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Chapter-Review

• Life on Earth depends on resources like soil, water and air, and energy from the Sun.
• We need to conserve our natural resources and use them in a
  sustainable manner.
• Water covers 75% of the Earth’s surface.
• The air that covers the whole of the Earth like a blanket, is called
  the atmosphere.
• 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.
• Living things constitute the biotic component of the biosphere.
• The air, the water and the soil form the non-living or abiotic component of the biosphere.
• Air is a mixture of many gases like nitrogen, oxygen, carbon dioxide and water vapour.
• Carbon dioxide constitutes up to 95-97% of the atmosphere on Venus and Mars.
• Eukaryotic cells and many prokaryotic cells need oxygen to break down glucose molecules and get energy for their activities.
• The process which results in the consumption of oxygen and the concomitant production of carbon dioxide is combustion.
• Carbon dioxide is ‘fixed’ in two ways: (i) Green plants convert carbon
  dioxide into glucose in the presence of Sunlight and (ii) many marine animals use carbonates dissolved in sea-water to make their shells.
• Air is a bad conductor of heat.
• The atmosphere keeps the average temperature of the Earth fairly steady during the day and even during the course of the whole year.
• During the night, atmosphere slows down the escape of heat into
  outer space.
• The surface of moon has the temperature ranges from -119^० C to 110^० C due to no atmosphere. 
• Uneven heating of air over land and water-bodies causes winds.
• Evaporation of water from water-bodies and subsequent condensation give us rain.
• Water vapour is formed due to the heating of water bodies and the activities of living organisms.
• The atmosphere can be heated from below by the radiation that is
  reflected back or re-radiated by the land or water bodies. On being heated, convection currents are set up in the air.
• Rainfall patterns are decided by the prevailing wind patterns.
• The hot air rises up carrying the water vapour with it.
• The fossil fuels like coal and petroleum contain small amounts of nitrogen and sulphur.
• On burning fossil fuels produces different oxides of nitrogen and sulpher. 
• Oxides of sulpher and nitrogen 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 hight levels of pollutants in fog cause visibility to be lowered, this is known as smog. This indicates air pollution. 
• An increase in the content of harmful substances in air is called air
  pollution.
• Water occupies a very large area of the Earth’s surface and is also found underground.
• Most of the water on Earth’s surface is found in seas and oceans
  and is saline.
• Fresh water is found frozen in the ice-caps at the two poles and on snowcovered mountains. The underground water and the water in rivers, lakes and ponds is also fresh.
• All cellular processes take place in a water medium.
• All the reactions that take place within our body and within the cells occur between substances that are dissolved in water.
• Substances are also transported from one part of the body to the other in a dissolved form.
• organisms need to maintain the level of water within their bodies in order to stay alive.
• Terrestrial life-forms require fresh water for  because their bodies cannot tolerate or get rid of the high amounts of dissolved salts in saline water.
• The quality of the topsoil is an important factor that decides
  biodiversity in that area.
• The sun, water, wind and some living organism like Lichen help in formation of soil.
• Removal of surfaces of soil by water and wind is known as soil erosion.  
• The upper most layer of earth contains bits of decayed living organisms which is called humus.
•  Humus is a major factor in deciding the soil structure because it causes the soil to become more porous and allows water and air to penetrate deep underground.
• The mineral nutrients that are found in a particular soil depends on the
  rocks it was formed from.
• The topmost layer of the soil that contains humus and living organisms in addition to the soil particles is called the topsoil.
• The quality of the topsoil is an important factor that decides biodiversity in that area.
• Use of large amounts of fertilizers and pesticides over long periods of time can destroy the soil structure by killing the soil micro-organisms that recycle nutrients in the soil.
• The roots of plants have an important role in preventing soil erosion.
• The water-cycle, the nitrogen-cycle, the carbon-cycle, the oxygen-cycle are parts of biogeochemical cycles. 
• Nitrogen gas makes up 78% of our atmosphere and nitrogen is also a part of many molecules essential to life like proteins, nucleic acids (DNA and RNA) and some vitamins.
• Nitrogen-fixing bacteria fixes atmospheric nitrogen to ntrates and nitrites. 
• Plants generally take up nitrates and nitrites and convert them into amino acids which are used to make proteins.
• All life-forms are based on carbon-containing molecules like proteins, carbohydrates, fats, nucleic acids and vitamins.
• The endoskeletons and exoskeletons of various animals are also
  formed from carbonate salts.
• The process of photosynthesis converts carbon dioxide from the atmosphere or dissolved in water into glucose molecules.

Text-book question with solutions:

Page (193).

Q1. How is our atmosphere different from the atmosphere on Venus and Mars? 

Ans: Earth's atmosphere is quite different from the atmosphere present on Venus and Mars. The atmosphere of earth consisits of Nitrogen 79%, Oxygen 21% and Carbon dioxide in very less percentage. Venus and Mars, where no life is known to exist, the major component of the atmosphere is found to be carbon dioxide. In fact, carbon dioxide constitutes up to 95-97% of the atmosphere on Venus and Mars.

Q2. How does the atmosphere act as a blanket?

Ans: The air is bad conductor of temperature. It keeps constant the average temperature of the earth during the day and the whole year. It regulates the raising day temperature. Thus the atmosphere act as a blanket. 

Q3. What causes winds?

Ans: The uneven heating of the atmosphere in different regions of the Earth like earth's surface and water surface cause winds. On heating up the air creating a low pressure region. The movement of air from high pressure region to low pressure region creates winds.

