Cbse guide

Monday, November 23, 2020

Class 8th keywords

Chapter 1:- Crop production and management

1. Agricultural practice:-Various tasks performed by farmers for crop production are termed as Agricultural practices

2. Animal husbandry:-. Animals reared at home or in farms have to be provided with proper food, shelter and care. When this is done on a large scale, it is called animal husbandry.

3. Crop:-Crop is a plant that is grown on a large scale commercially.

Pulses, Cereals, Oil seeds, Vegetables & fruits are different types of crop.

4. Fertiliser:-Fertilizers are commercially produced plant nutrients. They result in higher yields & healthy plants, if applied in proper dose

5. Granaries:- Storehouse where large scale storage of grains is done to protect them from pests like rats and insects.

6. Harvesting:-Harvesting is cutting of crop after it is matured. The season of harvesting brings a lot of happiness as this is time when the hard work of farmers brings results.

7. Irrigation:-Irrigation is artificial application of water to soil to ensure growth of agricultural crops.

8. Kharif:-Crops grown in rainy season are termed as Kharif crops. Examples: Maize, soyabean, sugarcane

9. Manure:-Manure is an organic substance that increases soil fertility. It is prepared from decomposition of animal excreta & plant wastes.

10. Plough:-Tool used for ploughing . It is made of iron/ wood. It is pulled by a pair of animals like cows/ oxen/ horses and operated by the farmer through the handle

11. Rabi :-Crops grown in winter season are termed as Rabi crops. Examples: Wheat, Gram, Pea

12. Seeds:- the small hard part of a plant from which a new plant of the same kind can grow.

13. Silo:- Towers where large scale storage of grains is done to protect them from pests like rats and insects.

14. Sowing:-Scattering seeds on the Earth after soil is prepared for cultivation is termed as Sowing

15. Storage:- Proper storage of food grains is important to protect against moisture, micro-organisms & insects.

16. Threshing:- In the harvested crop, the grain seeds need to be separated from the chaff. This process is called threshing. This is carried out with the help of a machine called combine which is a harvester as well as a thresher.

17. Weeds:-Weeds are unwanted plants in the cultivated field. They compete for nutrients, space, water & light, therefore, adversely affect crop growth.

18. Weedicides:-These are chemicals which kill weeds without damaging the crops.

19. Winnowing:-Threshing can be done manually using a process called ‘Winnowing’

In this process, grains are separated from chaff by throwing into the air. Chaff gets carried away by wind, while grains fall back.

Chapter :- 2 Micro-organisms friend and foe

1. Algae:- these are multicellular,aquatic microorganisms Example:-Spirogyra, Ulothrix, Chlamydomonas

2. Antibiotics:-Antibiotics are chemical substances that kill disease-causing microbes

3.Antibodies:- Proteins which are produce by our body to fight the invader.

4.Bacteria :- Bacteria are one of the oldest unicellular life form that appear appear in a variety of shapes & sizes (Spherical, elongated, spiral etc.)

5.Carrier:- Agents which carry pathogens to healthy person. Ex :- female anopheles mosquito , female Aedes

6. Communicable diseases:- Microbial diseases that can spread from an infected person to a healthy person through air, water, food or physical contact are called communicable disease . Ex cholera, common cold, chicken pox and tuberculosis.

7. Fermentation:- The process of conversion of sugar into alcohol is called fermentation.

8. Fungi:-Fungi are multicellular, Heterotrophic, immobile life form that found in moist and humid climate.

9. Lactobacillus:-Curd contains a bacterium, Lactobacillus

It is a friendly-bacterium

10. Micro-organisms:- organism which are too small to see with naked eyes. They can be seen with microscope or magnifying glass.

11. Nitrogen cycle:- Nitrogen cycle is all about the movement of nitrogen between various elements on Earth

12. Nitrogen fixation:- The process of fixing atmospheric nitrogen into soil by nitrogen fixers is called nitrogen fixation.

13. Pasteurization is a technique that makes use of heat & cold treatments to preserve food items. In this process, milk is heated to about 700C for 15-30 sec & then suddenly chilled & stored. This technique was invented by Louis Pasteur (1864).

14 Pathogen: disease-causing organisms are called Pathogens. Pathogens include bacteria, viruses, fungi & protozoa.

15. Preservation:- The process of protecting food from the attack of microorganisms is called preservation

16. Protozoa:- Group of single celled organisms like Amoeba, Paramecium etc is called Protozoa

17.Rhizobium:- Nitrogen fixing bacteria which is present in the roots on leguminous plants us called rhizobium

18:- vaccine:-vaccine is a biological preparation that resembles a disease causing microbe. These vaccines are made up of dead or very weak microbes.

19. Virus:-microorganisms which behave like non-living when outside host cell, and reproduce only when inside the host cell

20. Yeast:- A single celled organism which helps in fermentation .

Chap 3 synthetic fibres and plastics

1. Acrylic :-synthetic fibre which is formulated from a polymer called polyacrylonitrile.It is lightweight, soft, warm, and has resemblance with wool.

2. Artificial silk :- The fibre that is obtained by chemical treatment of wood pulp is called artificial silk Or rayon.

3. Nylon:- Synthetic fibre that is prepared from coal, water and air. It is the first fully synthetic fibre.

4. Plastic :- A light , strong and durable polymer that is used to make chairs , slippers, decoration pieces etc.

5. Polyester:- Synthetic fibre that doesn't get wrinkled easily.

6. Polymer :- Many small units combine together to form a large single unit called polymer

7. Polythene :- A type of plastic which is formed by combination of many ethene molecules.

8. Rayon :- The fibre that is obtained by chemical treatment of wood pulp is called artificial silk Or rayon

9. Synthetic fibres :- Man made fibre is called synthetic fibre. Ex:- Nylon , Rayon, polyester and acrylic etc.

10. Terylene :- It is a kind of polyester that can be drawn into very fine fibres that can be woven like any other yarn

11. Thermoplastics :- The plastic which gets deformed easily on heating and can be bent easily are known as thermoplastic

12. Thermosetting plastic :- The plastic which donot gets deformed easily on heating and can be bent easily are known as thermoplastic

Chap 4:- Materials: Metals and Non metals

1. Atom :- The smallest unit of matter which contains electron , proton and neutron as subatomic particles.

2. Conductor :- The substances which allow electricity to pass through it . Example:- metals are good conductors .

3. Displacement reaction :- A reaction in which a more reactive element displace less reactive element from its salt solution. Example:- Iron + Copper sulphate --> Iron sulphate + copper.

4. Ductility :- The ability of metals to be drawn into thin wires is called ductility. Example:- Gold is most ductile metal.

5. Elements :- Pure species which is made up of only one kind of atoms.

6. Hardness :- The ability of a substance to resist cutting and grinding is called hardness. Metals are generally hard. The hardness varies from metal to metal . Except :- lithium, sodium, potassium.

7. Malleability :- Some metals can be beaten into sheets. This property is called malleability. Example:- gold and silver are the most malleable metals

8. Metals :- Substances which are electropositive in nature i.e. they have a tendency to lose electrons. Example:- Sodium, iron, copper, gold, silver, etc.

9. Metalloids :- The elements which have properties in between metals and non metals. Example:- boron, silicon etc.

10. Non metals :- Substances which are electronegative in nature i.e. they have a tendency to gain electrons. Example:- Carbon, Sulphur, Iodine, Oxygen, Hydrogen etc.

11. Sonorous :- Metals produce ringing sounds this property is called sonorous.

Chap 5 :- Coal and Petroleum

1. Coal :- A black coloured hard substance that is composed of carbon, hydrogen, nitrogen, oxygen, minor amount of sulphur.

2. Coal gas :- It is a gaseous mixture of hydrogen, methane, and carbon monoxide

3. Coal tar :- Black, thick and viscous liquid that contains 42% carbon, 48% hydrocarbons and rest of the percentage is occupied by water

4. Coke :- Hard, black coloured and porous derivative of coal.It is a pure form of carbon with less content of impurities and has high carbon content.

5. Fossil fuels:- Fossil fuel refers to the deposits of organic materials, formulated from dead plants and animals under several thousand feet of silt. It's formation takes millions of years

6. Natural gas:- It is a cleaner fuel that is stored under high pressure as compressed natural gas.

7. Petroleum :- It is a clear, green or black coloured oily liquid matter that can be either thin like gasoline or thick like tar.

8. Petroleum refinery :- Process of separation of the wide variety of constituents of petroleum is called Refining of Petroleum carried out in petroleum refinery

Chap 6 :- Combustion and Flame

1. Acid Rain :- Oxides of sulphur and nitrogen dissolve in rain water and form acids . Such a rain is Called acid rain.

2. Calorific value:- Amount of heat energy produced on complete combustion of 1Kg of a fuel is called calorific value. It's unit is KJ/kg

3. Combustion :- A chemical process in which a substance reacts with oxygen to give off heat is called combustion.

4. Deforestation :- Clearing of forests(by cutting down forest trees)over a wide area is called deforestation.

5. Explosion :- The combination which is accompanied by heat, light and sound is called explosion.

6. Flame :- The visible gaseous part of fire which is hot, glowing ignited gas during combustion is called flame.

7. Fire extinguisher :-The job of a fire extinguisher is to cut off the supply of air or bring down the temperature of the fuel.

8. Fuel :- Combustible substance which release enough heat energy to be used for domestic and industrial purposes. Example :- LPG, CNG, Wood, Coal, petroleum etc .

9. Fuel efficiency:- The amount of heat produced by the complete combustion of unit mass of a fuel is known as fuel efficiency.

10. Global warming:- Rise in the temperature of the atmosphere of the earth due to production of acidic oxides during combustion of fuel is called global warming.

11. Ideal fuel :- The fuel which is cheap, easily available, have low ignition temperature ,high calorific value and doesn't produce residue is called ideal fuel.

