Natural Resources cbse class 9

(Q.) Name the outer layer of the earth. 

 (Ans)  Lithosphere.

(Q.) Write the name of two organisms, which take part in the nitrogen fixation.  

 (Ans)  Rhizobium and Azotobacter.

(Q.) Define hydrosphere.

 (Ans)  Water covers 75% of the Earth’s surface. This is called as hydrosphere.

(Q.) What is atmosphere? 

 (Ans)  The air that covers the whole of the Earth is called atmosphere.

(Q.) What is the percentage of CO₂ on Venus and Mars?

 (Ans)  95-97%.

(Q.) Define combustion.

 (Ans)  The process, which results in the consumption of the oxygen and production of carbon dioxide is called combustion.

(Q.) Which function does the ozone layer perform?

 (Ans)  This layer protects us from UV rays.

(Q.) What will be result if the CO₂ concentration in the atmosphere increases? 

 (Ans)  The temperature of the Earth will increase.

(Q.) How can you describe global warming? 

 (Ans)  Gradual increase in the earth's surface temperature is called global warming.

(Q.) How is Earth’s atmosphere different from that of Venus and Mars?

 (Ans)  In Earth’s atmosphere CO₂ is 0.03% and in Mars and Venus, it is 95-97%.

(Q.) At what stage water is said to be polluted?

 (Ans)  When there is any physical, biological or chemical change in water that adversely affects living organisms and makes it unfit for use, it is called polluted.

(Q.) Name the man-made component which is responsible for the depletion of ozone layer.

 (Ans)  CFC (Chloro Fluoro Carbon).

(Q.) How is ‘humus’ formed?

 (Ans)  ‘Humus’ is the organic constituent of soil formed by complete or partial decomposition of plant and animal materials.

(Q.) Why does the average temperature on earth remains fairly steady?                    

 (Ans)  The atmosphere acts as a blanket and prevents the extreme fluctuation of temperatures, as air is a bad conductor of heat.

(Q.)

What will be result if the CO₂ concentration in the atmosphere increases?         

 (Ans)  The temperature of the earth will increase due to global warming caused by greenhouse effect.

(Q.) Define photosynthesis, which gas is released as its byproduct?

 (Ans)  Photosynthesis is the production of food (carbohydrates) by plants from carbon dioxide and water in the presence of green pigment called chlorophyll, using energy, captured from sunlight and releasing of excess oxygen as a byproduct.

(Q.) Define nitrogen fixation.

 (Ans)  The conversion of atmospheric nitrogen into compounds that plants and other organisms can assimilate is called nitrogen fixation. This is done by certain soil microorganisms, such as rhizobium.

(Q.) What are the biotic and abiotic components?

 (Ans)  Living things constitute the biotic component of the Earth and the air, water and soil form the non-living or abiotic component.

(Q.) What is the mode of fixation of CO₂?  

 (Ans)  (i) Green plants convert CO₂ into glucose in the presence of sunlight. This process is called photosynthesis.
(ii) Many marine animals use carbonates dissolved in sea-water to make their shells.

(Q.) How can you define biosphere?

 (Ans)  The part of the earth and its atmosphere in which living organisms exist or that is capable of supporting life.

(Q.) At what stage is water called as polluted?

 (Ans)  When there is any physical, biological or chemical change in water which adversely affects living organisms and makes it unfit for use, it is called as polluted.

(Q.) Define humus and its function.

 (Ans)  A brown or black organic substance consisting of partially or wholly decayed vegetable or animal matter is called humus and it provides nutrients for plants and increases the ability of soil to retain water.

(Q.) Define ammonification and nitrification. 

 (Ans)  Ammonification: - The conversion of organic material of the plants and animals into ammonia and amino acids by microorganisms.
Nitrification: - The conversion of ammonia into nitrates.

(Q.) Why does the average temperature on earth remains fairly steady?

 (Ans)  Atmosphere acts as a blanket and prevents the extreme fluctuation of temperatures. Average temperature on earth remains fairly steady because air is a bad conductor of heat. The atmosphere slows down the escape of heat into outer space during night and prevents the sudden increase in temperature during day time.

(Q.) Mention two methods through which living organisms influence the formation of soil.

 (Ans) 
1. Roots of big trees penetrate into the crevices of rocks and enhance rock-breaking process.

2. Lichens, bryophytes (mosses) and other plants release some substances causing powdering of rock surfaces.

(Q.) List two ways in which water is useful to living organisms.

 (Ans)  1. All cellular processes take place in water medium. The reactions that take place within our body inside the cells occur between substances that are dissolved in water.
2. Water is a very good solvent.Also, substances are transported from one part of the body to the other in dissolved form.

(Q.) Mention any two human activities which would be responsible for air pollution.

