CBSE Questions for Class 9 Biology Natural Resources Quiz 2 - MCQExams.com

UNEP stands for United Nations Environment Programme is an agency of United Nations and coordinates its environmental activities, assisting developing countries in implementing environmentally sound policies and practices. 

So, the correct answer is 'United Nations Environment Programme'.

The primary greenhouse gases in Earth's atmosphere are water vapour, carbon dioxide $$(CO_2)$$, nitrous oxide $$(N_2O)$$, methane $$(CH_4)$$ and ozone $$(O_3)$$.

So, the correct answer is option 'D'.

• The thickness of ozone over the poles changes with the seasons, being the lowest in polar spring and maximum in polar autumn. 
• The ozone hole is formed each year when there is a sharp decline (currently up to 60%) in the total ozone over most of Antarctica for a period of about three months (September-November) during spring in the Southern Hemisphere. 
  
• This depletion of ozone is due to the action of sunlight over pollutants, which release chemicals like chlorine, that destroy ozone.
  
• Thus, the correct answer is option B.
  

• The presence of the layer of ozone (trioxygen) prevents the UV rays from reaching the surface of the earth.
• The reactions that occurs to form ozone from oxygen are shown below:

• The various greenhouse gases are carbon dioxide, methane, chlorofluorocarbons (CFCs), and nitrogen oxide. 
• Other minor contributors are water vapours and ozone. 
• The rise in carbon dioxide concentration is due to large scale deforestation (for grazing land, cropping land or urban settlements), change in land use pattern and large scale combustion of fossil fuels. 
• Methane is produced by incomplete biomass combustion, incomplete decomposition mostly by anaerobic methanogens. 
• CFCs are inert propellants used in aerosol cans and jet fuel, refrigerants in air conditioner and refrigerators. 
• Thus, the correct answer is option D. 

• The major source of $$O_2$$ liberation is photosynthesis and about 90% of total photosynthesis is done by phytoplankton (floating plants)

The fertility of the soil is not only determined by its ability to hold water or organic materials or its capacity to retain nutrients. It is determined by all of its characteristics combined and how well it can support life. It is considered to be very fertile soil when plants thrive in abundance, microorganisms thrive in abundance, and adequate resources are available.

So. the correct answer is option D.

Solution

Correct answer is option C
Explanation for correct option:

• Discharge of untreated sewage, surface run-off water from agricultural fields and industrial wastes lead to eutrophication and explosive growth of planktons and blue-green alga.
• This increases turbidity and reduces levels of dissolved oxygen, thus killing aquatic animals.

• In watery regions, forests regulate the water cycle (hydrological cycle).
• The water cycle, also known as the hydrological cycle or the H$$_2$$O cycle, describes the continuous movement of water on, above, and below the surface of the Earth. 
• The water cycle involves the exchange of energy, which leads to temperature changes. 
• For instance, when water evaporates, it takes up energy from its surroundings and cools the environment. When it condenses, it releases energy and warms the environment. 
• The heat exchange regulates the climate.
• Forests help control the water cycle by regulating precipitation, evaporation, and flows.
  

$$\textbf{Correct option: }$$ B

$$\textbf{ Solution: }$$

$$\textbf{ Option (A): }$$

$$\bullet$$The rocky or the stony part of the earth crust is known as the lithosphere. 

$$\textbf{ Option (B): }$$

$$\bullet$$The biosphere in the earth's atmosphere contains the whole ecosystem.

$$\bullet$$It maintains all the living matter together with water, air and soil on the surface of the earth. 

$$\bullet$$The forest and its organism, the aquatic life,  ocean and terrestrial ecosystems combines to form the biosphere. 

$$\textbf{ Option (C): }$$

$$\bullet$$The total percentage of the water in the earth is known as hydrosphere.

$$\textbf{ Option (D): }$$

$$\bullet$$The layer of gases surrounding the earth is known as atmosphere. 

Hence, the correct answer is option (B)

Correct Option - A

Explanation For Correct Option -

• Soil erosion can be effectively prevented by methods like afforestation and reforestation.
• Reforestation is the restoration of forests, which have been earlier destroyed by deforestation or other means, while afforestation is the raising of new forests.
• Plants hold the soil with their roots and thus prevent the soil from any erosion.

Explanation For Incorrect Options –

(B) Deforestation leads to an increase in soil erosion due to the decrease in the number of roots to hold the soil.
(C) Excessive use of fertilisers have deteriorating effects.
(D) Overgrazing leads to less grass cover so more soil erosion.

A)  Correct Option – C
B)  Explanation for correct option -

The two forms of oxygen found in the atmosphere are a diatomic molecular form that has a chemical formula as O22 or oxygen, the life-giving gas that we breathe in to survive. 
Another is a triatomic molecular form that has a chemical formula O33 called ozone gas, which protects us from harmful UV rays.