NCERT Solutions for Class 8 Science

Welcome to the NCERT Solutions for Class 8 Science. This page offers chapter-wise solutions designed to help students grasp key concepts easily. With detailed answers and explanations for each chapter, students can strengthen their understanding and prepare confidently for exams. Ideal for CBSE and other board students, this resource will simplify your study experience.

• Chapter 1 Crop Production and Management
  • In order to provide food to our growing population, we need to adopt certain agricultural practices.
  • In India, crops can be broadly categorized into two types based on seasons: Rabi and Kharif crops.
  • It is necessary to prepare soil by tilling and levelling. Ploughs and levelers both these are used for this purpose.
  • Sowing of seeds at appropriate depths and distances gives good yield. Good variety of seeds are sown after the selection of healthy seeds. Sowing is done by seed drills.
  • Soil needs replenishment and enrichment through the use of organic manure and fertilisers.
  • Supply of water to crops at appropriate intervals is called irrigation.
  • Weeding involves removal if unwanted plants are called weeds.
  • Harvesting is the cutting of the mature crops manually or by machines.
  • Separation of the grains from the chaff is called threshing.
  • Proper storage of grains is necessary to protect them from the pests and microorganisms.
  • Food is also obtained from the animals for which they are reared. This is called animal husbandry.

• Chapter 2 Microorganisms: Friend and Foe
  • Microorganisms are too small and are not visible to naked eyes.
  • Microorganisms are found in air, water and in the bodies of the plants and animals.
  • They may be unicellular or multicellular.
  • Microorganisms includes bacteria, fungi, protozoa and some algae. Viruses are different from the above mentioned living organisms, are considered microbes.
  • Viruses are quite different from the other microorganisms. They reproduce only inside the host organism: bacterium, plant and animal cell.
  • Some microorganisms decompose the organic waste and dead plants and animals into the simple substances and cleans up the environment.
  • Some bacteria present in the soil fixes the nitrogen from the atmosphere and convert into the nitrogenous compounds.
  • Microorganisms can live in all kind of environment ranging from cold climate to hot deserts.
  • Protozoan causes serious disease like malaria and dysentery.
  • Microorganisms grow on our food which may lead to food poisoning.
  • Algae is a type of microorganism which lives in the water and contain chlorophyll.
  • Antibiotics are the medicines which kill or stop the growth of disease causing organism.
  • WBCs (white blood cells) produces a protein called antibiotics which identify and destroy the microbes.
  • Carrier may be defined as the living beings which carry the microorganisms to spread disease.
  • The disease which can spread from an infected person to healthy person through air, water and by physical contact.
  • The process of conversion of sugar into alcohol is called as fermentation.
  • Pasteurization is the process, in which milk is heated to 70◦C for 15 to 20 seconds and then suddenly cooled and stored, then the growth of microbe is prevented in the milk. This process was discovered by Louis Pasteur, so it is known as pasteurization.
  • Preservation is the process in which food can be preserved from the actions of microorganisms.
  • Injecting the dead or weak microbes in healthy body is called as vaccine. It develops immunity.  

   

• Chapter 3 Synthetic Fibres and Plastics
  • Synthetic fibre are called as man- made fibre whereas natural fibres are obtained from the nature.
  • Polymers are made up of many smaller units.
  • Natural fibres are obtained from plants and animals whereas man- made fibres or synthetic fibres are obtained by chemical processing of petrochemicals.
  • Many household articles like ropes, buckets, containers, furniture etc. are made up of synthetic fibres. Some highly specialized use of synthetic fibres are ships, space, space- craft etc.
  • Nylon, Rayon, polyester and acrylic are the different types of synthetic fibre depending upon the type of chemical used.
  • Different types of fibres differ from one another in their strength, cost, durability and water absorbing capacity.
  • Plastic is non- biodegradable, it does not degenerate in the environment. It is not eco- friendly.
  • We should avoid plastics to make the environment clean.
  • Acrylic is the artificial wool that resembles to the natural wool but it is cheaper than it. More durable clothes are obtained from the acrylic wool as compare to the natural wool.
  • By chemical treatment of wood pulp artificial silk or rayon is obtained. It is cheaper than the natural silk.
  • Nylon is made from coal, water and air. It is man- made or synthetic fibre. Nylon is the first fibre which us fully synthetic.
  • Plastics can be molded into desired shape. It is a synthetic material. It is also a polymer.
  • Polyester may be defined as the synthetic fibre which does not get wrinkled easily. It is used for making dress.
  • A chain of small units joined together to make a large unit called polymer.
  • Plastic is used for making commonly used polythene bags.
  • Terylene is polyester.
  • The plastics which gets deformed easily on heating and which can bent easily are called as thermoplastics. For example: comb, toys etc.
  • Plastic which cannot be deformed easily are called as thermosetting plastics. For example: Floor tiles, plates etc.

