Force is a kind of push or a pull on an object. The interaction of one object with another results in a force between the two objects. If a force acts on an object in the directionof its motion, then the object movesfaster. If a force acts on an object opposite to the direction of its motion, then the objects slows down. Force may also change the direction of motion of an object. The effect of force changes with the direction of its application. Forces acting on an object in the same direction add to each other, while forces acting opposite to each other results in the difference of the forces.
The strength of force is called its magnitude. The international unit used to measure force is Newton. A force can change the shape and size of an object. There are many types of forces. The force resulting from the action of muscles is called muscular force. We make use of muscular force of animals like bullocks, horses and camels get our activities done. The point where force is applied on an object is called the point of contact. Friction is another type of contact force that always acts opposite to the direction of motion of the objects. Magnetic force and electro-static force are non-contact forces as they act on an object from a distance. The force of gravity is also a non-contact and an attractive force exerted by the earth on objects, due to which objects fall to the ground. Gravitational force is an attractive force between any two objects in the universe, and is a non-contact force.
Pressure The thrust acting per unit surface area is pressure. The force acting on an object perpendicular to its surface is thrust. Pressure is measured in newton/metre2, which is equal to 1 pascal (Pa). Liquids and gases exert pressure on the walls of the vessel in which they are carried. Air exerts pressure on all objects. The pressure exerted by air is called atmospheric pressure. A rubber sucker sticks to the surface of an object as atmospheric pressure acts on it. In order to fix nails to walls, sharp nails are used, as the area of contact of the nail with the wall is small and more pressure acts on it for a given force.
A suction pump sucks out all the air from a closed container, creating a vacuum in it.
Friction and its Types Friction is a force that opposes the relative motion between two surfaces of objects in contact. The force of friction always acts in a direction opposite to that of the applied force. Friction is due to irregularities on the surfaces of the objects in contact. Friction depends on the smoothness of the surfaces in contact. The force of friction depends on the nature of the surfaces in contact. The force of friction increases if the surfaces are pressed harder. Frictional force that comes into action before the start of the motion of an object is called static friction. When an object slides over another surface, the frictional force that comes into action is sliding friction. When a roller rolls over a surface, the frictional force that comes into action is rolling friction. Rolling friction is less than sliding friction, while sliding friction is less than static friction. Friction due to gases and liquids is called fluid friction, and is also called drag. Friction is a necessary evil. There are instances in daily life where friction is a necessity. For example, without friction, we cannot hold objects in our hands; we cannot walk and cannot light a match stick. Examples where friction has to be minimized and not desirable is the friction between machinery parts, which causes wear and tear.
Minimizing Friction Friction is a necessary evil. Without friction, we cannot walk, hold articles, the brakes of automobiles do not work, and the power of a motor cannot be transferred to a grinding machine. However, friction is undesirable in certain areas and we need to reduce it. Friction between the sliding surfaces of two objects can be reduced by making the surfaces in contact smooth by polishing the surfaces. Sliding friction between the moving parts of vehicles can be reduced by using oil, grease or graphite. In electrical plugs, graphite is used to reduce friction between the plug pins and the corresponding socket. In certain machines, like the drill used by a dentist, a layer of air is used as a lubricant to reduce friction between the moving parts. The interlocking of irregularities on the surfaces of two bodies in contact, which cause friction, is overcome to great extent by the use of lubricants, the material used to reduce friction, and friction is reduced. Rolling friction is less than sliding friction. Hence, sliding friction is replaced by rolling friction by using rollers, like ball bearings between the hub and the axles in the moving parts of machines and vehicles. When an object moves through a fluid, the friction offered is called fluid friction. It is also called drag. Fluid friction depends on the shape of the object and the nature of the fluid. Aeroplanes, boats, fishes and birds which move through fluids have bodies of special shape so as to reduce the friction due to fluid.
Production and Propagation of sound Sound is a form of energy that causes the sensation of hearing. Sound needs a medium to travel. Sound travels through gases, liquids and solids. The speed of sound is the maximum in solids, less in liquids and the least in gases. Sound cannot travel through vacuum. In humans, sound is produced by the voice box or the Larynx. Vocal cords in the larynx vibrate and produce sound. We hear sound with our ears. The ear drum has a vibrating membrane like a stretched rubber sheet. When a sound note reaches the ear, the ear drum vibrates, and the vibrations get converted into signals that are carried to the brain to get a sensation of hearing. To produce pleasant sounds, a number of musical instruments have been developed. Some instruments produce sound due to the vibration ofmembranes, some due to the vibration ofstrings, and some others produce sound due to the vibration of an air column. The to and fro or back and forth motion of an object is called vibration. The sitar, veena, violin, guitar and ektara are some stringed instruments. The tabla, cymbals, ghatam, kartal and manjira are some instruments that work on the vibration of a membrane, and instruments like the flute and the trumpet produce sound due to the vibration of an air column present in them.
Characteristics of sound Sound is a form of energy produced by a vibrating body. Sound requires a medium for its propagation. Sound does not propagate in vacuum. Sound is produced due to the vibration of an object.
The to and fro or back and forth motion of an object is called vibration. To produce pleasant sounds, a number of musical instruments have been developed. Some instruments produce sound due to the vibration ofmembranes, some due to the vibration ofstrings, and some others produce sound due to the vibration of an air column. The maximum displacement of a vibrating particle from its mean or equilibrium position is called its amplitude. The time taken by the vibrating particle for one full vibration or oscillation is called the time period of vibration. The number of vibrations per second is called the frequency. Frequency is measured hertz (Hz).Sound produced by any means has the following characteristics, namely, loudness, pitch or shrillness, and quality or timbre. The loudness of sound depends on its amplitude. The loudness of sound is proportional to the square of the amplitude. A roar of a lion is louder than a woman’s voice. The pitch of sound depends on its frequency. If frequency is more, then the pitch or shrillness is more. The pitch of a woman’s voice is more and it is shriller then a man’s voice. The loudness of sound is measured in Decibel (db). If loudness exceeds 80 db, then the sound becomes physically painful.
Not all sound produced by vibrating bodies is audible. The human ear can only recognise sounds of frequencies in the range of 20 Hz and 20,000 Hz. This range of frequency is called audible sound. Some animals like dogs and snakes can hear sounds of frequencies greater than 20,000 Hz. Sounds of frequencies less than 20 Hz are called infrasonic sounds, while sounds of frequencies greater than 20,000 Hz are called ultrasonic sounds
Noise and Music Any intolerable and irritating sound is called noise. The word noise comes from the Latin word nausea, meaning seasickness. Music refers to any sound that is pleasant to the ear. Sound produced by musical instruments is pleasing to the ear. But if the intensity of the sound exceeds a certain limit, then it becomes intolerable and is noise. Undesirable sounds and disturbances cause noise pollution. Noise pollution may cause high blood pressure, panic attacks and lack of sleep among those exposed to it. To reduce noise pollution, trees should be planted along roads and in residential areas, factories should not be set up in residential areas, vehicles should not blow horns around schools, hospitals and residential area, TVs and music systems should not be played at high volume. Continuous exposure to loud noise may cause temporary or even permanent hearing impairment.Sign language is used by the hearing disabled to communicate.
Conductivity of Liquids We can use a tester to check if electricity is flowing through a wire in a circuit. If the bulb in the tester glows, it indicates that current is flowing through the wire; else, current does not exist. Electrical conductivity of liquids can be explained by a simple activity of taking a liquid, like lemon juice, in a container, inserting electrodes in it, connecting the two electrodes to the terminals of a battery with a bulb between them. The bulb glows, indicating that lemon juice is a conductor of electricity. Several liquids can be checked for electrical conductivity on in the same way. We find that liquids like lemon juice, liquid soap, rain water, salt solution, etc. conduct electricity, whereas liquids like distilled water, oil, etc. do not conduct electricity. The materials that conduct electricity are conductors and those that do not conduct are called insulators. When electricity is passed through a conducting solution, the molecules of the solution dissociate into ions, which cause electrical conduction through the liquid. This process is due to the chemical effect of electric current.