12. Ignition temperature :- Lowest temperature at which a substance catches fire is called ignition temperature.

13. Inflammable substances The substances which have very low ignition temperature and can easily catch fire with a flame is called inflammable substances.

Chap 7 :- Conservation of Plants and animals

1. Biodiversity:- the existence of a number of different kinds of animals and plants which together make a good and healthy environment

2. Biosphere reserve:- biosphere reserve is a place where animals and some species of plants are kept safely.

3. Deforestation :- This process of removal of a forest or collection of trees from a land and thereafter converting the land to a non-forest use is called deforestation.

4. Desertification :- When a fertile land gets converted to a barren land by deforestation, this is called desertification

5. Ecosystem :- All the interacting organisms in an area together with non-living constituents of the environment forms an ecosystem.E.g. Forests, ponds.

6. Endangered species:- The species of plants and animals whose number is reducing to a level where they may no more exist in nature are called Endangered species

7. Endemic species :- The species of plants and animals that can be found only in a specific region are called Endemic species

8. Extinct :- The species of plants and animals that no more exist in nature due to unsuitable habitat are called Extinct species.

9. Fauna :- The animals of a particular region are called fauna of that region

10. Flora :- The plants of that region are called flora of that region

11. Migratory birds:- Birds that travel from their own habitat to a different habitat due to several reasons at a certain period of the year.

12. National park :- Protected areas intended to provide a natural habitat with all natural resources to the animals where they can freely roam and use the habitat are called national park.

13. Red data book :- The source book that is used to keep a record of endangered species of plants, animals and other species existing within the territory of the state or country is called red data book.

14. Reforestation :- the act of planting new trees in an area or region where they were cut down previously

15. Sanctuary :- a place where birds or animals are protected from being hunted

Chap 8 :- Cell - Structure and Functions

1. Cell:- Cell is the structural and functional unit of life

2. Cell membrane:- Thin , delicate, living and outermost membrane which bound cytoplasm.

3. Cell wall:- Non-living , rigid, outermost covering of plant cell which is fully permeable.

4. Chloroplast:- Green colour plastid which contain chlorophyll.

5. Chromosome:- Rod shaped structure that formed when chromatin condense together when the cell is about to divide

6. Cytoplasm:- Jelly like structure present between the cell membrane and the nucleus.

7. Eukaryotes:- Organisms whose cells have well organised nucleus with a nuclear membrane

8. Gene:-Unit of inheritance in living organisms which control the transfer of a hereditary characteristics from parent to offspring.

9. Multicellular:- organisms made up of more than one cell are called multicellular organisms

10. Nuclear membrane:- Double layered covering of nucleus which separate material inside nucleus from cytoplasm

11. Nucleolus:- Structure embedded in nucleoplasm and compose of proteins and RNA

12. Nucleus:- A structure which is present near centre of eukaryotic cell.

13. Organ:- Group of tissue together make functional unit called organ

14. Organelles:- Membrane bound structure due to which a cell is able to live and perform all its functions

15. Plasma membrane:- Thin, delicate, living outermost covering of cell which ensure protection of cell

16. Plastid :- Organelles present in plant cells only and provide colour and store food to it

17. Prokaryotes:- Organisms whose cells have nuclear material without nucleus membrane

18. Pseudopodia:- False finger like projection which Amoeba possess for intake of food

19. Tissue:- Group of cell which have common origin and perform same function is called tissue

20. Unicellular:- Single celled organism is called unicellular

21. Vacuole:- Organelles which store food and is surrounded by tonoplast

22. White blood cell (WBC) :- Blood cells which fight against germs

Chap 9 :- Reproduction in animals

1. Asexual reproduction:- The type of reproduction in which only a single parent is involved is called asexual reproduction

2. Binary fission:- A mode of asexual reproduction in which an organism reproduce by dividing itself into two is called binary fission. Ex:- Amoeba

3. Budding:- A mode of asexual reproduction in which new individuals develop from buds is called budding. Example:- Hydra

4. Eggs:- the ovary produces female gamete called egg or ovum

5. Embryo :- The zygote divide and redivide to form groups of cells that develop into different tissues and organs of the body. This developing structure is termed as an embryo.

6. External fertilization:- Fertilization that takes place outside the female bodies is called external fertilization

7. Fertilization:- The fusion of ovum and sperm is called fertilization

8. Foetus :- The stage of the embryo in which all the body parts are identifiable is called foetus

9. Internal Fertilization:- Fertilization that takes place inside the female body is called internal fertilization

10. Metamorphosis:- The transformation of the larva into adult through drastic changes is called metamorphosis

11. Oviparous Animals:- Animals such as hen, frog, lizard and butterfly which lay eggs are called oviparous animals

12. Sexual Reproduction:- Reproduction resulting from the fusion of male and female gametes is called sexual reproduction.

13. Sperms :- The testis produce male gametes called sperm

14. Viviparous animals:- Animals such as human beings, cows and dogs which give birth to young ones are called viviparous animals

15. Zygote :- The fertilized egg is called zygote

Chap 10 :- Reaching the age of Adolescence

1. Adam's apple :- At puberty, boys grow a larger voice box that appears as a bulging part of the throat. This is called Adam’s apple.

2. Adolescence :- period of life in which organism become capable to reproduce their offsprings.

3. Adrenalin :- Hormone that helps to adjust stress in a human body at the time of certain emotions like anger, embarrassment, etc. It is secreted by Adrenaline gland.

4. Balanced diet :- Balanced diet is a meal that includes adequate amount of proteins, carbohydrates, fats, vitamins and minerals.

5. Endocrine glands :- Ductless hormones which secrete hormones and released it into the bloodstream

6. Estrogen:- Female sex hormone that is secreted by ovaries.

7. Hormones:- Chemical substances that coordinate the activities of living organisms and also for their growth are called hormones.

8. Insulin:- Hormone produced by pancrease is called insulin.

9. Pituitary gland:- Gland which controls the release of other hormone glands in a human body, including the thyroid and adrenals, the ovaries and testicles.

10. Puberty:- The period in which rate at which general body growth begins to slow down and reproductive tissues begin to mature is called puberty.

11. Reproductive health:- A state of complete physical, mental and social well being in all aspects of reproduction.

12. Secondary sexual characters:- Secondary sexual characters refer to the external features that distinguish a male from a female.

13. Sex chromosomes:- The sex of baby is determined by a pair of chromosome called sex chromosomes.

14. Target site:- Endocrine glands release hormones into the bloodstream to reach a particular body part called target site.

15. Testosterone:- Male sex hormone that is secreted by testis

16. Thyroxine:- Hormone produces by thyroid gland is called thyroxine.

17. Voice box :- Sound box or larynx which begins to grow at puberty . It produces sounds.

Chapter 11 Force and Pressure

1. Atmospheric pressure:- The air all around us also exerts pressure. This is known as Atmospheric Pressure. The value of atmospheric pressure is very high.

2. Contact forces : Force that arises with the contact of 2 or more objects involved. Examples : Muscular force and Frictional Force

3. Electrostatic force is the force exerted by a charged body on another charged or uncharged body.

4. Force:-A push or a pull on an object is called a Force

5. Frictional Force is a force that acts on all moving objects by the surface which it is in contact with.

The Frictional force is always in the direction opposite to the applied force.

6. Gravitational : it is an attractive force between two massive bodies .

G= (gmM)/r2

7. Gravity:-force exerted by the earth on all objects on it. When a ball is thrown up, it falls to the ground because of gravity

8. Magnetic Force is a force that attracts certain metal objects (like iron and iron filings) towards a magnet.

9. Muscular force is the type of force wherein we use our physical strength to change the state of motion of an object. Eg: Man pushing a car, Bullocks pulling a cart of load, Cycling, Weight Lifting

10. Non-contact forces: Forces that arise without the contact of 2 or more objects involved. Examples: Magnetic Force, Electrostatic Force, Gravitational force

11. Force acting on unit area is called Pressure ie Pressure = Force/Area

12. Pull:-Pull refers to that force which tends to 'move the object towards' the direction of the force applied.

13. Push:-

Push refers to the force which tends to 'move the object away' from the direction of the force applied

Chap 12 :- Friction

1. Ball bearing :- Ball bearing is a device which consists of a ring of small metal balls. It is designed to make the moving parts of a machine to roll over each other rather than slide.

2. Drag :- Fluids (means liquids and gases) too exert friction on the objects. The frictional force exerted by fluids is called a drag

3. Fluid friction :- Fluids (means liquids and gases) too exert friction on the objects. The frictional force exerted by fluids is called fluid friction or drag

4. Friction:- Friction is a type of forces that opposes motion.It always acts in a direction opposite to that of the applied force.

5. Interlocking:- The irregularities on two surfaces tend to lock into each other . This is called interlocking.

6. Lubricants:- substances which make the surfaces smooth and thereby reduce friction are called lubricants.

7. Rolling friction:- when a body rolls over another surface is called Rolling Friction. The Rolling Friction is less that Sliding Friction.

8. Sliding friction:- when a body moves over another surface is called Sliding Friction

9. Static friction :- Static friction is friction between two or more solid objects that are not moving relative to each other.

Chap 13:- Sound

1. Amplitude:- The magnitude of maximum disturbance in the medium on either side of the mean value is called amplitude.

2. Audible:- A sound of 20Hz to 20,000 Hz that a human can hear is called audible range of sounds.

3. Eardrum:- The thin membrane present in the ear is called eardrum.

4. Hertz:- SI unit of frequency is called hertz

5. Larynx:- sound is produced by the vibration of an organ called voice box or larynx.

6. Loudness:- Amplitude determines the Loudness of sound. It is expressed in a unit called decibel (dB).

7. Noise:- Unpleasant sounds are called noise

8. Oscillation:- The motion in which object moves to and fro is called oscillation.

9. Pitch :-Perception of frequency of sound wave is called stillness of pitch. Frequency determines the shrillness or the pitch of the sound.