There are other factors that enfluence these winds: 

(i) The rotation of the Earth.

(ii) The presence of mountain ranges in the paths of the wind.

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.

Q4. How are clouds formed? 

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. Thus vapours condense onto a tiny droplets salt particles called condensation nuclei which form clouds. 

Q5.  List any three human activities that you think would lead to air pollution.

Ans: Three human activities leading to air pollution are as follows;

        (i) Combustion of fossil fuels like coal and petroleum. 

       (ii) Deforestaion that causes reduction of carbon dioxide utilisation. 

      (iii) Toxic smoke of industries and colloidal particles of incomplete

            combustion of carbon smog and fog.

Page 194. 

Q1. Why do organisms need water?

Ans: Organisms need water because;

(i) All cellular processes take place in a water medium.

(ii) All the reactions that take place within our body and within the cells occur between substances that are dissolved in water.

(iii)  Substances are also transported from one part of the body to the other in a dissolved form.

(iv) Hence, organisms need to maintain the level of water within their bodies in order to stay alive.

Q2. What is the major source of fresh water in the city/town/village where you live?

Ans: River and ground water. 

Q3. Do you know of any activity which may be polluting this water source?

Ans: There are following activities that polluting this water source.

(i) Adding poisonous and harmful chemical substances used by industries. 

(ii) Leaving dead and decay body into rivers.

(iii) Human activities like washing clothes, adding home wastes and sewage water etc. 

Page 196.

Q1. How is soil formed?

Ans: The rocks at or near the surface of the Earth are broken down by various
physical, chemical and some biological processes. This broken down rocks fine particles forms soil. 

Q2. What is soil erosion?

Ans: The upper most layer of soil contains humus and it is quite fertile. It is also lighter. Sometimes soil of this layer carried out by water or wind. The process of removing of soil surfaces is known as soil erosion.  

Q3. What are the methods of preventing or reducing soil erosion?

Ans: Deforestation is the main couse of soil erosion, so preventing or reducing this we should encourage the plantaion in very large scale. Because the roots of plants ties soil and it stops the removal of soil surface.   

Page 201.

Q1. What are the different states in which water is found during the water cycle?

Ans: The different states in which water is found during the water cycle,

Soild, Liquid and Gas

Q2. Name two biologically important compounds that contain both oxygen and nitrogen.

Ans: 

(i) Amino acids

(ii) Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA)

Q3. List any three human activities which would lead to an increase in the carbon dioxide content of air.

Ans: 

(i) Excessive using/burning fossil fuels in various process like coal, petrolium and industrial uses.  

(ii) Release of harmful gases from vehicles.

(iii) Human Induces forest in fire and deforestaion causes decreased uptake of carbon dioxide and releasing of oxygen. 

Q4. What is the greenhouse effect?

Ans: Some gases like carbon dioxide, methane, carbon monooxide and nitrous oxide absorb heat present in atmosphere and prevent the escape of heat from the Earth. ​This heat is trapped by our atmosphere. This is an atmospheric phenomenon.  An increase in the percentage of such gases in the atmosphere would cause the average temperatures to increase worldwide and this is called the greenhouse effect.

Q5. What are the two forms of oxygen found in the atmosphere?

Ans: The two forms of oxygen found in atmosphere are as follows;

(i) Diatomic molecular atom with chemical formula O₂.

(ii) Triatomic molecular atom with chemical formula O₃.

Exercise:

Q1. Why is the atmosphere essential for life?

Ans: Atmospher is very essential for life because of following reasons;

(i) It keeps the avearge temperature of earth rather steady. 

(ii) Oxygen is available from atmosphere in the form of life air. 

(iii) Ozone layer of our atmosphere protect us from harmful radiation coming from the sun. 

Q2. Why is water essential for life?

Ans: Water is essential for life because;

        (i) All cellular processes take place in a water medium.

       (ii) All the reactions that take place within our body and within the cells

            occur between substances that are dissolved in water.

       (iii) Substances are also transported from one part of the body to the

             other in a dissolved form.

       (iv) organisms need to maintain the level of water within their bodies in

             order to stay alive.

Q3. How are living organisms dependent on the soil? Are organisms that live in water totally independent of soil as a resource?

Ans: Living organisms dependent on soil because; 

(i) Soil is an important resource that decides the diversity of life in an area.

(ii) The minerals found in this upper layer (Crust) supply a variety of nutrients to life-forms.

(iii) Soil also contains various forms of microscopic life and they get their all forms of need from soil. 

(iv) All green plants grow in soil those are used as food energy by animals. 

Q4. You have seen weather reports on television and in newspapers. How do you think we are able to predict the weather?

Ans: 

Q5. We know that many human activities lead to increasing levels of pollution of the air, water-bodies and soil. Do you think that isolating these activities to specific and limited areas would help in reducing pollution?

Ans: 

Q6. Write a note on how forests influence the quality of our air, soil and water resources.

Ans: 

(i) Forests is one of the most important natural resource. Forests also keep balance between carbon dioxide and oxygen. They take CO₂ for photosynthesis and release oxygen from this process. In another process called respiration they take O₂ and release CO₂.

(ii) Forests prevent soil erosion. the roots of plants hold soil tightly and prevent thier removal by water and wind. Their dead and decay leaves form humus for soil and gain fertility.   

(iii) Forests play an important role in maintaining water cycle by transpiration. In the process of transpiration they release water vapour.