CBSE Questions for Class 9 Biology Natural Resources Quiz 7 - MCQExams.com

The biosphere is a narrow zone on the surface of the earth where soil, water, and air combine to sustain life. Life can only occur in this zone. From fungi and bacteria to large animals, there are several different types of life.

The biosphere can also be defined as the sum total of all ecosystems. The biosphere includes regions on, above, and below the Earth’s surface where life exists.

• The water cycle, carbon cycle, and nitrogen cycle are essential for maintaining balance in an ecosystem. 
• The water cycle is the cyclic movement of water on earth and its atmosphere. Water evaporates from the surface of the earth, rises into the atmosphere, cools and condenses as snow or rain clouds, and falls again to the surface as precipitation. 
• The carbon cycle is the movement of carbon from the atmosphere to the Earth and then back into the atmosphere. Photosynthesis utilizes carbon dioxide and releases oxygen while respiration utilizes oxygen and gives back carbon dioxide.
  
• The nitrogen cycle is the process by which atmospheric nitrogen is fixed by certain bacteria and converted into usable nitrogenous compounds which are used by plants. Nitrogen is released back into the atmosphere by the process of denitrification.
• So, the correct answer is option D

• The assimilation of oxygen from the atmosphere to the biosphere is called as oxygen cycle. 
• As shown in the given diagram, oxygen in the atmosphere is utilized by plants and animals for respiration. 
• It results in the formation of carbon dioxide and water. These are utilized by plants for photosynthesis, which results in the production of sugars and organic compounds and the release of oxygen back into the air. This cycle is then repeated. This is the oxygen cycle.

• The weight of the atmosphere acts as a force upon the underlying surface of the Earth. The amount of force exerted over an area of the surface is called atmospheric pressure or air pressure. 
• In the atmosphere, the air pressure at any point is caused by the weight per area of the air above that point. 
• As we go up the layers of the atmosphere, fewer air molecules are above us. So, there will be less weight of air above us. Hence, atmospheric pressure always decreases as we move upward in the atmosphere.

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

$$\textbf{Solution: }$$ 

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

$$\bullet$$Dissolved oxygen (DO) is defined as the amount of oxygen that is present in water. 

$$\bullet$$Water temperature is one of the factors determining amount of Dissolved Oxygen in water $$\bullet$$The cold water has the possibility to hold more dissolved oxygen as compared to the warm water. 

Conservation of resources is nothing but making use of resources such that they are not depleted and are left behind for replenishing in future. This can be achieved in many ways, for example for conservation of natural resources like natural gas, one can get tank less water heater as it reduces the usage of natural gas and the other example is to save natural gas, the use of another energy source like hydro, solar or wind power can be followed.