• Chapter 4 Materials: Metals and Non-Metals
  • Metals are good conductor of electricity and heat whereas non- metals are poor conductor of electricity and heat.
  • Metals are lustrous whereas non- metals are not lustrous.
  • Malleability is the property of metals by which metals can be drawn into thin sheets. Non- metals does not shows malleability.
  • Ductility is the property of metals by which they can be drawn into wires. Non- metals does not show the ductility. Hence, they are not ductile.
  • In the presence of air, metal forms metal oxide to react with the oxygen.
  • Metal oxides are basic in nature whereas non- metallic oxides are acidic in nature.
  • On reacting with water, metal produce metal hydroxides and hydrogen gas.
  • Non- metals does not react with water.
  • On reaching with acids, metals produce metal salt and hydrogen gas whereas non- metals do not reacts with acids.
  • Metal produces hydrogen gas on reacting with the base.
  • Atoms are the smallest unit which cannot be divided into the smaller one.
  • The materials or substances through which heat and electricity can pass easily are called as conductor. Metals are good conductor of electricity whereas non- metals are poor conductor.
  • The reaction in which a higher reactive element displace the less reactive element from its place, then the reaction is called as displacement reaction.
  • Substances which cannot be broken down into simpler substances are called as elements.
  • Hardness is defined as the rigidity of the substance, by which the substance cannot be broken down easily.
  • The elements which shows the properties of both metal and non- metals are known as metalloids.
  • The property of metal due to which it produces ringing sound. It is called as sonorous.

• Chapter 5 Coal and Petroleum
  • The resources which we get from nature are called as natural resources.
  • Natural resources are of two types: Inexhaustible natural resources and exhaustible natural resources.
  • The resources which are present in the unlimited quantity in nature are called as inexhaustible natural resources. For example: sunlight.
  • The resources which are present in the limited quantity in nature are known as exhaustible natural resources. For example: coal, petroleum.
  • Fossil fuel may be defined as the fuels which are formed from the dead vegetation and dead remaining of living organisms. They are present in limited quantity.
  • Coke is the pure form of carbon, it is used in the manufacture of steel.
  • Coal is as hard as stone, it is used to cook food.
  • A thick, black liquid with unpleasant smell is called as coal tar.
  • Petrol and diesel are obtained from the natural resources are called as petroleum.
  • The process of separating the various constituents of petroleum is known as refinery.
  • CNG and LPG are the clean fuels which does not produce and harmful gas behind.
  • We should use the inexhaustible natural resources.
  • We should use the exhaustible natural resources carefully because they are limited in nature.

• Chapter 6 Combustion and Flame
  • When a substance is burnt in the presence of oxygen than it gives off heat, process is called combustion and that substance is called combustible.
  • For the combustion reaction presence of oxygen (air) is must.
  • Heat and light are also produced with carbon dioxide during the process of combustion.
  • The lowest temperature at which a substance catches fire easily known as ignition temperature.
  • Inflammable substances generally have very low ignition temperature.
  • To extinguish fire generally, water is used.
  • If the fire involving electrical equipments or oils then water cannot be used to extinguish it.
  • Combustion is of various types: Rapid combustion, spontaneous combustion or explosion.
  • The substance which vaporize during the burning process gives flame.
  • Flame have different zones like: dark zone, luminous and non- luminous zone.
  • An ideal fuel have high calorific value and readily available. It is also easy to transport.
  • A calorific value shows the efficiency of the fuel.
  • Carbon monoxide is produced during incomplete combustion of fuel which is a poisonous gas.
  • As the increasing temperature of the earth with increase in the amount of carbon dioxide leads to the global warming.
  • When the oxides of nitrogen and Sulphur mix with the rain water, it forms the acid and then this type of rain is known as acid rain.
  • Calorific value may be defined as the heat energy produced on complete combustion of 1 kg of fuel.
  • On large scale, cutting down the trees, known as deforestation.
  • The reaction that takes place in sudden with the evolution of heat, light and a large amount of gas is known as explosion.
  • The region where combustion of gaseous substances take place is known as flame.

