15 January, 2015

Class VII: Chapter 6 - Natural Vegetation and Wildlife

Meaning of Natural Vegetation: Natural vegetation refers to a plant community which has grown naturally without human aid and has been left undisturbed by humans for a long time.

Thus, cultivated crops and fruits, orchards form part of vegetation but not natural vegetation.

The type and thickness of natural vegetation varies from place to place because of the variation in these factors. Natural vegetation is generally classified in to three broad categories as follows:

(a) Forests: Which grow where temperature and rainfall are plentiful to support a tree cover. Depending upon these factors, dense and open forests are grown.
(b) Grasslands: Which grow in the region of moderate rain.
(c) Desert Shrubs: Thorny shrubs and scrubs grow in the dry

 

Factors affecting the natural vegetation and wildlife:

1. Rainfall & Temperature
2. Relief
3. Soil & its fertility
4. Slope of land
5. Sunshine
6. Drainage

 

Types of Natural Vegetations:

 

FORESTS

Tropical Rainforests:
These forests are also called Tropical Evergreen.

Location:

  • Forests found near the Equator (10° North to 10° South) in Amazon & Zaire Basin and Southeast Asia.

Climate:

  • These regions are hot and receive heavy rainfall throughout the year.

Characteristics:

  • As there is no particular dry season, the trees do not shed their leaves altogether. This is the reason they are called evergreen.
  • Maximum varieties of trees are found. Trees are tall with large trunks.
  • The thick canopies of the closely spaced trees do not allow the sunlight to penetrate inside the forest even in the day time. Thus, grass is not found in these forests.
  • Hardwood trees like rosewood, teak, sal, ebony, and mahogany are the common trees found here.
  • Here the population found is very less. Due to dense forests commercial exploitation of these forests has not be possible, making them economically backward.

Wildlife:

  • Large variety and most colourful animals are found here.
  • Monkey, Ape, Birds, Hippopotamus, snake, python, Frog, Crocodile, etc. Anaconda, world's largest snake is also found in these areas.

 

Tropical Deciduous Forests:
These forests are also called Monsoon Forests.

Location:

  • Forests found in large part of India, Northern Australia and in Central America.

Climate:

  • These regions are warm and receive rainfall less than 200 cms.

Characteristics:

  • These regions experience seasonal changes. Trees shed their leaves in the dry season to conserve water.
  • Trees like sandalwood, teak, sal, ebony, bamboo, etc. are the common trees found here.
  • Forests are not very dense thus; commercial exploitation of these forests is possible.

Wildlife:

  • Tigers, lions, elephants, langoors and monkeys are the common animals of these regions.

 

Temperate Evergreen Forests:

  • These forests are also called Mixed Forests.

Location:

  • Forests found in South-eastern parts of USA, Australia, Brazil and China.

Climate:

  • These regions have cool winters and receive rainfall throughout the year.

Characteristics:

  • They comprise both hard and soft wood trees like oak, pine, eucalyptus, etc.
  • They look like Tropical Forest in thickness and variety.
  • Timber (wood) from these forests is used for commercial purpose.

Wildlife:

  • Deer, Wolves, Bears, Wild Boar, Foxes, Squirrels, Badgers, Skunks, Owls, Finches, etc. are the common animals of these regions.

 

Temperate Deciduous Forests:
Location:

  • As we go towards higher latitudes, there are more temperate deciduous forests. These are found in the north eastern part of USA, China, Japan, New Zealand, etc.

Climate:

  • These regions have cool winters and receive moderate rainfall.

Characteristics:

  • Trees shed their leaves in autumn season and remain leafless through winters.
  • The common trees are oak, ash, beech, etc.
  • Forests are not very dense thus; commercial exploitation of these forests is possible.

Wildlife:

  • Deer, foxes, wolves are the animals commonly found. Birds like pheasants, monals are also found here.

 

Mediterranean Forests:

 Location:

  • Found in areas around Mediterranean Sea, Central Chile, South-West USA, Australia, Africa.

Climate:

  • These regions have hot & dry summers and mild & wet winters.

Characteristics:

  • Mediterranean trees adapt themselves to dry summers with the help of their thick barks and wax coated leaves which help them reduce transpiration. Also, here the plants have long tap roots to reach underground water, called "Xerophytic Plants".
  • Mediterranean regions are known as 'Orchards of the world' for their fruit cultivation.
    Citrus fruits such as oranges, figs, olives and grapes are commonly cultivated here because people have removed the natural vegetation in order to cultivate what they want to.

Wildlife:

  • There isn't much wildlife here.

 

Coniferous Forests:
These forests are also called "Taiga Forest".

Location:

  • Found in the higher latitudes (50° – 70°) of Northern hemisphere.

Climate:

  • These regions have cool & short summers and cold & long winters. These forests are also seen in the higher altitudes. Norway, Sweden, Finland, Russia and Canada.

Characteristics:

  • Forests consist of tall, softwood evergreen trees.
  • Limited species of trees are found. These trees are evergreen and grow apart from each other.
  • Trees are conical shaped with needle shaped leaves and trees are found in large groups.
  • Chir, pine, cedar are the important variety of trees in these forests. Lumbering is the common activity. Soft wood is used for manufacturing paper.

Wildlife:

  • Fur-bearing animals like Silver fox, mink, and polar bear are the common animals found here.

 

GRASSLANDS

Tropical Grasslands:

 These grasslands are also known as "Savannas in Africa" and "Campos in Brazil".

Location:

  • Found within Tropical zone (i.e. between Tropic of Cancer and Tropic of Capricorn).

Climate:

  • These regions have hot & long summers and mild & short winters. Receives light rainfall in summers.

Characteristics:

  • The grass can grow very tall, about 3 to 4 metres in height, which is also known as "Elephant Grass".
  • Near river banks and water holes trees are found, which are deciduous in nature, e.g. Acacia, baobab, etc.
  • Climatic conditions in these grasslands do not support rich agriculture and animal rearing. Economically, these grasslands are backward.

