Detailed explanations in West Bengal Board Class 6 Geography Book Solutions Chapter 5 Realms of the Earth: Water-Land-Air offer valuable context and analysis.
WBBSE Class 6 Geography Chapter 5 Question Answer – Realms of the Earth: Water-Land-Air
Objective Type Questions [1 mark each]
Question 1.
Which layer of atmosphere protects us from the harmful ultra-violet rays of the Sun?
Answer:
Ozone layer
Question 2.
What is the upper limit of the atmosphere?
Answer:
Exosphere
Question 3.
What is the percentage of oxygen gas present in the atmosphere?
Answer:
21 %
Question 4.
What name is given to zone of living things?
Answer:
Biosphere
Question 5.
Which hemisphere is called water hemisphere?
Answer:
Southern Hemisphere
Question 6.
Which is the largest ocean?
Answer:
Pacific Ocean
Question 7.
Which is the main source of water on earth?
Answer:
Ocean
Question 8.
What do you mean by Hydrosphere?
Answer:
Sphere of water.
Write short notes on : [2 marks each]
Question 1.
Pangaea.
Answer:
500 million years ago, the world map was not as it is today. There was one huge integrated landmass or mothercontinent called the Pangaea.
Question 2.
Continent.
Answer:
Landmasses of large extent are called the continent. There are seven continents of the earth. These are Asia, Africa, Europe, North America, South America, Australia and Antarctica.
Question 3.
Panthalassa
Answer:
The Pangaea was surrounded by the gigantic water body or Super Ocean called the Panthalassa.
Question 4.
Ozonesphere.
Answer:
This is a zone of ozone gas. It absorbs ultra-violet rays of the Sun. It has high temperature. Due to excessive use of chemicals and carbons, the ozone layer is being depleted.
Question 5.
Why is life possible on the earth?
Answer:
The earth is a unique planet. It has plenty of water. The earth has air. Oxygen and Nitrogen gases support life. All kinds of life depend upon water and air. First life on earth evolved in the water.
Question 6.
Why is the Biosphere important for living organism?
Answer:
Life exists in Biosphere. All the living organisms are interlinked for their survival. It consists of plants and animals. In this sphere of life, lithosphere, atmosphere and hydrosphere meet.
Question 7.
How are oceans useful to us ?
Answer:
- Oceans modify land temperature.
- Oceans are source of water vapour that causes rainfall.
- Oceans are means of transport.
Question 8.
What is isthmus ?
Answer:
An isthmus is a narrow strip of land joining two large landmasses or separating two large water bodies.
Question 9.
What is Gulf ?
Answer:
A deep inlet of the sea almost surrounded by land with a narrow mouth is called a gulf.
Question 10.
What is Bay ?
Answer:
A bay is wide covering indentation in a coastline.
Question 11.
What is strait?
Answer:
A strait is a narrow passage of water that connects two large navigable bodies of water.
Answer the following questions briefly : [2 marks each]
Question 1.
What do you mean by the term global warming ?
Answer:
The burning of fossil fuels (coal, gas, petroleum) the cultivation of soil, large scale industrialisation, rapid means of transport and deforestation has raised the average temperature of the earth by 0.5° C.
Question 2.
Why is the earth considered a unique planet?
Answer:
Our earth is considered a unique planet in the Solar System because this is the only planet where life is possible. The environmental conditions are favourable for the origin of life.
Question 3.
Define environment.
Answer:
surroundings of a place. The environment includes land, water and air and living objects like plants, animals and humAnswer: Both living and non-living objects are dependent on one another. Our environment
Identify the correct answers : [1 Mark each]
Question 1.
The earth comprises
(a) One realm
(b) Two realms
(c) Three realms
(d) Four realms
Answer:
(d) Four realms
Question 2.
The domain of the earth consisting of solid rocks is
(a) The Atmosphere
(b) The Hydrosphere
(c) The Lithosphere
(d) The Biosphere
Answer:
(c) The Lithosphere
Question 3.
The landmasses form about of the earth’s surface.
(a) 20 %
(b) 30 %
(c) 40 %
(d) 50 %
Answer:
(b) 30 %
Question 4.
The smallest continent of the world is
(a) Australia
(b) Antarctica
(c) Europe
(d) South America
Answer:
(a) Australia
Question 5.
Which is the largest continent?
(a) Africa
(b) Asia
(c) Australia
(d) Antarctica
Answer:
(b) Asia
Question 6.
The two most abundant gases in the atomosphere are
(a) Oxygen and Carbondi oxide
(b) Water vapour and Carbon dioxide
(c) Nitrogen and Water vapour
(d) Nitrogen and Oxygen.
