Current Affairs 4th Class

       Global Warming   Global warming simply means increase in the average temperature of the earth's atmosphere. The sun's radiation falling on the earth is partly absorbed and a part of it is reflected back into the space. The part of the rays reflected back is trapped by our atmosphere. This trapped radiation further warms the earth, which is known as the greenhouse effect. This effect is however one of the major reason for life on this planet. The carbon dioxide present in the air is responsible for this greenhouse effect. Carbon dioxide is very essential for the life of the plants, but the excess amount of it is harmful. The amount of carbon dioxide is continuously on increase due to human activities and decreasing forest cover. The number of trees, which consume carbon dioxide is reducing, causing an increase in the carbon dioxide accumulation. Carbon dioxide traps heat and does not allow it to escape into the outer space.    Global Warming    This results in an increase in the temperature of the earth's atmosphere. The process of gradual increase in the earth's temperature is called global warming. Global warming has becomes major concern worldwide. This is a serious issue and needs everyone to work for this alarming cause. Rise in even 0.5°C can cause glacier to melt and sea levels to rise. It has a wide range of other effects like, on the pattern of rainfall, agriculture, forest, plants and animals.               The Gas responsible for greenhouse effect (a) Carbon dioxide (b) Methane (c) Nitrous oxide (d) Both (a) and (b) (e) (a), (b) and (c)   Answer: (e)          Global warming is known as: (a) Average temperature of the earth's atmosphere is gradually increasing (b) Average temperature of the sun's atmosphere is gradually increasing (c) Portion of the globe which faces the sun (d) Both A and B (e) None of the above   Answer: (a)

     Acid Rain   Harmful gases released by the burning of coal, by automobiles, factories, oil refinery mix with water vapour present in the air to form harmful substance called acid. The acid comes down with rain making the rain acidic. This is called acid rain. This acid rain can cause damage to soil, plants, organism that lives in the rivers, streams, lakes etc. Acid rain even causes damage to the buildings and results in harmful diseases in humans. The damaging effect of acid rain can best be seen in our great heritage building, Taj Mahal. The white marbles of Taj Mahal are getting discolored by the effect of acid rain. The monument does not look as white as it use to look some 30-40 years back. Government of India is taking several steps to save the Taj.               Formation of acid rain                Acid rain a very dangerous phenomenon is mainly due to which type of pollution? (a) Water (b) Soil (c) Air (d) Food (e) All of the above   Answer: (c)           Acid rain is caused due to which of the following activities: (a) Volcanoes (b) Smoke from factories (c) Fossil burning (d) All of these (e) None of the above   Answer: (d)

       Effects of Pollution   Any type of pollution is very harmful for the living things. Let's know about them.               Effects of Air Pollution Air pollution makes air unfit for breathing. Taking in this air causes breathing problems and lung diseases. Global warming and acid rain are other major effects of air pollution. Air pollution also has been damaging ozone layer which protects us from ultra violet rays coming from space and save the life on the earth.                            Effects of air pollution on plants              Effects of air pollution on human health              Effect of Water Pollution The unfit or polluted water if used for drinking can cause dysentery, diarrhea typhoid and many other diseases. The living organisms present in the water bodies, where chemical waste is thrown, too becomes poisonous. If we consume these fish, crab etc. we are likely to fall sick.  Effect of Water Pollution               Effect of Soil Pollution Soil gets polluted by the chemicals used to kill pest and weeds (unwanted plants). Chemical fertilizers used for higher productivity, seeps slowly into the soil layers. Crops grown on these soils is not good for our health. These chemicals are slowly getting into the food chain. Effects of land                Respiratory problems are rising day by day. This is due to which type of pollution? (a) Water pollution (b) Air pollution (c) Land pollution (d) Both (a) and (b)         (e) All of the above   Answer: (b)       Look at the following picture carefully It is one of the major source of_________. (a) Air pollution (b) Land pollution (c) Water pollution (d) A and B (e) None of these   Answer: (a)