10. Shrillness:- Perception of frequency of sound wave is called stillness of pitch. Frequency determines the shrillness or the pitch of the sound.

11. Time period:- Time taken to complete one oscillation is called time period.

12. Vibration :- Rapid to and fro motion of an object is called vibration.

13. Voice box :- sound is produced by the vibration of an organ called voice box or larynx.

14. Wind pipe :- Pipe which help in gases exchange. The Larynx is situated at the upper end of windpipe.

Chap 14 Chemical effects of electric current

1. Electrode:-Electrodes are the metal rods which are dipped in liquids, to which cells are attached are called electrodes

2. Electroplating:-Process by which metals are coated with another metal to give it their lustrous appearance and still keep it cost effective.

Process of depositing a layer of desired metal on another material by mean of electricity is called electroplating.

3. Good conductor:-The materials which conduct electricity are called good conductors of electricity. Eg: Iron, copper, aluminum, iron, human body etc

4. LED:- Light Emitting Diode. A device that produces a light on electrical and electronic equipment.

5. Poor conductor:-The materials which don't conduct electricity at all are bad conductors of electricity. Eg: plastic, glass, rubber.

Chap 15 Some Natural Phenomenon

1. Crust :- The uppermost layer of the earth is called crust.

2. Discharge:- The process of release of electric charges from a charged object to an uncharged object in contact with it , is called discharge.

3. Earth's plates:- The outermost layer of the earth is not in one piece but is fragmented . These fragments are called earth's plates

4. Earthquake:- It is a sudden shaking or trembling of the earth which lasts for a very short time is called earthquake

5. Electroscope:- A device that can be used to test whether an object is carrying charge or not , is called electroscope.

6 . Lightning:- The bright flash of light which we see in the clouds is called lightning.

Lightning is an electric discharge in the atmosphere between oppositely charged clouds

7. Lightning conductor:- Lightening conductor is a device used to protect buildings from the effect of lightening.

8. Negative charge:- If an object gains electrons, it now has surplus number of electrons. Thus, this object becomes negatively charged.

9. Positive charge:- If an object loses some electron, it is left with surplus number of protons. Thus, this object becomes positively charged.

10. Richter scale:- The power of an earthquake is expressed in terms of a magnitude on a scale clleca the Richter scale

11. Seismograph:- An instrument which record seismic waves produce by tremors.

12. Thunder:- Thunder is the sound caused by lightning

13. Thunderstorm:- A rain-bearing cloud that also produces lightning is called thunderstorm.

14. Transfer of charge:- When certain objects are rubbed against another object, electrons may get transferred from one object to another.

15. Tsunami:- A tsunami is a very large and powerful wave. It is caused by earthquakes under the sea.

16. Tremor:- A relatively minor seismic shaking or vibrating movement.

Chap 16 light

1. Angle of incidence:-angle between the Incident ray and normal

2. Angle of reflection:-Angle between the reflected ray and normal

3.Blind spot:- Spot where rod and cone cells are absent so no image formed.

4. Braille:-The Braille script is an alphabet set used by the blind for reading and writing. Each Braille character is made up of a combination of 6 dots arranged in a matrix form.

5. Cones:-cells which are Sensitive to bright light

6. Cornea:-Outermost, transparent, thin membrane of eye ball.

Light enters into eye through cornea.

7. Diffusion or irregular reflection:-

When light falls on a rough surface (like a stone, your body, your clothes etc), all the parallel incident rays are not reflected parallel to each other. This is called Diffused Reflection.

8. Incident rays:-Ray of light that strike the surface.

9. Iris:-Dark muscular diaphragm that control the size of pupil.

Provide colour to eye.

10. Kaleidoscope:-A kaleidoscope is an optical instrument with two or more reflecting surfaces tilted to each other in an angle, so that one or more (parts of) objects on one end of the mirrors are seen as a regular symmetrical pattern when viewed from the other end, due to repeated reflection.

11. Lateral inversion:- In mirror left appears right and right appears left . This is called lateral inversion

12. Laws of reflection:-1. Angle of incidence= angle of reflection

2. Incident ray, reflected ray and the normal all lie on the same plane.

13. Pupil:It is the window of the eye.

Central aperture In iris.

Regulates and control the amount of light entering the eye

14 Reflected rays:-Ray of light sent back by the surface after reflection

15. Reflection:-Bouncing back of ray of light into the same medium after striking a polished surface such as mirror is called reflection of light

16 Regular reflection:- When light falls on a smooth uniform surface (like a mirror), all the parallel incident rays are reflected perfectly parallel. This is called Regular Reflection.

17 Retina:-Delicate membrane having enormous number of light sensitive cells. Lens image form on the retina.

18 Rods:- cells which are Sensitive to dim light

Chap 17 Stars and the solar system

1. Artificial Satellites:- Man made satellites revolving round the Earth are called artificial satellites

2. Asteroids:- large gap in between the orbits of Mars and Jupiter that is occupied by a large number of small objects that revolve around the Sun are called asteroids

3. Cassiopeia:- constellation in the notthern sky that looks like a distorted letter W or M

4. Celestial objects:- the stars , the planets, the moon and many other objects in the sky are called celestial objects.

5. Comets:- Comets are cosmic snowballs of frozen gases, rock and dust that orbit the Sun.

6. Constellations:- Group of stars that appear to form recognisable shapes.

7. Light year:- It is the distance travelled by light in one year.

8. Meteorites:- meteors that reaches the Earth is called a meteorite

9. Meteors:- Bright streaks of light in the sky or shooting stars are called meteors

10. Natural satellites:- A natural satellite is any celestial body in space that orbits around a larger body.

11. Orbit:- A planet has a definite path in which it revolves around the Sun . This path is called an orbit.

12. Orion:- constellation which has seven or eight bright stars. It is also called the hunter

13. Phases of moon:- The various shapes of the bright part of the moon as seen during a month are called phases of the moon.

14. Planets:- Celestial bodies that revolves around the Sun in a fixed path, are called planets

15. Pole star:- Pole star is the only star in the sky which appears stationary to an observer on Earth.

16. Remote sensing:- Remote sensing is the science of obtaining information about objects or areas from a distance, typically from aircraft or satellites.

17. Solar system:- A collection of the Sun, eight planets , asteroids ,comets and meteors.

18. Stars:- Stars are huge celestial bodies made mostly of hydrogen and helium that produce light and heat.

19. Ursa Major:- There are seven prominent stars that appears like a big ladle or a question mark is called Ursa major.

Chap 18 Pollution of Air and Water

1. Air pollution :- It is defined as contamination of air by impurities which may have a harmful impact on the living organisms and non living components.

2. Chemical contamination :- When industries release chemicals including arsenic , lead and fluoride into waterways , it is called chemical contamination. This leads to toxicity in plants and animals.

3. Global warming:- the average temperature of the earth atmosphere is gradually increasing. This is called global warming.

4.Green house effect:- The trapping of radiations by the earth's atmosphere is similar to that of green house. So the effect is called green house effect

5. Pollutants:- those substance which contaminate air and water.

6. Potable water:- water which is purified and fit for drinking is known as potable water.

7. Water pollution:- It is the contamination of water by substances harmful to life

Sunday, October 4, 2020

"Some basic concepts of Chemistry" Important questions-answers

Some basic concepts of Chemistry

Assignment -1

Definition:-

1. Chemistry :-Chemistry is the science of atoms, molecules and their transformations.

It can also be defined as that branch of science that deals with the study of the composition, properties and interaction of matter.

2. Pure substance :-Pure substances have fixed composition.

For example: - Copper, silver, gold, water, glucose are some examples of pure substances.

Also, the constituents of pure substances cannot be separated by simple physical methods.

3. Elements:-An element consists of only one type of particles. These particles may be atoms or molecules.

For example: - Sodium (Na), copper (Cu), silver (Ag), hydrogen (H), oxygen (O) atoms etc. They contain only one type of atoms.

4. Compounds:-When two or more atoms of different elements combine, the molecule of a compound is obtained.

For example: - Water (H20), Ammonia (NH3), Sugar, carbon dioxide (CO2).

Constituents of a compound cannot be separated into simpler substances by physical methods. They can be separated by chemical methods.

5. Mixtures:-A mixture contains two or more substances present in it (in any ratio) which are called its components.

6. Mass:-Mass is defined as the amount of matter present in a substance.It is constant

7. Volume:- Space occupied by matter is called its volume. It has the units of (length) 3. So in SI system, volume has units of m3.

8. Meter:- The meter is the length of the path travelled by light in vaccum during a time interval of 1/299792458 of a second.

9. Homogeneous mixture:-In homogeneous mixture, the components completely mix with each other and its composition is uniform throughout.

For example: - Air, Sugar solution.

10. Heterogeneous mixture:-In heterogeneous mixtures, the composition is not uniform throughout and sometimes the different components can be observed.

For example: - Mixture of dal mot and bhujia, badam etc.

The components of a mixture can be separated by using physical methods such as simple hand picking, filtration, crystallisation, distillation etc.

11. Physical Properties:- They are those properties which can be measured or observed without changing the identity or the composition of the substance.

Some examples of physical properties are colour, odour, melting point, boiling point, density etc.

12. Chemical properties:- They are those properties which can be measured or observed without changing the identity or the composition of the substance.

Some examples of physical properties are colour, odour, melting point, boiling point, density etc.

13. Weight:-Weight is defined as the force exerted by the gravity on an object. It may vary from one place to another due to change in gravity.

14. Density:-Density of a substance is its amount of mass per unit volume.

SI unit of density = kg/m3.

15. Temperature:- Measure of hottest or coldness of an object is called temperature. There are three common scales to measure temperature — °C (degree Celsius), °F (degree Fahrenheit) and K (kelvin). Here K is the unit SI unit.