Chemical Effect of Electric Current The most common application of the chemical effect of electric current is electroplating. In this process, there exists a liquid through which current passes. Two electrodes, each connected to one terminal of a battery with a switch in between, are inserted in the liquid. Electroplating is carried in industries to have an anti-reactive coating on the parts of machines so that they do not react with the raw material, to have an anti-corrosive coating for the machines so that they do not get corroded, a heat-resistive coating for parts like boilers to resist the heat produced by the machinery. Gold plating is one of the most common applications of electroplating in ornament-making. In electroplating, the solution is dissociated into the respective ions. The current in the solution flows through the ions. In the process, generally, the atoms of the electrode connected to the negative terminal of the battery, get converted into ions and pass into the solution to compensate the loss of ions in the solution. The metal of the electrode that is connected to the negative terminal of the battery is coated on the object connected to the positive terminal of the battery. The process of electroplating is used in nickel and chromium plating of the parts of vehicles that protects them from corrosion.
Introduction and Lightning Lightning is a natural phenomenon that has fascinated people for ages. Several people thought and researched about the cause of lightning and its process. Benjamin Franklin discovered that there is an electric discharge between clouds that produces a spark, and it is the electric spark between the clouds and the earth that appears as lightning. His famous kite experiment proved this fact.
The occurrence of lightning is as follows. The formation of clouds involves friction between water particles in the atmosphere. The friction charges the particles. Among the positive and negative charges, the negative charge accumulates at the bottom of the cloud and the positive charges in its top. As the accumulation of the charge increases, the cloud will create a positive charge on the ground nearby. As the amount of charge increases, the negative charge on the cloud tends to make a path towards the ground, and it results in a narrow streak of electrical discharge, which we call lightning. An electroscope is a device that detects the type of charge on a body. Like charges repel and unlike charges attract each other. This is used in an electroscope. An electroscope consists of a glass jar fitted with a cork lid and a metallic wire passing through it. There are two metallic strips at the bottom of the wire. The upper end of the wire is connected to a metal disc. A body that is positively charged is touched to the metal disc, so that the charge is transferred to the metal strips through the wire, and they diverge from each other on gaining a like charge. Now, if a negatively charged object is brought into contact with the disc, the strips converge towards each other, indicating the unlike charge on the body. Similarly, if a positively charged body is brought in contact with the metal disc, the divergence of the metal strips increases, indicating the like charge on the body. If the metal disc of the electroscope is touched with the hand, it loses its charge to the ground by transfer of charge through the human body. This is called earthing.
Lightning and Safety Lightning is caused due to the heavy electric discharge from the clouds to the earth. If lightning is not controlled, it can cause heavy damage to life and property. Hence, protective measures are of utmost importance during lightning strikes. Interiors of buildings are safe places to protect ourselves from lightning strikes. Taking shelter in interiors and not staying in open areas is one of the best measures you can take. You should not take shelter under trees when in the open, or go to an open area if outside. If you are in a vehicle, you should not come out of it; you should also close the doors and windows of the vehicle. Tall buildings are provided with lightning rods. A lightning rod is a metal rod that is erected at the top of a building. It is connected to a thick metallic plate, made of a good conducting material like copper and buried under the earth, through a thick copper wire. If lightning is likely to strike the building, it is attracted by the lightning rod, and the electrical discharge is transferred through the wire to the ground. Thus, it keeps the building safe.
Earthquakes A natural phenomenon that cannot be predicted is an earthquake. The earth consists of three major layers, called the crust, the mantle and the core. The core is further divided into the inner core and the outer core. The mantle consists of semi-solid material above which the crust floats. The crust consists of oceans and continents. The crust is divided into several parts, called tectonic plates. The regions where one tectonic plate slides against another are referred to as fault zones, and these are the regions where an earthquake is likely to occur. Hence, these zones are referred to as seismic zones. The place in the interior of the earth where an earthquake occurs is the focus, and the region on the surface of the earth that is the closest to focus is likely to experience the largest damage. This region is called the epicenter of the earthquake.
The instrument that measures the severity of an earthquake is a seismograph. It basically consists of a drum that rolls and a pendulum with a stylus that traces the waves of an earthquake on a sheet like a graph paper. The severity of an earthquake is measured on the Richter scale. A major earthquake measures 7 or more on the Richter scale.
Reflection in Plane mirrors Light is a form of energy given out by a self luminous body, which travels into infinite media. Light makes things around us visible. Objects that do not give out light of their own are called non-luminous objects. They just reflect light that falls on them. We see with our eyes. When light reflected from an object enters our eyes, the object becomes visible. A mirror changes the direction of light that falls on it. The light ray that falls on a mirror is called the incident light ray. The ray that comes back from the surface after reflection is called the reflected light ray. The point where the incident ray strikes the reflecting surface is called the point of incidence. A line drawn perpendicular to the mirror at the point of incidence is the normal. According to the laws of reflection, the incident ray, the normal at the point of incidence, and the reflected ray lie in the same plane; and the angle of incidence is equal to the angle of reflection. Light rays are visualised as parallel rays. If the rays, after reflection from a surface, are parallel, then the reflection is termed as regular reflection. The reflection from a plane mirror is an example of regular reflection. When parallel rays, after reflection from a surface, are not parallel, then it is called diffused reflection or irregular reflection. The reflection from an uneven surface is diffused reflection. If a reflected light ray is reflected again on being incident on another surface, it is termed multiple reflections. Multiple reflections are used in periscopes. Periscopes are used in submarines, war tanks and by solders in bunkers to see objects that are not visible directly. In a barber’s shop, we see the back of the head using multiple reflections of two mirrors. In a kaleidoscope, beautiful patterns are formed due to multiple reflections.
Light and Eyes We see objects around us with our eyes. The eye is an important sense organ. The human eye is roughly spherical in shape. Its transparent front part is called the cornea. Behind the cornea, there is a muscular structure called the iris. There is a small opening in the iris, whose size can be controlled, and is called the pupil. The iris controls the amount of light entering the eye. Behind the pupil, the eye has a lens, which is thicker in the middle. The lens converges light on the retina, which has a number of nerves. The nerves carry the sensations to the brain through the optic nerve. The nerves contain two types of cells - cones and rods. The cones are sensitive to bright light, while the rods are sensitive to dim light. The cones also distinguish the colour of an object. The small region where the optic nerve and the retina meet has no sensory cells, and is called the blind spot. The impression of an image on the retina lasts for th of a second. If 16 still images of an object are flashed before the eye per second, then the eye perceives the object as moving. The eye lids protect the eye from dust. The eye has the ability to form a clear image of a near and a far object. This ability is called its power of accommodation. For a normal eye, the distance for clear vision is 25 cm. This differs from person to person, and varies with age. Some persons can see near objects clearly and some others far off objects. These defects can be corrected using suitable corrective lenses. The eye sight of some people becomes foggy in their old age, and objects appear dim, due to cataract. Some people have no vision since birth. Such people use Braille to read and communicate.
Celestial Bodies Stars are always fascinating to mankind. They are the most beautiful celestial bodies, about which mankind contemplates. All the bodies in the universe, including the earth, constitute the celestial bodies. The moon is the celestial body closest to us. Phases of the moon are the most fascinating thing for people of all ages in spite of knowing the science behind the formation of the phases. The moon is a natural satellite of the earth, and it reflects the sunlight incident on it. Due to its revolution around the earth, when it is at different positions in its path, the apparent disc of the moon changes, which gives rise to its phases. When the moon is positioned between the sun and the earth, the illuminated portion of the moon is away from the earth, and we are not able to see the moon. We call this day as the ‘new moon day’. With time, the position of the moon changes and the illuminated portion of the moon exposed to the earth gradually increases. Thus, the size of the apparent disc of the moon increases gradually from a crescent to a full round when the earth lies between the moon and the sun. We call this day the ‘full moon day’.