       Types of Pollution   Pollution is spoiling of natural resources like air, water and soil by releasing harmful substances. Pollution of air, water and soil has had harmful effects not only on us but on the entire living world.            Air Pollution Harmful substance in the air causing bad effect on the living thing, is called air pollution. Most of the air pollution comes from the smoke of factories, vehicles, burning of fuels etc.              Air pollution                Water pollution When harmful substance from factories, farms/ hospitals, sewage from homes are thrown into the water bodies like river, pond, lake and ocean, this causes water pollution. Mixing of unwanted substances, which makes water unfit for drinking and other purposes, is called water pollution. The release of harmful substances kills the living organisms present in water. The balance of the living things in the water bodies is destroyed and the water becomes unfit for use.           Water pollution                Land or Soil Pollution When harmful and poisonous substances are released into the soil, it pollutes the soil. This is known as soil pollution. The use of chemical fertilizer and chemicals pesticides (kill pest) in the farmland pollutes the soil. Throwing of the waste is also a major cause of soil pollution. The waste like plastic bags, tyre-tube (non-biodegradable) remains on the surface of the soil for a very long time, because non-biodegradable substances are not easily disintegrated into soil. Thus non-biodegradable substances are one of the major cause of soil pollution. Land pollution due to accumulation of waste                  The substances that cause pollution are called___________. (a) Dirt (b) Pollutants (b) Smoke (d) Both A and C (e) None of the above   Answer: (b)            Consider the statements given bellow and select the right answer. Statement A: Pollution are caused by natural factors also. Statement B: Human being also contributes to pollution in a large way. (a) Statement A is correct (b) Statement B is correct (c) Both Statement A and B are correct (d) Statement A is correct but B is false (e) Both Statement A and B are false   Answer: (c)

   Environment   Environment is the natural surroundings of a living thing in which it lives and survives. Environment is everything that makes up the surrounding of a living thing.                                                                                                                        Natural Environment                 Environment comprise of both living (biotic) and non living things (abiotic). The non living things in the environment are sunlight, water, air, temperature etc. The living things in the environment are human, plants, animals, etc. Each living thing has its own environment where it lives and grows. For example environment of a plant are sunlight, weather, air, water, soil in which it grows and the animal that consumes it. We, human beings, depend on our environment for all our need?. Each of the living things depends on the other living and non living thing in its environment for its survival. Humans, while making life more comfortable for themselves, have damaged the environment in which they live, in many ways. Our actions are causing disastrous change in the environment. We exploit our environment to our maximum utility and in turn do nothing for its good. The condition is very alarming and needs proper thinking and action. We should do everything possible to save our environment before it is too late.

     Soil Conservation   Soil conservation is the process in which we use techniques that will protect the soil from agents like wind and water. This also takes into account the methods that add to the fertility and protects the natural qualities of the soil.               The Technique and the Methods of Soil Conservation are              Afforestation Afforestation is also known as planting of trees. This is a major check on the rate of soil erosion. Trees and grasses grown on hilly areas prevents soil erosion by water flowing down the slope.       Afforestation                Soil Cover The farm land should be covered with grasses or dried trees and bushes after harvesting of a crop. This will ensure that the soil is not bare and wind cannot easily carry it away.            Soil Cover             Shelter Belts Soil erosion can be reduced by reducing the speed of the wind. Hedges and small bushy trees can be grown along the edge of the farmland as wind breakers.        Shelter Belts                Crop Rotation Crop rotation simply means rotation of planing of the crops. Different crops should be grown on the farmland one alternating the other. This gives soil the time to recoverthe minerals that earlier crop have used. It also helps to maintain the quality and fertility of the soil.    Crop Rotation              Terrace or Step Farming Terrace or step farming is done in hills by cutting steps in the slopes. This type of farming reduces the speed of water as it flow down. As a result erosion of soil gets reduced. The soil removed from one step is deposited on the next step. This helps in further slowing down of erosion. Terrance or step Farming              Construction of Embankments Rivers constantly remove soil of their banks. Strong embankments of rocks so that it can bind the soil or by building dams along the banks can prevent the soil erosion by flooding.   Construction of Embankments                  Method used to retain the quality of soil and its mineral content more...

     Soil Erosion   Soil erosion means the removal of the topsoil (the fertile layer) by the action of natural forces, like, wind and water. It is a slow and steady process where the top layer is lost and the land becomes barren and unfit for agriculture. Soil erosion is a natural process but the rate of this process has greatly increased by human activities, which are discussed below.               Soil Erosion                Deforestation Cutting down of trees is called deforestation. We cut down trees, clear up forests to build our farms, hotels, houses. This provides us both space and the wood for our need. But in the process, as land gets cleared of vegetation, no roots remained to hold the top soil. This leads to an increase in soil erosion. Ploughing of the land leaves the soil loose and this also leads to soil erosion        Deforestation             Overgrazing by Animals Overgrazing of the land by cattle, goat, sheep, which is reared by human’s beings for their needs, is another cause of soil erosion. Overgrazing exposes the soil by removing the plants shield that protects it. This in turn causes an increase in soil erosion.        Overgrazing of the land by the camels                  The carrying away of the top soil by natural agents like wind and water is called: (a) Degradation (b) Soil pollution (c) Soil erosion (d) Leaching                                       (e) All of the above.   Answer: (c)           Deforestation is: (a) Growing of trees (b) Cutting of trees (c) Trimming trees (d) Caring of trees                           (e) None of the above   Answer: (b)