The temperatures on two scales are related to each other by the following relationship:-

°F = (9/5) (°C) + 32

The Kelvin scale is related to Celsius scale as follows:-

K =°C + 273.15

16. Atomic mass:-Atomic mass is the mass of the atom.

17. Average atomic mass:- mass of an atom based upon the existence of its isotopes is called average atomic mass.

18. Molecular mass:-Molecular mass is the sum of atomic masses of the elements present in a molecule.

For example:-Molecular mass of methane CH4 = (12.011 u) + 4 (1.008 u) = 16.043 u.

19. Formula mass:- Formula mass is the sum of all the atomic masses of all the constituents of the formula.

20. Molar mass :-The mass of one mole of a substance in grams is called its molar mass.

The molar mass in grams is numerically equal to atomic /molecular/formula mass in u.

21. Limiting reagent:-In a chemical reaction, reactant which is present in the lesser amount gets consumed after sometime and after that no further reaction takes place whatever be the amount of the other reactant present. Hence, the reactant which gets consumed, limits the amount of product formed and is, therefore, called the limiting reagent.

22. Mass % or weight % :-Mass percentage is one way of representing the concentration of an element in a compound or a component in a mixture.

Mass percentage is calculated as the mass of a component divided by the total mass of the mixture, multiplied by 100%.

23. Mole fraction :-It is the ratio of number of moles of a particular component to the total number of moles of the solution.

Mole fraction of A

= (No. of moles of A)/(No. of moles of solution)

(nA )/( nA + nB)

Mole fraction of B

=(No. of moles of B)/(No. of moles of solution)

(nB )/( nA + nB)

24. Molarity :-Molarity is defined as the number of moles of the solute in 1 litre of the solution.

It is widely used unit and is denoted by ‘M’.

Molarity (M) = (No. of moles in solute)/(Volume of solution in litres)

25. Molality:-It is defined as the number of moles of solute present in 1 kg of solvent.

It is denoted by m.

Thus Molality(m) =

(No. of moles of solute)/(Mass of solvent in kg)

26. % composition:-The percentage composition of a given compound is defined as the ratio of the amount of each element to the total amount of individual elements present in the compound multiplied by 100

27. Empirical formula:-An empirical formula represents the simplest whole number ratio of various atoms present in a compound.

Write advantages of Chemistry and mention two problems that is still challenge to scientists.

Chemistry plays a central role in our life some advantages are listed below:-

Advantages of studying chemistry

With a better understanding of chemical principles it has now become possible to design and synthesise new materials having specific magnetic, electric and optical properties.

Safer alternatives to environmentally hazardous refrigerants like CFCs (chlorofluorocarbons), responsible for ozone depletion in the stratosphere, have been successfully synthesised.

Problems which can be tackled with the study of chemistry:-

Management of Green House gases like methane, carbon dioxide etc.

Understanding of bio-chemical processes, use of enzymes for large-scale production of chemicals and synthesis of new exotic materials are some of the intellectual challenges for the future generation of chemists.

Understanding of bio-chemical processes, use of enzymes for large-scale production of chemicals.

Write drugs for treatment of

1. Cancer

2. AIDS

Ans:- 1. Cis-platin and taxol

2. AZT (Azidotgymidine)

Define matter and it's physical states.

Anything that has mass and occupies space is defined as matter.

For example:-soap, notebook, pencil, apple, battery etc.

Physical States of matter

Matter can exist in 3 physical states namely solid, liquid and gas.

Solids

In case of solids, the constituent particles are held very close to each other in an orderly fashion and there is not much freedom of movement.

Solids have definite shape and definite volume.

For example: - Apple it has definite shape as well as definite volume.

Liquids

In liquids, the particles are close to each other but they can move around.

Liquids have definite volume but not definite shape. They take the shape of the container in which they are placed.

For example: Water it takes the shape of the tumbler in which it is poured but has volume.

Gases

In gases, the particles are far apart as compared to those present in solid or liquid states and their movement is easy and fast.

It takes the shape of container in which they are placed.

For example: - Smoke does not have definite shape or volume.

Define 5 laws of chemical combination.

The combination of elements to form compounds is governed by the following five basic laws:-

Law of Conservation of Mass.

Law of Definite Proportions.

Law of Multiple Proportions.

Gay Lussac’s Law of Gaseous Volumes.

Avogadro Law.

Law of Conservation of Mass

Law of conservation of mass states that the matter cannot be created nor be destroyed.

This law was put forth by Antoine Lavoisier in 1789.

He performed careful experimental studies for combustion reactions for reaching to the above conclusion.

Law of Multiple Proportions

According to this law, if two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element, are in the ratio of small whole numbers.

For example: - Hydrogen combines with oxygen to form 2 compounds, water and hydrogen peroxide.

H2(2g) + (1/2)O2 (16g) -- >H2O(18g)

H2(2g) + O2 (32g) -- > H2O2 (34g)

The masses of oxygen O (16g and 32g) combine with the fixed mass of (2g) hydrogen H. Therefore the simple ratio is 16:32 or 1:2.

This law was given by Dalton in 1803.

Law of Definite Proportions

According to this law, a given compound always contains exactly the same proportion of elements by weight.

This law was given by French chemist, Joseph Proust in 1806.

Gay Lussac’s Law of Gaseous Volumes

Gay Lussac’s law was given by Gay Lussac in 1808.

He observed that when gases combine or are produced in a chemical reaction they do so in a simple ratio by volume provided all gases are at same temperature and pressure.

For example: -

H (Hydrogen) (100mL) + O (Oxygen) (50mL) -- >Water(100mL).

The volumes of hydrogen (H) and oxygen (O) which combine together (i.e. 100mL and 50mL) bear a simple ratio of 2:1.

Avogadro Law

In 1811, Avogadro proposed that equal volumes of gases at the same temperature and pressure should contain equal number of molecules.

He made distinction between atoms and molecules

Write Dalton's atomic theory.

Matter consists of indivisible atoms.

All the atoms of a given element have identical properties including identical mass. Atoms of different elements differ in mass.

Compounds are formed when atoms of different elements combine in a fixed ratio.

Chemical reactions involve reorganisation of atoms. These are neither created nor destroyed in a chemical reaction.

Electricity

Introduction:-

In an atom, there are 3 sub-atomic particles.

Electrons-- > carry negative charge -- > -1.6*10^-19C

Proton -- > carry positive charge -- > 1.6*10^19 C

Neutron-- > carry no charge.

All matter is made up of atoms

In this lesson we will consider only two types of charges; positive and negative.

Like charges (similar charge) repel each other

Unlike charges(opposite charges) attract each other.

SI unit of charge (electric charge) is coulomb C

If a net charge Q , flow across any cross section of a conductor in time t, then the current I through cross section is

I = Q/t

Where I = Electric current,

Q = Electric charge,

t = time

S I unit of charge is coulomb,C

One coulomb of charge is that quantity of charge which flows through a circuit when one ampere of current flows through it in one second.

1C = 1A * 1s

What is electric current (I)?

General :- Flow of charge.

Definition:- Amount of charge flowing through a particular area in unit time.

Direction of current is similar to the direction of flow of proton.

Direction of current is opposite to the direction of flow of electron

S I unit of current is ampere,A

One ampere is the amount of current flowing through a circuit when one coulomb of charge flows through it in one second.

1A = 1C/1s

Instrument which measures current is called ammeter (Ammeter has low resistance)

Electric circuit:- A continuous and closed path of an electric current is called electric circuit.

In outer circuit direction of flow of electric circuit is from positive terminal of the cell to negative terminal and cell.

Conductor:- Substances through which charges can easily pass. Example:- Silver, copper etc

Numerical:- Calculate the number of electrons constituting one coulomb of charge.

Solution:-

1e- = -1.6* 10^-19 C

So 1C = 1/1.6*10^-19e-

= 0.625 * 10^19 e-

= 6.25 * 10^18 e-

Draw a schematic diagram of an electric circuit comprising - cell, electric bulb, ammeter and plug key.

Electric Potential:-

Definition 1:- Electric Potential at a point in an electric field is defined as work done in moving a unit positive charge from infinity to that point.

Electric Potential = Electric potential energy (work)/ charge

Definition 2:- Electric Potential energy per unit charge is called electric Potential.

Electric potential difference:-

For flow of charge in a conducting metallic wire, the gravity has no role to play, electrons move only if there is a difference of electric potential along the conductor.

This difference is called electric Potential difference.

Definition:- The potential difference between two points in an electric circuit is defined as the amount of work done in moving a unit positive charge from one point to another point.

Potential difference = work done (W)/ Quantity of charge moved(Q)

V = W/Q

SI unit of potential difference is volt.

One volt is the potential difference between two points in a current carrying conductor when 1 joule of work is done to move a charge of 1 coulomb from one point to other.

1volt = 1joule/1coulomb

1V = 1J/C

Voltmeter measure the potential difference.

Voltmeter is always connected in parallel across the points between which potential difference is to be measured.

Voltmeter has a high resistance so that it takes a negligible current from the circuit.

Symbols of some commonly used components in circuit diagrams:-

Ohm's law:-

At constant temperature, the current flowing through a conductor is directly proportional to potential difference across its ends.

Mathematical expression:-

I directly proportional to V

V directly proportional to I

V = IR

Where V = potential difference,

I = Current,

R = resistance.

Resistance :- It is defined as the ratio of potential difference applied between the ends of a conductor and the current flowing through it

It is a constant quantity.

SI unit is ohm

1ohm = 1volt/1Ampere.

Define 1 ohm .

The resistance of a conductor is said to be one ohm if a current of one ampere flows through it when a potential difference of one volt is applied across its ends.

Definition:-

Good conductors:- Those substances which have very low electrical resistance are called good conductors. Example:- Silver is the best conductor.

Resistor:- Those substance which have comparatively high electrical are called resistors. Example :- Nichrome (Alloy of nickel, chromium, manganese and iron metals)

Insulators:- Those substances which have infinitely high electrical resistance are called insulators. Example:- Rubber.

Draw a graph which show relationship between potential difference and current.