The duration from one new moon day to the succeeding new moon day is the lunar month. If the moon is observed closely, we find craters, depressions on the surface of the moon, which might have been formed by the collision of some heavenly body like a meteorite with the moon. Even before astronauts landed on the moon, we were able to find information about the universe by celestial objects like meteorites. Meteors are dust-like material, which vary from a small pebble to a big boulder of several hundred kilometers in size, from outer space that enters the earth’s atmosphere. Due to friction between the meteor and the atmosphere, the meteor may get burnt while reaching the surface of the earth. If the size of the meteor is large, a lump of it may be left without getting destroyed in the course of reaching the earth. This part of the meteor is called a meteorite.
The huge distances between the earth and other celestial bodies are measured in light years. A light year is the distance covered by light in one year.
Solar System The sun is a major source of heat and light for all the planets in the solar system. Planets reflect sunlight that is incident on them. They have no light of their own, so they don’t twinkle like the stars. Planets have definite paths called orbits in which they revolve around the sun. The time taken by a planet to complete one full revolution around the sun is called its period of revolution. The time taken by a planet to rotate a full 360 degrees on its axis is called its period of rotation. A celestial body that revolves around another celestial body is called a satellite. Mercury is the smallest planet in the solar system as well as the closest to the sun. It takes about 88 days to complete one revolution around the sun. Venus is the second closest planet to the sun. It takes about 225 days to complete one revolution around the sun. It has no satellites or moons. Venus rotates from east to west.
Earth is the only planet on which life is known to exist. It takes 365 days for the earth to complete one revolution around the sun. Mars completes one revolution around the sun in about 687 days. It has two moons of its own. Jupiter is the largest planet in the solar system. Jupiter’s four larger moons are called Io, Europa, Callisto and Ganymede. It rotates the fastest among all planets. The rings of Saturn are made of ice particles and dust. Saturn is the only planet that is lighter than water. The largest of Saturn’s moons is Titan. Uranus is the coldest planet. Neptune was discovered through mathematical calculation. Mercury, Venus, Earth and Mars are called the inner planets. Jupiter, Saturn, Uranus and Neptune are called the outer planets. The outer planets have several moons and a system of rings.
Other Members of Solar System Apart from the sun and the planets, the solar system also consists of celestial bodies such as meteors, comets and artificial satellites. A meteor is made up of debris. A meteor enters the Earth’s atmosphere at a very high speed. The friction with the atmosphere makes the meteor hot and it burns till it disintegrates. As it falls to the ground, it glows brightly. This is why it is called a shooting star. Some meteors reach the ground before they burn completely and evaporate. These are called meteorites. Asteroids are made of rubble and are found in the gap between the orbits of Jupiter and Mars. This gap is called the asteroid belt. An asteroid does not have a tail. However, a comet is made up of a bright head and a long tail. A comet consists of rock, dust, water, ice and frozen gases. Comets, too, revolve around the sun periodically, but their period of revolution is larger as compared to that of planets. One of the most famous comets is Halley’s comet, named after the discoverer. Its period of revolution is 76 earth years. Artificial satellites are man-made and are launched from the earth. Artificial satellites are used for transmission of television and radio signals, telecommunication, weather forecasting and remote sensing.
Constellations Stars are always fascinating to mankind. They are the most beautiful celestial bodies about which mankind contemplate. In ancient times, the revolution of the earth around the sun and the apparent position of many groups of stars were studied extensively to explore the universe. A group of stars that can be identified with the shape of an identifiable object like an animal or a known object is called a constellation. Major constellations are the Ursa Major, Ursa Minor and Cassiopeia.
The Ursa Major is shaped like a ladle and is also referred to as the Big Dipper. It consists of seven stars placed in the form of a dipper. The stars in the constellation form the shape of a bear, and hence it is also referred to as the Big Bear.
In India, it is popularly called the Saptarshi. Another popular constellation is the Orion, which is shaped in the form of a hunter. Three middle stars in the Orion lead to a brighter star in the sky, called Sirius. The Cassiopeia is another constellation, which can be located in the northern sky. As the earth rotates on its axis from west to east, the stars appear to move from east to west. But the pole star, which is located along the axis of the earth’s rotation, does not appear to move as it lies along the earth’s axis and is towards the north of the earth. It helps in identifying directions during the night.
All fabrics are materials made from many fibres. Cotton is a natural fibre obtained from the cotton plant. All synthetic fibres are man-made fibres that are prepared by a number of processes using raw material of petroleum origin, called petrochemicals. A polymer is made up of many repeating units called monomers. Cotton is a form of polymer called cellulose, which is made of a large number of glucose units.
Characteristics of synthetic fibres:
Easy to maintain,
Fibre obtained by chemically treating wood pulp is called rayon or artificial silk. Rayon cannot be called a natural fibre as it is man-made.
Characteristics of rayon:
Cheaper than silk and can be woven like silk fibres.
soft and comfortable.
Easy to dye in a wide range of colours, and
Uses of rayon:
Widely used in all types of clothing and home furnishings.
Mixed with cotton to make bed sheets and curtains, or with wool to make carpets.
Nylon is a synthetic fibre made from coal, water and air. Nylon is elastic, light, very lustrous and easy to wash. It dries quickly and retains its shape.
Uses of nylon:
To make seat belts in cars, curtains, sleeping bags, tents, tooth brushes, socks and ropes, To make parachutes and ropes for rock-climbing.
Polyester is a synthetic fibre, derived from coal, air, water and petroleum. Polyester is made of repeating chemical units called esters. Polycot is a mixture of polyester and cotton, and polywool is a mixture of polyester and wool. Fabric made from polyester retains its shape and remains crisp. Polyester is easy to wash and dry. Terylene is a popular form of polyester, which can be drawn into very fine fibres. These fibres can be woven like any other yarn. PET, or poly-ethylene terephthalate, is another familiar form of polyester, which is used to make bottles, utensils, films and wires. Polyester is also used for making hoses, ropes, nets, thread, raincoats, fleece jackets, clothing and medical textiles. Acrylic is a synthetic polymer of methyl methacrylate. Fabric made from acrylic is warm to wear, retains its shape and is durable. Acrylic is easy to wash and dries quickly. Acrylic is used in apparel like sweaters and socks, and in home furnishings such as furniture, carpets, blankets and upholstery fabrics. Industrial uses of acrylic include craft yarns, awnings, boat and vehicle covers, and luggage.
Plastics are polymers of long carbon chains. Plastics that get deformed easily on heating and can be bent easily are known as thermoplastics. PVC polythene, nylon, acrylic, celluloid and cellulose acetate are examples of thermoplastic. Plastics that, when moulded, cannot be softened by heating are called thermosetting plastics. Bakelite, melamine, vulcanised rubber, duroplast and epoxy resin are examples of thermosetting plastics. Characteristics of plastics:
-Do not corrode easily
-Light in weight
-Strong - Durable
Can be easily moulded into different shapes and sizes.Poor conductors of heat and electricity.