     Layers of Soil   Soil is defined as the upper layer of the earth's surface, which contains sand, organic matter (dead animals or plants), minerals with little amount of water and air. It is the one of the most important natural resources, which is capable of supporting life on earth. Soil support and nourish plant life. It is also home to many small animals and microorganism. Soil profile is the vertical section of the soil, from the surface to the bedrock below. Each layer of the soil has different colour and texture. These layers are called horizons. A typical soil profile has four different layers.        Different Layers of Soil                  A Horizon or Topsoil This is the dark coloured uppermost layer rich in humus.              Horizon or Subsoil This is middle layer generally coarse and rich in minerals. It is light in colour due to very less amount of humus              Horizon or Weathered Rocks This is the third layer which is made up of small lumps of rocks crevices cracks. It is the zone of infertility.              Horizon or Bedrocks The fourth layer is made up of unweathered, non-porous and impervious parent rocks. This is the bedrock. This layer is hard and very difficult to dig. This layer provides the base for the upper three layers               Which one of the following is the uppermost layer of the soil? (a) A-horizon (b) B-horizon (c) C-horizon (d) D-horizon                                     (e) All of these   Answer: (a)            Julia took some soil in a covered container. She heated it slowly, after some time she observed some droplets of water under the cover of the container. What does this show? (a) Soil has humus (b) Soil has sand (c) Soil has gravel   (d) Soil has moisture                       (e) Soil has air   Answer: (d)

     Introduction   The earth as we see it is made up of rocks, soil, and minerals.                                                       Rocks                                                                 Soil                                                     Minerals   The lower layers of the soil are the rocks. If you observe a rock closely you wilt see small grains on it. A single rock may have grains of different colour. These grains are the minerals occurring naturally. Many rocks that contain metals are called ores. We get iron, copper, aluminium from their respective ores. Gemstones are the minerals in the form of crystals e.g. diamond, emeralds, rubies etc. Soil is the uppermost layer of the earth's surface. Soil is responsible for the greenery and life on the earth's surface. It supports the plants, which produces food for the entire living world. Soil is also home to many microorganisms and insects. There are different kinds of soil. Sandy soil, clayey soil and loamy soil.          Types of Rocks and Their Uses Our earth is made up of rocks. There are 3 kinds of rocks. They are: (a) Igneous rocks (b) Sedimentary rocks (c) Metamorphic rocks              Igneous Rocks Igneous rocks are formed from the molten rock material. The hot liquid material comes out on the earth surface, from deep inside the earth, through cracks and then cools down. These rocks contain minerals such as quartz, mica, silica, iron etc. Granite and pumice are two important type of igneous rocks.          Igneous Rock                Sedimentary Rocks Sedimentary rocks are formed by splitting up of materials, such as gravels and pebbles, by wind, water and snow of the surface of the soil. As the materials pile up on the top, the pressure hardens the lower layer and converts it into rocks. For example sandstone and limestone.                   Sedemonary Rock              Metamorphic Rocks Metamorphic rocks are formed by the action of heat and pressure on clay rocks. They are rocks that have gone through changes. As the name suggests metamorphic means change. These rocks were originally sedimentary or igneous rocks. The changes make them tougher and harder, for example slate and marble.       Metamorphic Rock     more...

     Physical Change   Physical change is the change in which a substance undergoes the change in its physical properties (shape, size, colour or the state of a substance). A physical change is only a temporary change. This change can be reversed. For example tear a page from your note book into 4 square pieces. Now lay these pieces on the table in such a manner that it occupies the shape of the original piece of paper. The physical change, brought about by tearing the paper, is back by putting it in order. There is no change in the property of the paper. Change in states of water (physical change)               Chemical Change A chemical change is the change is which new substances are formed and the original substance can't be get back. The change Is permanent. For example burning of a cracker is a chemical change in which heat, sound, light and gases are produced and we cannot get back crackers. Burning of a cracker (chemical change)                Coconut oil in winter solidifies. We leave it in the sunlight and it liquefies again. This type of change in property is called. (a) No change (b) Chemical change (c) Physical change  (d) Both B and C (e) None of the above   Answer: (c)          Iron gate of a park is exposed to moist air. It gets rusted. Can you name the type of change? (a) Chemical change (b) Reversible change (c) Physical change (d) All of the above (e) None of the above   Answer: (a)     It is believed that an atom is made of 200 or more than 200 subatomic particles. A human hair is about 1 million carbon atoms. A speck of dust might contain 3 trillion atoms.     Atom: Smallest particle of an element. Molecule: A molecule is defined as a group of at least two atoms. States of Matter: Matter exist in three different states. Physical Change: Change in physical property. Chemical Change: Change in chemical property.