• Chapter 7 Conservation of Plants and Animals
  • The areas which are meant for conservation of forest and wild animals are named as wildlife sanctuary, biosphere and national parks.
  • Flora and fauna are the plants and the animals of that particular area.
  • The species which is found in a particular area is known as endemic species.
  • The species which are facing the danger of extinction called as endangered species.
  • The book that contains all the data or the records of all the endangered species known as Red Data Book.
  • Movement of species from its own habitat to some other habitat for a particular period of time for the specific purpose known as migration.
  • In order to save trees, we should save paper.
  • A variety of living organisms found in a specific area is known as biodiversity.
  • The areas which are meant for conservation and preservation of biodiversity, are known as biosphere reserve.
  • Conversion of fertile land into the desert by the soil erosion is called as desertification.
  • A system which involve plants, animals, microorganisms along with the abiotic factors like climate, soil, river etc. is known as the ecosystem.
  • Disappearance of a species from the earth is known as extinct species.
  • The reserves which are very large and diverge enough to protect whole sets of ecosystem, known as National parks. It includes flora and fauna etc.
  • Planting trees in the particular area where forests were destroyed is called as reforestation.
  • A place where wild animals are protected, in a particular area with the suitable living conditions known as sanctuary. Sanctuary means safety.

• Chapter 8 Cell - Structure and Functions
  • Cells are the basic structural and functional unit of life.
  • Organs are the smaller parts which collectively made a full organism.
  • Robert Hook in 1665 observed cells in the cork for the first time.
  • Cells are of different shapes and size.
  • Number of cells are also differ from organisms to organisms.
  • Some cells are of large size and some are of small size.
  • The organisms which contains large number of cells are known as multicellular organisms.
  • In unicellular organisms, all the basic functions are performed by the single cell.
  • In multicellular organisms, all the basic functions are performed by the various cells.
  • Cells have mainly three parts: cell membrane, cytoplasm and nucleus.
  • A cell without nuclear membrane is known as prokaryotic cells.
  • Cells with the nucleus is known as eukaryotic cells.
  • A green pigment chloroplast is present in the body of plants that contains chlorophyll.
  • Cell membrane is thin sheet of skin around the cell. It controls the movement of substances “into the cell” and “out of the cell”.
  • A thick layer around the cell membrane is present, is known as cell wall. It helps in giving the shape of the cell.
  • Thread like structures are present in the nucleus of the cell that are known as chromosomes. And, they carry genes.
  • Cytoplasm is the jelly like substances which is present between the cell membrane and the nucleus.
  • Genes are the unit of inheritance in the organisms.
  • Nucleus is covered by a membrane called nuclear membrane.
  • In a nucleus a dense stained structure is found which is known as nucleolus.
  • Group of tissues which are adapted to perform the specialized functions in the body known as organs.
  • In amoeba, false feet are known as pseudopodia. 

• Chapter 9 Reproduction in Animals
  • Animals can reproduce by two modes:

  Sexual reproduction and asexual reproduction

  • The fusion of male and female gametes fuses to form a zygote and then make an offspring and this process is known as sexual reproduction.
  • Ovaries, oviducts and uterus are the female reproductive organs.
  • Testis, sperm ducts and penis are the male reproductive organs.
  • Female gamete is produced by ovary which is called as ova and the male gamete is produced by testis called sperms.
  • The fusion of male and female gamete is called fertilization.
  • Zygote is the fertilized egg.
  • Fertilization takes place inside the female body is called as internal fertilization.
  • Fertilization that takes place outside the female body is known as external fertilization. Mainly occurs in frog, fish etc.
  • Zygote divide in a repeating manner to give rise to an embryo.
  • Foetus is the stage of embryo in which all body parts are identifiable.
  • Viviparous animals are those who give birth to their young one. For example: humans.
  • Oviparous animals are those which lay eggs.
  • Through drastic changes; the transformation of larva into adults is called metamorphosis.
  • The type of reproduction in which only a single parent is involved is called asexual reproduction.
  • Binary fission is the type of asexual reproduction which generally occur in amoeba, it reproduces by dividing itself into two. 