Uses of plastics: Special plastic is used in the making of cookware used in microwave ovens for cooking food. Teflon is a special plastic on which oil and water do not stick, hence used in non-stick cookware. a packaging material for tablets, syringes, threads used for stitching wounds and doctor’s gloves. The interior parts of a car like the dash board, and some parts of helicopters and aeroplanes are made of plastic. Used in the making of computer parts, circuit boards, food processors, shavers and hair dryers. Material that gets decomposed through natural processes, such as by the action of bacteria, is termed as biodegradable. For example, peels of vegetables, fruits, other food stuff, paper and pieces of clothes. On the other hand, material that is not easily decomposed by natural processes is termed as non-biodegradable.For example, plastic, polythene covers, thermocol, etc. Polythene bags are non-biodegradable and cause environmental pollution. They undergo a process known as photo degradation, in which they break down into smaller and smaller toxic particles. These particles contaminate soil and water, and end up entering the food chain when eaten accidentally by animals like cows. Besides, polythene bags can choke cattle to death.Hundreds and thousands of whales, dolphins, sea turtles and other marine mammals die every year after consuming discarded polythene bags, mistaking them for food. Carelessly thrown polythene bags are also responsible for the clogging of drainage systems in cities and towns .Plastics take several years to decompose. Ways to reduce the use of plastic materials:
Reduce- Avoid the use of disposable plastic bags, instead make use of cotton or jute bags for shopping.
Reuse: Plastic items should be reused wherever possible.
Recycle: It is better to recycle plastic waste. Most thermoplastics can be recycled.
Physical Properties Chemical Properties of Metals
Metals are used in making machinery, automobiles, aeroplanes, buildings, trains, satellites, gadgets, cooking utensils, water boilers, etc.Sodium and potassium are soft metals that can be cut with a knife. Mercury is a liquid metal. The metal base in an electric iron is for conducting heat, not electricity. Metals are very good conductors of heat, too. That’s why cooking utensils, irons, heaters, etc. are all made of metals. Metals can be easily shaped into wires. This property of metals is called ductility. Metals can be easily shaped into thin flat sheets. This characteristic of metals is called malleability. Metals make a sound when struck with hard objects. Metals can be polished to a shiny appearance. That’s why gold and silver jewellery shine so much. Iron reacts with atmospheric oxygen and moisture to form iron oxide, which is commonly known as rust. Metals burn in the presence of oxygen to form metal oxides, which are basic in nature. For example, if you burn a strip of magnesium, magnesium will burn in oxygen to form magnesium oxide.
Magnesium oxide dissolves in water to form magnesium hydroxide, which is basic in nature. When a copper vessel is exposed to moist air, a green coating forms on its surface. The coating is a mixture of copper hydroxide and copper carbonate. Nails rust because of the moisture present in air. Sodium reacts vigorously with water and oxygen, and produces so much heat that it catches fire! That’s why sodium is stored in kerosene - to prevent it from coming into contact with moisture and oxygen. Red litmus paper turns blue in solutions basic in nature. Lime juice contains citric acid. Acids react with salts of metals. Metals react with acids, such as hydrochloric acid and sulphuric acid, to give out hydrogen gas. Copper does not react with dilute hydrochloric acid even on heating, but it reacts with dilute sulphuric acid on heating. Metals react with bases, such as sodium hydroxide, to produce hydrogen gas. More reactive metals can displace the less reactive metals in a compound.
Physical Properties & Chemical Properties of Non-Metals
Sulphur, phosphorus, nitrogen, chlorine, iodine, boron, silicon, carbon, bromine, fluorine and oxygen are non-metals. Non-metals exist in all the three states. Silicon and carbon are solids; bromine is a liquid; chlorine, fluorine and oxygen are gases. Non-metals are non-lustrous, non-malleable and not ductile, except for carbon fibres, which are ductile. Non-metals do not produce any sound when hit, which means they are not sonorous. Non-metals do not conduct heat and electricity, except for graphite.
Non-metals react with oxygen and form acidic or neutral oxides.
For example, sulphur reacts with oxygen to form sulphur dioxide, which is acidic. Carbon monoxide and nitric oxide are neutral oxides. Phosphorus is a very reactive non-metal. It catches fire if exposed to air. To prevent the contact of phosphorus with atmospheric oxygen, it is stored in water.Non-metals do not react with acids.The reaction of non-metals with bases is complex.For example, when chlorine reacts with a base like sodium hydroxide, it gives multiple products like sodium hypochlorite, sodium chloride and water.
Resources supplied by nature are called natural resources. The sun, air, water, soil, trees and forests, wildlife, coal, petroleum, natural gas and minerals are all natural resources. Many industries, like fishing, mining, hunting, agriculture and forestry, revolve around the sensible use of natural resources. Natural resources are classified as renewable and non-renewable resources. Renewable resources are those that are present in unlimited quantity in nature or those that will replace themselves over time. These resources are not likely to be exhausted by human activities. As they are unlimited, they are also called inexhaustible resources. Non-renewable resources are those that are limited in nature and will not replace themselves. They can be exhausted by human activities. As they are limited, they are also called exhaustible resources. Coal, petroleum and natural gas are exhaustible fossil fuels, which cannot be prepared in the laboratory. It takes millions of years for dead organisms to get converted into these fuels. ,Studies show that the known reserves of these fuels are fast depleting. Burning of these fuels is also a major cause for air pollution and, along with cutting down of trees, is contributing to global warming. The Petroleum Conservation Research Association (PCRA) of India has some tips for people on how to save petrol/ diesel while driving:
Drive vehicles at a constant and moderate speed.
While waiting or at a traffic junction, switch off the engine.
Ensure correct tyre pressure.
Ensure regular maintenance checks of the vehicle.
Tips for conserving energy at home and school:
Switch off lights and electrical appliances when not in use.
Turn off air conditioning when leaving the room.
Do not let the tap run while you brush your teeth or soap your hands.
Check all leaky taps.
Take shorter showers.
Buy rechargeable batteries and a charger for them.
Avoid plastic bags.
Recycle your newspapers.
During the carboniferous age, the earth had large amounts of plant life and dense forests in swampy and low-lying wetland areas. Plants and other life forms, after their death, drifted down to the bottom of the swamps, where they were compressed and decomposed to form peat. Coal was formed due to the compression of the peat at high temperature and pressure. As coal was formed from the remains of vegetation, it is called a fossil fuel. Carbonisation is the slow process of conversion of dead vegetation into coal. Coal is primarily made up of carbon, also hydrogen, oxygen, nitrogen and some amounts of sulphur. Surface mining is used when coal is found close to the surface or hillsides. Underground mining is used to extract coal that is deep beneath the surface of the earth. Coal is processed in the industry to get useful products coke, coal tar and coal gas. Coke is an almost pure form of carbon that is used in the manufacture of steel and extraction of metals. Coal tar is a black, thick mixture of almost 200 substances. It is used as a starting material for manufacturing synthetic dyes, explosives, perfumes, drugs and plastics, synthetic resins, paints and stains. Naphthalene balls, which are used to repel moths and other insects, are also obtained from coal tar. Bitumen, a petroleum product, is now used in place of coal tar for surfacing roads. Coal gas is obtained during the processing of coal to get coke. It is mainly used as a fuel in industries around coal processing plants.
Uses of coal:
Coal is the largest source of fuel used to generate electricity world-wide.
Coal is used in manufacturing industries for heat and power applications.
Coal is used to make steam for heating.
It is also used as coke in steel making.
Petroleum, a natural resource formed from organisms living in the sea, is a dark and oily liquid mixture with a very unpleasant odour. Petroleum and natural gas are formed from compressed organic matter. As petroleum and natural gas are lighter than water, the deposits of petroleum and natural gas occur above that of water. The first oil well in the world was drilled in Pennsylvania, USA. Oil in India is found in Assam, Gujarat and Mumbai High, and in the river basins of Godavari and Krishna. Petroleum is a mixture of various constituents like petroleum gas, petrol, diesel, lubricating oil, paraffin wax, etc., and the process of separating its many constituents is called refining. It is refined in a petroleum refinery. At the refinery, the crude oil mixture is 'fractionated' into different components by fractional distillation. Light gases are the topmost fraction, followed by petrol and kerosene. Diesel is the heaviest. The other heavier fractions are not useful and are usually used to make asphalt to surface roads. Constituents of petroleum and their uses:
LPG or petroleum gas is used as a fuel for home and industry.
Petrol is used as a motor fuel, aviation fuel and a solvent for dry cleaning.