Variable resistance:- A component used to regulate current without changing the voltage source is called variable resistance.

Rheostat:- A device used to change resistance in the circuit.

Factors on which the resistance of a conductor depends:-

Resistance depends upon:-

Length of conductor

Area of cross section of conductor and

On nature of material.

How it depends?

Resistance is directly proportional to length of conductor

Resistance is inversely proportional to area of cross section.

Where rho is resistivity or specific resistance

SI unit of resistivity is ohm-m

Resistance also depends upon nature of material.

Resistivity range:-

Good conductors; eg metals and alloys; resistivity= 10^-8 ohm-m to 10^-6 ohm-m

Insulators; eg rubber and glass, resistivity= 10^12 ohm-m to 10^17 ohm-m

Note:- Resistance and resistivity of material vary with temperature and nature of substance.

Resistivity of alloy is generally higher than that of its constituent metals.

Applications of alloys:-

Heating elements of electrical heating appliances such as electric iron and toaster etc are made up of alloys

Reasons:-

High resistivity of alloy.

Doesn't undergo oxidation (burn) even at high temperature.

Application of metals based upon resistivity:-

Tungsten is used for filaments of electric bulbs.

Copper and aluminium re generally used for electrical transmission lines.

Combination of resistors in series:-

When two or more resistance are combined end to end consecutively they are said to be connected in series.

Example:-

Resistors connected in series.

In series combination of resistors, current flow in each part of circuit is same. { I1 = I2 = I3 = I }

Potential difference V is equal to sum of potential difference;

Vtotal = V1 + V2 + V3....

According to Ohm's law:-

Vital = IRtotal ;. V1 = IR1 ;.

V2 = IR2 ; V3 = IR3

So put values in above equation , we get:-

IRtotal = IR1 + IR2 + IR3.....

IRtotal= I (R1 + R2 + R3.....)

Rtotal = R1 + R2 + R3.....

Thus resistance of combination is equal to sum of their individual resistances; R1, R2 and R3

Combination of resistance in parallel:-

When two or more resistances are connected between same two points, they are sad to be connected in parallel.

Example:-

Resistors connected in parallel.

In parallel combination, total current I is equal to sum of separate currents through each branch of combination.

I = I1 + I2 + I3......

According to Ohm's law:-

I1= V/R1. , I2 =V/R2. ,

I3 = V/R3. ,I = V/R

Put in 1 , we get

I = I1 + I2 + I3..

V/R = V/R1 + V/R2 + V/R3

V/R = V (1/R1 +1/R2 +1/R3)

1/R =1/R1 +1/R2 +1/R3

So Reciprocal of equivalent resistance joined in parallel is equal to sum of reciprocal of individual.

Note :-In parallel combination potential difference is same.

Disadvantages of series circuit for domestic wiring:-

In series circuit, if one electrical appliance stop working due to some defect, then all other appliances also stop working.

All appliances have only one switch due to which they cannot be turned on or off separately.

Appliances do not get the same voltage as that of power supply.

Overall resistance of circuit increases too much due to which current from power supply is low.

Advantages of parallel circuits in Domestic wiring:-

If one electrical appliance stops working due to some defects then all other appliances keep working normally.

Each electrical appliance has its own switch due to which it can be turned on or off independently without affecting other appliances.

Each electrical appliance get same voltage (220V) as that of power supply line.

In the parallel connection of electrical appliances the overall resistance of household circuit is reduced due to which current from power supply is high.

Heating effect of current:-

When an electric current is passes through a high resistance wire, like Nichrome wire, the resistance wire becomes very hot and Produce heat. This is called the heating effect of current.

When an electric charge Q moves against a potential difference V, the amount of work done is given by:- W = Q * V

We know:-

I = Q/t

Q = It

From Ohm's law:-

V/I = R

V= IR

Put the values of V and Q in

W= Q*V we get:-

W = It*IR

W = I2Rt

Assuming all electric work done is converted into heat energy:-

So H = W = I2Rt

H = I2Rt ( joules law of heating)

SI unit of heat Produced , H is joules (J)

According to joules law of heating given by the formula:-

H = I2Rt

Heat Produced in a wire is directly proportional to

Square of current (I2)

Resistance of wire (R)

Time for which current is passed.

Note:- total work done by a current in an electric circuit is called electric energy.

Applications of heating Effect of current:-

Used in working of electrical heating appliances such as electric iron, electric kettle, electric oven etc.

Used in Electric bulbs for producing light

Used in electric fuse for protecting household wiring and electrical appliance.

Electric power, P and Interrelation between P, V, I, R

The rate at which work is done by an electric current is called electric power. Or

The rate at which electric energy is consumed or dissipated is called electric power.

W = VQ

Now Q = It and V = IR

W= VIt = I2Rt

So Power = work/time

P = W/t

P = VQ/t =VIt/t = VI

P =VI

P = I2R

P= V2/R where I =V/R in eq P=VI

Note :-

P = I2R is used when I is constant;

P =V2R is used when V is constant

P = VI is used in all cases

Commercial unit of electric energy:- kilowatt hour

The electric energy consumed when an electric appliance of power one kilowatt works for one hour is called one kilowatt hour.

1 kWh = 1kW * h

1 kWh = 1000W * 3600s

1 kWh = 3.6 *10^6 joule (W-s=J)

1kWh = 3.6 MJ

Property -- > unit --- > symbol

Current -- >ampere (A) ---- > I

Charge -- > coulomb (C) --- > Q

Time -- > sec -- > t

Temperature -- > °k -- > T

Potential difference -- > volt -- > V

Work done --- > joule -- > W

Resistance --- > ohm -- > R

Resistivity -- > ohm-m -->

Power -- > watt --- > P

Heat --- > joule -- > H

Formula used = >

I = Q/t

Current = charge / time

V= W/Q

Potential

difference = work done /charge

V = IR (Ohm's law)

Potential

difference = current * Resistance

R = rho *L/A

Resistance = resistivity * length of conductor /area of cross section

For series connection=

R = R1 + R2 + R3.....

V = V1 + V2 + V3 ....

Here current flow is same

For parallel connection =

1/R = 1/R1 + 1/R2 + 1/R3

I = I1 +I 2+ I3......

Here potential difference is same

P = VI

Power = Potential difference * current

H = I^2Rt (joule's law of heating)

Heat = current ^2 *resistance*time

Friday, September 25, 2020

Class 7 back exercise NCERT

Back exercise

Chap 1

Q.6. Fill in the blanks:

(a) Green plants are called ________________ since they synthesise their own food.

(b) The food synthesised by the plants is stored as ________________ .

(d) During photosynthesis plants take in ________________ and release ________________ .

Ans. (a) autotrophs (b) starch (c) chlorophyll (d) carbon dioxide, oxygen

Q.7. Name the following:

(i) A parasitic plant with yellow, slender and tubular stem.

(ii) A plant that has both autotrophic and heterotrophic mode of nutrition.

(iii) The pores through which leaves exchange gases.

Ans. (i) cuscuta (ii) Insectivorous plant (iii) Stomata

Q.8. Tick the correct answer:

(a) Amarbel is an example of:

(i) Autotroph (ii) Parasite (iii) Saprotroph (iv) Host

(b) The plant which traps and feeds on insects is:

(a) Cuscuta (ii) China rose {iii) Pitcher plant (iu) Rose

Ans. (a) (ii) Parasite (b) (iii) Pitcher plant

Q.9. Match the items given in Column I with those in Column II:

Chlorophyll --- > Leaf

Nitrogen ----- > Rhizobium

Cuscuta ------ > Parasite

Animals ------ > Heterotrophs

Insects -------- > Pitcher plant

Q.10. Mark T’ if the statement is true and ‘F’ if it is false:

(i) Carbon dioxide is released during photosynthesis. (T/F)

(ii) Plants which synthesise their food themselves are called saprotrophs. (T/F)

(iii) The product of photosynthesis is not a protein. (T/F)

(iv) Solar energy is converted into chemical energy during photosynthesis. (T/F)

Ans. (a) F (ii) F (iii) T (iu) T

Q.11.Choose the correct option from the following.

Which part of the plant takes in carbon dioxide from the air for photosynthesis?

(i) Root hair (ii) Stomata (iii) Leaf veins (iv) Sepals

Ans. (ii) Stomata

Q.12. Choose the correct option from the following:

Plants take carbon dioxide from the atmosphere mainly through their:

(i) Roots (ii) Stem (iii) Flowers (iv) Leaves

Ans. (iv) Leaves

Chapter :- 2

Q.1.Fill in the blanks:

(a) The main steps of nutrition in humans are ___________, ___________, ___________ , ___________ and ___________

(b) The largest gland in the human body is ___________.

(d) The inner wall of the small intestine has many finger-like outgrowths called ___________

(e) Amoeba digests its food in the ___________ .

Ans.(a) ingestion, digestion, absorption, assimilation, egestion

(b) liver (c) digestive (d) villi (e) food vacuole.

Q.2. Mark ‘T’ if the statement is true and ‘F’ if it is false:

(a) Digestion of starch starts in the stomach. (T/F)

(b) The tongue helps in mixing food with saliva. (T/F)

(d) The ruminants bring back swallowed grass into their mouth and chew it for sometime. (T/F)

Ans. a) F (b) T (c) T (d) T

Q.3.Tick (S) mark the correct answer in each of the following:

(a) Fat is completely digested in the

(i) stomach (ii) mouth (in) small intestine (iv) large intestine

(b) Water from the undigested food is absorbed mainly in the:

(i) Stomach (ii) Food pipe (iii) Small intestine (iv) Large intestine

Ans.(a) (iii) Small intestine (b) (iv) Large intestine

Q.4.Match the items of column I with those given in column II:

Food components ---- > Products of digestion

Carbohydrates ------ > Sugar

Proteins --------> Amino acids

Fats ---------- > Fatty acids and glycerol

Q.9. Which part of the digestive canal is involved in:

(i) Absorption of food ________ .