Wildlife:

  • Lions, Tigers, Leopards, Elephants, Giraffes, Zebras, etc. are the species of animals found here. Birds like Ostrich, Emu, Cassowary, etc. can also be seen.

 

Temperate Grasslands:

These grasslands are also known as "Prairies in North America", "Pampas in South America", "Downs in Australia", "Velds in South Africa" and "Steppes in Europe".

Location:

  • These are found in the mid- latitudinal zones and in the interior part of the continents. Central Asia from Black Sea to Central Russia, North Central USA and Southern Canada, South-East Australia and Southern Africa, Argentina.

Climate:

  • These regions have warm & moist summers and cold & snowy winters.

Characteristics:

  • The grass found here is short and juicy, which is suitable for cattle feed.
  • Maize and wheat are grown in large amount, that's why this area is also known as "Bread Basket" of world.

Wildlife:

  • Herbivores like Wild Ass, Antelopes, and Horses. Kangaroos in Australia. Carnivores like Rodents and Reptiles are also found.

 

DESERTIC SCRUBS

Tropical Deserts:

Location:

  • Located on the western margins of the continents between 15° – 30° North & South of Equator. Biggest desert, Sahara in North Africa is hot desert while Ladakh in India is cold desert.

Climate:

  • These regions have hot & dry summers and receive very less rainfall.

Characteristics:

  • Plants found are very less with succulent stems, long roots and leaves are reduced to spines.
  • Nature has been very kind, at some places "Oasis" is found in deserts with palm trees surrounding them.

Wildlife:

  • Camel is the most common animal found in these deserts. Wild Yak, Hyena, Scorpion, fox, jackal, etc. are also found.

 

Tundra Regions:

Location:

  • Tundra means barren land. Located in North Canada, North Russia, North Sweden and Finland islands in Arctic Ocean.

Climate:

  • These regions have long & very cold winters and very short and cold summers.
  • Land is always frozen

Characteristics:

  • Trees are not found; as trees don't grow below 10° C. Very less vegetation is found.
  • Mosses, Lichens and some shrubs grow here.
  • Economically underdeveloped.

Wildlife:

  • Most common animal found in these area are Penguins, Polar Bears, Musk, Ox, Wolf, etc.

 

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01 January, 2015

Class VII: Chapter 5 (Water) Question & Answer

 

Very Short Answer Questions

Q1. What are streams of water moving in a definite pattern called?
Ans: Streams of water moving in a definite pattern are called Ocean Currents.

Q2. What are the giant waves caused by earthquakes on ocean floors called?
Ans: Tsunami giant waves caused by earthquakes on ocean floors.

Q3. What are the three movements of ocean water?
Ans: Waves, Tides and Ocean Currents are the three movements of ocean water.

Q4. Define the term Salinity.
Ans: The amount of salt in the ocean water is called salinity.

 

Short Answer Questions

Q1. What is the hydrological cycle?
Ans. The process by which water continually changes its form and circulates between lithosphere, atmosphere and hydrosphere is known as the Water Cycle or the Hydrological Cycle. It is a never ending process.

Q2. Is water a renewable resource?
Ans. Yes, water is called as a renewable resource because it can be used again and again. Water changes its form, due to heat water evaporates, when cools it condenses to form clouds and then through precipitation water comes back to the earth, this is a continuous process.

Q3. What does the word 'Tsunami' means?
Ans. An earthquake, a volcanic eruption or underwater landslides can shift large amounts of ocean water. As a result a huge tidal wave called tsunami originates.
Tsunami is a Japanese word that means "Harbour waves" as the harbours get destroyed whenever there is tsunami. The term "Tsunami" has been derived from: - "Tsu" – Harbour and "Nami" – Waves. Meaning huge tidal waves.

Q4. Explain why warm ocean currents are less dense than cold ocean currents.
Ans. Warm ocean currents are less dense than the cold ocean currents because the warm ocean currents originate near the equator and move towards the poles. Due to high temperature, moisture content in the air becomes very less making the warm currents rise the temperature over land surface. Whereas, cold ocean currents blow from Poles towards the equator. Here the temperature is less and moisture content is more, making these currents more dense than the warm currents

 

Long Answer Questions

Q1. What are the different types of tides and how are they caused? How are tides useful?
Ans. The tides are broadly classified into two types: Spring Tides and Neap Tides.
• During the full moon and new moon days, the sun, the moon and the earth are in the same line and the tides are highest. These tides are called spring tides. It is high tide when water covers much of the shore by rising to its highest level.
• But when the moon is in its first and last quarter, the ocean waters get drawn in diagonally opposite directions by the gravitational pull of sun and earth resulting in low tides. These tides are called neap tides. It is low tide when water falls to its lowest level and recedes from the shore.

Tides help us in the following ways:
• High tides help in navigation. This helps the ships to arrive at the harbour more easily.
• The high tides also help in fishing.
• Tides are also helpful in generating electricity.

Q2. How are ocean currents different from waves? Which factors are responsible for giving rise to ocean currents?
Ans.

Factors affecting the Ocean Currents: -
1. Planetary Winds.
2. Rotation of the Earth
3. Variation in the temperature
4. Density of ocean water
5. Shapes of the coastlines

Q3. Suggest measures to conserve water. When do we celebrate 'World Water Day'?
Ans. Some of the important ways to conserve water are:
1. Decrease of water pollution: Discharge of untreated sewage, agriculture chemicals & industrial effluents.
2. Proper irrigation method.
(a) Sprinklers can be used to irrigate very large area.
(b) Drip irrigation can be used in dry regions, where evaporation is very high.
3. Water Harvesting Method: This water can be used for cleaning, washing, gardening, etc.
4. Water conservation in the home.
• Check faucets and pipes for leaks.
• Check your toilets for leaks.
• Use your water meter to check for hidden water leaks.
• Install water-saving shower heads and low-flow faucet aerators.
• Put plastic bottles or float booster in your toilet tank.
• Insulate your water pipes.
• Take shorter showers.
• Turn off the water after you wet your toothbrush.
• Use your dishwasher and clothes washer for only full loads.
• When washing dishes by hand, don't leave the water running for rinsing.