Answer:
(d) Nitrogen and Oxygen.
Question 7.
The lowermost layer of atmosphere is the
(a) Stratosphere
(b) Exosphere
(c) Troposphere
(d) Mesosphere.
Answer:
(c) Troposphere
Question 8.
What is the percentage of Nitrogen gas present in atmosphere ?
(a) 18 %
(b) 38 %
(c) 58 %
(d) 78 %
Answer:
(d) 78 %
Question 9.
Atmosperic disturbances are found in
(a) Stratosphere
(b) Mesosphere
(c) Troposphere
(d) Lithosphere
Answer:
(c) Troposphere
Question 10.
Largest ocean is
(a) Atlantic Ocean
(b) Pacific Ocean
(c) Indian Ocean
(d) Arctic Ocean
Answer:
(b) Pacific Ocean
Fill in the blanks with correct words : 1 mark each.
1. The surface of the earth surrounded by a blanket of air is called ____.
Answer:
Atmosphere
2. Heights and depths of the landmasses are measured from the ____.
Answer:
Sea level
3. The big landmasses are called ____.
Answer:
continent
4. _____ is the largest continent.
Answer:
Asia
5. No permanent human settlement is on the continent of ____.
Answer:
Antarctica
6. ____ is the smallest continent.
Answer:
Australia or Oceania
7. The narrow zone of contact between the land, water and air is the ____.
Answer:
Biophere
8. The deepest point on the earth is ____ in the Pacific Ocean.
Answer:
Mariana Trench
9. The sphere of living things is called ____.
Answer:
Biosphere.
If the sentence is true, write ‘T’ and if false write ‘F’ against the following 1 mark each
1. Europe is the smallest continent.
Answer:
False
2. Oceans cover about 50 % of the earth’s surface.
Answer:
False
3. Nitrogen is the most abundant gas in the atmosphere.
Answer:
True
4. Africa is the second largest continent.
Answer:
True
5. The combined landmass of Asia and Europe is called Eurasia.
Answer:
True
6. The Arctic Ocean lies to the south.
Answer:
False
7. The Arctic Ocean in the North Polar Region is the smallest ocean.
Answer:
True
Realms of the Earth: Water-Land-Air Class 6 WBBSE Notes
Unique Planet: Our Earth is considered a unique planet in the Solar System because this is the only planet where life is possible. The environmental conditions are favourable for the origin of life.
Lithosphere: The solid layer of the earth’s surface is called lithosphere.
Hydrosphere: The surface of the earth that consists of water is known as Hydrosphere.
Atmosphere : The surface of the earth surrounded by a blanket of air is called the atmosphere.
Biosphere : The narrow zone of contact between atmosphere, hydrosphere and lithosphere results in the life which is called the Biosphere.
Introduction :
In this chapter you will study about the realms of the Earth, that is, the liquid hydrosphere (water), the solid lithosphere (land) and the gaseous atmosphere (air).
This will help to understand how the three spheres have together given rise to the Biosphere-the realms of living organisms and made the Earth a unique planet. Earth is the only planet of the solar system that supports life.
Our environment consists of these four realms or parts. The surface of the land consists of rocks and soils. This part of the environment is called the Lithosphere, meaning a layer of rocks. You know that oceans cover much larger area of the earth’s surface than landmasses. Water also occurs on the land and in the atmosphere as water vapour. This realm of water is called the Hydrosphere. There is an envelope of air around the Earth. This is called the Atmosphere. All forms of life occur in the narrow zones of containing various forms of life is called Biosphere. Though there are four realms in our environment, they are all interdependent on one another.
hydrosphere : Realm of water: The earth is commonly known as the blue planet. More than 71 per cent of its is covered with water and 29 per cent is covered with land. Hydrosphere consists of water in all its forms. The water cycle describes the continuous movement of water on, above and below the surface of the Earth. Water goes through changes of state and is converted to cloud, rain, ice or snow as it travels constantly from the air to the surface of the earth and back. This cyclic movement of water through the phases of nature is called the water cycle or the Hydrological cycle. As running water in oceans and rivers and in lakes, ice in glaciers, underground water and the water vapour in atmosphere, all comprise the hydrosphere.
More than 97 % of the Earth’s water is found in the oceans and is too salty for human use. A large portion of the rest of the water is in the form of ice sheets and glaciers or under the ground and a very small percentage is available as fresh water for human use. Hence, despite being a ‘blue planet’ we face a shortage of water!! Hydrosphere consists of oceans, seas, bays, gulfs and lakes.