(ii) Chewing of food ________ .

(iii) Killing of bacteria ________ .

(iv) Complete digestion of food ________ .

(v) Formation of faeces ________ .

Ans. (i) Small intestine (ii) Mouth (iii) Stomach (iv) Small intestine (v) Large intestine

Q.11. Match the items of Column I with suitable items in Column II.

Salivary gland----- > Saliva secretion

Stomach------ > Acid release

Liver ------- > Bile juice secretion

Rectum ----- > Storage of undigested food

Small intestine ---- > Digestion is completed

Large intestine ------ > Absorption of faeces.

Chap 3:-

Q.2. The silkworm is (a) a caterpillar (b) a larva. Choose the correct option.

(i) (a) (ii) (b) (iii) both (a) and (b) (iv) neither (a) nor (b)

Ans. (iii) both (a) and (b).

Q.3. Which of the following does not yield wool?

(i) Yak (ii) Camel (iii) Goat (iv) Woolly dog

Ans. (iv) Woolly dog

Q.5. Given below is a sequence of steps in the processing of wool. Which are the missing steps? Add them.

Shearing, ________ , sorting,________, __________

Ans. Shearing, scouring, sorting, picking out of burrs, colouring, rolling.

Q.7. Out of the following, which are the two terms related to silk production? Sericulture, floriculture, moriculture, apiculture and silviculture.

Hints: (i) Silk production involves cultivation of mulberry leaves and rearing silkworms. (ii) Scientific name of mulberry is Morus alba.

Ans. (i) Sericulture (ii) Moriculture

Q.8 Match the words of Column 1 with those given in Column 2:-

Scouring --------> cleaning sheared skin

Mulberry leaves ------> Food of silk worm

Yak -------- > Wool yielding animal.

Cocoon--------- >Yields silk fibres

Chap :- 4

Q.3.Fill in the blanks

The hotness of an object is detetmined by its ____________ .

(b) Temperature of boiling water cannot be measured by a ____________ thermometer.

(d) No medium is required for transfer of heat by the process of ____________.

(e) A cold steel spoon is dipped in a cup of hot milk. It transfers heat to its other end by the process of ____________

(f) Clothes of ___________ colours absorb heat better than clothes of light colours.

Ans. (a) temperature (b) clinical (c) Celsius (d) radiation (e) conduction (f) dark

4. Match the following :-

(i) Land breeze blows during - > night

(ii) Sea breeze blows during - > day

(iii) Dark coloured clothes are preferred during ------- > winter

(iv) Light coloured clothes are preferred during ----- > summer

Q.8. One litre of water at 30°C is mixed with one litre of water at 50°C. The temperature of the mixture will be:

(a) 80°C (b) More than 50°C but less than 80°C

(c) 20°C (d) Between 30°C and 50°C

Ans.(d) Between 30°C and 50°C.

Q.9. An iron ball at 40°C is dropped in a mug containing water at 40°C. The heat will:

(a) flow from iron ball to water.

(b) not flow from iron ball to water or from water to iron ball.

(d) increase the temperature of both.

Ans. (b) not flow from iron ball to water or from water to iron ball

Q.10. A wooden spoon is dipped in a cup of ice-cream. Its other end:

(a) becomes cold by the process of conduction

(b) becomes cold by the process of convection

(d) does not become cold

Ans.(d) does not become cold.

Q.11.Stainless steel pans are usually provided with copper bottoms. The reason for this could be that:

(a) copper bottom makes the pan more durable

(b) such pans appear colourful

(d) copper is easier to clean than the stainless steel

Ans.(c) copper is better conductor of heat than the stainless steel

Chap :-5

Q.2.Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. What is its nature?

Ans.Ammonia has basic nature

Q.6.Mark ‘T’ if the statement is true and ‘F’ if it is false:

(i) Nitric acid turns red litmus blue. (T/F)

(ii) Sodium hydroxide turns blue litmus red. {T/F)

(iii) Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water. (T/F)

(id) Indicator is a substance which shows different colours in acidic and basic solutions. . (T/F)

(v) Tooth decay is caused by the presence of a base. (T/F)

Ans.(1) F (ii) F (iii) T (iv) T (V) F

Q. 11. Consider the following statements:

(a) Both acids and bases change colour of all indicators.

(b) If an indicator gives a colour change with an acid, it does not give a change with a base.

(d) Change of colour in an acid and a base depends on the type of the indicator. Which of these statements are correct?

(i) All four (ii) (a) and (d) (iii) (b) and (c) (iv) only (d)

Ans. (ii) (a) and (d)

Chap 6

Q.1.Classify the changes involved in the following processes as physical or chemical changes:

(a) Photosynthesis

(b) Dissolving sugar in water

(c) Burning of coal

(d) Melting of wax

(e) Beating aluminium to make aluminium foil

(f) Digestion of food

Ans.(a) Chemical change (b) Physical change

(e) Physical change (/) Chemical change

Q.2.(a) Cutting a log of wood into pieces is a chemical change. (True/ False)

(b) Formation of manure from leaves is a physical change. (True/ False)

(c)Iron pipes coated with zinc do not get rusted easily. (True/ False)

(d)Iron and rust are the same substances. (True/ False)

(e)Condensation of steam is not a chemical change. (True/ False)

Ans. (a)False

Correct statement: Cutting a log of wood into pieces is an irreversible physical change.

(b)False

Correct statement: Formation of manure from leaves is a chemical change.

(d)False

Correct statement: Iron and rust are two different chemical substances.

(e)True

Q.3.Fill in the blanks in the following statements:

(a) When carbon dioxide is passed through lime water, it turns milky due to the formation of _________.

(b) The chemical name of baking soda is .

(d) Changes in which only ____________ properties of a substance change are called physical changes.

(e) Changes in which new substances are formed are called _____________ changes..

Ans. (a)calcium carbonate

(b) sodium hydrogen carbonate

(d) physical

(e) chemical

Q.11. The gas we use in the kitchen is called liquified petroleum gas (LPG). In the cylinder it exists as a liquid. When it comes out from the cylinder it becomes a gas (Change- A) then it bums (Change-B). The following statements pertain to these changes. Choose the correct one.

(i) Process-A is a chemical change.

(ii) Process-B is a chemical change.

(iii) Both processes A and B are chemical changes.

(iv) None of these processes is a chemical change.

Ans. (ii) Process-B is a chemical change.

Q.12.Anaerobic bacteria digest animal waste and produce biogas (Change-A). The biogas is then burnt as fuel (Change-B). The following statements pertain to these changes. Choose the correct one.

(i) Process-A is a chemical change.

(ii) Process-B is a chemical change.

(iii) Both processes A and B are chemical changes.

(iv) None of these processes is a chemical change.

Ans.(iii) Both processes A and B are chemical change

Chap :- 7

Q.3.Fill in the blanks

(i) The average weather taken over a long time is called __________

(ii) A place receives very little rainfall and the temperature is high throughout the year, the climate of that place will be ________ and _________

(iii) The two regions of the earth with extreme climatic conditions are __________ and ____________

Ans. climate of the place (ii) hot, dry (iii) polar, tropical regions

Q.4.Indicate the type of climate of the following areas:

(a) Jammu and Kashmir:

(b) Kerala:,

(c) Rajasthan:

(d) North-east India:

Ans.(a) Jammu and Kashmir—moderately hot and moderately wet climate.

(b) Kerala—very hot and wet climate.

(d) North-east India—The north eastern India receives rain for a major part of the year, hence wet climate.

Q.5.Which of the two changes frequently, weather or climate?

Ans.Weather

Q.6.Followings are some of the characteristics of animals:

(i) Diets heavy on fruits

(ii) White fur

(iii) Need to migrate

(iv) Loud voice

(v) Sticky pads on feet

(vi) Layer of fat under skin

(vii) Wide and large paws

(viii) Bright colours

(ix) Strong tails

(x) Long and large beak

For each characteristic indicate whether it is adaptation for tropical rainforests or polar regions. Do you think that some of these characteristics can be adapted for both regions?

Ans:-

(i) Diets heavy on fruits --------------- > Tropical rainforest

(ii) White fur --- > Polar region

(iii) Need to migrate --->Polar region

(iv) Loud voice----------- >Tropical rainforest

(v) Sticky pads on feet------------- >Tropical rainforest

(vi) Layer of fat under skin------------------ >Polar region

(vii) Wide and large paws----------------- >Polar region

(viii) Bright colours ------ >Tropical rainforest

(ix) Strong tails --------- >Tropical rainforest

(x) Long and large beak ----------------------- >Tropical rainforest

Q.10.Choose the correct option which answers the following question:

A carnivore with stripes on its body moves very fast while catching its prey. It is likely to be found in:

(i) polar regions (ii) deserts

(iii) oceans (iv) tropical rainforests

Ans. (iv) tropical rainforests

Q.11.Which features adapt polar bears to live in extremely cold climate?

(i) A white fur, fat below skin, keen sense of smell.

(ii) Thin skin, large eyes, a white fur.

(iii) A long tail, strong claws, white large paws.

(iv) White body, paws for swimming, gills for respiration.

Ans.(iv) A white fur, fat below skin, keen sense of smell.

Q.12.Which option best describes a tropical region?

(i) hot and humid

(ii) moderate temperature, heavy rainfall (iii) cold and humid (iv) hot and dry

Ans.(i) Hot and humid

Chap :-8

1.Fill the missing word in the blank spaces in the following statements:

(a) Wind is ___________air.

(b) Winds are generated due to _________ heating on the earth.

(d) Air moves from a region _________of pressure to a region _________of pressure.

Ans.(a) moving (b) uneven

Q.8. Which one of the following places is unlikely to be affected by cyclone?

(i) Chennai (ii) Mangalore

(iii) Amritsar (iv) Puri

Ans.(iv) Amritsar

Q.9.Which of the statements given below is correct?

