Category: CBSE

Class 11 Geography Notes Chapter 16 Biodiversity and Conversation

The average half-life of a species is estimated at between one and four million years, and 99 per cent of the species that have ever lived on the earth are today extinct.

Biodiversity is not found evenly on the earth. It is consistently richer in the tropics. As one approaches the polar regions, one finds larger and larger populations of fewer and fewer species.

Genes are the basic building blocks of various life forms. The diversity in gene in a species is called genetic biodiversity.

Human beings genetically belong to the homo sapiens group and also differ in their characteristics such as height, colour, physical appearance, etc., considerably. This is due to genetic diversity. This genetic diversity is essential for a healthy breeding of population of species.

Genetic diversity has given a great contribution in development of human culture. In a similar way human species has also contributed in maintaining natural diversity at genetic, species and ecosystem level.

Different species of ecosystem are busy in one activity or the other. Without activities they can neither survive nor develop.

Ecosystem evolves and sustains without any reason. That means, every organism, besides extracting its needs, also contributes something of useful to other organisms.

Ecological functions are important for ecosystem function and human survival. The more diverse an ecosystem, better are the chances for the species to survive through adversities and attacks, and consequently, is more productive. Just like a species with a high genetic diversity, an ecosystem with high biodiversity may have a greater chance of adapting to environmental change. In other words, the more the variety of species in an ecosystem, the more stable the ecosystem is likely to be.

Biodiversity as we have today is the result of 2.5-3.5 billion years of evolution. Before the advent of humans, our earth supported more biodiversity than in any other period.

Since, the emergence of humans, however, biodiversity has begun a rapid decline, with one species after another bearing the brunt of extinction due to overuse. The number of species globally vary from 2 million to 100 million, with 10 million being the best estimate.

For all humans, biodiversity is an important resource in their day-to-day life. One important part of biodiversity is ‘crop diversity’, which is also called agro-biodiversity. Biodiversity is seen as a reservoir of resources to be drawn upon for the manufacture of food, pharmaceutical, and cosmetic products.

Since the last few decades, growth in human population has increased the rate of consumption of natural resources. It has accelerated the loss of species and habitation in different parts of the world.

Tropical regions which occupy only about one-fourth of the total area of the world, contain about three- fourth of the world human population. Over-exploitation of resources and deforestation have become rampant to fulfil the needs of large population. As these tropical rain forests contain 50 per cent of the species on the earth, destruction of natural habitats have proved disastrous for the entire biosphere.

Natural calamities such as earthquakes, floods, volcanic eruptions, forest fires, droughts, etc. cause damage to the flora and fauna of the earth, bringing change to the biodiversity of respective affected regions. Pesticides and other pollutants such as hydrocarbons and toxic heavy metals destroy the weak and sensitive species.

The International Union of Conservation of Nature and Natural Resources (IUCN) has classified the threatened species of plants and animals into three categories for the purpose of their conservation: (a) Endangered species (b) Vulnerable species and (c) Rare species.

Biodiversity is important for human existence. All forms of life are so closely interlinked that disturbance in one gives rise to imbalance in the others. If species of plants and animals become endangered, they cause degradation in the environment, which may threaten human being’s own existence.

The Government of India along with 155 other nations have signed the Convention of Biodiversity at the Earth Summit held at Rio de Janeiro, Brazil in June 1992.

Government of India passed the Wild Life (Protection) Act, 1972, under which national parks and sanctuaries were established and biosphere reserves declared.

There are some countries which are situated in the tropical region; they possess a large number of the world’s species diversity. They are called mega diversity centers. There are 12 such countries, namely Mexico, Columbia, Ecuador, Peru, Brazil, Democratic Republic of Congo, Madagascar, China, India, Malaysia, Indonesia and Australia in which these centers are located.

Hotpots are defined according to their vegetation. Plants are important because these determine the primary productivity of an ecosystem. Most, but not all, of the hotpots rely on species-rich ecosystems for food, firewood, cropland, and income from timber. In Madagascar, for example, about 85 per cent of the plants and animals are found nowhere else in the world. Other hotspots in wealthy countries are facing different types of dangers.