• Chapter 10 Reaching The Age of Adolescence
  • Adolescence is the period of life where many changes takes place in the body to reproductive maturity.
  • The most apparent change during the puberty is sudden increase in height, voice change, change in body shape, development of sex organ etc.
  • In females. One egg is released by either of the ovary during each month. After that, the uterus develops a thick lining to the support of foetus to prepare for possible pregnancy. If fertilization does not take place, this results in bleeding through vagina for some days which is known as menstruation.
  • The thread like structure called chromosomes.
  • The male hormone is known as testosterone and female hormone is known as estrogen.
  • The production of these hormones are under the control of another hormone that is secreted from the endocrine gland called pituitary gland.
  • Endocrine gland secretes hormones which are poured into the blood stream directly.
  • The protruding part of the throat which can be easily seen in boys are called as Adam’s apple.
  • The period of time when body undergoes several changes along with reproductive maturity is known as adolescence.
  • Adrenaline hormone is secreted by adrenal gland which helps the body to control the stress.
  • A meal that include proteins, carbohydrates, fats and vitamins in appropriate amount and is known as balanced diet.
  • Endocrine glands are ductless glands.
  • Pancreas secreted insulin which help to lower the blood sugar level.
  • Voice box is called as larynx.
  • Pituitary gland is also known as master gland of the body.
  • The physical, mental and social well- being of a person and the healthy reproductive organs with normal functions, is called as reproductive health.

• Chapter 11 Force and Pressure
  • Force is simple called as push or pull of the body.
  • Interaction between two surfaces is must for force to come into play.
  • Magnitude is called as the strength of the force.
  • If two forces applied on the same direction to the body then the force are ready.
  • If two forces applied in the different directions then the net force acting on the body is the difference between two forces.
  • Force brings change in the state of motion of an object.
  • Force brings change in the shape of an object.
  • Force come in play when two bodies comes in contact with each other called as contact force.
  • Muscular force may be defined as the force which is due to the action of muscles.
  • Friction is the opposing force which can change in the state of the motion of the body.
  • Force exert by the magnet is the example of non- contact force.
  • Force exerted by a charged body on another charged or uncharged body is known as electrostatic force.
  • Earth attracts things towards itself is known as gravity.
  • Gravitational force is the force exerted by the every small things on the earth.
  • Force per unit area is known as pressure.
  • Gases, liquid exerts pressure on the walls of their container.
  • Pressure exerted by the air is known as atmospheric pressure.

• Chapter 12 Friction
  • Push or pull is known as force.
  • Friction is the opposing force which is exerted by a moving body.
  • Friction helps in moving, running and stops the body.
  • Friction is of different types: static friction, rolling, sliding and dynamic.
  • Interlocking of irregularities in two surfaces called as friction.
  • Rolling friction is usually less than sliding friction.
  • Sliding friction is smaller than the static friction.
  • The substance which helps in reducing the friction or make the surface smooth is called as lubricant.
  • When one body rolls over another body, this is called rolling friction.
  • When one body slides over another body is known as sliding friction.
  • Ball bearing are the small balls which are used between hubs and the axles of ceiling fans to reduce the friction.
  • The frictional force exerts by the fluids is known as drag.
  • Aero-plane have such shape to reduce the friction.
  • Friction is more felt on the rough surfaces.
  • Friction depends on the point of contact of two surfaces.
  • Heat is produced by friction.

• Chapter 13 Sound
  • Vibrating objects produce sound.
  • In humans sound is produced by vibration of the vocal cords.
  • Sound cannot travel in vacuum.
  • Sound can travel through a solid, liquid or a gas medium as well.
  • The vibration of sound are senses by the eardrum.
  • Eardrum is a stretched membrane.
  • Eardrum send signals to brain. This process is known as hearing.
  • Frequency of oscillation may be defined as the number of oscillation or vibrations in one second.
  • Hertz (Hz) is the unit of frequency.
  • The unpleasant and unwanted sound is called as noise. It may lead to noise pollution.
  • Many health hazards are produced by noise pollution.
  • Loudness of sound is called as amplitude or we can say the displacement of vibrating object from its main position is called amplitude.
  • Eardrum is a stretched membrane which separates the middle ear from the outer ear which vibrated to produce sound.
  • Larynx is known as the voice box which produces sound.
  • Loudness is the characteristics of sound which depends upon the amplitude.
  • Oscillation is the complete to and fro motion of an object about at its mean position.
  • Pitch is known as the flatness or shrillness of a sound.
  • Time period may be defined as the time taken by vibrating objects to complete one oscillation.
  • Vibration is the to and fro movement of a body.
  • Windpipe connects the larynx to the lungs, it is tube like structure of respiratory tract.

• Chapter 14 Chemical Effects of Electric Current
  • Some liquids are good conductor of electricity and some are poor conductors.
  • Most of the liquids that conduct electricity are the solution of acid, base and salt.
  • The passage of an electric current through an conducting liquid causes chemical reactions and these final resulting effects are called chemical effects of current.
  • The process of depositing a layer of any metal on another material with the electricity is called electroplating.
  • Positive terminal of the cell is connected to the negative terminal of another cell. Such combination of two or more cells is known as battery.
  • The substances which allows the electric current to pass through them are called as good conductor of electricity.
  • The substances which does not allow the electric current to pass through them are called as bad conductor of electricity.
  • Electrode may be defined as the conductor through which electricity or current enters or leaves.
  • A semi-conductor device which is used in mobiles, computers and torches are known as LED (Light emitting Diode).