'World Water Day' is celebrated on 22 March every year.

Q4. Give reasons:
(a) Ocean currents are important. How?
(b) Tides are very useful. How?
Ans.
(a) Following are the importance of ocean currents:
• Warm and cold currents help in controlling the climatic conditions of the world.
• Ocean currents help in navigation.
• ocean currents are important to the distribution of the world's sea life.
• Ocean currents also act as the convectional source of energy.

(b) Tides are very useful, following are the different ways:
• High tides help in navigation. This helps the ships to arrive at the harbour more easily.
• The high tides also help in fishing.
• Tides are also helpful in generating electricity.

Q5. The ocean currents are broadly divided into warm and cold currents. Why are they called so? What makes them warm and cold?
Ans. The ocean currents are broadly divided into warm and cold currents. These currents get influence by the temperature conditions of an area. The warm ocean currents originate near the equator and move towards the poles. Warm currents rise the temperature over land surface.
Whereas, the cold currents carry water from polar or higher latitudes to tropical or lower latitudes. Cold currents reduces the temperature of the coastal areas.
Movement of these currents make them warm or cold. The general circulation of ocean currents is clockwise in the Northern Hemisphere and anti-clockwise in the Southern Hemisphere.

 

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26 December, 2014

Class VII: Chapter 5 - Water

Some Facts and Figures of Water:

  • TWO-THIRD OF THE EARTH'S SURFACE IS COVERED WITH WATER.
  • Earth is also known as "Watery Planet", because 71% of the earth's surface is covered with water and only 29% is land.
  • World Water Day is celebrated on 22 March.

 

Distribution of Water:

1. 97% of the total volume of water is covered by Seas and Oceans

2. 3% as fresh water available on earth.

    (a) Out of 2% of the fresh water available, nearly 70% is in the form of "ICE" and is found in glaciers in Antarctica, Greenland, mountain regions, etc.

    (b) Only 1% of water is fit to use. It is found as underground water, surface water in rivers and lakes and also, water vapors' in the Atmosphere.

 

Water is available in three forms:

1. Water vapor's

2. Water in ocean, lakes & rivers

3. Ice in the glaciers & ice caps

 

HYDROLOGICAL CYCLE

  • The fresh water is continuously being renewed and recharged through hydrological cycle.
  • The sun's heat causes evaporation of water vapour.
  • When the water vapour cools down, it condenses and forms clouds.
  • From there it may fall on the land or sea in the form of rain, snow or sleet which is known as precipitation.
  • The process by which water continually changes its form and circulates between oceans, atmosphere and land is known as the Water Cycle or the Hydrological Cycle.

 

Usage of Water:

1. Drinking                                         2. Bathing                                           3. Washing

4.  Cooking                                        5. Irrigation                                         6. Construction, etc.

7. Water used in Industries                  8. Generating Electricity

 

PROBLEM OF WATER AVAILABILITY

  • Water is available in abundance and is renewable. Then why we suffer from water scarcity?
  • Water is not evenly divided around the world. Some places have lots and others have very little. Water supply is a big problem in some countries like, Africa, West Asia, South Asia, etc.

According to Mr. Falkenmark (a Swedish Expert), Water Stress Indicator, a country or region is said to experience "water stress" when annual water supplies drop below 1,700 cubic metres per person per year. At levels between 1,700 and 1,000 cubic metres per person per year, periodic or limited water shortages can be expected. When water supplies drop below 1,000 cubic metres per person per year, the country faces "water scarcity".

 

CONSERVATION OF WATER

Some of the important ways to conserve water are: -

1.  Decrease of water pollution:- Discharge of untreated sewage, agriculture chemicals & industrial effluents.

2.  Proper irrigation method.

     (a) Sprinklers can be used to irrigate very large area.

     (b) Drip irrigation can be used in dry regions, where evaporation is very high.

3.  Water Harvesting Method: This water can be used for cleaning, washing, gardening, etc.

4.  Water conservation in the home.

  • Check faucets and pipes for leaks.
  • Check your toilets for leaks.
  • Use your water meter to check for hidden water leaks.
  • Install water-saving shower heads and low-flow faucet aerators.
  • Put plastic bottles or float booster in your toilet tank.
  • Insulate your water pipes.
  • Take shorter showers.
  • Turn off the water after you wet your toothbrush.
  • Use your dishwasher and clothes washer for only full loads.
  • When washing dishes by hand, don't leave the water running for rinsing.

 

MOVEMENT OF OCEAN WATER OR OCEAN CIRCULATION

  • March 22 is celebrated as World Water Day.
  • Ocean water keeps moving continuously. It is never still.
  • The movements that occur in oceans can be broadly categorized as:Waves, Tides and Currents.

 

WAVES

  • When the water on the surface of the ocean rises and falls alternately, they are called waves.
  • During a storm, the winds blowing at very high speed form huge waves.
  • These may cause tremendous destruction.An earthquake, a volcanic eruption or underwater landslides can shift large amounts of ocean water. As a result a huge tidal wave called tsunami.
  • Tsunami is a Japanese word that means "Harbour waves" as the harbours get destroyed whenever there is tsunami. The term "Tsunami" has been derived from: - "Tsu" – Harbour and "Nami" – Waves. Meaning huge tidal waves.

 

TIDES

  • The rhythmic rise and fall of ocean water twice in a day is called a tide.
  • It is high tide when water covers much of the shore by rising to its highest level.
  • It is low tide when water falls to its lowest level and recedes from the shore.
  • During the full moon and new moon days, the sun, the moon and the earth are in the same line and the tides are highest. These tides are called spring tides.
  • But when the moon is in its first and last quarter, the ocean waters get drawn in diagonally opposite directions by the gravitational pull of sun and earth resulting in low tides. These tides are called neap tides.
  • High tides help in navigation.
  • This helps the ships to arrive at the harbour more easily.
  • The high tides also help in fishing.
  • Also, the rise and fall of water due to tides is being used to generate electricity in some places.

