❖ Crop: Same kinds of plants cultivated on a large scale
|Kharif crops||Sown in rainy season (June to September).||soyabean, paddy, maize|
|Rabi crops||grown during winter season (October to March)||wheat, gram, pea|
❖ Basic crop production practices
|Preparation of soil||Loosening and upturning of the soil. This process is known as tilling or ploughing.||• Plough
|Sowing||Placing of seeds of a crop in the soil is called sowing.
||• Funnel shaped traditional tool driven by animals
• Seed Drills
|Adding manure and fertilizers||Adding nutrients to the soil||Manures - Prepared from decomposed animals and plant waste.
Commercially available inorganic salts rich in plant nutrients
|Irrigation||Supplying of water to plants at various intervals is called irrigation.
||• Moat (pulley system)
• Chain pump
• Rahat (chain system)
• Sprinkler system
• Drip system
|Protection from weeds (weeding)||Removal of unwanted plants from the field that compete with crops for space, water and nutrients||• Manually by hands
• Seed drills
• Weedicides like 2,4-D
|Harvesting||The process of cutting of mature crops from the field is called harvesting||• Sickle
|Threshing||The process of removing grains from chaff is called threshing.||Combine|
|Storage||The process of keeping seeds safe from spoilage due to moisture, insects, rats, and microorganisms for a long time is called storage||• Jute bags and metallic bins for small scale storage
• Silos and granaries for large scale storage
❖ Sources of irrigation: Wells, tube wells, ponds, lakes, canal, river, dams etc.
❖ The process of separating grains from the husk in the mixture of threshed chaff is called winnowing.
❖ Small scale storage of grains: It is usually done in jute bags and metallic bins.
❖ Large scale storage of grains: It is done in.
❖ Food from animals - Milk from cow, buffalo, goat, and camel; Meat from chicken, goat, and sheep; Eggs from chicken and ducks.
❖ Animal husbandry - The rearing of animals, which includes feeding, breeding, and disease control on a large scale, is called animal husbandry.Chapter 2: Microorganisms
❖Microorganisms: The living organisms that cannot be seen with unaided eye are called microorganisms.
❖Classification of microorganisms: There are five major groups of microorganisms.
|Bacteria||• Single-celled organisms
• Found in wide range of habitats ranging from glaciers to deserts and hot springs
• Example – curd bacteria (Lactobacillus)
|Fungi||• Multicellular, heterotrophic organisms
• Lack chlorophyll and are generally found in colonies
• Example – Penicillium, Aspergillus
|Protozoa||• Unicellular or multicellular microorganisms
• Usually found in water
• Example – Amoeba and Paramecium
|Algae||• Unicellular or multicellular autotrophic organisms
• Contain chlorophyll pigment and carry out photosynthesis
• Example – Chlamydomonas and Spirogyra
|Viruses||• Ultramicroscopic organisms
• Require cells of host organisms to reproduce
• Example – Influenza virus, polio virus
❖Importance of microorganisms
⚬ Yeast is used in preparation of breads, pastries, and cakes.
⚬ Louis Pasteur discovered fermentation.
⚬ Yeast is used for commercial production of alcohol, wine and vinegar (acetic acid).
⚬ Antibiotics are obtained from bacteria and fungi.
⚬ Commonly used antibiotics are streptomycin, tetracycline, and erythromycin.
⚬ First antibiotic i.e. penicillin was prepared by Alexander Fleming
⚬ Vaccine includes dead or weakened microbes that trigger the production of antibodies in the body.
⚬ These antibodies help in preventing attack from disease-causing microorganisms.
⚬ Vaccination helps in controlling diseases such as cholera, polio, small pox, hepatitis, etc.
⚬ Vaccine for small pox was discovered by Edward Jenner
⚬ They fix atmospheric free nitrogen to enhance soil fertility.
❖ Harmful microorganisms – Disease-causing microorganisms are called pathogens.
⚬ The example includes cholera, chicken pox, and tuberculosis
⚬ The organisms that transmit diseases from one place to the other are called carriers.
⚬ Example of carriers:
|Housefly||Cholera, dysentery and typhoid.|
⚬ Foot and mouth disease in cattle is caused by virus
⚬ Rust of wheat is caused by fungi
⚬ Yellow mosaic of Bhindi is caused by virus
• Process of preventing the spoilage of food items by the action of microbes is called food preservation.