Class 11 Geography Notes Chapter 16 Important Terms:

• Biodiversity: Biodiversity refers to the varieties of plants, animals and micro-organisms, the genes they contain and the ecosystems they form. It relates to the variability among living organisms on the earth, including the variability within and between the species and that within and between the ecosystems.
• Species: Groups of individual organisms having certain similarities in their physical characteristics are called species.
• Genetic biodiversity: Genetic biodiversity refers to the variation of genes within species.
• Species diversity: Species diversity refers to the variety of species. It relates to the number of species in a defined area. The diversity of species can be measured through its richness, abundance and types.
• Ecosystem diversity: The broad differences between ecosystem types and the diversity of habitats and ecological processes occurring within each ecosystem type constitute the ecosystem diversity.
• Hotspots: Some areas are richer in species than others. Areas rich in species diversity are called hotspots of diversity.
• Exotic species: Species which are not the natural inhabitants of the local habitat but are introduced into the system, are called exotic species.
• Sensitive species: Pesticides and other pollutants such as hydrocarbons and toxic heavy metals destroy the weak species. These are called sensitive species.
• Mega diversity centre: There are some countries which are situated in the tropical region; they possess a large number of the world’s species diversity. They are called mega diversity centres.
• IUCN: The International Union of Conservation of Nature and Natural Resources is an international organization which published information about species under the red list.
• Endangered species: Endangered species includes those species which are in danger of extinction. The IUCN publishes information about endangered species world-wide as the red list of threatened species.
• Vulnerable species: Vulnerable species includes the species which are likely to be in danger o’f extinction in near future if the factors threatening to their extinction continue. Survival of these species is not assured as their population has reduced greatly.
• Rare species: Rare species are those species whose population is very small in the world and they are confined to limited areas or thinly scattered over a wider area.

Class 11 Geography Notes

Class 11 Geography Notes Chapter 15 Life on the Earth

Life on the earth is found almost everywhere. Living organisms are found from the poles to the equator, from the bottom of the sea to several km in the air, from freezing waters to dry valleys, from under the sea to underground water lying below the earth’s surface.

The biosphere includes all the living components of the earth. It consists of all plants and animals, including all the micro-organisms that live on the planet earth and their interactions with the surrounding environment.

The biosphere and its components are very significant elements of the environment. These elements interact with other components of the natural landscape such as land, water and soil.

They are also influenced by the atmospheric elements such as the temperature, rainfall, moisture and sunlight. The interactions of biosphere with land, air and water are important to the growth, development and evolution of the organism.

The term ecology is derived from the Greek word ‘oikos’ meaning ‘house’, combined with the word ‘logy’ meaning the ‘science of or ‘the study of. Literally, ecology is the study of the earth as a ‘household’, of plants, human beings, animals and micro-organisms.

A German zoologist Ernst Haeckel, who used the term as ‘oekologie’ in 1869, became the first person to use the term ‘ecology’. The study of interactions between life forms (biotic) and the physical environment (abiotic) is the science of ecology. Hence, ecology can be defined as a scientific study of the interactions of organisms with their physical environment and with each other.

Ecosystems are of two major types: terrestrial and aquatic. Terrestrial ecosystem can be further be classified into ‘biomes’.

A biome is a plant and animal community that covers a large geographical area. The boundaries of different biomes on land are determined mainly by climate.

From a structural point of view, all ecosystems consist of abiotic and biotic factors. Abiotic factors include rainfall, temperature, sunlight, atmospheric humidity, soil conditions, inorganic substances (carbon dioxide, water, nitrogen, calcium, phosphorus, potassium, etc.).

Biotic factors include the producers, the consumers (primary, secondary, tertiary) and the decomposers. The producers include all the green plants, which manufacture their own food through photosynthesis.

The primary consumers include herbivorous animals like deer, goats, mice and all plant-eating animals.

The carnivores include all the flesh-eating animals like snakes, tigers and lions. Certain carnivores that feed also on carnivores are known as top carnivores like hawks and mongooses.

Decomposers are those that feed on dead organisms (for example, scavengers like vultures and crows), and further breaking down of the dead matter by other decomposing agents like bacteria and various micro-organisms.

Generally, two types of food-chains are recognised: grazing food-chain and detritus food- chain. In a grazing food-chain, the first level starts with plants as producers and ends with carnivores as consumers at the last level, with the herbivores being at the intermediate level.

There are five major biomes — forest, desert, grassland, aquatic and altitudinal biomes.

The sun is the basic source of energy on which ail life depends. This energy’ initiates life processes in the biosphere through photosynthesis, the main source of food and energy for green plants.

During photosynthesis, carbon dioxide is converted into organic compounds and oxygen. Out of the total solar insolation that reaches the earth’s surface, only a very small fraction (0.1 per cent) is fixed in photosynthesis. More than half is used for plant respiration and the remaining part is temporarily stored or is shifted to other portions of the plant.