 

OCEAN CURRENTS

The horizontal movement of ocean water in the form of streams flowing constantly in definite directions is known as Ocean Currents.

 

Factors affecting the Ocean Currents: -

1.  Planetary Winds

2.  Rotation of the Earth

3.   Variation in the temperature

4.  Density of ocean water

5.  Shapes of  the coastlines

 

  • The ocean currents may be warm or cold.
  • The warm ocean currents originate near the equator and move towards the poles.
  • The cold currents carry water from polar or higher latitudes to tropical or lower latitudes.
  • The ocean current influence the temperature conditions of the area.
  • The place where warm and cold currents meet, dens fog is produced, reducing the visibility and thus, making it difficult for navigation. But at the same time these are the best fishing grounds of the world.
  • The general circulation of ocean currents is clockwise in the Northern Hemisphere and anti-clockwise in the Southern Hemisphere.

 

 

CASE STUDY

(TSUNAMI IN THE INDIAN OCEAN ON 26 DECEMBER 2004)

  • Tsunami or the harbour wave struck havoc in the Indian Ocean on the 26 December 2004.
  • The wave was the result of the earthquake that had its epicenter close to the western boundary of Sumatra in Indonesia.
  • The magnitude of the earthquake was 9.0 on the Richter scale.
  • Tsunami affected the coastlines of South and Southeast Asian countries. India, Indonesia, Sri Lanka, Thailand, etc were some of the countries where destruction was maximum.
  • Tsunami travelled at a speed of about 800km. per hour and completely washed away some of the islands in the Indian ocean.
  • The Indira point in the Andaman and Nicobar islands that marked the southernmost point of India got completely submerged. In India, the worst affected were the coastal areas of Andhra Pradesh, Tamil Nadu, Kerala, Puducherry and the Andaman and Nicobar Islands.
  • The earthquake-induced tsunami resulted in at least 1.8 lakh dead, 500,000 injuries, and damages that exceeded $10 billion. Also, it is estimated that 5 million people lost their homes or access to food and water.
  • Relief work was carried out at a great speed. All types of helps were received from all the corners of the world. Serious efforts were made by the government and non-government agencies to bring back life of the leftovers on track.

 

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25 November, 2014

Class VII: Chapter 4 (Air) Question & Answer

Very Short Answer Questions

Q1. What is the composition of the air?
Ans: Atmosphere is composed of various gases. Major gases present are:
(i) Nitrogen – 78%
(ii) Oxygen – 21%
(iii) Argon - .93%
(iv) Carbon Dioxide – 0.03%
Other Gases – 0.04% (like – helium, hydrogen, methane, ozone, etc. and water vapours & dust particles.

Q2. What is normal lapse rate?
Ans: Temperature decreases at the rate of 1 degree Celsius from every 165 mtrs of ascent. This decline is known as normal lapse rate.

Q3. Define: (a) Weather (b) Climate?
Ans:
(a) Weather: The condition of atmosphere at a particular place and time is known as weather.
(b) Climate: The sum total or average of the weather conditions of a large area over a longer period of time is known as climate.

Q4. What is dew point?
Ans: Temperature at which air gets saturated is known as "Dew Point".

Q5. Which layer of the atmosphere enables wireless communications?
Ans: Thermosphere or Ionosphere is the layer of the atmosphere enables wireless communications.

Q6. Name the unit used for measuring air pressure.
Ans: Barometer is the unit used for measuring air pressure.

 

Short Answer Questions

Q1. What are the factors affecting temperature of any place?
Ans. Following are the factors affecting temperature of any place:
(a) Latitude or Distance From Equator.
(b) Altitude or Height Above The Sea Level
(c) Distance From The Sea
(d) Prevailing Winds and Ocean Currents
(e) Slope of Land

Q2. Why is atmosphere important for us?
Ans. Importance of atmosphere and various gases present in it are:
(a) Life giving gases like oxygen for breathing of animal kingdom and carbon dioxide is inhaled by plant kingdom.
(b) Ozone layer protects us from harmful ultraviolet rays of the sun.
(c) Tiny dust particles help in the formation of the rain droplets.
(d) It acts as a blanket which prevents the earth from becoming too hot during day and too cold during night.
(e) It protects us from falling meteors and other cosmic dusts. They burn when coming in contact with the atmosphere.
(f) Presence of gases, dust particles and water vapours lend colours to sky.

Q3. What do you mean by precipitation? What is the main source of freshwater on the earth's surface?
Ans: The process in which water vapour falls on the surface of the earth is known as precipitation. Types of precipitation: Rainfall, Snowfall, Hail, Sleet, etc. Underground water is the main source of freshwater on the earth's surface.

Q4. What is atmospheric pressure? How is it important to us?
Ans: The weight of air on the earth's surface is referred to as "Atmospheric Pressure". Atmospheric Pressure is a very important element of weather and climate. A difference in the air pressure defines the direction of wind flow and accordingly, brings changes in the weather conditions.

Q5. What is the main cause of air pollution?
Ans: Any change in the composition of air is termed as "Air Pollution". Following are the main cause of air pollution:
(a) Rapid industrial growth.
(b) Excessive burning of the fossil fuels.
(c) Increase in numbers of automobiles.
(d) Burning of solid waste.
(e) Fire, etc.

Q6. Define: (a) Breeze (b) Drizzle
Ans:
(a) Breeze: These are local winds which blow only during a particular period of the day or year in a small area. For example, land and sea breeze.
(b) Drizzle: Light rainfall in the form of very tiny drop of water is called "Drizzle".

 

Long Answer Questions

Q1. Describe the structure of the atmosphere. Draw a diagram also.
Ans. Structure of Atmosphere: Atmosphere is divided into five different layers (Troposphere, Stratosphere, Mesosphere, Ionosphere and Exosphere). It extends upto 500 kms.