❖Methods of food preservation
⚬ Common salt is used as preservative in pickles. It is also used to preserve meat and fish.
⚬ Sugar is used as preservative in jams and jellies.
⚬ Oil and vinegar are used as preservatives in pickles and vegetables.
⚬ Pasteurization is a technique of preserving milk in which it is boiled to about 70°C for 15 to 30 seconds and then suddenly chilled and stored.
• Storage and packing: Dry fruits and vegetables are sealed in air tight packets to prevent microbe attack.
❖Nitrogen cycle: It involves the circulation of nitrogen through living and non-living components of nature.
• First process of nitrogen cycle is fixation of nitrogen gas into nitrogenous compounds caused by Rhizobium bacteria and lightning.
• Nitrogen compounds in soil are taken up by plants through roots and used up in synthesis of plant proteins. Animals obtain nitrogen by feeding on plants.
• Waste of plants and animals are converted to nitrogenous compounds by the action of bacteria and fungi in the soil.
• Some bacteria convert nitrogenous compounds back to nitrogen to maintain atmospheric levels of nitrogen.
❖ Synthetic fibres (or man-made fibres) : Chains of small units joined together (each small unit is a chemical substance).
❖ Types of Synthetic fibres:
• Nylon: Strong, elastic, light and used for making clothes, parachutes and ropes for rock climbing.
• Polyester: Remains crisp and is easy to wash. Terylene (used for making dress materials) and PET (used for making utensils, films, wires and bottles) are two well known polyesters.
❖ Characteristics of synthetic fibres :
• Less expensive
• Readily available
• Easy to maintain
❖ Plastics : Polymer like synthetic materials where the arrangement of small units is linear or cross-linked
❖ Types of plastics :
• Thermosetting plastics: If moulded once, cannot be softened by heating. Examples: bakelite and melamine
❖ Characteristics of plastics:
• They are light, strong, and durable.
• They are poor conductors of heat and electricity.
❖ Harmful effects of plastics:
❖ Biodegradable substances: Get decomposed through natural processes such as by the action of bacteria. Examples: paper, peels of vegetables, wood and fruits, etc.
❖ Non-biodegradable substances: Do not get decomposed easily by natural processes. Examples: plastic bags, metals, etc.Chapter 4: Materials - Metals And Non-Metals
❖ Differences in physical properties of metals and non-metals:
|Generally, found in solid states (Exception: Mercury is a liquid metal)||Generally, found in liquid and gaseous states.|
|Generally, these are hard and lustrous (Exception: Sodium and potassium are soft and can be cut with knife).||These are soft and have no lustre.|
|These are malleable and ductile.||These do not show such properties.|
|These are sonorous (produce ringing sound when struck).||These are not sonorous.|
|These are good conductors of heat and electricity.||These are poor conductors of heat and electricity.|
❖ Differences in chemical properties of metals and non-metals:
|These react with oxygen to produce metal oxides, which are basic in nature.||These react with oxygen to form non-metallic oxides, which are acidic in nature.|
|Some metals react with water to produce metal hydroxides and hydrogen.||These do not react with water.|
|These react with acids to produce metal salts and hydrogen gas.||These do not react with acids.|
|Some metals react with bases to produce hydrogen gas.||Reactions of non-metals with bases are complex.|
❖ Displacement reactions → A more reactive metal can displace a less reactive metal from their compounds in aqueous solutions.
❖ Uses of metals: In making machinery, automobiles, jewellery, trains, aeroplanes, cooking utensils, etc.
❖ Uses of non-metals: In fertilizers, in water purification process, crackers, etc. Oxygen, a non-metal, is essential for our life as all living beings inhale it during breathing.Chapter 5: Coal And Petroleum
❖ In the light of availability of natural resources in nature, they can be broadly classified into exhaustible and inexhaustible natural resources.
• Exhaustible natural resources: The amount of these resources in nature is limited. Examples: coal, petroleum, natural gas, etc.
❖ Fossil fuels : These are formed from the dead remains of living organisms. Examples: coal, petroleum, and natural gas
❖ Coal: A fossil fuel used to cook food, in railway engines to produce steam, in thermal power stations to generate electricity.
❖ Products of coal: Coke, coal tar, and coal gas
• Coal tar: It is the mixture of about 200 substances. The products obtained from coal tar are used as starting materials for dyes, drugs, paints, perfumes, etc.