Oxygen is the main by-product of photosynthesis. Oxygen occurs in a number of chemical forms and combinations. It combines with nitrogen to form nitrates and with many other minerals and elements to form various oxides such as the iron oxide, aluminium oxide and others. Much of oxygen is produced from the decomposition of water molecules by sunlight during photosynthesis and is released in the atmosphere through transpiration and respiration processes of plants.

Other than carbon, oxygen, nitrogen and hydrogen being the principal geochemical components of the biosphere, many other minerals also occur as critical nutrients for plant and animal life. These mineral elements required by living organisms are obtained initially from inorganic sources such as phosphorus, sulphur, calcium and potassium.

Class 11 Geography Notes Chapter 15 Important Terms:

• Biosphere: The biosphere includes all the living components of the earth. It consists of all plants and animals, including all the micro-organisms that live on the planet earth and their interactions with the surrounding environment.
• Environment: The environment is made up of abiotic and biotic components.
• Ecology: The term ecology is derived from the Greek word ‘oikos’ meaning ‘house’, combined with the word ‘logy’ meaning the ‘science of or ‘the study of. Literally, ecology is the study of the earth as a ‘household’, of plants, human beings, animals and micro-organisms.
• Ecological systems: The interactions of a particular group of organisms with abiotic factors within a particular habitat resulting in clearly defined energy flows and material cycles on land, water and air, are called ecological systems.
• Habitat: A habitat in the ecological sense is the totality of the physical and chemical factors that constitute the general environment.
• Ecosystem: A system consisting of biotic and abiotic components is known as ecosystem.
• Ecological adaptation: All these components in ecosystem are inter-related and interact with each other. Different types of ecosystems exist with varying ranges of environmental conditions where various plants and animal species have got adapted through evolution. This phenomenon is known as ecological adaptation.
• Abiotic factors: Abiotic factors include rainfall, temperature, sunlight, atmospheric humidity, soil conditions, inorganic substances (carbon dioxide, water, nitrogen, calcium, phosphorus, potassium, etc.).
• Biotic factors: Biotic factors include the producers, the consumers (primary, secondary, tertiary) and the decomposers.
• Producers: The producers include all the green plants, which manufacture their own food through photosynthesis.
• Primary consumers: The primary consumers include herbivorous animals like deer, goats, mice and all plant-eating animals.
• Carnivores: The carnivores include all the flesh-eating animals like snakes, tigers and lions. Certain carnivores that feed also on carnivores are known as top carnivores like hawks and mongooses.
• Decomposers: Decomposers are those that feed on dead organisms (for example, scavengers like vultures and crows), and further breaking down of the dead matter by other decomposing agents like bacteria and various micro- organisms.
• Biome: A biome is a plant and animal community that covers a large geographical area. The boundaries of different biomes on land are determined mainly by climate. Therefore, a biome can.be defined as the total assemblage of plant and animal species interacting within specific conditions.
• Food Chain: This sequence of eating and being eaten and the resultant transfer of energy from one level to another is known as the food-chain.
• Flow of energy: Transfer of energy that occurs during the process of a food chain from one level to another is known as flow of energy.
• Food web: The food- chains get interlocked with one another. This inter- connecting network of species is known as food web.
• Water cycle: All living organisms, the atmosphere and the lithosphere maintain between them a circulation of water in solid, liquid or gaseous form. This is known as the water or hydrologic cycle.
• Oxygen cycle: Oxygen is the main by-product of photosynthesis. It is involved in the oxidation of carbohydrates with the release of energy, carbon dioxide and water. The cycling of oxygen is a highly complex process.
• Denitrification: Some bacteria can even convert nitrites into nitrates that can be used again by green plants. There are still other types of bacteria capable of converting nitrates into free nitrogen, a process known as denitrification.
• Biogeochemical cycle: Bio refers to living organisms and geo to rocks, soil, air and water of the earth. These cyclic movements of chemical elements of the biosphere between the organism and the environment are referred to as biogeochemical cycles.
• Ecological balance: Ecological balance is a state of dynamic equilibrium within a community of organisms in a habitat or ecosystem. It can happen when the diversity of the living organisms remains relatively stable.
• Succession: This change is due to competition where the secondary forest species such as grasses, bamboos or pines overtakes the native species changing the original forest structure. This is called succession.

Class 11 Geography Notes

Class 11 Geography Notes Chapter 14 Movements of Ocean Water

The ocean water is dynamic. The horizontal and vertical motions are common in ocean water bodies.

