Thursday 7 February 2013

CBSE Class 9 - Science - CH 14 Natural Resources (NCERT Q and A)

Natural Resources

(Q & A, NCERT Chapter Solution)
CBSE Class 9 - Science - CH14 - Natural Resources (Worksheet)
Ozone Layer

Q1: What is lithosphere?

Answer:  The outer crust of the Earth is called the lithosphere.

Q2: What is hydrosphere?

Answer: The water available on the earth's surface as well as underground water comprise together as hydrosphere. Water covers 75% of the Earth's surface.

Q3: What is the atmosphere?

Answer: The envelope of air that surrounds the earth is called atmosphere.

Q4: List the four zones of the atmosphere.

Answer: Four zones of the atmosphere are:
  1. Troposphere
  2. Stratosphere
  3. Mesosphere
  4. Thermosphere

Q5:  What is biosphere?

Answer: This life-supporting zone of the Earth where the atmosphere, the hydrosphere and the lithosphere interact and make life possible, is known as the biosphere. It accommodates several types of living organisms which remain dependent on natural resources. The biosphere ranges between 6km, above sea level and 10kms below the sea.

Q6(NCERT): How is our atmosphere different from the atmosphere on Venus and Mars?

Answer: Earth's atmosphere is quite different from the atmosphere present on Venus and Mars. The atmosphere of the earth consists of Nitrogen(79%), Oxygen(20%), a small fraction of carbon dioxide and other gases which make it suitable for living. The atmosphere of Venus or Mars has carbon dioxide as the major component  (95-97%)

Q7(NCERT): How does the atmosphere act as a blanket?

Answer: The atmosphere acts as a blank due to its following functions:
  1. It plays an important role in temperature control. It maintains the average temperature of the earth fairly constant during the course of the whole year.
  2. It prevents the sudden increase in temperature during the daylight hours.
  3. During the night, it slows down the escape of heat into outer space.

Q8(NCERT): What causes winds?

Answer: Uneven heating of the earth's surface and water surface causes winds. On heating up the air rises up creating a low-pressure region. Air travels from high-pressure region to low-pressure region forming winds. In addition, the rotation of the Earth and the presence of mountain ranges in the paths of the wind also influence to winds.

Q9(NCERT): How are clouds formed?

Answer: Due to various weather phenomena (e.g. uneven heating of land and water bodies on the earth surface), warm and cold convection of air currents generated. Water vapours which are also present in the air due to evaporation also rise up. Since air cools down on rising, it leads to condensation of water vapours present in it. Thus vapours condense onto tiny salt particles called condensation nuclei which form clouds.
Nimbostratus (image credits:wikipedia)

Broadly clouds formed are of four types:
  1. Nimbostratus: (Nimbus means rain). These clouds carry thick precipitation or rains.
  2. Altostratus: These clouds form a foggy, grey and dull weather look.
  3. Cirrostratus: these clouds form fluffy cotton like pattern. 
  4. Cirrus: These are high-level clouds seen during fair weather.

Q10: Which gets heated faster land or water?

Answer: Land

Q11: Define air-pollution?  (Short Answer Q)

Answer: An increase in the content of these harmful substances in the air is called air pollution.

Q12(NCERT): List any three human activities that you think would lead to air pollution.

Answer: Three human activities leading to air pollution are:
  1. Rapid urbanization and industrialization.
  2. Deforestation
  3. Burning of fuels like coal and petroleum.
  4. Burning of coal in thermal power plants.

Q13(CBSE 2011): Name two diseases caused due to an increased content of pollutants in the air produced due to the burning of fossil fuels. 

Answer: Bronchitis, asthma, lung cancer.

Q14(CBSE 2011): What is smog?

Answer: Smoke + Fog = Smog. The presence of unburnt hydrocarbons in the air, when mixed with condensed water vapours, forms a thick layer called smog. It lowers the visibility during the winter season and is an indication of air pollution.

Q15: How do fossil fuel cause air pollution?

Answer: The fossil fuels like coal and petroleum contain traces of nitrogen and sulphur. When these fuels are burnt, nitrogen and sulphur too are burnt and this produces different oxides of nitrogen and sulphur. These oxides of nitrogen and sulphur are poisonous and can cause respiratory problems. These oxides when mix with rainwater give rise to acid water due to the formation of nitric and sulphuric acids.

Q16(Value Based): Meenakshi saw a reduction in the greenish layer of lichens at the bark of trees at the biology garden of the school. The garden was few metres away from diesel generator placed for electricity back up. She immediately informed the school authorities to check the pollution level of diesel and kerosene used in the generator. 

(a) How reduction in Lichens layer is related to pollution?
(b) What measures should be taken by school authorities to check the reduction?
(c) What qualities are shown by Meenakshi by informing the school about the Lichens?

(a) Lichens are found to be very sensitive to the levels of contaminants like sulphur dioxide in
the air. Diesel and Kerosene contain traces of nitrogen and sulphur which for deadly oxides when mixed in the air.