(i) In winter the winds flow from the land to the ocean.

(ii) In summer the winds flow from the land towards the ocean.

(iii) A cyclone is formed by a very high-pressure system with very high-speed winds revolving around it.

(iv) The coastline of India is not vulnerable to cyclones.

Ans.(i) In winter the winds flow from the land to the ocean.

Chapter 9

Tick the most suitable answer in question 1 and 2.

In addition to the rock particles, the soil contains

(i) Air and water

(ii) Water and plants

(iii) Minerals, organic matter, air and water

(iv) Water, air and plants

Answer:

In addition to the rock particles, the soil contains

(iii) Minerals, organic matter, air and water.

Q2. The water holding capacity is the highest in

(i) Sandy soil

(ii) Clayey soil

(iii) Loamy soil

(iv) Mixture of sand and loam

Answer:

The water holding capacity is the highest in

(ii) Clayey soil

Q3. Match the items in Column I with those in Column II:

1. A home for living organisms----------> All kinds of soil

2. Upper layer of soi----- > Dark in colour

3. Sandy soil----------> Large particles

4. Middle layer of soil--------> lesser amount of humus

5. Clayey soil -----> small particles and packed light.

Chapter 10

Tick the correct answer:

(a) In cockroaches, air enters the body through

(i) lungs

(ii) gills

(iii) spiracles

(iv) skin

Answer: (iii) spiracles

(b) During heavy exercise, we get cramps in the legs due to the accumulation of

(i) carbon dioxide

(ii) lactic acid

(iii) alcohol

(iv) water

Answer: (ii) lactic acid

(c) Normal range of breathing rate per minute in an average adult person at rest is:

(i) 9 – 12

(ii) 15 – 18

(iii) 21 – 24

(iv) 30 – 33

Answer: (ii) 15 – 18

(d) During exhalation, the ribs

(i) move outwards

(ii) move downwards

(iii) move upwards

(iv) do not move at all

Answer: (ii) move downwards

Mark T if the statement is true and F if it is false:

(i) During heavy exercise the breathing rate of a person slows down. (T/ F)

(ii) Plants carry out photosynthesis only during the day and respiration only at night. (T/ F)

(iii) Frogs breathe through their skins as well as their lungs. (T/ F)

(iv) The fishes have lungs for respiration. (T/ F)

(v) The size of the chest cavity increases during inhalation. (T/ F)

Answer:

(i) F

(ii) F

(iii) T

(iv) F

(v) T

Chapter 11

Q.1.Match structures given in Column I with functions given in Column II

1. Stomata. -------> Transpiration

2. Xylem-----> Transport of water

3. Root hairs----- > Absorption of water

4. Phloem-----> Transport of food

Q.2.-Fill in the blanks :

(i) The blood from the heart is transported to all parts of the body by the _____________

(ii) Haemoglobin is present in ___________ cells.

(iii) Arteries and veins are joined by a network of ___________ .

(iv) The rhythmic expansion and contraction of the heart is called ___________

(v) The main excretory product in human beings is ___________

(vi) Sweat contains water and .

(vii) Kidneys eliminate the waste materials in the liquid form called .

(viii) Water reaches great heights in the trees because of suction pull caused by .

Ans.(i) arteries (ii) red blood cells • (in) capillaries (iv) heartbeat (v) urea (vi) salts (vii) urine (viii) transpiration.

Q.3.Choose the correct options:

(a) In plants, water is transported through

(i) Xylem (ii) Phloem (iii) Stomata (iv) Root hair

(b) Water absorption through roots can be increased by keeping the plants

(i) In the shade (ii) in dim light (iii) under the fan (iv) covered with a polythene bag

Ans.(a) (i) Xylem {b) (iii) under the fan

Chap 12

Q.1.Fill in the blanks:

(a) Production of new individuals from the vegetative part of parent is called ___________.

(b) A flower may have either male or female reproductive parts. Such a flower is called _______.

another flower of the same kind is known as __________.

(d) The fusion of male and female gametes is termed as ____________ .

(e) Seed dispersal takes place by means of ________ and __________.

Ans. (a) vegetative reproduction (b) unisexual flower (c) pollination (d) fertilization (e) wind, water

Q.9.Match items in Column I with those in Column II

1. Bud ---> yeast

2. Eyes----> potato

3. Fragmentation-----> Spirogyra

4. Wings------ > Maple

5. Spores ------ > Bread mould

Tick the correct answer:

(a) The reproductive part of a plant is the

(i) leaf (ii) stem (iii) root (iv) flower

(b) The process of fusion of the male and the female gametes is called

(i) fertilisation (ii) pollination (iii) reproduction (iv) seed formation

c) Mature ovary forms the

(i) seed (ii) stamen (iii) pistil (iv) fruit

(d) A spore producing plant is

(i) rose (ii) bread mould (iii) potato (iv) ginger

(e) Bryophyllum can be reproduced by its

(i) stem (ii) leaves (iii) roots (iv) flower

Ans.(a) (iv) flower (b) (i) fertilisation (c) (iv) fruit (d) (ii) bread mould (e) (ii) leaves

Chap 13

Q.1.Classify the following as motion along a straight line, circular or oscillatory motion :

(i) Motion of your hands while running.

(ii) Motion of a horse pulling a cart on a straight road.

(iii) Motion of a child in a merry-go-round. •

(iv) Motion of a child on a see-saw.

(v) Motion of the hammer of an electric bell.

(vi) Motion of a train on a straight bridge.

Ans.(i) Oscillatory motion

(ii) Linear motion

(iii) Circular motion

(iv) Oscillatory motion

(v) Oscillatory motion

(vi) Linear motion

Q.2.Which of the following are not correct?

(i) The basic unit of time is second.

(ii) Every object moves with a constant speed.

(iii) Distances between two cities are measured in kilometers.

(iv) The time period of a given pendulum is not constant.

(v) The speed of a train is expressed in m/h

Ans. (ii), (iv), (v)

.8. Which of the following relations is correct?

(i) Speed = Distance Time

(ii) Speed = Distance/Time

(iii)Speed – Time/Distance

(iv)Speed = 1/Distance Time

Ans. (ii) Speed = Distance/Time is correct

Q.9.The basic unit of speed is:

(i) km/min (ii) m/min (iii) km/h (iv) m/s

Ans. (iv) m/s

10.A car moves with a speed of 40 km/h for 15 minutes and then with a speed of 60 km/h for the next 15 minutes. The total distance covered by the car is:

(i) 100 km (ii) 25 km (iii) 15 km (iv) 10 km

Ans.(ii) 25 km

Q.11.Suppose the two photographs, shown in fig. 13.1 and fig. 13.2 of NCERT had been taken at an interval of 10 seconds. If a distance of 100 metres is shown by 1 cm in these photographs, calculate the speed of the blue car.

Ans.0.1 cm/s or 10 m/s

Q.12.Fig 13.10 shows the distance-time graph for the motion of two vehicles A and B. Which one of them is moving faster?

Ans. ‘A’ is moving faster.

Q.13.Which of the following distance-time graphs shows a truck moving with speed which is not constant?

Ans. (iii)

Chap 14

Q.8.Fill in the blanks:

(a) Longer line in the symbol for a cell represents its ___________terminal

(b) The combination of two or more cells is called a ____________.

(d) The safety device based on the heating effect of electric current is called a _____________.

Ans.(a) positive (b) battery (c) becomes red hot and emits heat (d) fuse.

Q.9.Mark ‘T’ if the statement is true and ‘F’ it is a false:

(a) To make a battery of two cells, the negative terminal of one cell is connected to the negative terminal of the other cell. [T/F]

(b) When the electric current through the fuse exceeds a certain limit , the fuse wire melts and breaks. [T/F]

(d) An electric bell has an electromagnet. [T/F]

Ans. (a) F (b) T (c) F (d) T

Chap 15

Q.1.Fill in the blanks:

(a) An image that cannot be obtained on a screen is called ___________ .

(b) Image formed by a convex is __________ always virtual and smaller in size.

(d) An image which can be obtained on a screen is called a __________ image.

(e) An image formed by a concave __________ cannot be obtained on a screen.

Ans.(a) virtual image (b) mirror (c) plane (d) real (e) lens

Q.2.Mark ‘T’ if the statement is true and ‘F’ if it is false:

(a) We can obtain an enlarged and erect image by a convex mirror. (T/F)

(b) A concave lens always form a virtual image. (T/F)

(d) A real image cannot be obtained on a screen. (T/F)

(e) A concave mirror always form a real image. (T/F)

Ans. a) F (b) T (c) T (d) F (e) F

Q.3. Match the items given in Column I with one or more items of Column II

1. A plane mirror ---- >The image is erect and of the same size as the object

2. A convex mirror ---- > Can form image of objects spread over a large area

3. A convex lens --- > Used as magnifying glass

4. A concave mirror---- >used by dentist to see enlarged image of teeth

5. A concave lens----- > The image is erect and smaller in size than the object.

Q.9. Which type of mirror can form a real image?

Ans. Concave mirror can form a real image.

Q.10. Which type of lens forms always a virtual image?

Ans. Concave lens always forms a virtual image.

Choose the correct option in Questions 11-13:

Q.11. A virtual image larger than the object can be produced by a

(i) concave lens (ii) concave mirror (iii) convex mirror (iv) plane mirror

Ans. (ii) concave mirror

Q.12. David is observing his image in a plane mirror. Die distance between the mirror and his image is 4 m. If he moves 1 m towards the mirror, then the distance between David and his image will be

(i) 3 m (ii) 5 m (iii) 6 m (iv) 8 m

Ans. (iii) 6 m

Q.13. The rear view mirror of a car is a plane mirror. A driver is reversing his car at a speed of 2 m/s. The driver sees in his rear mew mirror the image of a truck parked behind his car. The speed at which the image of the truck appears to approach the driver will be

(i) 1 m/s (ii) 2 m/s (iii) 4 m/s {iv) 8 m/s

Ans. (ii) 4 m/s

Chap 16

Mark ‘T’ if the statement is true and ‘F’ if it is false:

(a) The freshwater stored in the ground is much more than that present in the rivers and lakes of the world. (T/F)

(b) Water shortage is a problem faced only by people living in rural areas. (T/F)

(d) Rain is the ultimate source of water. (T/F)

Ans. (a) T (b) F (c) F (d) T

Q.6.Fill in the blanks with the appropriate answers: .