The horizontal motion refers to the ocean currents and waves. The vertical motion refers to tides. Ocean currents are the continuous flow of huge amount of water in a definite direction while the waves are the horizontal motion of water.

Water moves ahead from one place to another through ocean currents while the water in the waves does not move, but the wave trains move ahead.

Water particles only travel in a small circle as a wave passes. Wind provides energy to the waves. Wind causes waves to travel in the ocean and the energy is released on shorelines.

The largest waves are found in the open oceans. Waves continue to grow larger as they move and absorb energy from the wind.

Most of the waves are caused by the wind driving against water. When a breeze of two knots or less blows over calm water, small ripples form and grow as the wind speed increases until white caps appear in the breaking waves. Waves may travel thousands of kilometers before rolling ashore, breaking and dissolving as surf. A wave’s size and shape reveal its origin.

The moon’s gravitational pull to a great extent and to a lesser extent the sun’s gravitational pull, are the major causes for the occurrence of tides. Another factor is centrifugal force, which is the force that acts to counter balance the gravity.

Together, the gravitational pull and the centrifugal force are responsible for creating the two major tidal bulges on the earth.

On the side of the earth facing the moon, a tidal bulge occurs while on the opposite side though the gravitational attraction of the moon is less as it is farther away, the centrifugal force causes tidal bulge on the other side.

The highest tides in the world occur in the Bay of Fundy in Nova Scotia, Canada. The tidal bulge is 15 – 16 m. Because there are two high tides and two low tides every day (roughly a 24 hour period); then a tide must come in within about a six hour period. As a rough estimate, the tide rises about 240 cm an hour (1,440 cm divided by 6 hours).

The most common tidal pattern is semi-diurnal tide, featuring two high tides and two low tides each day. The successive high or low tides are approximately of the same height.

The height of rising water (high tide) varies appreciably depending upon the position of sun and moon with respect to the earth. When the sun, the moon and the earth are in a straight line, the height of the tide will be higher. These are called spring tides and they occur twice a month, one on full moon period and another during new moon period.

Normally, there is a seven day interval between the spring tides and neap tides. At this time the sun and moon are at right angles to each other and the forces of the sun and moon tend to counteract one another.

Once in a month, when the moon’s orbit is closest to the earth (perigee), unusually high and low tides occur. During this time the tidal range is greater than normal.

When the earth is closest to the sun (perihelion), around 3rd January each year, tidal ranges are also much greater, with unusually high and unusually low tides. When the earth is farthest from the sun (aphelion), around 4th July each year, tidal ranges are much less than average.

Usually, the currents are strongest near the surface and may attain speeds over five knots. At depths, currents are generally slow with speeds less than 0.5 knots. We refer to the speed of a current as its “drift.” Drift is measured in terms of knots. The strength of a current refers to the speed of the current. A fast current is considered strong. A current is usually strongest at the surface and decreases in strength (speed) with depth. Most currents have speeds less than or equal to 5 knots.

Surface currents constitute about 10 per cent of all the water in the ocean, these waters are the upper 400 m of the ocean and deep water currents make up the other 90 per cent of the ocean water. These waters move around the ocean basins due to variations in the density and gravity.

Heating by solar energy causes the water to expand. That is why, near the equator the ocean water is about 8 cm higher in level than in the middle latitudes. This causes a very slight gradient and water tends to flow down the slope. Wind blowring on the surface of the ocean pushes the water to move.

Ocean currents are classified into cold currents and warm currents on the basis of temperature. Cold-water ocean currents occur when the cold water at the poles sinks and slowly moves towards the equator. Warm-water currents travel out from the equator along the surface, flowing towards the poles to replace the sinking cold water.

The mixing of warm and cold currents help to replenish the oxygen and favour the growth of planktons, the primary food for fish population. The best fishing grounds of the world exist mainly in these mixing zones.