Kerosene is used as a fuel for stoves and lamps and also in jet aircraft.
Diesel is used as a fuel for heavy motor vehicles and electric generators.
Lubricating oil is used for many lubricating purposes.
Paraffin wax is used in ointments, candles and Vaseline.
Bitumen is used in paints and also to surface roads.
Petrochemicals are used in the manufacture of detergents, polyester and nylon fibres, polythene and other man-made plastics.
Simple steps to reduce consumption of petrol/diesel:
Use public transport. Combine many errands into one trip. Car pooling to school and work.
Burning petroleum releases carbon dioxide into the air, which contributes to global warming. Oil spills at sea are devastating to the animal and plant life in and around the sea.
Natural gas is another fossil fuel, like coal and petroleum. It is a non-renewable fuel. Natural gas is used for waste treatment and incineration. Gases like butane, ethane and propane may be extracted from it and used as feedstock for products such as fertilizers and pharmaceutical products Natural gas is one of the most useful, clean and safe energy sources. It is a colourless and odourless gas in its pure form, and is made up of many gases, of which methane is the most prominent. The chemical formula for methane is CH4. When natural gas burns, it gives off a great deal of energy, and unlike other fossil fuels, leaves no ash. It causes very little air pollution, as methane burns almost completely. It is one of the cleanest burning fuels and produces mostly heat, carbon dioxide and water vapour. Thus, it is said that it contributes to a cleaner and greener environment. Natural gas is odourless. To detect gas leaks, a harmless but pungent odorant that smells like rotten eggs is added to it, as a safety measure. It can be smelt in case of even a small leak. Natural gas is measured in British Thermal Units (BTU). Uses of natural gas: For cooking. To run central heating and cooling systems and cloth dryers. For electricity generation through the use of gas turbines and steam turbines. In the manufacture of fabrics, glass, steel, plastics, paint and other products. Natural gas is compressed to a high pressure and stored in hard cylindrical or spherical containers, for distribution. It is then known as Compressed Natural Gas or CNG.CNG is also distributed to homes and industries through pipes, For example, in India, such a network of pipelines exists in Vadodara in Gujarat and some parts of Delhi. CNG is now used as a fuel for transport vehicles – from light duty trucks, auto rickshaws and taxi cabs to delivery vans and heavy duty vehicles like buses.
The chemical process in which a substance reacts with oxygen to give off heat is called combustion. A substance that undergoes combustion is called a combustible substance, or a fuel. Liquefied Petroleum Gas or LPG burns very quickly producing a lot of heat. This is called rapid combustion. When white phosphorous is left out in the open at room temperature for some time, it burns all by itself. This is called spontaneous combustion. Forest fires and fires in coal mines are because of spontaneous combustion. The burning of crackers produces a large amount of heat, light and sound because of chemical reaction. This type of combustion is called explosion. Without oxygen, even a combustible substance will not burn. Temperature is an important condition for combustion to occur. The lowest temperature at which a substance catches fire is called its ignition temperature. Kerosene is a fuel that has a low ignition temperature. A low ignition temperature means the substance will catch fire quickly and is highly inflammable. Some inflammable substances are petrol, LPG, ether and alcohol. A matchstick is made of a mixture of antimony trisulphide and potassium chlorate mixed with a little bit of red phosphorous. A lighter depends on lighter fluid, which is highly inflammable as well. It is made out of naphtha or liquid butane. Air, heat and fuel are needed for a fire to be created. Fire can be easily stopped by stopping the supply of either air or heat. Water is not a good extinguisher for electrical fires. If electrical wiring is on fire, pouring water on it will conduct the electricity through the water and may cause the person dousing the fire to be electrocuted. As water is heavier than petrol, it is not useful for extinguishing oil or petrol fires. For electrical and oil fires, it is best to use carbon dioxide as an extinguisher. Carbon dioxide is heavier than oxygen, so it covers the flame like a blanket, cutting off contact between the fuel and oxygen. Powder of sodium or potassium bicarbonate can also be used to get carbon dioxide. The first automatic fire extinguisher was patented in England by a celebrated chemist called French C. Hopffer. The modern fire extinguisher was invented by British Captain George William Manby.
Kerosene oil and molten wax are substances that give a flame while burning. Wood and charcoal are substances that do not vaporise, but still burn, without any flame. A luminous flame is a bright yellow flame that gives off light. A luminous flame undergoes incomplete combustion as it does not get the oxygen that it requires. A non-luminous flame is colourless and is much hotter. A non-luminous flame undergoes complete combustion as it draws much more oxygen and gets much hotter. There are several "zones" within a non-luminous flame, and each zone has a different temperature, The outermost zone of the flame is blue in colour and it is the hottest part. This is due to complete combustion. The middle zone is moderately hot and is yellow in colour. This is because of partial combustion. The innermost zone is the least hot and black in colour. This is due to the presence of unburned wax vapours.
Fuel is any material that is burned to obtain energy that can be used to heat or move another object. Fuel releases energy through a chemical reaction known as combustion. A good fuel must:
Be readily available.
Be cheap. Burn easily at a moderate rate. Produce a large amount of heat. Not leave behind any undesirable substances. Wood was the first fuel that was used 2 million years ago by homo erectus, the predecessor of human beings.
Calorific value is defined as the amount of heat energy produced on complete combustion of 1 kilogram of a fuel. It is expressed in a unit called kilojoule per kg. The higher the calorific value of a fuel, the more is its efficiency. Each kilogram of LPG produces much more heat than one kilogram of wood or coal. The calorific value of LPG is the highest among wood, charcoal and LPG. In rural areas, cow dung and wood are still used as fuel because these are very cheap and easily available. However, burning wood produces a lot of smoke, which is very harmful to humans, since it causes respiratory problems. Cutting down trees for fuel also leads to deforestation, which harms the environment and also deprives us of all the other benefits of trees. Unburned carbon particles released when carbon fuels like wood, coal and petroleum burn, cause pollution and respiratory diseases such as asthma. Incomplete combustion of carbon fuels causes the release of carbon monoxide – a very harmful gas. Combustion of fuels causes the release of carbon dioxide, which leads to global warming. Such rise in temperatures can cause melting of polar glaciers, a rise in sea level, and the flooding of low-lying areas of the world. Oxides of sulphur and nitrogen dissolve in rain water to form acid rain, which ruins soil, crops and buildings. By choosing the right fuel, we can reduce the negative impact on the environment. A great example of this is cars, buses and auto rickshaws that run on Compressed Natural Gas, or CNG, instead of petrol. CNG is a much cleaner and cheaper fuel.
Substances that cause harmful changes in the air are called pollutants. Air pollution is caused due to the presence of pollutants in the air.Air pollution is caused by burning fossil fuels, like coal and petroleum, in industries, power plants and vehicles, and by burning of firewood and dung cakes. Pollutants are also released into the air by natural events like a dust storm, forest fire or volcanic eruption. Incomplete burning of fossil fuels, like petrol and diesel, results in the production of colourless, odourless and toxic carbon monoxide gas. Smog is a mix, in the air, of smoke and chemicals with fog. The chemical components of smog can include ozone, sulphur dioxide, nitrogen dioxide and carbon monoxide. Smog can trigger breathing difficulties like asthma and coughing. Pollutants like sulphur dioxide and nitrogen dioxide are released in large quantities by petroleum refineries. These emissions can cause respiratory problems and also permanent lung damage. CFCs or chlorofluorocarbons are synthetic products that contain carbon, chlorine and fluorine. They were formerly used as a refrigerant and as a propellant in aerosol or air sprays.
