands on freezing in crevices of rocks and cracks rocks into smaller pieces.

Question 48:

Fertile soil has lots of humus. Why?


Fertile soil contains lots of microorganisms which decompose the complex dead bodies of plants and animals into a simple substance called Humus. This is so because humus contains remains of dead plants and animals which in turn contain carbon and nitrogen which when decomposed by microorganisms gives carbon dioxide and complex nitrogen compounds are used by plants as soluble compounds.

Question 49:

Why step farming is common in hills?


This is practiced to check soil erosion through water currents on the slopes.

Graduated terrace steps are commonly used to farm on hilly or mountainous terrain. Terraced fields decrease both erosion and surface runoff, and may be used to support growing crops that require irrigation, such as rice.

Question 50:

Why are root nodules useful for the plants?


In root nodules nitrogen fixing Rhizobium bacteria are present which increases the soil fertility.

Bacteria living in the root nodules fix atmospheric nitrogen to the plant. Plants cannot utilize atmospheric nitrogen directly. Hence, leguminous plants establish a symbiotic relationship with bacteria like Rhizobium. Both the organisms of symbiotic relationship are mutually benefited. Leguminous plant provides shelter and nourishment for the bacteria and in turn bacteria fix atmospheric nitrogen to the plant. The bacteria and the leguminous plant involved in this symbiotic relationship are called as symbionts

Image Pils Crop with Root Nodules