Topic outline


    Â In order to provide food to our growing population, we need to adopt certain agricultural practices. Â Same kind of plants grown and cultivated at a place constitute a crop. Â In India, crops can be broadly categorised into two types based on seasons - rabi and kharif crops. Â It is necessary to prepare soil by tilling and levelling. Ploughs and levellers are used for this purpose. Â Sowing of seeds at appropriate depths and distances gives good yield. Good variety of seeds are sown after selection of healthy seeds. Sowing is done by seed drills. Â Soil needs replenishment and enrichment through the use of organic manure and fertilisers. Use of chemical fertilisers has increased tremendously with the introduction of new crop varieties.

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    Microorganisms are too small and are not visible to the unaided eye. 

     They can live in all kinds of environment, ranging from ice cold climate to hot springs and deserts to marshy lands.  Microorganisms are found in air, water and in the bodies of plants and animals. 

     Microorganisms include bacteria, fungi, protozoa and some algae. Viruses, though different from the above mentioned living organisms, are considered microbes. 

     Viruses are quite different from other microorganisms. They reproduce only inside the host organism; bacterium, plant or animal cell.  Some microorganisms are useful for commercial production of medicines and alcohol. 

     Some microorganisms decompose the organic waste and dead plants and animals into simple substances and clean up the environment.


    Synthetic fibres and plastics, like natural fibres, are made of very large units called polymers. Polymers are made up of many smaller units.

      While natural fibres are obtained from plants and animals, synthetic fibres are obtained by chemical processing of petrochemicals. Like natural fibres, these fibres can also be woven into fabrics. 

     Synthetic fibres find uses ranging from many household articles like ropes, buckets, furniture, containers, etc. to highly specialized uses in aircrafts, ships, spacecrafts, healthcare, etc.  Depending upon the types of chemicals used for manufacturing synthetic fibres, they are named as Rayon, Nylon, Polyester and Acrylic. 

     The different types of fibres differ from one another in their strength, water absorbing capacity, nature of burning, cost, durability


    Metals are lustrous whereas non-metals have no lustre. Generally, metals are malleable and ductile. Non-metals do not have these properties. Generally, metals are good conductors of heat and electricity but non-metals are poor conductors. On burning, metals react with oxygen to produce metal oxides which are basic in nature. Non-metals react with oxygen to produce non- metallic oxides which are acidic in nature. Some metals react with water to produce metal hydroxides and hydrogen gas. Generally, nonmetals do not react with water. Metals react with acids and produce metal salts and hydrogen gas. Generally, non-metals do not react with acids.


    Coal, petroleum and natural gas are fossil fuels. 

     Fossil fuels were formed from the dead remains of living organisms millions of years ago. Fossil fuels are exhaustible resources.  Coke, coal tar and coal gas are the products of coal. 

     Petroleum gas, petrol, diesel, kerosene, paraffin wax, lubricating oil are obtained by refining petroleum. 

     Coal and petroleum resources are limited. We should use them judiciously.


    There are various types of combustions such as rapid combustion, spontaneous combustion, explosion, etc. 

     There are three different zones of a flame - dark zone, luminous zone and non-luminous zone. 

     An ideal fuel is cheap, readily available, readily combustible and easy to transport. It has high calorific value. It does not produce gases or residues that pollute the environment. Fuels differ in their efficiency and cost. 

     Fuel efficiency is expressed in terms of its calorific value which is expressed in units of kilojoule per kg. 

     Unburnt carbon particles in air are dangerous pollutants causing respiratory problems.


    Wildlife sanctuary, national park and biosphere reserve are names given to the areas meant for conservation and preservation of forest and wild animals.

      Biodiversity refers to the variety of living organisms in a specific area. 

     Plants and animals of a particular area are known as the flora and fauna of that area.

      Endemic species are found only in a particular area. 

     Endangered species are those which are facing the danger of extinction.  Red Data Book contains a record of the endangered species.


    Some organisms are single-celled, while others contain large number of cells.

      The single cell of unicellular organisms performs all the basic functions performed by a variety of cells in multicellular organisms. 