1. Troposphere:
• This layer is next to earth surface. It Extends upto 15 kms from the earth's surface.
• Temperature decreases at the rate of 1 degree Celsius from every 165 mtrs of ascent. This decline is known as normal lapse rate.
• Average height: 13 kms at poles and 18 kms over the equator.
• All weather changes take place in this layer. Oxygen exists in this layer.
• The boundary separating troposphere and stratosphere is known as tropopause.

2. Stratosphere:
• This layer is next to troposphere and it extends from 15 kms to 50 kms.
• This layer is free from weather changes, cloud formation and dust particles. Hence, this layer is ideal for the air transportation.
• Ozone layer is present here. Ozone layer absorbs/reflects the harmful ultraviolet rays of the sun.
• The boundary separating stratosphere and mesosphere is known as stratopause.

3. Mesosphere:
• This layer is next to stratosphere and it extends from 50 kms to 80 kms.
• Temperature again drops in this layer and can reach upto -100 degree Celsius at the upper boundary layer.
• The boundary separating mesosphere and ionosphere is known as mesopause.

4. Thermosphere:
• This layer is next to mesosphere and it extends from 80 kms to 400 kms.
• This layer contains electrically charged particles called ions, which are found at a height of 250 kms. Due to presence of these ions, this layer is also known as ionosphere.
• This layer protects us from the harmful radiation. Temperature increase with increase in height.

5. Exosphere:
• This is the uppermost layer above the ionosphere and it extends from 400 kms onwards and there is no end. It is a very thin layer and it merges with the space.
• This layer protects us from the harmful radiation.
• Temperature is very high. Light gases like hydrogen and helium float into space from here.

Q2. What are the different types of winds? Describe each giving examples.
Ans. Permanent or Planetary Winds: These winds blow constantly throughout the year in a particular direction. These winds are broadly classified as: -
(a) Trade Winds
(b) Westerlies
(c) Polar Easterlies

(a) Trade Winds: These winds blow from Sub-Tropical high pressure belt towards Equatorial low pressure belt. They blow from North-East in the northern hemisphere and South-East in the southern hemisphere.
(b) Westerlies: These winds blow from Sub-Tropical high pressure belt to Sub-Polar low pressure belt.
(c) Polar Easterlies: These winds blow from Polar high pressure belt to Sub-Polar low pressure belt.

2. Seasonal or Periodic Winds: These winds change their direction in different seasons. The best example is "Monsoon Winds".

3. Local Winds: These winds blow only during a particular period of the day or year. For example, land and sea breeze. These winds bring short time changes in the weather conditions over a smaller area. Some of the examples are: -
(a) Chinook: Chinook means 'snow eater'. These winds are strong, warm and dry. They blow in North America.
(b) Loo: These are hot and dry winds which, blow during the summer season in the northern part of India.
(c) Sirocco: These are hot and moist winds, which blow from Sahara desert to Mediterranean Sea.
(b) Mistral: These are very cold winds, which blow down from the Alps over France.

Q3. Describe the different types of rainfall, Support your answer with appropriate diagram.
Ans. Rainfall can be classified into three types:
1. Convectional Rainfall: When hot air expands and rise to the upper layer of the atmosphere, condensation takes place which leads to formation of clouds. These clouds produce sudden and heavy rainfall. It's a daily feature in the equatorial regions.

2. Relief Rainfall: Relief rain occurs when warm air is forced to cool when it rises over a hill or mountain and then condenses. The other name for relief rain is orographic rainfall. The windward side of the mountains receives heavier rainfall in comparison to that of the leeward side (opposite) of the mountain receives little or no rain at all. It always produces a rain shadow effect.

3. Cyclonic Rainfall: When warm air mass and cold air mass meet, the warm air being lighter climbs over the cold air and cools down, leading to formation of clouds and then rainfall. This type of rain usually is due to the occurrence of cyclonic activities.

Q4. Why do places lying the windward side get rainfall while the leeward side remains dry?
Ans: The windward side gets more rainfall than the leeward side of a mountain. This is because the prevailing winds come up and the cool air tries to hold that much moisture. But since cool air can't hold as much moisture as warm air, it begins to precipitate on the windward side (the side of mountain that is facing the prevailing winds). The dry air moves on to the leeward side (the side of a mountain that is not facing prevailing winds) and stays there, usually causing deserts to form. This makes the leeward side of the mountain have a dry climate.

 

Q5. What is a cyclone? How is it different from anti cyclone?
Ans. A cyclone is a large wind system that moves around an area of low atmospheric pressure. Surrounding air moves toward the low-pressure area and starts to circulate, cyclone moves clockwise in the Southern Hemisphere and anticlockwise in the Northern Hemisphere. Cyclones can produce cloudy weather and broad areas of rain and even snow. In the United States, cyclones often are called tornadoes.
An anticyclone system has characteristics opposite to that of a cyclone. That is, an anticyclone's central air pressure is higher than that of its surroundings, and the airflow is anticlockwise in the Southern Hemisphere and clockwise in the Northern Hemisphere.

 

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08 November, 2014

Class VII: Chapter 4 - Air

Some important points to remember:

  • The gaseous envelope around the earth's surface consisting of mixture of gases, water vapour and tiny dust particles is called atmosphere.
  • The atmosphere has its own weight called atmospheric pressure.
  • Concentration of gases and other constituents of atmosphere decrease with the increase in height.
  • Atmosphere is endless with no visible boundary.

 

COMPOSITION OF ATMOSPHERE:

Atmosphere is composed of various gases. Major gases present are:
(a) Nitrogen – 78%
(b) Oxygen – 21%
(c) Argon - .93%
(d) Carbon Dioxide – 0.03%
(e) Other Gases – 0.04% (like – helium, hydrogen, methane, ozone, etc. and water vapours & dust particles.