Class 11 Geography Notes Chapter 14 Important Terms:

• Waves: Waves are actually the energy, not the water as such, which moves across the ocean surface.
• Tides: The periodical rise and fall of the sea level, once or twice a day, mainly due to the attraction of the sun and the moon, is called a tide.
• Surges: Movement of water caused by meteorological effects (winds and atmospheric pressure changes) are called surges.
• Tide generating force: The ‘tide-generating’ force is the difference between two forces; i. e. the gravitational attraction of the moon and the centrifugal force.
• Tidal currents: When the tide is channelled between islands or into bays and estuaries they are called tidal currents.
• Ebb: The time between the high tide and low tide, when the water level is falling, is called the ebb.
• Flow or Flood: The time between the low tide and high tide, when the tide is rising, is called the flow or flood.
• Crest: The highest point of a wave is called the crest
• Trough: The lowest point of a wave is called trough.
• Wave height: It is the vertical distance from the bottom of a trough to the top of a crest of a wave.
• Wave amplitude: It is one-half of the wave height.
• Wave period: It is merely the time interval between two successive wave crests or troughs as they pass a fixed point.
• Wavelength: It is the horizontal distance between two successive crests.
• Wave speed: It is the rate at which the wave moves through the water, and is measured in knots.
• Wave frequency: It is the number of waves passing a given point during a one second time interval.
• Semi-diurnal tide: The most common tidal pattern, featuring two high tides and two low tides each day. The successive high or low tides are approximately of the same height.
• Diurnal tide: There is only one high tide and one low tide during each day. The successive high and low tides are approximately of the same height.
• Mixed tide: Tides having variations in height are known as mixed tides. These tides generally occur along the west coast of North America and on many islands of the Pacific Ocean.
• Spring tides: The position of both the sun and the moon in relation to the earth has direct bearing on tide height. When the sun, the moon and the earth are in a straight line, the height of the tide will be higher. These are called spring tides.
• Perigee: The time when the moon’s orbit is closest to the earth is called perigee.
• Apogee: The time when the moon is farthest from earth is called apogee.
• Perihelion: When the earth is closest to the sun.
• Aphelion: When the earth is farthest from the sun
• Gyres: Gravity tends to pull the water down the pile and create gradient variation. The Coriolis force intervenes and causes the water to move to the right in the northern hemisphere and to the left in the southern hemisphere. These large accumulations of water and the flow around them are called Gyres.

Class 11 Geography Notes

Class 11 Geography Notes Chapter 12 World Climate and Climate Change

Three broad approaches have been adopted for classifying climate. They are empirical, genetic and applied.

Koeppen identified a close relationship between the distribution of vegetation and climate. He selected certain values of temperature and precipitation and related them to the distribution of vegetation and used these values for classifying the climates.

Climatic Groups According to Koeppen:

Group	Characteristics
A – Tropical	Average temperature of the coldest month is 18° C or higher.
B – Dry Climates	Potential evaporation exceeds precipitation.
C – Warm Temperature	The average temperature of the coldest month of the (Mid-latitude) climates years is higher than minus 3°C but below 18°C.
D – Cold Snow Forest Climates	The average temperature of the coldest month is minus 3°C or below.
E – Cold Climates	Average temperature for all months is below 10°C.
H – High Land	Cold due to elevation.

Koeppen introduced the use of capital and small letters to designate climatic groups and types.

It was developed in 1918 and modified over a period of time, but Koeppen’s scheme is still popular and in use. Koeppen recognized five major climatic groups, four of them are based on temperature and one on precipitation.

The capital letters: A,C, D and E delineate humid climates and B dry climates. The climatic groups are subdivided into types, designated by small letters, based on seasonality of precipitation and temperature characteristics. The seasons of dryness are indicated by the small letters : f, m, w and s.

Tropical humid climates exist between Tropic of Cancer and Tropic of Capricorn. The sun being overhead throughout the year and the presence of Inter Tropical Convergence Zone (ITCZ) make the climate hot and humid. Annual range of temperature is very low and annual rainfall is high.

The tropical group is divided into three types, namely

• Af – Tropical wet climate;
• Am – Tropical monsoon climate;
• Aw – Tropical wet and dry climate.

Tropical wet climate is found near the equator. The major areas are the Amazon Basin in South America, western equatorial Africa and the islands of East Indies. Significant amount of rainfall occurs in every month of the year as thunder showers in the afternoon.

The temperature is uniformly high and the annual range of temperature is negligible. The maximum temperature on any day is around 30°C while the minimum temperature is around. 20°C. Tropical evergreen forests with dense canopy cover and large biodiversity are found in this climate.

Tropical monsoon climate (Am) is found over the Indian sub-continent, North Eastern part of South America and Northern Australia. Heavy rainfall occurs mostly in summer. Winter is dry.

Climatic Types:

Dry climates are characterized by very low rainfall that is not adequate for the growth of plants. These climates cover a very large area of the planet extending over large latitudes from 15° – 60° north and south of the equator.