 (Ans) 
1. Increased use of vehicles run by fossil fuels raises the gaseous air pollutants.
2. Factory outlets, low efficiency engines throw exhaust gases in the air.

(Q.) Give one visible indication of air pollution.   

 (Ans)  Formation of smog is a visible indication of air pollution. Presence of high level of pollutants such as hydrocarbons causes visibility to be lowered, especially in cold weather when water also condenses out of air. Increase in the content of these harmful substances in air causes air pollution.

(Q.) What do you understand by fixed nitrogen?

 (Ans)  Fixed nitrogen is the more stable form of nitrogen as ammonia or nitrate. Ammonia is formed by biological fixation of nitrogen and nitrate is the product of high energy fixation by lightning or cosmic radiation.

(Q.)

While digging the soil, a farmer notices that there are lots of earthworms in one part of his ground but none in the other part. Justify this observation.      

 (Ans)  One part of ground must have rich humus (decomposed plant and animal material) content, which makes the soil fertile. Earthworms play a major role in converting large pieces of organic matter into richhumus, improving soil fertility. Thus, they are present in greater numbers in that type of soil. Moreover, humus permits lots of air and moisture, both of which are needed by earthworms for their existence.

(Q.) Suggest any two measures for avoiding misuse and wastage of potable water.

 (Ans)  1. Development of integrated water shed plan for drinking, irrigation and industrial uses.
2. Transfer of surplus water to water deficit basins by interlinking rivers.

(Q.) What is the role of atmosphere in the climate control ?

 (Ans) 
The atmosphere keeps the average temperature of the Earth fairly steady during the day and even during the course of the whole year. The atmosphere prevents the sudden increase in temperature during the daylight hours. And during the night, it slows down the escape of heat into outer space.

(Q.) Draw the neat and clean diagram of the C-cycle.

 (Ans) 

(Q.) What are pollutants? Give the different types of the air pollutants with example.

 (Ans) 
The agents which cause pollution are called pollutants.
Different type of pollutants are :
Gaseous pollutants: - Sulphur dioxide, nitrogen peroxide.

Particulate pollutants: - Carbon particles and dust.

(Q.) Why do organisms need water? 

 (Ans)  Water is essential for the survival of the life.
(i) All cellular processes take place in water as medium.
(ii) All reactions that occur within our body and cells, take place between substances that are dissolved in water.
(iii) Substances are transported from one part of the body to the other in the dissolved form in water.

(Q.) By what ways carbon returns to the C-cycle?

 (Ans)  (i) Both plants and animals release carbon dioxide to the atmosphere as a product of the respiration.
(ii) By decomposition of organic wastes and dead bodies by decomposers.
(iii) By burning of fossil fuels like coal and petroleum.

(Q.) Describe the wind movement in the coastal regions.

 (Ans)  The situation in coastal regions during the day: The air above the land gets heated faster and starts rising. As this air rises, a region of low pressure is created and air over the sea moves into this area of low pressure. The movement of air from one region to the other creates winds. During the day, the direction of the wind would be from the sea to the land. At night, both land and sea start to cool. Since water cools down slower than the land, the air above water would be warmer than the air above land. Thus during night, movement of wind would be from land to sea.

(Q.) What are the reasons which lead to water pollution?

 (Ans)  The reasons which lead to water pollution are:
(i) Agricultural substances like fertilizers and pesticides are used to increase crop yield, and some percentage of these is washed into the water bodies that pollute the water.
(ii) Sewage from homes and wastes from factories are dumped into rivers or lakes.
(iii) Hot and cold water discharged from industries make a change in temperature which is harmful for aquatic organisms.

(Q.) a) What is symbiosis?                 
b) Name a symbiotic life form. Mention the specific organisms and their roles which display the symbiotic relationship in this life form.    

 (Ans)  a) Symbiosis is the relation between two different species of organisms that are interdependent; each gains benefit from the other.
b) A symbiotic life form— Lichen (association of a specific fungus and a specific alga)

Lichens are complex organisms consisting of algae and fungi in a symbiotic relationship between them. The algae provide energy to the fungus by means of photosynthesis and the fungus provides nutrients and protection to the algae from the harsh climate.

(Q.) What are the various methods to control pollution? 

(Ans)  The methods to control pollution are:
(i) Conversion of organic waste and feacal material into compost.
(ii) Dumping of non-degradable waste in low lying areas.
(iii) Proper disposal of sewage.
(iv) Installation of gobar gas plants.
(v) Growing of plants capable of fixing carbon monoxide and nitrogen oxides.
(vi) Use of CNG in automobile.

(Q.) Describe the nitrogen cycle in brief without diagram.