• Coal gas: It is obtained during the processing of coal to obtain coke.
❖ Petroleum: A fossil fuel formed from the dead organisms present in the sea. The process of separating various constituents of petroleum is known as refining.
|Constituents of Petroleum||Uses|
|LPG||As fuel for home and industry|
|Petrol||As motor fuel, aviation fuel|
|Paraffin wax||Candle, vaseline, etc.|
|Diesel||As fuel for heavy motor vehicles|
|Kerosene||As fuel for stoves, lamps|
❖ Natural gas: It is stored under high pressure as compressed natural gas (CNG). It is used as a fuel for transport vehicles because it is a cleaner fuel (less polluting).
❖ Resources such as coal and petroleum are limited. Burning of such fuels is the major cause of air pollution. Therefore, these fuels should be used only when necessary.Chapter 6: Combustion And Flame
❖ Combustion: It is a chemical process in which a substance reacts with oxygen to give off heat and light.
❖ Oxygen (in air) is essential for combustion.
❖ Substances that burn in air are called combustible substances (also called fuels) and those that do not burn in air are non-combustible substances.
❖ Ignition temperature: It is the lowest temperature at which a substance catches fire.
❖ Control of fire:
• For fires involving oil, petrol, and electrical equipments, carbon dioxide is the best extinguisher.
❖ Inflammable substances → They have very low ignition temperature and can easily catch fire with flame.
❖ Types of combustion: Rapid combustion, spontaneous combustion, and explosion
❖ Zones of candle flame:
|Innermost (Non-luminous)||Minimum||Black||Unburnt carbon particles|
❖ A good fuel is one which
• is readily available
• burns easily in air at a moderate rate
• produces large amount of heat
• does not leave behind any undesirable substances
❖ Fuel efficiency: It is expressed in terms of calorific value. The unit is kilojoule per kg.
❖ Calorific value: It is the amount of heat energy produced by complete combustion of 1 kg of a fuel.
❖ Harmful effects of burning of fuels:
• Incomplete combustion of fuels produces carbon monoxide gas (poisonous gas).
• Increased percentage of carbon dioxide in the atmosphere causes global warming.
• Oxides of sulphur and nitrogen produced by burning of fuels (coal, diesel, petrol, etc.) cause acid rain, which is harmful for crops, buildings, and soil.
❖Deforestation: Deforestation is the process of removal of forests for industrial, agricultural, and other purposes.
❖Causes of deforestation
⚬ Severe droughts
⚬ Rapid urbanization
⚬ Procurement of wood for fuel and furniture
❖Consequences of deforestation
• Lowering of ground water levels
• Increase in pollution levels and temperature
• Decrease in fertility of soil and amount of rainfall
• Increase in frequency of droughts and floods
• Conversion of fertile land into deserts (desertification)
❖Conservation of forests and wildlife
• Forests help in maintaining the delicate balance of nature.
• Animals living in forests are called wild animals.
• Flora: The plants found in a particular area.
• Fauna: The animals found in a particular area.
• Endemic species: Species of plants and animals that are found only in a particular area, are called endemic species.
• Species: It is a group of population which are capable of interbreeding.
• Endangered animals: The animals, whose numbers are diminishing to a level that they might face extinction. For example: tiger, lion, and elephants
• Project tiger was launched to protect endangered tigers in their natural habitat.
• The flora and fauna of a particular habitat can be protected through special protected areas.
For example: Mudumalai wildlife sanctuary in Tamil Nadu, Chilika bird sanctuary in Orissa, etc.
• National parks: These are the areas reserved for wildlife where they can freely use the habitats and natural resources. For example:
Ranthambore national park in Rajasthan, Kanha national park in Madhya Pradesh, etc. Satpura national park is the first reserve forest of India.
The finest Indian teak is found in this forest.
• Biosphere reserves: It is a large protected land for conservation of wild life, plant and animals resources, and the traditional life of the tribals living in the area.
For example: Pachmarhi Biosphere reserve and Nilgiri Biosphere reserve in India
❖Red Data Book:
It keeps a track record of various endangered species of plants and animals.
• Numerous migratory birds including ducks, geese, sandpipers, and cranes fly to India every year.
• Migration by birds every year occurs due to
⚬ lack of food availability in their original habitats during winters
❖Recycling of paper
• Papers should be recycled and reused to conserve forest.
• Each paper can be recycled three to seven times.
• Recycling of paper saves energy and water.