Oceans : The oceans have a greater extent of water in the southern hemisphere than in the northern hemisphere. There are five oceans. These are the Pacific Ocean, the Atlantic Ocean, the Indian Ocean, the Arctic Ocean and the Antarctic Ocean.
The Pacific Ocean: It is the deepest ocean and the largest ocean. It covers nearly one-third of the Earth’s surface. In fact, it is so big that all the continents could easily fit into it.
The explorer Ferdinand Magellan named the ocean ‘Pacific’ meaning calm or tranquil. The International Date Line passes through the Pacific Ocean. The deepest part of the earth, the Mariana Trench, lies under this ocean. This ocean is bounded on the west by Asia and Australia and on the east by North and South Americas.
The Atlantic Ocean : It is the second largest ocean, about half the size of the Pacific Ocean and it is ‘S ‘ shaped. It is flanked by the North and South America on the Western side, and Europe and Africa on the eastern side. Some of the world’s best seaports (e.g., London, New York, Montreal) are along the Atlantic coast.
The Indian Ocean : The Indian Ocean is the only ocean named after a country. It is bordered by Africa on the west, Asia on the north and Australia in the east.
The Arctic Ocean : It is the smallest ocean and lies within the Arctic Circle. It extends into the Atlantic Ocean and the Bering Strait connects it with the Pacific Ocean.
Seas : The world’s largest seas include the South China Sea, the Caribbean Sea, the Mediterranean Sea and the Bering Sea. The Earth appears bright, blue from the space as three fourths of its surface is covered with water. This is why Earth is called the ‘Blue planet’. Around 3.5 billion years ago the first life on Earth was originated in water. 97 % of all the water on earth is in the oceans. The remaining 3 % is distributed in rivers, lakes, glaciers and underground water reserves.
Lithosphere : Realm of Earth consisting of rocks.
The word ‘Lithos’ means ‘stone’. The solid portion of the earth on which we live is called the Lithosphere. It comprises the rocks of the earth’s crust and the thin layers of soil that contain nutrient elements which sustain organisms.
There are two main divisions of the Earth’s surface. The large landmasses are called the continents and the huge water bodies are known as the ocean basins. All oceans of the world are connected with one another. Are all the landmasses connected with one another?
The level of seawater remains the same everywhere. Elevation of land is measured from the level of the sea, which is taken as zero. The highest mountain peak Mt. Everest is 8,848 metres above the sea level. The greatest depth of 11,022 metres is recorded at Mariana Trench in the Pacific Ocean. Could you imagine that depth of sea is much more than the highest point?
Continents : There are seven major continents. These are-Asia, Africa, North America, South America, Europe, Australia and Antarctica. All these continents are separated by large water bodies. Look at the world map and notice that the greater part of the landmass lies in the Northern Hemisphere.
Asia: It is the largest continent. It lies in the Eastern Hemisphere and covers about one third of the total land area of the earth. This continent is separated from Europe by the Ural mountains on the west. The Tropic of cancer passes through this continent. The combined landmass of Europe and Asia is known as Eurasia [Europe + Asia].
Asia is separated from Africa by Suez Canal.
Africa : It is the second largest continent after Asia. A large part of this continent lies in the Northern Hemisphere. The equator or 0° latitude passes through the middle of the continent. It is the only continent through which the Tropic of cancer (23 1/2° N) the Equator (0°) and the Tropic of capricorn (23 1/2° S) pass.
The world’s largest hot desert, the Sahara is located in this continent. It is bound on all sides by seas and oceans. Look at the map of world. The world’s longest river Nile, flows through Africa. Notice where Equator, the Tropic of cancer and the Tropic of capricorn pass in the map of Africa.
North America : It is the third largest continent of the world. It is completely lies in the Northern and Western Hemisphere. North America is linked to South America by a narrow strip of land known as the Isthmus of Panama. The continent is surrounded by three oceans namely the Pacific Ocean, the Atlantic Ocean and the Arctic Ocean.
South America : Most part of South America lies in the Southern Hemisphere. The World’s longest mountain range, the Andes, runs through its length from north to south. South America is the home of the world’s largest river, the Amazon River. Can you name the two oceans that surround it on the east and the west?
Europe : It is the sixth largest continent. This continent lies to the west of Asia and it is much smaller than Asia. It is bound by water bodies on three sides and the Arctic circle passes through this continent.
Australia : It lies entirely in the Southern Hemisphere. It is the smallest continent and is often called the “Island continent”, as it is surrounded by water.
Antarctica : It is entirely in the Southern Hemisphere. It is frozen land found around the south pole. It contains 75 % of the ice in the world. It is estimated that the ice is about 4 km thick.