CFCs contribute to the depletion of the ozone layer that protects us from the harmful ultraviolet rays of the sun. Soot is released when automobiles burn fossil fuels, like petrol and diesel. Pollutants like sulphur dioxide and nitrogen dioxide, which are produced by industries like rubber processing, automobile chemicals and the Mathura oil refinery near Agra, are responsible for the decolourisation of the Taj Mahal. These gases react with water vapour in the atmosphere and form sulphuric acid and nitric acid. Precipitation carries these acids back to the earth as acid rain. The corrosion of the Taj Mahal due to acid rain is called ‘marble cancer.’ Global warming has already started melting the polar ice caps, which has resulted in a rise in the global sea level. Gases, like methane, nitrous oxide and water vapour, also contribute to the greenhouse effect, and, along with carbon dioxide, are collectively called the greenhouse gases. Steps to prevent air pollution:
Use of fuels like CNG and unleaded petrol in automobiles. Switching to alternative fuels, like solar energy, hydropower and wind energy. Planting trees. Travelling to school on a bicycle or on public transport or car pooling. Avoiding the burning of leaves, trash and vegetable matter. Restricting cigarette smoking.
Water covers two-thirds of the earth’s surface and makes up 75 per cent of the human body. A water body is said to be polluted when toxic substances damage it, making it undrinkable and also dangerous for organisms to live in it. Harmful substances, like sewage, silt, toxic chemicals and domestic waste, are called water pollutants. They spoil the quality of water by altering its smell and colour, and render it unfit for drinking. Pollution can enter a body of water in many ways, such as domestic sewage, agricultural run-off containing fertilisers and pesticides, eroded soil, acid rain, chemicals released from industries or other wastes from cities and towns. At places along the Ganga, people bathe, wash clothes and even defecate in the water. They also throw huge quantities of garbage, flowers, idols of gods and goddesses, untreated sewage, animal carcases and non-biodegradable polythene bags directly into the river. Chemical contamination of water due to chemicals, such as compounds of arsenic, fluorides and lead, cause plants and animals to die. The soil is also affected by polluted water, causing changes in its acidity, and, therefore, the growth of plant life. Polluted water is unsuitable for drinking, recreation, agriculture and industry. Contaminated water destroys aquatic life and reduces its reproductive ability. Water pollution drastically reduces the quantity of dissolved oxygen in water, which results in the death of aquatic organisms. Anaerobic micro-organisms release gases like methane and hydrogen sulphide, leaving a foul-smelling, waste-filled body of water. The large quantities of chemicals that are washed in from the fields are responsible for the excessive growth of algae. Once the algae die, it serves as a food for bacteria. As a result, a lot of oxygen in the water is used up and many aquatic organisms die. Water that is suitable for drinking is called potable water. Sewage treatment plants treat wastewater to purify it before releasing it back into rivers and lakes. Municipal bodies treat water before supplying it to our households. Some popular ways of making water potable are:
Using candle type water filters
Reduce, reuse and recycle is a popular mantra and one that is so important for us to practise. Steps to conserve water: Rain water harvesting Using drip irrigation method in agriculture Reusing the water used to wash vegetables Minimizing water consumption
The term crop is used to describe plants of the same kind that are grown and cultivated at one place in significant quantities. Plants that are planted during the rainy season are called kharif crops. Crops that grow during the winter season are called rabi crops. Many activities are performed before cultivating a crop, which are termed as agricultural practices. Soil preparation means loosening the soil or turning it. Earthworms decompose plant and animal waste, and thereby benefit the soil by increasing the humus and nutrient level in it. Ploughs have been in use since ancient times for tilling soil, adding manure and fertilizers, and for scraping of soil. Depending upon the animals available on a farm, ploughing is done using horses and camels to pull ploughs. A plank is used to break the crumbs into fine soil. The next step is to level the soil with the help of a leveler.
Ploughs were made from wood. Nowadays, iron ploughs have become more popular. Earlier, a hoe was used for tilling, but these days we use it only to remove weeds. When the cultivator is pulled by a tractor, the teeth assist in breaking the soil. Healthy seeds contain more nutrients. Damaged seeds are hollow, discolored and contain fewer nutrients. Seed selection is done by soaking the seeds in a beaker containing water. Modern seed drills sow seeds at a proper depth and distance, and cover them with a layer of soil, keeping them well out of a bird’s reach. The traditional seed drill contains a funnel-shaped container, from where the seeds pass and get placed into the soil. Bananas are first sown in a nursery and the saplings are planted in the field.
Agriculture is cultivating on large areas. Manure provides soil with nutrients. The crop has been harvested last week and is left fallow to recover nutrients. Decomposition occurs in pits dumped with organic waste with the help of earthworms and bacteria. Fertilizers are chemicals used to add minerals like potassium, phosphorus and nitrates to the soil. The supply of water to crop is irrigation. The frequency of irrigation varies from season to season. Manure increases the water retention capacity of soil, making it porous. Plants contain nearly 90% water, and need water for proper development of flowers, fruits and seeds. In dry conditions, seeds do not germinate. Water protects plants from frostbite and hot air currents. Water protects crops from hot air by evaporation, and traps cold breeze. Traditional methods of irrigation include moat, chain pump, dhekli and rahat, and need animal and human labour to draw water. Wells, tube wells, ponds, lakes, rivers, dams and canals are sources of water. Sprinklers and drip systems are used when the soil is sandy or uneven. Pumps lift water and run on biogas or solar energy. During summer, it is difficult for farmers to water crops. Weeds are removed manually before they produce flowers and seeds. Weeds are controlled by chemicals such as 2, 4-D, a systemic weedicide that kills weeds. Weedicides are poisonous to humans. Drip irrigation waters fruit plants and suits regions that have scarcity of water. Khurpi is used to remove weeds. Farmers use weedicides in diluted form and they handle weedicides carefully by covering their nose and mouth while spraying. This stops their propagation in the field. Tilling the soil uproots the weeds.
Harvest and Storage
Cutting the crop after it has ripened and gathering the grains is known as harvesting. We can use the word crop ripened rather than using the word crop mature. A sickle has a sharp serrate-edged metal blade attached to a wooden handle. A sickle is used for cutting the crop. A harvester is a machine that helps to cut the ripened crop from the fields. Threshing is the process of separating the grains from the straw and chaff. A thresher is used for threshing. A combine is a combination of a thresher and a harvester. Winnowing is a process in which we allow natural wind to blow through the grains, so the lighter substances fly away, whereas the heavier grains fall to the ground.
The fan in a winnowing machine blows away the chaff. Protection of crops against microorganisms, rodents, pests and moisture is done by drying in sun and exposing to fumes. Silos are huge, air-tight cylindrical structures used to store grains. Granaries are large rooms built above ground level to prevent rodents and pests from getting near the grains. In cold storage, vegetables and fruits are stored at low temperatures. Animal husbandry means rearing and breeding livestock on a large scale. Poultry farming means rearing hens, ducks and turkey for meat and eggs.
World of Micro Organisms
It’ll be exciting to learn about microbes because we humans have microbes in our bodies, too. Living organisms invisible to the naked eye are called microorganisms. Some microbes can be seen on bread with the help of a magnifying glass, while others are visible only under a microscope. Microorganisms are everywhere, in the air, water and soil. Bread mould belongs to the fungi group. Microbes can be classified into four groups – bacteria, fungi, algae and protozoa. Cold and influenza (flu) are caused by viruses. Serious diseases like polio and chicken-pox are also caused by viruses. Viruses need to be inside a living organism to reproduce. Hence, viruses form the boundary between the living and the non-living world. An amoeba is a free living organism. Microbes can survive under all types of environment, ranging from ice cold climate to hot springs and deserts to marshy lands.
Microorganisms made of single cells are called unicellular organisms. Most fungi and some algae are made up of many cells, and are called multicellular organisms. Milk is turned into curd by the action of Lactobacillus. Microbes are used in the preparation of cake and bread. Yeast reproduces rapidly in dough and produces carbon dioxide. This dough, when baked, yields porous and spongy cakes. Microbes are also used to prepare pickles, cheese and alcohol. Bacteria clean up organic waste and decompose them into usable substances. Louis Pasteur discovered the process of fermentation. The process of converting sugar into alcohol is called fermentation. Yeast convert the natural sugars present in grains into alcohol. Wine is produced by the process of fermentation.