Subtropical Steppe (BSh) and Subtropical Desert (BWh) climates have common precipitation and temperature characteristics. These are located in the transition zone between humid and dry climates, subtropical steppe receives slightly more rainfall than the desert, adequate enough for the growth of sparse grasslands.

Maximum temperature in the summer is very high. The highest shade temperature of 58° C was recorded at A1 Aziziyah, Libya on 13 September 1922. The annual and diurnal ranges of temperature are also high.

Mediterranean climate occurs around Mediterranean sea, along the west coast of continents in subtropical latitudes between 30° – 40° latitudes.

Central California, Central Chile, along the coast in south eastern and south western Australia are examples of Mediterranean climate. These areas come under the influence of subtropical high in summer and westerly wind in winter. Hence, the climate is characterised by hot, dry summer and mild, rainy winter. Monthly average temperature in summer is around 25° C and in winter below 10°C. The annual precipitation ranges between 35 – 90 cm.

Humid subtropical climate occur in eastern United States of America, southern and eastern China, southern Japan, north eastern Argentina, coastal south Africa and eastern coast of Australia. The annual average of precipitation vary from 75-150 cm. Thunderstorms in summer and frontal precipitation in winter are common. Mean monthly temperature in summer is around 27°C, and in winter it varies from 5°-12° C. The daily range of temperature is small.

India also witnessed alternate wet and dry periods. Archaeological findings show that the Rajasthan desert experienced wet and cool climate around 8,000 B.C. The period 3,000-1,700 B.C. had higher rainfall. From about 2,000-1,700 B.C., this region was the centre of the Harappan civilisation.

Dry conditions accentuated since then. In the geological past, the earth was warm some 500-300 million years ago, through the Cambrian, Ordovician and Silurian periods. During the Pleistocene epoch, glacial and inter-glacial periods occurred, the last major peak glacial period was about 18,000 years ago. The present inter-glacial period started 10,000 years ago.

The 1990s recorded the warmest temperature of the century and some of the worst floods around the world. The worst devastating drought in the Sahel region, south of the Sahara desert, from 1967-1977 is one such variability.

During the 1930s, severe drought occurred in south-western Great Plains of the United States, described as the dust bowl. Historical records of crop yield or crop failures, of floods and migration of people tell about the effects of changing climate.

Europe witnessed “Little Ice Age” from 1550 to about 1850. From about 1885-1940 world temperature showed an upward trend. After 1940, the rate of increase in temperature slowed down.

The term greenhouse is derived from the analogy to a greenhouse used in cold areas for preserving heat. A greenhouse is made up of glass. The glass which is transparent to incoming short wave solar radiation is opaque to outgoing long wave radiation. The glass, therefore, allows in more radiation and prevents the long wave radiation going outside the glass house, causing the temperature inside the glasshouse structure warmer than outside. When you enter a car or a bus, during summers, where windows are closed, you feel more heat than outside. Likewise during winter the vehicles with closed doors and windows remain warmer than the temperature outside. This is another example of the greenhouse effect.

Greenhouse gases are carbon dioxide (C02), Chlorofluorocarbons (CFCs), methane (CH4), nitrous oxide (N20) and ozone (03). Some other gases such as nitric oxide (NO) and carbon monoxide (CO) easily react with GHGs and affect their concentration in the atmosphere.

The largest concentration of GHGs in the atmosphere is carbon dioxide. The emission of C02 comes mainly from fossil fuel combustion (oil, gas and coal).

Ozone occurs in the stratosphere where ultra-violet rays convert oxygen into ozone. Thus, ultra violet rays do not reach the earth’s surface. The CFCs which drift into the stratosphere destroy the ozone. Large depletion of ozone occurs over Antarctica. The depletion of ozone concentration in the stratosphere is called the ozone hole.

International efforts have been initiated for reducing the emission of GHGs into the atmosphere. The most important one is the Kyoto protocol proclaimed in 1997.