Hence, Antarctica is called the “Frozen Continent”. There are no permanent human settlements. Many countries have research stations in Antarctica. India also has research stations in Antarctica. These are named as Maitri and Dakshin Gangotri.
Continental Drift : 500 million years ago, the world map was not as it is today. There was one huge integrated landmass or mother-continent called the Pangaea. It was surrounded by the gigantic water body or super ocean called the Panthalassa. The Pangaea started breaking up about 200 million years ago. Tectonics meaning building activity is the bases of the Theory of Continental Drift. 100 million years hence the world map can actually appear much much different from what it is today.
Planet Earth is enveloped by a thin blanket of gases, which we call the atmosphere. It is composed of three elements-gases, water vapour and dust particles. The atmosphere is composed mainly of nitrogen and oxygen, which make up about 99 per cent of clean, dry air. Nitrogen 78 %, Oxygen 21 % and other gasses like carbon dioxide, argon and others comprise 1 % by volume. Nitrogen helps in the growth of living organisms while oxygen is the breath of life.
The atmosphere appears to be very thin but there are actually seven or more layers in the atmosphere-each with its own characteristic.
Layers of Atmosphere : Three important layers are :
1. Troposphere : I extends upto 20 km above the ground and contains air.
2. Stratosphere: It extends from 20 to 50 km above the ground and contains the Ozone layer.
3. Ionosphere : It extends from 80 to 450 km above the ground. It contains electrically charged gas particles (ions) that reflect radio waves. Hence this layer is important for communications.
Humidity and Atmosphere: The amount of water vapour present in the air determines the humidity of the air. It varies from time to time and from place to place.
Humidity decreases with height in the troposphere because water enters the atmosphere through evaporation from the Earth’s surface. Higher the temperature, faster is the rate of evaporation.
Density of the Atmosphere : Air is a homogeneous mixture of gases. Due to the gravity of the Earth, this air, which is easily compressible, is squashed nearer the surface of the Earth. Therefore. the atmosphere is densest near the surface, i.e., nearly 80 % of the atmosphere is in the Troposphere, giving it the highest value of density. As altitude (height) increases, the density decreases.
Pressure and Atmosphere : Air may seem weightless but it is not. Gravity pulls the atmosphere down to the Earth. This is air pressure. Atmospheric pressure is defined as the weight of a column of air. The higher we go, there are less air. Hence the pressure decreases the altitude increases.
Temperature Distribution and Atmosphere: The Earth’s atmosphere is heated by the heat absorbed by the gas molecules and impurities like dust particles present in the air. Within the troposphere, temperature decreases evenly with increase in height.
Biosphere : Realm of Living Organism
Earth is the only planet of the solar system that supports life. Life is possible because of its unique hydrosphere, lithosphere and atmosphere.
The Lithosphere: The upper most layer of the Earth’s crust which is capable of supporting life is called soil. The soil provides nutrients for land organisms. It is also the medium for the fixation of plants. Minerals are cycled through the soil.
Hydrosphere: The water dissolves and supports nutrients. Water is used by plants for making food. It is also necessary for carrying out the chemical reactions within the body of living organisms.
Atmosphere : It maintains an even life supporting temperature on the earth. It (Ozone layer of atmosphere) protects living organisms from the harmful ultra-violet radiations of the Sun. The gases (O2 and CO2) present in air supporting life. Oxygen (O2) helps in respiration, carbon dioxide (CO2) in food manufacture by green plants and nitrogen in growth.
There are several species of organism that vary in size from microbes and bacteria to huge mammals.All the living organisms including humans are linked to each other and to the biosphere for survival. Biosphere supports about 10,00,000 varieties of animals and 3,00,000 varieties of plants. It includes minutes bacteria as well as huge trees and whales. The non-living component includes lithosphere, hydrosphere and atmosphere. It is known as physical environment.
The non-living organisms are broadly divided into two groups i.e. Plant Kingdom and Animal Kingdom. Plants produce their own food by the process of Photosynthesis, which is possible because of the solar energy. Animals cannot produce their own food themselves. They are dependent upon the plants directly or indirectly. All the food for the animals come from the vegetal world directly or indirectly. Man, being a part of the biosphere is also dependent upon the biosphere for his major needs.
What is Biosphere?
The narrow zone of contact between the land (lithosphere), water (hydrosphere) and air (atmosphere) is the biosphere. It is in this zone that life, that is unique to this planet, exists. Bios is an ancient Greek word meaning ‘life’. Life is biosphere is possible only because of a proper balance between land, water and air. Life exists on and in the ground (land), in water and in the air, the biosphere can be defined as the relatively narrow belt of living organisms found a little above the surface and a little below the surface of the Earth.