Importance of atmosphere and various gases present in it are:
(a) Life giving gases like oxygen for breathing of animal kingdom and carbon dioxide is inhaled by plant kingdom.
(b) Ozone layer protects us from harmful ultraviolet rays of the sun.
(c) Tiny dust particles help in the formation of the rain droplets.
(d) It acts as a blanket which prevents the earth from becoming too hot during day and too cold during night.
(e) It protects us from falling meteors and other cosmic dusts. They burn when coming in contact with the atmosphere.
(f) Presence of gases, dust particles and water vapours lend colours to sky.

 

STRUCTURE OF ATMOSPHERE:
Atmosphere is divided into five different layers (Troposphere, Stratosphere, Mesosphere, Ionosphere and Exosphere). It extends upto 500 kms.

1. Troposphere:

  • This layer is next to earth surface.
  • It Extends upto 15 kms from the earth's surface.
  • Temperature decreases at the rate of 1 degree Celsius from every 165 mtrs of ascent. This decline is known as normal lapse rate.
  • Average height: 13 kms at poles and 18 kms over the equator.
  • All weather changes take place in this layer.
  • Oxygen exists in this layer.
  • The boundary separating troposphere and stratosphere is known as tropopause.

2. Stratosphere:

  • This layer is next to troposphere and it extends from 15 kms to 50 kms.
  • This layer is free from weather changes, cloud formation and dust particles. Hence, this layer is ideal for the air transportation.
  • Ozone layer is present here. Ozone layer absorbs/reflects the harmful ultraviolet rays of the sun.
  • The boundary separating stratosphere and mesosphere is known as stratopause.

3. Mesosphere:

  • This layer is next to stratosphere and it extends from 50 kms to 80 kms.
  • Temperature again drops in this layer and can reach upto -100 degree Celsius at the upper boundary layer.
  • The boundary separating mesosphere and ionosphere is known as mesopause.

4. Thermosphere:

  • This layer is next to mesosphere and it extends from 80 kms to 400 kms.
  • This layer contains electrically charged particles called ions, which are found at a height of 250 kms. Due to presence of these ions, this layer is also known as ionosphere.
  • This layer protects us from the harmful radiation.
  • Temperature increase with increase in height.

5. Exosphere:

  • This is the uppermost layer above the ionosphere and it extends from 400 kms onwards and there is no end.
  • It is a very thin layer and it merges with the space.
  • This layer protects us from the harmful radiation.
  • Temperature is very high.
  • Light gases like hydrogen and helium float into space from here.

 

GLOBAL WARMING:

  • Earth's atmosphere acts as a green house with the presence of harmful gases coming out from the factories, vehicles, refrigerators, etc.
  • There is a layer of carbon dioxide around the earth which does not allow the heat to radiate into the space, rather this layer blocks the heat, due to which there is increase in the temperature. This increase in temperature is known as global warming.
  • When the temperature increases – snow melts – due to which the water level increases causing floods.
  • There may be major changes in the climate leading to the extinction of some vegetation and wildlife.

WEATHER:
The condition of atmosphere at a particular place and time is known as weather.

METEOROLOGY:
The scientific study of weather is known as meteorology.

Temperature, pressure, wind, humidity, moisture, sunshine, precipitation, etc. are the major elements of weather and climate.

CLIMATE:

  • The sum total or average of the weather conditions of a particular place over a longer period of time is known as climate.
  • Climate influence the type of vegetation, agricultural crops grown, animals found, lifestyle, houses build, eating habits, etc.

INSTRUMENTS USED FOR MEASURING WEATHER:

1. Thermometer - Temperature
2. Barometer - Air Pressure
3. Rain Gauge - Rainfall
4. Wind Vane - Wind
& Anemometer

 

TEMPERATURE:

  • The intensity of heat (warm or cold) is known as temperature.
  • Main source of heat is sun.
  • Surface temperature of sun is around 5500 degree Celsius.
  • Heat energy given out by sun is known as solar radiation.
  • Incoming solar radiation is known as insolation.
  • The solar radiation takes 7 minutes to reach the earth's surface.
  • Due to the spherical (round) shape of the earth, all parts does not receive same amount of insolation.
  • On an around equator, insolation is maximum and it decrease when we move towards the poles.
  • On the basis of the insolation received, earth is divided into different zones, which are as follows:-

          1. Torrid Zone
          2. Temperate Zone
          3. Frigid Zone 

 

Heating and Cooling of Atmosphere:
The heat energy given out by the earth is known as terrestrial radiation. It is the same heat which was absorbed by the earth through insolation.
Heat is transferred by the earth's surface into the atmosphere through the following ways: -
1. Conduction: The transfer of heat through contacts is known as conduction. In this, a cooler body comes in contact with the warmer body a gets heated up. This process is carried out until the temperature of both the bodies become same.

2. Convection: The actual movement of heat molecules from lower level to the higher level is known as convection. This process is common on equator and in tropics during the summers.

3. Advection: Transfer of heat from one place to another by the winds and the oceanic currents is known as advection. In this process, the cooler wind lowers the temperature of the warm wind and vice-versa, when they come in contact with each other.

4. Radiation: The process of releasing heat energy is known as radiation. The head energy absorbed by earth during the day time is radiated to the atmosphere during the night time.

 

Factors Affecting the Temperature:
Temperature is unequally distributed on the earth's surface and it differs from place to place. Factors controlling the temperature are as follows:

1. Latitude or distance from equator: Places located near the equator are warmer in comparison to the places located near the poles. Places near the equator receive direct sunrays because here the sunrays travel shorter distance and cover small area.
On contrary, in Polar Regions, sunrays travel longer distance and cover large area.

2. Altitude or height above the sea level: As we go higher the temperature decreases (i.e. 1 degree for every 165 metres). Mountainous areas are therefore cooler. The lower layers of atmosphere are denser and have water vapour and dust particles which absorb heat, which is not prevalent in the higher altitude. E.g. Missouri is cooler than Delhi.