• It prevents the release of harmful chemicals (used during paper manufacturing) in nature.
• It helps in checking environmental degradation.
❖Ecosystem: An ecosystem is a natural unit consisting of all plants, animals and micro-organisms in an area functioning together with all of the non-living physical factors of the environment
Chapter 8: Cell - Structure And Function
❖ Cell: Cells are the basic structural units and the building blocks of living organisms.
❖ Discovery of the cell
• Hooke coined the term “cell”.
❖ Number of cells
• Single cell in these organisms performs all the basic functions such as digestion, respiration, and excretion.
• Organisms made up of more than one cells are called multicellular organisms. For example: Humans, cow, etc.
• In these organisms, the cells show division of labour as particular set of cells are involved in performing a specific body function.
❖ Shape of the cells
• The human red blood cell (RBC) is spherical-shaped.
• The muscle cells in humans are spindle-shaped.
• The human nerve cells have elongated branched structure.
• In plants and bacteria, the cell is enclosed in a protective covering called cell wall, which gives shape and rigidity to the cells.
❖ Size of the cells
• The largest cell is the egg of an ostrich which is about 170 mm ´ 130 mm in size.
❖ Cell structure and functions
• Organs are further made up of tissues.
• Tissues are groups of similar cells performing a specific function
❖ Components of the cell
⚬ Cell membrane selectively allows the entry of only some substances and prevents the movement of other materials. Hence, it checks the transport of substances in and out of the cell.
⚬ It contains various cell organelles such as mitochondria, golgi bodies, lysosomes etc.
⚬ It contains spherical body called nucleolus.
⚬ It also contains thread-like structures called chromosomes.
⚬ Chromosomes are the structures that carry genes and play an important role in inheritance.
⚬ Genes are the structural and functional unit of inheritance.
⚬ The entire living substance in a cell is known as protoplast.
⚬ In plant cells, a single large vacuole is present.
⚬ In animal cells, numerous small vacuoles are present.
⚬ Plastid that contains green colour pigment called chlorophyll is known as chloroplasts. It is the chlorophyll that gives green colour to the leaves.
⚬ Chloroplast traps solar energy and utilizes this energy to manufacture food for the plant.
❖ Types of cell
• Eukaryotic cells - Cells having nucleus with well defined nuclear membrane. For example - plant and animal cells
❖ Differences between plant and animal cells
|Cell organelle||Plant Cell||Animal Cell|
❖ Reproduction: It is a biological process through which living organisms produce offsprings similar to themselves.
❖ Modes of reproduction: Sexual and asexual reproduction.
❖ Sexual reproduction
• Male gametes are called sperms and female gametes are called ova.
• Male reproductive system: Consists of testis, sperm duct and penis.
⚬ Sperm contains three parts: Head, middle piece and tail.
⚬ A single matured egg is released from ovum into oviduct every month.
⚬ External fertilization: In this, the fusion of sperm and eggs takes place outside the female body in a surrounding medium, generally water. It occurs in frogs, fishes, starfish, etc.
❖ Test tube baby: A baby conceived by fertilization that occurs outside mother’s body is called test tube baby.
❖ Development of embryo
• The ball of cells then starts differentiating into tissues and organs. At this stage, it is called embryo.
• Embryo gets attached to the wall of the uterus and develops various body parts such as hands and legs.
• Foetus is a stage of embryo that shows main recognizable feature of mature organism.
• Foetus develops for nine months inside the mother’s womb and is finally delivered.
❖ Viviparous animals: The animals that give birth to live young ones. Example: cows, dogs, and humans.
❖ Oviparous animals: The animals that lay eggs outside the body. Example: birds, lizards, snakes, and frogs.
• The life cycle of frog consists of the following stages.
Egg → Tadpole (larva) → Adult
• The life cycle of a silk worm consists of the following stages.
Egg → Larva → Pupa → Adult
❖ Asexual reproduction: Involves only a single parent and the new individuals are formed without fusion of gametes.
❖ Two common methods of asexual reproduction
⚬ This phenomenon is very common in plants, fungi and animals such as Hydra and yeast.
⚬ It is a type of asexual reproduction in which a single cell divides into two halves.
❖ Cloning: The process used to create an exact copy of a cell, tissue or an organism. Dolly, a sheep was the first mammal to be cloned by Ian Wilmut and his colleagues in 1996.Chapter 10: Reaching the Age Of Adolescence
❖ Adolescence: The time period when the body undergoes changes to reach reproductive maturity is known as adolescence.