Class 11 Geography Notes Chapter 12 Important Terms:

• Empirical Classification: It is based on observed data, particularly on temperature and precipitation.
• Genetic Classification: It attempts to organise climates according to their causes.
• Applied Classification: It is used when classification is done for specific purpose.
• Koeppen’s scheme of classification of climate: It is the most widely used classification of climate is the empirical climate classification scheme developed by V. Koeppen. Koeppen identified a close relationship between the distribution of vegetation and climate. He selected certain values of temperature and precipitation and related them to the distribution of vegetation and used these values for classifying the climates.
• Ozone Hole: The depletion of ozone concentration in the stratosphere is called the ozone hole.
• Greenhouse gases: The gases that absorb long wave radiation are called greenhouse gases.
• Greenhouse effect: The processes that warm the atmosphere are often collectively referred to as the greenhouse effect.
• Daily range of temperature: The differences between the highest and lowest temperature of a place in a day is called daily range of temperature.
• Dust bowl: During the 1930’s, severe drought occurred in southwestern Great Plains of the United States. These are described as the dust bowl.
• Greenhouse: The term greenhouse is derived from the analogy to a greenhouse used in cold areas for preserving heat. A greenhouse is made up of glass. The glass which is transparent to incoming short wave solar radiation is opaque to outgoing long wave radiation.
• Sunspots: Sunspots are dark and cooler patches on the sun which increase and decrease in a cyclical manner.

Class 11 Geography Notes

Class 11 Geography Notes Chapter 11 Water in the Atmosphere

The air contains water vapour. It varies from zero to four per cent by volume of the atmosphere and plays an important role in the weather phenomena.

Water is present in the atmosphere in three forms namely—gaseous, liquid and solid.

The moisture in the atmosphere is derived from water bodies through evaporation and from plants through transpiration. Thus, there is a continuous exchange of water between the atmosphere, the oceans and the continents through the processes of evaporation, transpiration, condensation and precipitation.

The air containing moisture to its full capacity at a given temperature is said to be saturated. It means that the air at the given temperature is incapable of holding any additional amount of moisture at that stage. The temperature at which saturation occurs in a given sample of air is known as dew point.

The ability of the air to hold water vapour depends entirely on its temperature. The absolute humidity differs from place to place on the surface of the earth. The percentage of moisture present in the atmosphere as compared to its full capacity at a given temperature is known as the relative humidity.

With the change of air temperature, the capacity to retain moisture increases or decreases and the relative humidity is also affected. It is greater over the oceans and least over the continents.

Movement of air replaces the saturated layer with the unsaturated layer. Hence, the greater the movement of air, the greater is the evaporation.

The transformation of water vapour into water is called condensation. Condensation is caused by the loss of heat. When moist air is cooled, it may reach a level when its capacity to hold water vapour ceases.

Condensation also takes place when the moist air comes in contact with some colder object and it may also take place when the temperature is close to the dew point.

After condensation the moisture of atmosphere or humidity gets converted into dew, fog, mist, frost and clouds.

The ideal conditions for formation of dew are clear sky, calm air, high relative humidity, and cold and long nights.

Frost forms on cold surfaces when condensation takes place below freezing point (0°C), i.e. the dew point is at or below the freezing point.

The only difference between the mist and fog is that mist contains more moisture than the fog. In mist each nuclei contains a thicker layer of moisture.

Fogs are drier than mist and they are prevalent where warm currents of air come in contact with cold currents. Fogs are mini clouds in which condensation takes place around nuclei provided by the dust, smoke, and the salt particles.

Cloud is a mass of minute water droplets or tiny crystals of ice formed by the condensation of the water vapour in free air at considerable elevations. According to their height, expanse, density and transparency or opaqueness clouds are grouped under four types :

• cirrus
• cumulus
• stratus
• nimbus.

Cirrus clouds are formed at high altitudes (8,000-12,000m). They are thin and detatched clouds having a feathery appearance. They are always white in colour.

Cumulus clouds look like cotton wool. They are generally formed at a height of4,000-7,000 m. They exist in patches and can be seen scattered here and there. They have a flat base.

Stratus are layered clouds covering large portions of the sky. These clouds are generally formed either due to loss of heat or the mixing of air masses with different temperatures.

Nimbus clouds are black or dark gray. They form at middle levels or very near to the surface of the earth.

On the basis of origin, rainfall may be classified into three main types — the convectional, orographic or relief and the cyclonic or frontal.

Convectional rain takes place when the air on being heated, becomes light and rises up in convection currents. As it rises, it expands and loses neat and consequently, condensation takes place and cumulous clouds are formed. With thunder and lightening, heavy rainfall takes place but this does not last long.

Orographic rain occurs when the saturated air mass comes across a mountain, it is forced to ascend and as it rises, it expands; the temperature falls, and the moisture is condensed. The chief characteristic of this sort of rain is that the windward slopes receive greater rainfall.

Different places on the earth’s surface receive different amounts of rainfall in a year and that too in different seasons. In general, as we proceed from the equator towards the poles, rainfall goes on decreasing steadily. The coastal areas of the world receive greater amounts of rainfall than the interior of the continents. The rainfall is more over the oceans than on the landmasses of the world.