 (Ans)  Nitrogen is an essential nutrient for all life-forms and life. However, other than a few forms of bacteria, life-forms are not able to convert the comparatively inert nitrogen molecule into forms like nitrates and nitrites which can be taken up and used to make the required molecules. Other than these bacteria, the only other manner in which the nitrogen molecule is converted to nitrates and nitrites is by a physical process. During lightning, the high temperatures and pressures created in the air convert nitrogen into oxides of nitrogen. These oxides dissolve in water to give nitric and nitrous acids and fall on land along with rain. These are then utilised by various lifeforms.
Plants generally take up nitrates and nitrites and convert them into amino acids which are used to make proteins. Some other biochemical pathways are used to make the other complex compounds containing nitrogen. These proteins and other complex compounds are subsequently consumed by animals. Once the animal or the plant dies, other bacteria in the soil convert the various compounds of nitrogen back into nitrates and nitrites. A different type of bacteria converts the nitrates and nitrites into elemental nitrogen.

(Q.) Describe the process which results in rain.

 (Ans)  When water bodies are heated during the day, a large amount of water evaporates and goes into the air. Some amount of water vapour also get into the atmosphere because of various biological activities. This air also gets heated. The hot air rises up carrying the water vapour with it. As the air rises, it expands and cools. This cooling causes the water vapour in the air to condense in the form of tiny droplets. This condensation of water is facilitated if some particles could act as the ‘nucleus’ for these drops to form around. Normally dust and other suspended particles in the air perform this function. Once the water droplets are formed, they grow bigger by the ‘condensation’ of these water droplets. When the drops have grown big and heavy, they fall down in the form of rain.

(Q.) Describe the effects of the air pollution. 

 (Ans)  When fossil fuels are burnt, nitrogen and sulphur too are burnt and this produces different oxides of nitrogen and sulphur. Not only is the inhalation of these gases dangerous, they also dissolve in rain to give rise to acid rain. The combustion of fossil fuels also increases the amount of suspended particles in air. These suspended particles could be unburnt carbon particles or substances called hydrocarbons. Presence of high levels of all these pollutants cause visibility to be lowered, especially in cold weather when water also condenses out of air. This is known as smog and is a visible indication of air pollution. Studies have shown that regularly breathing air that contains any of these substances increases the incidence of allergies, cancer and heart diseases.

(Q.) a) Mention two ways by which water helps in formation of soil.
b) Explain oxygen cycle in nature with diagram.  .  

 (Ans)  a)i) Water finds the cracks in the rocks formed due to uneven heating by the sun. If this water freezes later on, it would cause the cracks to widen as water expands in the process.
ii)Fast flowing water carries away big and small particles of even hard rock downstream over long period of time. Water deposits these particles down its path to form the soil.
b) Oxygen is required for respiration by all the living organisms. Oxygen oxidizes the food materials and produce energy and carbon dioxide. The carbon dioxide is utilized by the plants to produce food materials during the process of photosynthesis. The free oxygen released in photosynthesis is again used in respiration or it may return to

(Q.) a) What are biogeochemical cycles?
b) Explain water or hydrological cycle in the nature with diagram.

 (Ans)  a) The chemical elements in the environment tend to circulate in the biosphere in characteristic paths from environment to organisms and back to the environment. These circular paths of chemical elements are known as biogeochemical cycles.

b) Water is an essential component of the environment. Ocean is the biggest source of water which on evaporation forms clouds and after condensation falls down as rain or snow. After rain, it passes through ponds, lakes and rivers and gets collected again in the ocean. This circulation of water is called water cycle or hydrological cycle.

(Q.) With the help of a labelled diagram,
a) show nitrogen cycle in nature.
b) list four steps involved in the cycling of N₂ in the environment.

 (Ans)  a)

b)

1.Fixing of nitrogen in atmospheric conditions, industrial process or by N₂ fixing bacteria which are found in root nodules of legumes or which are free living.
2.Ammonification by bacteria in the soil.
3.Conversion of ammonia to nitrites or nitrites to nitrates by different type of bacteria.
4.Nitrates to nitrogen in air by different bacteria.

(Q.) (a) Name three processes through which oxygen is used from the atmosphere and one process through which oxygen is returned to the atmosphere.
(b) Mention three ways by which carbon returns to the C-cycle.

 (Ans)  (a) Three processes by which oxygen is used from the atmosphere are:
1. Combustion
2. Respiration
3. Formation of oxides of nitrogen

The process by which oxygen is returned to the atmosphere is – photosynthesis.

(b) Three processes by which carbon is returned to the C-cycle are:
1. Both plants and animals release carbon dioxide to the atmosphere as a product of respiration.
2. By decomposition of organic wastes and dead bodies by decomposers.
3. By burning of fossil fuels like coal and petroleum.

 (Q.) Draw the labelled diagram of the O₂ cycle.

 (Ans)