It begins at the age of 10 or 11 and lasts till about 18 or 19 years of age.
❖ Puberty: The various changes that occur in the body during adolescence marks the onset of puberty.
❖ Changes that take place during puberty
⚬ In girls the region below the waist becomes wider
⚬ It protrudes in males in the neck region and is called Adam’s apple.
⚬ Boys develop deep low-pitched voice while girls develop high-pitched voice.
⚬ The oily secretions from sebaceous glands increase. The accumulation of oil and bacterial action leads to acne problems in teenagers.
⚬ Ovaries develop completely and start producing eggs in girls.
⚬ Intellectual development takes place during adolescence.
|In boys||In girls|
⚬ Appearance of moustaches and beard
⚬ Appearance of hair on chest
⚬ Growth of hair in genital area and other parts of skin
⚬ Increase in breast size⚬ Growth of hair in the pubic regions
• They are produced by endocrine glands.
• These glands release hormones into blood to reach specific target site.
• Production of hormones is under the control of hormones produced from pituitary gland.
• Sex hormones
⚬ Female sex hormone is called Oestrogen. It is produced by ovaries.
⚬ It is required for regulating metabolism in the body.
⚬ Lack of iodine leads to deficiency of thyroxine, which results in a disease called goitre.
⚬ It maintains blood sugar level.
⚬ Deficiency of insulin results in diabetes.
⚬ It helps the body to adjust various stress conditions.
⚬ It is required for proper body growth.
❖ Role of hormones in other animals
• Thyroxine: Thyroxine produced by thyroid glands play an important role in the metamorphosis of tadpoles into adults.
❖ Reproductive phase in humans
• In females, the reproductive phase starts from 10-12 years and continues till 45-50 years.
• The female reproductive tract undergoes series of cyclic changes, called menstrual cycle, which is of 28 to 30 days.
• One ovum is produced during one cycle.
• The wall of uterus becomes thick to receive fertilized egg.
• If pregnancy does not occur, the unfertilized egg and uterus lining are shed off, which results in bleeding, called menstruation.
• First menstrual flow in a female is called menarche.
• Stoppage of menstruation in females is called menopause.
❖ Sex determination in babies
• Sex chromosomes are of two types, X and Y.
• Females have two X chromosomes (XX) while males have one X and one Y chromosomes (XY).
• Sex chromosome of the male parent decides the sex of the child.
• When a sperm with X chromosome fuses with an egg containing X chromosome, it leads to the development of a female child.
• When a sperm with Y chromosome fuses with X chromosome of an egg, it leads to the development of a male child.
❖ Reproductive health
• They should maintain cleanliness to prevent bacterial infections.
• They should avoid usage of drugs and alcohols.
• Sharing of syringes during drug abuse leads to spread of HIV virus causes AIDS.
• AIDS is also caused by unsafe sexual contact and from infected mother to her infant through milk.
❖ Force is a physical quantity which can change speed, direction or shape of a body.
• Pull→ When an object is moving towards the applier of force
❖ Resultant of more than one force acting on a body:
• Force applied in the opposite direction → Subtraction, direction same as of the greater force
❖ Effects of force
• Force can change the shape or size of an object.
❖ Contact forces: when the applier is in contact with the body.
• Friction – The force which always opposes the relative motion of two bodies in contact.
❖ None-contact forces
• Electrostatic force – Force of attraction/repulsion between electric charges
• Gravitational force – Force of attraction between any two bodies in the universe
❖ Pressure → Force per unit area
❖ Water and gas exert pressure on the walls of their container, which varies with depth (or height)
❖ At a given depth, pressure is always the same irrespective of the shape/size of the vessel.
❖ Atmospheric pressure = Weight of the atmosphere per unit areaChapter 12: Friction
❖ The force which always opposes relative motion of the two surfaces which are in contact.
❖ Cause of friction - the irregularities on the two surfaces in contact lock into one another.❖ Factors affecting friction
• Rough surfaces → greater friction
• How hard an object is pressed – Greater pressing force → Greater friction
• Mass of object – Greater mass → Greater friction
• Sliding friction < Static friction
• Rolling friction < Sliding friction
❖ Reducing friction
• In many machines, friction is reduced by using ball-bearing.
• Shoe soles and tires are threaded to increase friction for a better grip.
