Chapter 14 : Natural Resources - Ncert Solutions for Class 9 Biology CBSE

Biology is the study of life. It is the study of living organisms and how they interact with the environment. Biology recognizes the cell as the basic unit of life, genes as the unit of heredity and evolution as an engine which boosts the formation of new species. The study of life has helped in shaping the world. It has credible answers to why things happen in a scientific manner.

TopperLearning is a platform where students of CBSE Class 9 Biology can study various behaviors of living beings and discover interesting facts as well. Let’s learn and appreciate together the diversity of nature.

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Chapter 14 - Natural Resources Excercise 193

Solution 1
Atmosphere of Venus and Mars:
 
(i) Consists of 95-97% carbon dioxide,   
(ii) Life supporting gases are not present there.
 
Atmosphere of Earth:
 
(i) Consists of a mixture of many gases like oxygen, nitrogen, carbon dioxide and water vapours which are life supporting gases.
(ii) Carbon dioxide is green house gas which maintains temperature on earth during night.
(iii) Oxygen is needed by organisms for survival.
 

Concept insight: Recall the difference in the composition of the atmosphere of Venus and Mars.

Solution 2
The atmosphere prevents the sudden change in temperature during the daylight hours and during the night.
 
It is because air is a bad conductor of heat and our atmosphere contains mainly the air. Thus the atmosphere keeps the average temperature of earth fairly steady.
 
Concept insight: Recall the uses of atmosphere.

Solution 3
Winds are caused due to unequal heating of atmospheric air in different regions of the earth.
 
This phenomenon can be easily seen near the coastal regions during the daytime. The air above the land gets heated faster as compared to the air above water and starts rising. As this air rises, a region of low pressure is created and air over the sea moves into this area.     
 
In the same way, during the day, the air over the sea moves to the land. These air movements cause winds.
 
Concept insight: Recall the difference in the heating of the earth's atmosphere at different places.
Solution 4
During evaporation, water from various sources goes into the air. Due to heat, the air also gets heated and starts rising up, taking along water vapours.
 
The rising air expands and cools, and this cooling causes the water vapours in the air to condense. This condensation of water is facilitated if some particles like dust or the air are available to act as the nucleus for these drops to form around. 
 
These tiny droplets grow bigger due to more and more condensation of other droplets and form clouds.                         
 
Concept insight: Recall the different phases of water cycle.

Solution 5
Three major human activities which are causing air pollution are:

i. Excessive use and burning of fossil fuels like coal and petroleum.
ii. Deforestation.
iii. Smoke from industries and automobiles.
 

Concept insight: Students should recall the major causes of air pollution.

Chapter 14 - Natural Resources Excercise 194

Solution 1
Importance of water:
 
(i) Around 60-70% of our body is made up of water.
(ii) All the substances are transported in the body in dissolved state in water.
(iii) All the metabolic activities require water.     
 
Concept insight: Recall the functions of water in living organism's life.
Solution 2
The major source of fresh water in the city where I live is the underground water which is taken out by tube wells and at household level by hand pumps.
 
Also, huge tanks have been built by the municipal department from where it is supplied to various households through a network of pipelines.
 
Apart from that, the rivers flowing in the nearby areas and ponds also serve as a source of fresh water.
Concept insight: Recall the various sources of fresh water.
Solution 3
 Activities due to which water sources are being polluted are:

(i) Dumping of sewage and wastes from factories into water bodies.
(ii) Washing clothes and bathing at river shores also pollutes water.
(iii) Dumping of hot water from the cooling towers also affect the aquatic life.
 
Concept insight: List the main causes of water pollution.

Chapter 14 - Natural Resources Excercise 196

Solution 1
Soil is formed by the process of weathering.
 
The following factors help in the weathering of rocks:
  1. Sun- Sun rays heat the rocks during the day time which causes the rocks to expand. During night, the rocks cool and contract. Due to this contraction and expansion cracks develop in the rocks and they break down.
  2. Water- Water helps in the formation of soil both by freezing as well as fast flow. Water freezes in the rock crevices and widens the crack causing the rocks to break. Fast flowing water causes the rocks to break slowly and also carries it from one place to another.
  3. Wind- Under the effect of strong winds and storms, the stone pieces further break down and are also carried from one place to another.        
  4. Living organisms- Lichens grow on rock surfaces and release certain substances that convert the rocks into powdery form and make thin soil layer. Other small plants like mosses grow on the surface of rocks that cause them to break further.

Concept insight: Recall the factors and process of soil formation.

Solution 2

The removal of the fertile top soil is called soil erosion.

Concept insight: Recall the definition of soil erosion.

Solution 3
The various methods for preventing or reducing soil erosion are:

i. By preventing over grazing.
ii. By planting more and more trees, as the roots of the trees hold the soil in place.
iii. By contour ploughing.
iv. By keeping the vegetation cover on the ground to reduce the effect of wind and  water.   
v. By reducing use of chemical fertilizers and using manure and practicing organic farming.
 