• Chapter 15 Some Natural Phenomena
  • Some objects can be charged by rubbing with other objects.
  • There are two kinds of charges: positive and negative.
  • Like charges repel and unlike charges attracts.
  • The process of transfer of charge from the charged object to the earth is called earthing.
  • The process of electric discharge between clouds and the earth or between different clouds causes lightening.
  • Lightening conductors can protect building from the lightening effects.
  • Earthquake is caused by the disturbance inside the crust.
  • Destructive energy of an earthquake measured on Richter scale. The earthquake measuring one or more on Richter scale can cause damage to life and property.
  • Earthquake generally occurs at the boundaries of the Earth’s plate. These boundaries are called as fault zone.
  • Topmost layer of the earth is called as crust.
  • Discharge may be defined as the transmission of electricity through a medium in an applied electric field.
  • Electroscope is an instrument which is used to detect the presence of the electric charge on body.
  • In a dark sky, on a rainy day, when a shiny streak of light appears accompanied with the thunder is called as lightening. 
  • An instrument which is used to record the details of earthquake is known as seismograph.
  • Sound caused by the lightening is called as thunder.
  • A storm with lightning and thunder is known as thunderstorm.
  • The giant waves which are caused by earthquake or volcanic eruptions under the sea called as tsunami.  

• Chapter 16 Light
  • Light is reflected from all the surfaces.
  • Regular reflection takes place when light is incident on smooth, polished and regular surfaces.
  • Diffused/ irregular reflection takes place from rough surfaces.
  • Image formed in a plane mirror undergoes lateral inversion.
  • Beautiful patterns are formed in a kaleidoscope because of multiple reflection.
  • Spelling of light into seven colours are called dispersion.
  • Angle of incidence is the angle between the incident ray and the normal. It is denoted as (∠i).
  • Angle of reflection is the angle between the reflected ray and normal. It is denoted as (∠r).
  • The area on retina that does not have any light sensing nerves. This area have zero vision. It is known as blind spot.
  • Braille may be defined as the system for blind persons in which raised dots represent the letter. By this blind person can read and write by touching.
  • In retina, photoreceptor cells are present, are called as cones which are sensitive to light and colour.
  • The transparent part of the eye called as cornea which covers the most of the part of eye.
  • In plane mirror, generally the right part seems as left and left is seems as right, it is due to the phenomenon of lateral inversion.

• Chapter 17 Stars and The Solar System
  • The phases of the moon occurs because we can see only that part of them which reflects the light of the sun towards us.
  • Stars appears to move from east west.
  • The solar system consists of eight planets and a host of asteroid comets and meteors.
  • A body revolving around another body is known as satellite.
  • Moon is natural satellite of the earth. Some planets also have natural satellites.
  • Artificial satellite is an man- made device which is orbiting around the earth, moon or other planet. It transmits the scientific information.
  • Asteroids are the small pieces of rock or metals that revolve around the sun in between the orbits of Mars and Jupiter.
  • Cassiopeia is a prominent constellation which is visible in the northern sky, in winter season.
  • A small heavily body which is made up of ice and dust that revolve around the sun is called as comets.
  • The sun, moon and other objects which are present in the sky are known as celestial objects.
  • Constellation is a group of stars which forms a recognizable pattern in the sky.
  • Distance travelled by light in one year is called as one light year.    

• Chapter 18 Pollution of Air and Water
  • When some harmful substance or some polluted gases are mixed in air, then the air becomes impure. It contaminated the air, this is called as air pollution.
  • The substances which contaminate air and water called as pollutants.
  • The major pollutants of air are the carbon dioxide, carbon monoxide, nitrogen oxides, methane and Sulphur dioxide.
  • When the concentration of carbon dioxide increases in the atmosphere which may leads to the increase in the temperature of the Earth. It may lead to global warming.
  • When some harmful substances or some impurities dissolved in water. This is called as water pollution.
  • Water is contaminated by sewage, agricultural and industrial waste.
  • Potable water is fit for drinking because it is purified.
  • Water is the natural resource which is precious. So, we have to conserve it.
  • Chemical contamination is done by chemical fertilizers and detergents contains water.