❖ The friction between layers of fluid or between a solid object and fluid is called fluid friction.
• Shape and size of the object
• Nature of fluid
❖ Fluid friction is minimised by giving suitable shapes to vehicles moving through fluids.❖ Fluid friction is also called dragChapter 13: Sound
❖ Vibrating body produces sound.
❖ Vibration – to-and-fro or back-and-forth or up-and-down motion of a body
❖ Musical instruments and their vibrating parts
|Musical instrument||Vibrating part producing sound|
❖ Sound requires a medium to propagate (solid, liquid, or gas).
❖ Sound cannot travel through vacuum.
❖ In humans, sound is produced by larynx (voice-box).
❖ In human ear, the eardrum vibrates and passes vibration to the inner ear
• Higher frequency → higher pitch
• It depends on amplitude.
• Higher amplitude → louder sound
❖ Audible sound – Human ear can hear sounds having frequency in the range of 20-20,000 Hz.
❖ Noise pollution – Presence of unwanted and excessive sound in the environment.
❖ Some liquids are good conductor while some are bad conductors.
• Greater the deflection of needle or brighter the light, better is the conductivity of the liquid.
• Classification of some liquids on the basis of their conductivity.
|Good conductor||Poor conductor|
|Basic solutions||Vegetable oil|
(tap water, sea water)
❖ The electric current passing through a conducting liquid causes chemical reactions. The resulting effects are called chemical effects of electric current.
❖ The process of depositing a desired metal or material, by means of electricity is called electroplating.Chapter 15: Some Natural Phenomena
❖ Objects get charged when rubbed with another material.
|Objects that get charged||Material used for rubbing|
|Refill||Polythene, woollen cloth|
|Balloon||Polythene, woollen cloth, dry hair|
|Steel spoon||Polythene, woollen cloth|
|Ebonite comb||Dry hair, silk cloth|
|Glass rod||Woollen cloth, silk cloth|
❖ There are two kinds of charges, positive and negative.
• Opposite charges attract each other.
• Charge generated by rubbing is static.
• When charges move they constitute an electric current.
❖ Electroscope is used to detect whether an object is charged or not. It cannot detect the nature of charge.
❖ The process of transfer of charge from a charged object to Earth is called earthing.
❖ The sudden flow of charge (discharge) from cloud to objects on Earth is called lightening.
❖ Lightening safety
• Unsafe places → open spaces, beneath tall trees, any elevated place
• Using an umbrella is not safe during lightning.
• During lightning, one should avoid using electrical appliances (should be unplugged) and running water.
❖ Lightning conductor is the pointed metal rod on top of tall buildings.
❖ It transfers charge from lightening to Earth via conducting wire.
❖ Earthquake is the sudden shaking or trembling of the earth’s surface because of disturbance deep inside the earth’s crust. Earthquakes cannot be predicted.
❖ Causes of Earthquake:
• Movements of earth’s plates cause Earthquake. Plate boundaries are called seismic zones or fault zones.
• Earthquake may also occur because of volcanic eruption.
• Power of earthquake is measured on Richter scale.
❖ Reflection of light is the change in the path of a light ray upon collision with an interface of two medium.
❖ Laws of reflection:
• Rays AO, OM and OB lie in the same plane.
❖ Image formation by a plane mirror
• The image is laterally inverted.
❖ Regular and irregular reflection
|Regular reflection||Irregular reflection|
❖ Kaleidoscope works on the theory of multiple reflections which forms beautiful patterns.
❖ Sunlight consists of several colours.
❖ Splitting of white light is called dispersion.
❖ Human eye
• Iris controls the size of pupil.
• Pupil controls the amount of light.
• Optic nerves sense the image and send it to the brain.
• The junction of optic nerve and the retina is called blind spot.
❖ Impression of an image persists for seconds in our brain.
❖ Vitamin A (raw carrots, broccoli, green vegetables, cod-liver oil, etc.) is necessary for good vision.
❖ Braille system is helpful for visually challenged persons for reading.CHAPTER 17: Stars and the Solar System
❖ All natural objects in the sky are celestial objects.
❖ New Moon day: when moon is not visible
❖ Full Moon day: when full moon is visible
❖ Gap between consecutive new moon day and full moon day is of 15 days.
❖ Moon’s surface: Because of lack of atmosphere, one cannot hear any sound on moon.