Concept insight: List the causes and methods to prevent soil erosion.

Chapter 14 - Natural Resources Excercise 201 (Ex.)

Solution 1
Atmosphere is essential for life because of the following reasons:
i. It acts as a blanket and keeps the average temperature of the earth fairly steady as it prevents the sudden increase in temperature during the day and slows down the escape of heat into outer space during the night.
ii. It contains all the gases which are essential for sustaining life on the earth.
iii. Ozone present in the atmosphere prevents UV rays from reaching the earth, which are very harmful to us.
iv. Winds are generated due to the movement of air present in the atmosphere, and rain and rainfall patterns are decided by these winds.
v. Water cycle is not possible without atmosphere.
 
Concept insight: Recall the importance of atmosphere.
Solution 2
Water is important due to the following reasons:
(i) It constitutes 60-70% of our body.
(ii) Water is necessary for all metabolic activities in the body.
(iii) It is required for transport of substances in the body.
(iv) It helps in maintaining body temperature.
 
Concept insight: List the various uses of water in our day to day life activities.
Solution 3
Living organisms are dependent on the soil because of the following reasons:
i. All the plants, (even aquatic), on which almost all the organisms depend directly or indirectly for food, grow in the soil, which provides them with nutrients and water.
ii. Soil also supports the existence of forests, which provide us with wood, building material, fiber and medicinal plants. Forests are also natural habitat for large number of animal species.
iii. A number of insects and animals make their homes in the soil.

The organisms that live in water are not totally independent of soil as a resource. The mineral nutrients are present in water in the dissolved form. But their recycling takes place with the help of decomposers that are present in soil. Water bodies like rivers get supply of minerals from the soil. Moreover, the minerals locked in rocks also can't reach aquatic organisms till rocks are converted into soil.

Concept insight: Importance of soil as a natural resource.

Solution 4
Weather of a place is determined by many elements like speed and direction of wind, temperature, air pressure, rainfall, relative humidity and oceanic features.
 
All these informations are collected by meteorological department through remote sensing and weather forecasting satellites which are then transformed into a weather report. This collective information helps us to predict the weather of a place.
 
Concept insight: Recall the various elements of weather.

Chapter 14 - Natural Resources Excercise 201

Solution 1
During the water cycle, water is found in all the three states, i.e., solid (ice, snow, hail or sleet), liquid and gaseous (water vapours).
 
Concept insight: Student should remember the various stages of water cycle.

Solution 2
Two biologically important compounds that contain both nitrogen and oxygen are proteins and nucleic acids (DNA and RNA).
Concept insight: Important from Exam point
Solution 3
Following are the activities:
i. Burning of fossil fuels like coal and petroleum.
ii. Industrialization.
iii. Deforestation, due to which the utilization of atmospheric CO2 during photosynthesis is reduced to a great extent because of the reduction in the number of plants and trees.
Concept insight: List the causes of air pollution.
Solution 4

The increase in the percentage of the gases which prevent the escape of heat from the earth, which cause the average temperatures to increase worldwide is called greenhouse effect.

Concept insight: Most popular Exam question from this topic.

Solution 5
In the atmosphere oxygen is found in two forms:
i. Diatomic molecule having two oxygen atoms (O2) and found in the lower regions of the atmosphere.
ii. Triatomic molecule having three oxygen atoms (O3) also called as ozone and is found in the upper regions of the atmosphere.

Concept insight: Various forms of oxygen in atmosphere.

Chapter 14 - Natural Resources Excercise 202 (Ex.)

Solution 1
Isolating the human activities that lead to increasing pollution would not help in reducing pollution because air, water and soil are interrelated. They cannot be limited to a certain area.
 
For instance, if air in an area is polluted with certain pollutant, say CO2, it will get warmed. So, it will rise and air from the surrounding areas will move in there. Thus, CO2 will spread in the atmosphere. Other air pollutants also diffuse in the atmosphere.
 
Water pollution causes decrease in the level of oxygen dissolved in water. This causes the death of aquatic life forms. This, in turn, affects the food chains and food webs in some other areas. Thus, by limiting different human activities to specific areas the problem of pollution can't be resolved.   
 
Concept insight: Correlate how human activities and pollution of air, water and soil are interlinked.             
Solution 2
Forests influence the quality of our air, soil and water resources in the following ways:
 
(i) Forests maintain the balance between carbon dioxide and oxygen. The plants present in forests need CO2 for photosynthesis and release oxygen during this process. Thus, oxygen consumed during respiration and combustion is returned by forests.

(ii) Forests prevent soil erosion. The roots of plants hold soil tightly and prevent it from being eroded away. Moreover, forest trees also check the speed of wind and running water.
 
(iii) Forests are also essential for replenishing the water sources. They play an important role in maintaining water cycle by transpiration.
 
Thus, forests affect the quality of air, water and soil.
     

Concept insight: Effects of forest on the climate of a region.

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