3. Distance from the sea: The Sea is cooler than the land in summer, but warmer in winter. This is because it takes the sea a long time to heat up, but it is slower to cool down than land.
Areas experiencing uniform and mild temperature throughout the year as they are located near the sea have maritime type of climate. E.g. Mumbai.
Areas experiencing hot temperatures in summers and cold temperatures in winters due to longer distance from the sea have extreme or continental type of climate. E.g. Delhi.

4. Prevailing winds and ocean currents: Both winds and ocean currents (hot and cold) influence the temperature of the land. For e.g. hot and dry winds 'loo' in summers from Rajasthan increase the temperature of Delhi and in winters cold winds from Himachal Pradesh decreases the temperature of Delhi.

5. Slope of land: Slopes more exposed to sun, received more sunlight and these places are warmer. On contrary, slopes exposed less to sunlight are cooler and have less vegetation.

 

Temperature of a place is very important as it controls:

1. The presence or absence of water vapours or moisture.
2. Dryness or wetness of air and rainfall.
3. Type of crops to be grown.
4. Type of vegetation in an area.

 

ATMOSPHERIC PRESSURE:

  • The weight of air on the earth's surface is referred to as "Atmospheric Pressure".
  • Weight of dry air is about 1.2 ounce per cubic foot of air.
  • Pressure decreases with increase in height. Pressure is highest at the sea level.
  • The air always moves from high pressure to low pressure areas.
  • Barometer is the instrument through which pressure variation can be measured.
  • Pressure is measured in millibars. Average atmospheric pressure at sea level is 1013 millibars.

Factors responsible for difference in the Atmospheric Pressure:
1. Variations in Temperature Conditions.
2. Changing Altitude.

Distribution of Atmospheric Pressure:

High Temperature – Low Pressure
Low Temperature – High Pressure
The world is divided into seven different pressure belts:
1. Equatorial low pressure belt also called "Doldrums".
2. Subtropical high pressure belt from 30 to 35 degree in North.
3. Subtropical high pressure belt from 30 to 35 degree in South.
4. Sub Polar low pressure belt from 65 degree in North.
5. Sub Polar low pressure belt from 65 degree in South.
6. Polar high pressure belt in North Pole.
7. Polar high pressure belt in South Pole.

 

WIND:

  • The movement of air from high pressure area to low pressure areas is called "Wind".
  • Winds play a vital role as they are very important.
  • Winds transports temperature and moisture from one place to another.
  • Slope of pressure from high to low is known as "Pressure Gradient" and this decides the direction of the winds.
  • Deflection of the winds is affected by the "Coriolis Force", which is caused by the rotation of the earth. Coriolis is absent on the equator and it increases towards the poles.

Types of Winds: Winds can be broadly divided into three types:
1. Permanent or Planetary Winds.
2. Seasonal or Periodic Winds.
3. Local Winds.

1. Permanent or Planetary Winds: These winds blow constantly throughout the year in a particular direction. These winds are broadly classified as: -
(a) Trade Winds
(b) Westerlies
(c) Polar Easterlies

(a) Trade Winds:

  • These winds blow from Sub-Tropical high pressure belt towards Equatorial low pressure belt.
  • They blow from North-East in the northern hemisphere and South-East in the southern hemisphere.

(b) Westerlies:

  • These winds blow from Sub-Tropical high pressure belt to Sub-Polar low pressure belt.

(c) Polar Easterlies:

  • These winds blow from Polar high pressure belt to Sub-Polar low pressure belt.

2. Seasonal or Periodic Winds: These winds change their direction in different seasons. The best example is "Monsoon Winds".
(a) Land Breeze: The offshore breeze is called "Land Breeze".
(b) Sea Breeze: The onshore breeze is called "Sea Breeze".

3. Local Winds: These winds blow only during a particular period of the day or year. These winds bring short time changes in the weather conditions over a smaller area. Some of the examples are: -
(a) Chinook: Chinook means 'snow eater'. These winds are strong, warm and dry. They blow in North America.
(b) Loo: These are hot and dry winds which, blow during the summer season in the northern part of India.
(c) Sirocco: These are hot and moist winds, which blow from Sahara desert to Mediterranean Sea.
(b) Mistral: These are very cold winds, which blow down from the Alps over France.

 

LOCAL STROMS:

  • Stroms are very strong blowing winds and they are serious threat to life and property in the coastal areas.
  • Cyclones, hurricanes, typhoons and tornadoes are some of the examples of stroms.

 

Cyclones:

  • Cyclones refer to a violent and destructive form of winds followed by heavy rainfall.
  • Cyclonic winds cause 7 to 10 km high tidal waves that sweep 20 kms inland and bring massive destruction.
  • Hurricanes are type of cyclones, which are experienced by eastern coast of India.

Prevention:
These are the natural calamities which cannot be prevented but we can try to minimize the effect by the following ways:
1. People should live far away from the coastal lands.
2. Houses should be constructed with stronger building material.

Instruments:
1. Wind Vane is used to measure the direction of the wind.
2. Anemometer is used to measure the wind velocity.

 

CASE STUDY
CYCLONE IN ORISSA

On 29th of October 1999, a cyclone (hurricane) emerged from the Bay of Bengal. With winds up to 300 km/h and 30 feet tidal waves, it affected the state of Orissa for more than 36 hours. The impacts on people and the environment were massive because of poor preparation.

Effects:

  • 20,000 people and 700,000 cattle died.
  • 90 million trees have been uprooted or damaged.
  • 20 million people were made homeless
  • 5 million farmers are out of work
  • 1.2 million hectares of standing cropland were destroyed.
  • £1.5Billion damage

      

MOISTURE:

  • Moisture content in air is called "Humidity".
  • When the air is full of water vapour we call it a humid day. As the air gets warmer, its capacity to hold the water vapour increases and so it becomes more and more humid. On a humid day, clothes take longer to dry and sweat from our body does not evaporate easily, making us feel very uncomfortable.
  • Instrument used to measure humidity is called "Hygrometer".
  • Temperature at which air gets saturated is known as "Dew Point".
  • When the water vapour rises, it starts cooling. The water vapour condenses causing formation of droplets of water. Huge masses of water droplets are known as "Clouds". When these droplets of water become too heavy to float in air, then they come down as precipitation.
  • Types of precipitation: Rainfall, Snowfall, Hail, Sleet, etc. A very tiny drop of rain water is called "Drizzle".