Dealing with Harmful Micro Organisms
It is exciting to see Vex explaining about disease-causing microbes, which are called pathogens. Microbes spoil leather, clothing etc. Some more information was given on the transmission and spread of diseases. Female mosquitoes carry the pathogens for diseases like malaria and dengue, and spread infection from one person to another. By using a handkerchief while sneezing or coughing, we can prevent the spread of infection. Infections are transmitted from animals to humans by eating uncooked chicken. Human diseases like cholera, common cold, chicken pox and tuberculosis spread from an infected person to a healthy person through air, water, food or physical contact. Microbial infection can be transmitted by direct contact with an infected person or animal, or by eating meat prepared from an infected animal. To prevent microbial infection in animals, antibiotics are mixed with the feed of livestock and poultry. Many pathogens attack crop plants like sugarcane, wheat, rice, potato and orange, and reduce their yield. Antibiotics, insecticides and pesticides are sprayed in the field to control many plant diseases. Anthrax, caused by a bacterium, is a dangerous human and cattle disease. The foot and mouth disease in cattle is caused by a virus. Antibiotics are used to cure a variety of diseases caused by fungi, bacteria and protozoa, but antibiotics are not effective against diseases caused by viruses. We should take antibiotics only on the advice of a qualified doctor. Medicinal use of microbes- Bacteria or fungi produce a specific chemical that prevents the growth of or kills microbes that cause disease. Penicillin was discovered by Alexander Fleming in 1929.Inactivated or weakened microbes introduced into the body are called a vaccine. When disease-carrying microbes enter our body, it produces self-protecting proteins called antibodies, to fight against the invader. Small pox has been completely eradicated from the world. Several diseases, including cholera, tuberculosis and hepatitis, can be prevented by vaccination.
Food poisoning may cause infection. We need to store our food properly as food poisoning can cause serious illness and even death. Spoiled food emits a bad smell, has a bad taste and changes colour. Chemical methods of preservation of jams and squashes use preservatives like sodium benzoate and sodium metabisulphite. Common salt absorbs moisture from food, making it dry and uninhabitable for microbes. Sugar reduces moisture in food, which inhibits the growth of microbes that spoil food. Jams, jellies and squashes are preserved using sugar. Bacteria and fungi cannot live in an environment of oil and vinegar. Louis Pasteur discovered the process of pasteurization. During pasteurization, milk is first heated to about 70 degrees Celsius for 15 to 30 seconds and then suddenly chilled. Sudden chilling of milk is done during pasteurization to prevent the growth of microbes. Boiling and freezing are the two other methods used to preserve food.
The conversion of atmospheric nitrogen into nitrogenous compounds is nitrogen fixation. Rhizobium bacteria living in the root nodules of legume plants, fix nitrogen from the atmosphere. Microorganisms in the soil convert atmospheric nitrogen into ammonium compounds, thereby enabling the survival of plants and animals. Nitrogen is an essential constituent of proteins, nucleic acids, chlorophyll and vitamins. Blue green algae are able to fix nitrogen from the atmosphere. Nitrogen from the atmosphere is fixed by biological nitrogen fixers like blue green algae and some bacteria. Fungi are decomposers that degrade organic waste compounds into simple substances, ready for reuse by plants. The circulation of nitrogen between organisms and the atmosphere is called the nitrogen cycle. Some microorganisms reside in the root nodules of leguminous plants and fix nitrogen from the air into the soil, and increase soil fertility. Nitrogen is also fixed by lightning to a small extent. Microorganisms in soil decompose harmful and smelly substances, leading to a cleaner environment.
Deforestation and Reforestation
Deforestation is the clearing of forests to use the land for cultivation, building houses and factories, making furniture, and the construction of dams, or for using wood for fuel. Cases where human beings are responsible for deforestation are known as man-made causes, while cases such as forest fires are known as natural causes. Other causes of deforestation include forest fires, severe floods and severe droughts. For the survival and well-being of the human species, a vast variety of plants and animals exist on the earth. A consequence of deforestation is global warming that has a severe impact on the environment. Reforestation means planting new trees in destroyed forest area. Carbon dioxide released into the atmosphere traps sunlight reflected by the earth’s surface, and results in an increase in temperature levels on the earth. This increase in the temperature levels is called global warming. It is advisable to replant trees of the same species that are found in a forest. In India, we have the Forest Conservation Act, which is aimed at preserving and conserving natural forests. Significance of the recycling process of paper - Used paper is sent back to the factories for recycling, after the recycled paper has been used, the amount of waste paper being disposed off would be much lesser. It takes 17 fully grown trees to make one tonne of paper. Even harmful chemicals are used in making paper. Trees are cut down and the wood is taken to a paper factory for producing paper. The paper that is produced is then sent to towns and cities for use.
Conservation of Forest and Wildlife
Humans cleared up forests, leaving animals homeless and hungry, so there is a need for conservation of forests. Documentaries on ‘Conservation of Forests and Wildlife’ are usually shown on television. Biosphere means the regions of the earth, where living organisms exist. A biosphere reserve is a place reserved for all life forms found in a particular area. Biodiversity is the diversity of plant and animal life found in a particular area. A biosphere reserve consists of a number of national parks and wildlife sanctuaries, like the Rajiv Gandhi National Park, the Silent Valley National Park, the Mukurthi Wildlife Sanctuary and the Mudumalai Tiger Reserve. The Mudumalai National Park hosts a variety of flora such as the Begonia malabarica, rosewood, coral trees, etc. The Nilgiri Biosphere Reserve is the first Indian biosphere reserve. Plants and animals confined to a particular area are referred to as the flora and fauna. Endemic species found in the Nilgiri Biosphere Reserve are Nilgiri langurs, great Indian horn bills, thorny costers, blue mormons etc.Endangered species or threatened wild animals in the Waynad Wildlife Sanctuary are the black buck, marsh crocodile, python, etc.Killing or poaching of animals is prohibited in the Waynad Wildlife Sanctuary. The only way to protect these animals from extinction is by increasing awareness. Project Tiger is a government initiative, launched to ensure the survival of the tiger population. Information about endangered species is recorded in the Red Data Book.A number of birds migrate to the Vedanthangal Bird Sanctuary. When natural habitats are not conducive for breeding, birds move to safer areas to breed, which is called migration. Birds that fly from far-off places to reach a new habitat are known as migratory birds.
Introduction to Cells
With the help of a microscope, an English scientist, Robert Hooke, first discovered the existence of cells in 1665.Scanning electron microscopes are used to examine the external parts of various organisms. The transmission electron microscope is used to view the internal structure of a cell and its organelles. Organisms that are made up of a single cell and perform all their vital activities, like reproduction, locomotion and digestion, are called unicellular organisms. Organisms that are made up of more than one cell are called multicellular organisms. Amoeba uses small finger-like projections called pseudopodia for locomotion and to capture prey. Paramecium is a single cell and is built in such a way that it performs all its vital activities, like reproduction, locomotion, digestion, and so on. The White Blood Corpuscle (WBC) is the only animal cell that changes its shape. The branched structure of a neuron helps it to transfer messages to all parts of the body.
Structure and Function of Cells
The black layer or the scab that you see on the wound is a result of the aggregation of dead Red Blood Cells (RBCs).The nose and the lungs form part of an organ system, the respiratory system. All organ systems work together to form a complex organism. The cytoplasm is a jelly-like fluid present between the nucleus and the cell membrane. The cell membrane allows the movement of minerals and other substances in and out of the cell. The nucleus controls the activities of a cell. Methylene blue is the stain placed on plant and animal cells to differentiate the nucleus under a microscope. Chromosomes are called vehicles of heredity because they carry genes and help in the inheritance or transfer of characteristics from the parents to the offspring.