(b)  School authorities should check the pollution level and quality of fuel used in a diesel generator. They should also replace the generator with a better which does not pollute the environment. The generator should be placed away from the school premises to avoid inhalation of smoke from it.

(c) She is concerned about air pollution and showed her social responsibility to keep the environment clean and pollution free.

Q17: Give an example of fungi which are known as 'indicator of air pollution'.

Answer: Lichens.

Q18(NCERT): Why do organisms need water?
Q(NCERT): Why is water essential for life?
Q(CBSE 2011): Water is known as ‘A Wonder Liquid’. Justify this statement by giving any two reasons.

Answer:  Water is an essential part of living organisms:
  • Most of the biochemical processes involve water e.g. photosynthesis takes water as one of the raw material to prepare food.
  • The major component of blood is water (plasma) which helps in the transportation of food and excretory substances.
  • Water is used as part of food as a source of energy.
  • Water in sweat cools down the body temperature. Similarly, water as transpiration loss in plants controls the temperature of the plant as well as it helps in the ascent of sap.
  • Water is used in many activities like drinking, food preparation, irrigation, power generation and industries.
  • Water is an essential medium for aquatic life. Amphibians also need water to carry out reproduction.
  • Water is a universal solvent hence it is used in medicines and a many chemical reaction takes place when dissolved in water.
  • Water makes up 70% of body weight of human beings and it carries out various metabolic activities in all animals. 

Q19: What are the effects of acid rain?

Answer:  Effects of acid rain are:
  • Acidification of soil reduces the fertility of the soil.
  • Destroys aquatic life and pollutes water resources. 
  • Causes irritation to eyes and skins of human beings and cattle.
  • Causes corrosion to buildings, bridges, statues etc.

Q20: What are biogeochemical cycles? Names two examples.

Answer: Biogeochemical cycles are the cyclic pathways through which chemical substances move through the biotic environment (biosphere) and abiotic environment (lithosphere, atmosphere and hydrosphere) components of the earth.

A few examples of biogeochemical cycles are:
  • Water Cycle
  • Nitrogen Cycle
  • Carbon Cycle
  • Oxygen cycle

Q21(CBSE 2013-14): In which regions is soil erosion very difficult to revert?

Answer: The regions with bare vegetation, mountains and hilly regions, soil erosion is very difficult to reverse.

Q22(CBSE 2013-14): What is meant by depletion of ozone layer? Mention one important feature of ozone in the atmosphere. Identify the factors responsible for the formation of the ozone hole. 

Answer: The part of the atmosphere, at height 320 km above sea level, there is a 5km thick ozone layer. This layer acts as a shield/ blanket which absorbs UV radiations from sunlight. Thus it saves biotic life on the earth from the harmful effects of UV radiation.

Over Antarctica, there is declining ozone layer thickness and hole is seen. If depletion of ozone layer dwindles further, it would have severe consequences on the lives of living beings.

Following are the main chemicals responsible for the destruction of the ozone layer:

1. chlorofluorocarbons(CFCs)
2. halogens (used in fire extinguishers)
3. methane and nitrous oxide

CFCs used as propellants in aeroplanes and coolant in refrigeration are the most damaging, which catalytically destroy ozone and convert it into oxygen.

Q23(NCERT): What is the major source of freshwater in the city/town/village where you live?

Answer: In city/town/village, the major source of water is underground water. It is drawn with
the help of hand pumps and tube-wells. The other nearby sources are rivers, lakes and ponds.   

Q25: How is soil formed?

Answer: The formation of the soil takes place in the following ways:

(i) Rocks near the surface of Earth are broken down by various physical, chemical and some biological processes. This process takes millions of years.

(ii) This weathering leads to the formation of fine particles called soil.

(iii) Some other factors also lead to the formation of soil. These are:
  (a) Sun causes heating of rocks that causes cracking and breaks down them into small particles.
  (b) Water dissolves into rocks by freezing and fast flowing.
  (c) Wind causes erosion of rocks by fast blowing.
  (d) Liches and mosses grow on rock surfaces and break them into powder down and form a thin layer of soil. The big trees sometimes enter into cracks in the rocks and force them to break further during their growth.

Q26: List any three human activities which would lead to an increase in the carbon dioxide content of the air.

Answer: The human activities which would lead to an increase in the CO2 content of air are:
(i) Respiration is the natural way to release of CO2 by both plants and animals. It is balanced by the release of oxygen by plants. So, it is not harmful to the environment.

(ii) Deforestation increases the level of CO2 in the environment. Trees carry out photosynthesis and convert CO2 into organic compounds such as glucose, starch, etc. In their absence, CO2 cannot be utilized.

(iii) Combustion of fuels leads to an increase in CO level in the atmosphere. Fuels are burnt to carry out activities like cooking, transportation and in industrial processes.


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