 

TYPES OF RAINFALL:

Rainfall can be classified into three types:

1. Convectional Rainfall: Sudden and heavy rainfall
2. Relief Rainfall: The windward side of the mountains receives heavier rainfall in comparison to that of the other side.
3. Cyclonic Rainfall: Rainfall is associated with cyclones.

 

POLLUTION:

  • Any change in the composition of air is termed as "Air Pollution".
  • Some of the air pollutants are: Chlorofluorocarbons (CFC), Carbon Dioxide, Carbon Monoxide, Shulphur Dioxide, Nitrogen Oxide, etc.
  • Some of the hazards of air pollutions are: Health problems, Loss of biodiversity, Damage to the historical monuments (e.g. Taj Mahal is getting harmed), etc.
  • Serious steps should be taken to protect the environment and the human life.

 

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04 September, 2014

SA-I (Answer Key - Geography) Class VII

Multiple choice questions:

Q1. .............. environment consists of plants, animals and human beings. (1)
(a) Abiotic (b) Chemical (c) Human (d) Biotic

Ans: (d) Biotic

Q2. "NIFE" is related to which layer of the earth? (1)
(a) Core (b) Mantle (c) Crust (d) Mountains

Ans: (a) Core

 

Very short answer questions:

Q3. Study of relationship between living organisms and their surrounding is called? (1)
Ans: Study of relationship between living organisms and their surrounding is called Ecology.

Q4. Fossil fuels are found in which type of rocks? (1)
Ans: Fossil fuels are found in Sedimentary rocks.

Q5. What is oceanic crust called? (1)
Ans: The ocean crust is called SIMA.

 

Short answer questions:

Q6. What is lithosphere? Why it is important? (2)
Ans: The hard outermost solid layer of the earth which is made up of rock material is called crust. This solid crust of the earth is called Lithosphere. On this lithosphere we find different landforms such as the mountains, plateaus and plains. It provides us land where we live and also, it is a great source of vegetation, wildlife and mineral wealth. The crust is covered by a thin layer of soil which is of great importance for life. Lithosphere provides us the three basic necessities of life, i.e. Food, Cloth and Shelter.

Q7. Distinguish between: Crust and Mantle. (2)
Ans:

Q8. Define the terms: (a) Focus (b) Epicenter (2)
Ans:
(a) Focus: The point of origin of an earthquake is called its Focus.
(b) Epicenter The point directly/vertically above the focus on the earth's surface is known as Epicenter.

 

Medium answer questions:

Q9. What is igneous rock? Write its main features. (3)
Ans: The word 'Igneous' is derived from Latin word "Ignis" meaning "Fire". This is also called Primary rock. These are the first rocks to be formed and are known as the ancestors of all the rocks. Igneous rocks are the hardest rocks available and it is formed by cooling and solidification of the Lava coming out from the interior of the Earth's interior. E.g. Granite, Basalt, etc. Igneous rocks are of two types:
(a) Solidification of rocks below the earth's surface is known "Intrusive rocks".
(b) The magma which reaches the earth's surface and gets solidified is known as "Extrusive Rocks".

Features of igneous rocks are:
1. These rocks do not form layers.
2. They contain crystals of varying sizes.
3. They do not contain fossils.

Q10. Describe the rock cycle with a suitable diagram. (3)
Ans: Rocks undergo a cycle of transformation. Change into sedimentary rock or into metamorphic rock. Sedimentary rock can change into metamorphic rock or into igneous rock. Metamorphic rock can change into igneous or sedimentary rock. Hence, this cycle of change from one type of rock to another is called 'rock cycle'.

Rocks are continually being formed, destroyed and reformed due to changing weather conditions and forces of nature (eg. Wind, river, glaciers, earth movements, etc.)

Q11. Explain the types of volcanoes? (3)
Ans: Natural openings in the earth's crust through which molten materials, rocks, ashes, gases, etc are thrown out are called 'Volcanoes'. Volcanoes are classified into three types:
(a) Active Volcanoes: These volcanoes erupt frequently and give out gases, ash, lava, etc. e.g. Mt. Etna in Italy.
(b) Dormant Volcanoes: These are also known as 'Sleeping Volcanoes'. They erupt after a very long time. E.g. Mt. Vesuvius in Italy.
(c) Extinct Volcanoes: These are also known as 'Dead Volcanoes'. They have been inactive since a very long time. E.g. Mt. Kilimanjaro in East Africa.
Long answer questions:

Q12. With a suitable diagram write a note on the domains of the earth. (5)
Ans:
Lithosphere: The solid crust of the earth is called Lithosphere.
Hydrosphere: The water bodies on the earth's surface together form the Hydrosphere.
Atmosphere: The layer of air around us is called Atmosphere.
Biosphere: The living world where land, water & air interact with each other to support life is called the Biosphere.
Plant and animal kingdom together make Biosphere or the living worlds. It is a narrow zone of the Earth where Air (Atmosphere), Water (Hydrosphere) and Land (Lithosphere) interact with each other to support life. All the three spheres are equally important for the existence of life or the Biosphere.

Q13. Explain the following. (5)
(a) Aggradation (b) Endogenis forces (c) Tectonic plates (d) Delta (e) Meanders
Ans:
(a) Aggradation: The process of depositing the eroded material is called aggradation.
(b) Endogenic Forces: Forces which are working in the interior of the earth leading to earth movements, earthquakes and volcanic eruption are known as endogenic forces.
(c) Tectonic Plates: The crust of the earth is broken into a number of large and small plates known as the Tectonic Plates or the Lithospheric plates.
(d) Delta: The network of distributaries forming a triangular shaped feature on the river mouth is known as delta.
(e) Meanders: Curves and large bends or loops formed by rivers in the plains are known as meanders.

 

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