     The cell has three main parts, (i) the cell membrane, (ii) cytoplasm which contains smaller components called organelles, and (iii) the nucleus. 

     Nucleus is separated from cytoplasm by a nuclear membrane. 

     Cells without well organised nucleus, i.e. lacking nuclear membrane, are called prokaryotic cells. 

     Plant cells differ from animal cells in having an additional layer around the cell membrane termed cell wall.


    The processes are essential for the survival of every individual. You have also learnt about the process of reproduction in plants. Reproduction is essential for the continuation of a species. Imagine what would have happened if organisms had not reproduced. You will realise that reproduction is very important as it ensures the continuation of similar kinds of individuals, generation after generation.


    Hormones are secretions of endocrine glands which pour them directly into the blood stream. 

     Pituitary gland secretes hormones which include growth hormone and hormones that make other glands such as the testes, ovaries, thyroids and adrenals, secrete hormones. Pancreas secretes insulin, thyroid produces thyroxine and adrenals produce adrenalin. 

     Testosterone is the male hormone and estrogen, the female hormone. The uterine wall in females prepares itself to receive the developing fertilised egg. In case there is no fertilisation, the thickened lining of the uterine wall breaks down and goes out of the body along with blood. This is called menstruation.

      Sex of the unborn child depends on whether the zygote has XX or XY chromosomes.


    Force could be a push or a pull. 

     A force arises due to the interaction between two objects.  Force has magnitude as well as direction. 

     A change in the speed of an object or the direction of its motion or both implies a change in its state of motion. 

     Force acting on an object may cause a change in its state of motion or a change in its shape. 

     A force can act on an object with or without being in contact with it. 

     Force per unit area is called pressure


    Friction opposes the relative motion between two surfaces in contact. It acts on both the surfaces. 

     Friction depends on the nature of surfaces in contact.

      For a given pair of surfaces friction depends upon the state of smoothness of those surfaces. 

     Friction depends on how hard the two surfaces press together. 

     Static friction comes into play when we try to move an object at rest. 

     Sliding friction comes with play when an object is sliding over another. 

     Sliding friction is smaller than static friction

  • 13 SOUND

    Sound plays an important role in our life. It helps us to communicate with one another. We hear a variety of sounds in our surroundings.


    Some liquids are good conductors of electricity and some are poor conductors.

      Most liquids that conduct electricity are solutions of acids, bases and salts.

      The passage of an electric current through a conducting liquid causes chemical reactions. The resulting effects are called chemical effects of currents. 

     The process of depositing a layer of any desired metal on another material, by means of electricity, is called electroplating


    There are two kinds of charges — positive charge and negative charge Like charges repel and unlike charges attract each other. The electrical charges produced by rubbing are called static charges. When charges move, they constitute an electric current. An electroscope may be used to detect whether a body is charged or not. The process of transfer of charge from a charged object to the earth is called earthing. The process of electric discharge between clouds and the earth or between different clouds causes lightning.

  • 16 LIIGHT

    Diffused/irregular reflection takes place from rough surfaces. Two laws of reflection are (i) The angle of incidence is equal to the angle of reflection. (ii) Incident ray, reflected ray and the normal drawn at the point of incidence to the reflecting surface, lie in the same plane. Image formed in a plane mirror undergoes lateral inversion.


    The phases of the moon occur because we can see only that part of the moon which reflects the light of the Sun towards us.  Stars are celestial bodies that emit light of their own. Our sun is also a star. 

     It is convenient to express distances of stars in light years.  Stars appear to move from east to west. 

     The pole star appears to be stationary from the Earth, because it is situated close to the direction of the axis of rotation of the Earth.  Constellations are groups of stars that appear to form recognisable shapes. 

     The solar system consists of eight planets and host of asteroids, comets and meteors.

      A body revolving around another body is called a satellite.


    Air pollution is the contamination of air by impurities which may have a harmful impact on the living organisms and the non-living components. Pollutants are the substances which contaminate air and water. Carbon monoxide, nitrogen oxides, carbon dioxide, methane and sulphur dioxide are the major pollutants of air. Increasing levels of greenhouse gases like CO2 are leading to global warming. Water pollution is the contamination of water by substances harmful to life.