❖ All stars emit their own light. In day time, stars are not visible because of bright sunlight.
❖ The biggest star that can be seen is the sun.
❖ Stars appear to move from east to west because of earth’s rotation from west to east.
❖ Constellations: Groups of stars of particular shapes
❖ Planets revolve around the sun along definite paths, called orbits.
❖ Time taken by a planet to complete one revolution of its orbit is called revolution period.
❖ Time taken by a planet to rotate about its axis is called period of rotation.
|Inner planets||Outer planets|
• Nearest planet to the sun
• It is seen just before sunrise and just after sunset near horizon. It has no satellite.
• Brightest planet planet and nearest to the earth
• Also known as morning or evening star
• Has no satellite and rotates from east to west (sun rises in the west of Venus)
• From space, it appears blue because of 75% water content.
• It appears reddish and therefore, is known as red planet
• Largest planet in the solar system
• Rotates very fast about its axis and has large numbers of satellites
• Has prominent ring system and large numbers of satellites
• Its density is less than water and is the least among the planets
Uranus and Neptune
• Both have ring system.
• Uranus has a tilted rotational axis and appears to roll on its side.
• Uranus rotates from east to west similar to Venus.
• Have a bright head and long gaseous tail which always directed away from sun
• Halley’s comet appears after every 76 years.
❖ Meteors & Meteorites
• Large meteors that reach earth’s surface are called meteorites.
❖ Artificial satellite
• Used for weather forecasting, remote sensing, communication system, etc.
❖ Atmosphere: The layer of air present around the earth. It is composed of 78% of nitrogen, 21% of oxygen, and 1% percent other gases such as carbon dioxide, ozone, water vapour, methane, etc.
❖ Air pollution: The phenomenon of contamination of air with unwanted substances so that it becomes harmful for living organisms and non-living substances.
• Sources of air pollution are
⚬ Burning of firewood
⚬ Sulphur dioxide: Produced from combustion of fuels and causes respiratory problems including permanent lungs damage. It causes formation of acid rain.
⚬ Nitrogen dioxide: Produced from incomplete burning of fuels and causes respiratory problems. It causes formation of acid rain.
⚬ Chlorofluorocarbons (CFCs): These are released from refrigerators, air conditioners, and aerosol spray and cause damage to the ozone layer resulting in the formation of ozone hole.
⚬ Suspended particulate matter: These are produced during burning of fossil power plants, mining, steelmaking, and other industrial processes and comprises of tiny particles, which remain suspended in air for a long time.
❖ Acid rain: It is formed when sulphur dioxide and nitrogen dioxide present in air react with water droplets to form nitric and sulphuric acid.
It has caused corrosion of the marble of Taj Mahal.
❖ Green house effect: The trapping up of reflected solar radiations by the earth’s atmosphere and gradual heating up is known as greenhouse effect.
❖ Greenhouse gases: These are the gases, which trap the solar radiations, and prevent them from escaping into the atmosphere.
Example: carbon dioxide, methane, nitrous oxide, and water vapours.
❖ Global warming: The gradual warming up of the earth’s atmosphere by the increased carbon dioxide level.
The CO2 level in atmosphere is increasing due to various human activities such as deforestation and burning of fossil fuels.
❖ Prevention of air pollution:
• Use of renewable sources of energy such as solar, wind, and hydel energy
• Planting more and more trees to prevent pollution
• Prevent burning of dry leaves and use them in composting
❖ Water pollution: Mixing of harmful substances in water such as sewage and toxic chemicals so that its physical and chemical properties get altered and it becomes toxic for living organisms.
❖ Water pollutants: Substances that pollute water
❖ Sources of water pollution in Ganga river:
• Disposal of agricultural discharge from near-by fields, which are rich in pesticides and weedicides, into the river
• Flow of untreated domestic sewage into the river
• Cremation of dead bodies into the river
• Immersion of idols of gods and goddesses, flowers, garbage, and polythene bags into the river
❖ Types of water pollutants
• Industrial waste.
• Agricultural waste: Rich in agricultural pesticides and weedicides which causes ground water pollution and an increase in the population of algae in water resulting in eutrophication.
❖ Potable water: Water that is fit for drinking is called potable water.
❖ Methods of obtaining potable water
⚬ Use of domestic filters such as candle type filter
❖ Prevention of water pollution
• Strict implementation of environmental laws in industrial units
• Reusing water
• Preventing wastage of water