Between the latitudes 35° and 40° N and S of the equator, the rain is heavier on the eastern coasts and goes on decreasing towards the west. But, between 45° and 65° N and S of equator, the rainfall is first received on the western margins of the continents and it goes on decreasing towards the east.

In some regions rainfall is distributed evenly throughout the year such as in the equatorial belt and in the western parts of cool temperate regions.

Distribution Of Clouds:

Classification of clouds on the basis of average height	Sub-categories or types of clouds	Features or characteristics
High Clouds 5 km to 14 km	Cirrus	Cirrus clouds are formed at high altitudes. They are soft and silk like shaped.
	Cirrostratus	They are thin and detatched clouds having a feathery appearance. They are always white in colour.
	Corrocumulus	These clouds look like small white circular shaped. They do not have any shadow
Medium Clouds	Altostratu	They are blue or brown in colour. They have fibres like look.
	Altocumulus	These are flattened circles like clouds which are organised like waves.
Low Clouds	Stratocumulus	Soft and brownish clouds in a group which have a shining.
	Nimobostratus	They are low and same layer clouds which look like fog but they are not stable on surface of the earth.
Clouds with extensive vertical development	Cumulus	Cumulus clouds look like cotton wool. They are generally formed at a height of 4,000-7,000 m. They exist in patches and can be seen scattered here and there. They have a flat base.
	Cumulonimbus	They are formed on mountains and cause rainfall.

 

Class 11 Geography Notes Chapter 11 Important Terms:

• Humidity: Water vapour present in the air is known as humidity.
• Evaporation: It is a process by which water is transformed from liquid to gaseous state. Heat is the main cause for evaporation.
• Latent heat of vaporisation: The temperature at which the water starts evaporating is referred to as the latent heat of vaporisation.
• Absolute humidity: The actual amount of the water vapour present in the atmosphere is known as the absolute humidity. It is the weight of water vapour per unit volume of air and is expressed in terms of grams per cubic metre.
• Relative humidity: The percentage of moisture present in the atmosphere as compared to its full capacity at a given temperature is known as the relative humidity.
• Dew points: The temperature at which saturation occurs in a given sample of air is known as dew point.
• Dew: When the moisture is deposited in the form of water droplets on cooler surfaces of solid objects (rather than nuclei in air above the surface) such as stones, grass blades and plant leaves, it is known as dew.
• Condensation: The transformation of water vapour into water is called condensation. Condensation is caused by the loss of heat.
• Sublimation: When moist air is cooled, it may reach a level when its capacity to hold water vapour ceases. Then, the excess water vapour condenses into liquid form. If it directly condenses into solid form, it is known as sublimation.
• Precipitation: After the condensation of water vapour, the release of moisture is known as precipitation. This may take place in liquid or solid form.
• Rainfall: The precipitation in the form of water is called rainfall.
• Snowfall: When the temperature is lower than the 0°C, precipitation takes place in the form of fine flakes of snow and is called snowfall.
• Orographic rain: When the saturated air mass comes across a mountain, it is forced to ascend and as it rises, it expands; the temperature falls, and the moisture is condensed. It is also known as the relief rain.
• Rain shadow area: The area situated on the leeward side, which gets less rainfall is known as the rain-shadow area.
• Cyclonic rain: Rain caused by a cyclone is called cyclonic rain.
• Hailstones: Sometimes, drops of rain after being released by the clouds become solidified into small rounded solid pieces of ice and which reach the surface of the earth are called hailstones.
• Convectional rain: The air on being heated, becomes light and rises up in convection currents. As it rises, it expands and loses heat and consequently, condensation takes place and cumulous clouds are formed. With thunder and lightening, heavy rainfall takes place but this does not last for long.
• Frost: Frost forms on cold surfaces when condensation takes place below freezing point (0°C), i.e. the dew point is at or below the freezing point.
• Fog and Mist: When the temperature of an air mass containing a large quantity of water vapour falls all of a sudden, condensation takes place within itself on fine dust particles. So, the fog is a cloud with its base at or very near to the ground.
• Smog: A condition when fog is mixed with smoke, is described as smog.
• Clouds: Cloud is a mass of minute water droplets or tiny crystals of ice formed by the condensation of the water vapour in free air at considerable elevations. As the clouds are formed at some height over the surface of the earth, they take various shapes.

Class 11 Geography Notes