Bacteria and blue-green algae that contain nucleoids are called prokaryotes. Organisms that have a well-organised nucleus are called eukaryotes. The nuclear material in unicellular organisms does not contain a nuclear membrane, and hence is called a nucleoid. The nucleolus is a small, spherical body in the nucleus. Chloroplast is a type of plastid involved in photosynthesis in plants. A vacuole is present in both plant and animal cells, but it looks much smaller in animal cells.
Sexual Reproduction in Animals
Amoeba and bacteria adopt the asexual mode of reproduction. Reproductive organs in humans produce gametes - eggs and sperms. A zygote is formed by the fusion of an egg and a sperm. The male reproductive organs include a pair of testes, two sperm ducts, and a penis. Sperms have a head, a middle piece and a tail. Sperms contain cell membrane, cytoplasm and nucleus. The female reproductive organs consist of a pair of ovaries, two oviducts, also called fallopian tubes, and the uterus. The ovary produces female gametes called ova or eggs. During pollination in plants, the male gamete fuses with the female gamete. The nuclei of the sperm and the egg fuse to form a zygote, and the process is called fertilization. An organism inherits some characteristics from the egg and some from the sperm. Copulation is the act in which a male reproductive organ enters the female reproductive tract. When male and female gametes unite outside the body, it is called external fertilization. When fertilization takes place inside the body, it is called internal fertilization. When fertilization takes place in a test tube, the offspring are called test tube babies. Fertilization that takes place outside the human body is in vitro fertilization. Super cell – the zygote, marks the beginning of a new individual. The zygote divides repeatedly to form a ball of cells, which, in turn, develops into tissues and organs of the body. The development of the embryo takes place in the mother’s uterine wall. All parts of the body start developing in an embryo, called foetus.
Oviparous and Viviparous Animals
Oviparous animals undergo external fertilization, while viviparous animals undergo internal fertilization. The zygote undergoes rapid division after fertilization and moves down the oviduct. During this period, many protective layers form as a hard shell around the developing embryo. The chick hatches from the egg after three weeks. There are three distinct stages in the life cycle of a frog - egg, tadpole and adult. In the first stage, the egg fuses with a sperm to form a zygote. The zygote further divides to form an early tadpole, which matures into a late tadpole. During metamorphosis, the larva transforms into an adult frog. Our bodies undergo certain changes as we develop from childhood to adolescence stage.
Asexual Reproduction in Animals
In asexual reproduction, only one parent is involved. Binary fission involves the splitting of an organism into two. Amoeba is a simple, unicellular organism. Reproduction in amoeba begins with the division of the nucleus. The parent organism divides into two individual organisms is fragmentation or binary fission. Bulges that appear as outgrowths on hydra are called buds. These buds separate as new individuals, called budding. Dolly was the first cloned mammal, and is genetically identical to its parent sheep. Cloning is creating an exact copy of a biological entity. A clone is created by inserting the complete genetic material of a regular body cell from a donor into a recipient. Sheep are viviparous animals, and so propagate their offspring sexually. Sir Ian Wilmut from Roslin Institute in Edinburgh, Scotland created Dolly. A mammary gland cell of the Finn Dorsett sheep species and an enucleated cell of the Scottish Blackface ewe were subjected to an electric pulse to cause fusion, thereby resulting in a fertilised egg that developed into a zygote. The embryo was implanted into the uterus of the ewe to undergo rapid cell division to form a foetus. Offspring inherit characteristics from both the parents. Dolly received all the genetic information from the Finn Dorsett sheep. Dolly produced several offspring. Cloning involves certain abnormalities. Dolly suffered from arthritis. Cloning could impact mental development. Advocates of human therapeutic cloning believe that cloning could help in producing organs for transplantation and in regenerative medicine.
Changes during Puberty
After the age of ten years, an individual becomes an adolescent, and experiences a lot of physical changes in the body. Adolescent is a general term for teenagers of both sexes. Adolescence is the period of life between the onset of puberty and reaching adulthood, that is, the period that leads to reproductive maturity. An increase in height is the most apparent physical change during puberty. Exercise and eat healthy food to gain height faster. Everyone will not have the same rate of increase in height, as the height of individuals is controlled by the genes inherited from parents. During adolescence, the body shapes of boys and girls also change an increase in their heights. The larynx or voice box in boys grows during puberty and protrudes out, making it clearly visible, and is commonly called Adam’s apple. During puberty, sweat glands become active and start producing more sweat. During puberty, pimples or acne appear due to increased action of sebaceous glands or oil glands. During puberty, the sex organs grow and become functionally active. The testes start producing male gametes, called sperms. During puberty, the ovaries grow and result in the maturation of the ovum. There is an increase in size of the penis with respect to different ages in males. Adolescents may experience mood swings during puberty. Puberty also results in mental and intellectual maturity. During puberty, the brain is very active and so will have a greater capacity to learn. Adolescence is the period of life that leads to reproductive maturity, making a person capable of reproduction. The growth of facial hair, that is, the beard and moustache, is a secondary sexual characteristic visible during adolescence. Puberty is marked by the development of breasts in girls Secondary sexual characters are used to distinguish a male from a female.
Hormones and Reproductive Function
Hormones are chemical messengers that regulate most functions in the human body. Endocrine glands or ductless glands secrete hormones directly into the bloodstream. Sex hormones control the onset of puberty and initiate the reproduction function. Body changes such as the growth of facial hair and cracking of voice, are initiated due to the secretion of testosterone. Body changes in females during puberty, such as breast development, are initiated by estrogen. At puberty, the level of sex hormones is sufficient to bring about the maturation of gametes, sperm and ovum. The reproductive phase of life lasts longer in males than in females. Menarche is the first occurrence of menstruation. The shedding of the uterine thickening along with its blood vessels is menstruation. Menopause is the stoppage of menstruation. Fertilisation is the fusion of a sperm and an ovum. The menstrual cycle takes place every 28-30 days. Sex chromosomes in sperms determine the baby’s gender. Humans have 23 pairs of chromosomes in each cell. A gamete is a mature reproductive cell - a sperm or an ovum. Gender determination of an unborn baby is considered illegal in India. Goitre is caused by the enlargement of the thyroid gland. Insulin deficiency causes diabetes. The thyroid gland produces thyroxine and calcitonin. The adrenal glands secrete adrenalin. The pituitary gland is the master gland and controls all the endocrine glands. The life cycle of the silk moth is controlled by insect hormones. Thyroxine is responsible for metamorphosis of the larva or tadpoles into adult frogs.
Adolescents need to avoid junk food. A balanced diet contains nutrients like carbohydrates, proteins, fats, vitamins, minerals and water in the right proportions. Healthy foods have more nutritional value, whereas junk foods have no or little nutritional value. A person with complete physical and mental health is termed a healthy individual. Personal hygiene is the first step in maintaining health. Cleanliness - Cleaning of private parts is important to prevent possible infections. Many myths and taboos about menstruation and pregnancy prevail in society. Body parts such as hair, skin, nails and feet are vulnerable to bacterial and fungal infections, if we don’t keep them clean. The activity of sweat glands increases in puberty and makes the body smell. Physical exercise keeps your body fit and healthy. Sweating helps you to release toxins and wastes from your body. Outdoor games and exercise in addition to indoor games will help you build a healthy, muscular body. A lot of people take anabolic steroids to increase body mass, but it has dangerous side effects. Peer pressure is best addressed by self confidence and a healthy lifestyle. During adolescence, with drastic changes taking place in the body and mind, you might feel insecure and confused. Drugs are addictive and should only be taken under prescription of a physician. AIDS is caused by a virus called HIV. AIDS can be transmitted from an infected person to a healthy person by sharing syringes used for injecting drugs. Pregnancy occurs only by sexual contact. In India, the legal age for marriage is 21 years for a boy and 18 years for a girl.
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