(a) People obtain groundwater through and .

(b) Three forms of water are solid, and .

(d) The process of water seepage into the ground is called .

Ans.(a) wells, hand pumps

(b) liquid, gas

(d) infiltration

Q.7.Which one of the following is not responsible for water shortage?

(i) Rapid growth of industries

(ii) Increasing population

(iii) Heavy rainfall

(iv) Mismanagement of water resources

Ans.(iii) heavy rainfall

Q.8.Choose the correct option. The total water

(i) in the lakes and rivers of the world remains constant.

(ii) under the ground remains constant.

(iii) in the seas’and oceans of the world remains constant.

(iv) of the world remains constant.

Ans.(iv) of the world remains constant.

Chap 17

Q.7.Fill in the blank:

(a) The insects, butterflies, honeybees and birds help flowering plants in .

(b) A forest is a purifier of and .

(d) The decaying leaves and animal droppings in a forest enrich the .

Ans. (a) pollination (b) water, air (c) lowest (d) soil as humus.

Q.11.Which of the following is not a forest product?

(i) Gum (ii) Plywood (iii) Sealing wax (iv) Kerosene

Ans.(iv) Kerosene

Q.12.Which of the following statements is not correct?

(i) Forests protect the soil from erosion.

(ii) Plants and animals in a forest are not dependent on one another.

(iii) Forests influence the climate and water cycle.

(iu) Soil helps forests to grow and regenerate.

Ans.(ii) Plants and animals in a forest are not dependent on one another.

Q.13.Micro-organisms act upon the dead plants to produce

(i) sand (ii) mushrooms (iii) humus (iu) wood

Ans. (i) Humus

Chap 18

.1. Fill in the blanks:

(a) Cleaning of water is process of removing __________

(b) Wastewater released by houses is called __________.

(d) Drains get blocked by __________ and __________.

Ans.(a) pollutants (b) sewage (c) sludge (d) (d) chemicals, kitchen waste

.7. Name two chemicals used to disinfect water.

Ans. Chlorine and ozone

Study the following statements about ozone:

(a) It is essential for breathing of living organisms.

(b) It is used to disinfect water.

(d) Its proportion in air is about 3%.

Which of these statements are correct?

(i) (a), (b) and (c) (ii) (b) and (c) (iii) (a) and (d) (iv) All four

Ans. (ii) (b) and (c)

Class 7 chap 15 light

Chap 15 Light notes

Introduction:-

Light is a form of energy which enable us to see world.

Speed of light = 30000Km/sec

Travels along a straight path.

Luminous objects:- Produce their own light .

Eg -- > Sun

Illuminous objects:- Donot Produce their own light . Eg:- Chair

Capable of reflecting light to our eyes coming from luminous objects.

Uses of Light:- Images formed by Mirror and lens

Rainbow formation

Ray of light:- Straight line path of light is called ray of light.

Beam of light:- Bunch of rays of light is called beam of light.

Reflection of light:-

Bouncing back of ray of light into the same medium after striking a polished surface such as mirror is called reflection of light.

Incident ray :- Ray of light that strike the surface.

Reflected ray :- Ray of light sent back by the surface after reflection.

Normal:- Perpendicular to the surface at the point of incident . It is an imaginary line.

Angle of incidence= angle between the Incident ray and normal.

Angle of reflection= Angle between the reflected ray and normal.

Law of reflection:-

1. Angle of incidence= angle of reflection

2. Incident ray, reflected ray and the normal all lie on the same plane.

Types of mirror:- two types

1. Plane mirror

2. Spherical mirror

Plane mirror:- mirror with a flat reflective surface.

Characteristics of image formed by plane mirror:-

1. Virtual and erect image.

2. Same size as that of object.

3. Image formed behind mirror.

4. Distance of the image behind mirror is same as distance of object from mirror.

Virtual image:- Image formed when reflected rays appear to meet. It can't obtained on screen.

Real image:-Image formed when reflected rays actually meet. It can obtained on screen.

Lateral inversion:- In mirror left appears right and right appears left . This is called lateral inversion.

Spherical mirror:- Mirror having spherical reflecting surface.

Two types :-

1. Convex mirror

2. Concave mirror

CONCAVE MIRROR:- mirror whose reflecting surface is curved inward. It is a converging mirror.

CONVEX MIRROR:- Mirror whose reflecting surface is curved outward. It is a diverging mirror.

Use of Convex mirror:-

1. Can use as rear view mirror to get wider field view to help driver to see traffic behind them.

Used of concave mirror:-

1. Doctor use concave mirror for examining eyes, nose, ears and throat.

2. Dentists use concave mirror to see enlarge image of teeth.

3. Reflectors of torches, headlights of cars and scooters are concave in shape.

Lens:- Transparent optical medium bounded by two surfaces at least one being spherical is called lens.

Types of lens:-

1. Convex lens( converging lens)

Thicker at middle and thinner at edges

2. Concave lens( diverging lens)

Thicker at edges and thinner at middle.

Uses:-

1. Magnifying glass.(Convex lens)

2. Used in Spectacles, telescopes and microscopes.

Sunlight:- It is a white light that is made up of seven colours.

Prism:- Transparent element with three rectangular and two triangular surface.

Dispersion of light:-

Splitting of white light into its constituent colours is called dispersion of light. For example :- rainbow is formed when sunlight split into its 7 coloured band (VIBGYOR)

This pattern of colour obtained is called spectrum.

Thursday, August 27, 2020

Obelia

Subject: Coelenterata : Obelia (sea fur)

Systematic position:-

Phylum :- Coelenterata or cnidaria ( Diploblastic, tissue organisation, coelenteron and cnidoblasts)
Class:- Hydroids (fixed polyps; medusa with ectodermal sense organs)
Order:- Hydroida( Fixed polyps; medusa with ectodermal sense organs)
Family:- Campanularidae( cup shaped hydrotheca)
Genus:- Obelia ( Free swimming and discoidal medusae)
Species:- geniculata (Colourless)

Habitat:-

Obelia is a marine, cosmopolitan, polymorphic, colonial and sedentary hydrozoan Coelenterate found attached on the stones, rocks, molluscan shells, ships, weeds, etc. In shallow coastal waters upto the depth of 80 metres.
It is branched like a tree, so called zoophyte (zoo= animal ; phyte = plant) or sea fur.
There are many species of Obelia but the most common species is O. geniculata.

Habits :-

(1) Feeding :-

Obelia is carnivores and feeds upon the living insect larvae, small crustaceans and worms.
Food is captured and paralysed with the help of stinging cells.
Digestion is partly intercellular and partly intracellular.

(2) Reproduction:-

Obelia shows asexual as well as sexual reproduction.
Asexual reproduction occurs by external budding.
In Obelia reproductive zooids are meduse which are inside or dioecious but don't show sexual dimorphism.
Fertilization is external.
Development is indirect and includes a free swimming planula larva which brings about dispersal.
Life history of Obelia shows alternation of generation.

(3) Respiration and Excretion :-

These occur through general body surface.

Morphology :-

(A) Shape, size , colour and symmetry:-

Obelia appears as a network of branched threads giving fur-like appearance, so called sea fur.
It is about 25-30 mm in height, creamish- white or greyish in colour and radially symmetrical.

(B) Two types of filaments:-

Obelia colony is formed of 2 types of filaments:-
(a) Hydrorhizae:- These are horizontal branched which creep over the substratum and fix the colony to the substratum.
(b) Hydrocauli:- These are upright branches.
Each hydrocaulus grows in a scorpioid cymose manner.
Each branch stops growing ends into a zooid and gives rise a new branch.
Adjoining branches are on alternate sides.
So it is formed of lower parts of all the true branches and grows in a zig zag manner.
Each side branch and main hydrocaulus end into a terminal bud which later forms a polyp.

Coelenteron also called gastro-vascular cavity, Is the central cavity running through both types of filaments.
It is bounded by 2 coats:-
(a) Coenosarc:- It is inner and living coat.
It is formed of two layers:-
Inner gastrodermis lining the Coelenteron, and outer epidermal.
Between the two cellular layers is a non- cellular and gelatinous mesoglea.
(b) Perisarc :- It is outer and non-living coat.
It is chitinous in nature and is secreted by myoepithelial cells is epidermis.
In early stages, it is in contact with Coenosarc but later two are separated by a fluid-filled space except at certain points.
It is supportive and protective in function,so acts as exoskeleton.
At the base of zooids and near the bends of the hydrocaulus, Perisarc forms ring like grooves, called perisarcal annuli, which give flexibility to it , so it sways in water to withstand the wave action.

Polymorphism in Obelia :-

Polymorphism us the phenomenon in which a colonial organism is formed of many types of organisms (called zooids in coelenterates) which Differ in structure and function for the benefit of whole Colony.
Obelia is a polymorphic (trimorphic) Coelenterate as the colony has three types of zooids which through are homologous zooids but are specialized in their morphology and physiology.

So polymorphism is associated with division of labour.

(1) Hydrants or polyps ( nutritive and protective zooids)

(2) Blastostyles or Gonozooids(budding zooids)

(3) Medusae or Gonophores( sexual zooids)

(1) Hydranth or Polyp:-

(i) Position :-

These are more numerous in number than other zooids.
These are distributed throughout the colony and are terminal in position.

(ii) Structure :-

(a) External structure:-

Polyp or Hydranth is a hollow and cylindrical zooid which is proximally continuous with the hydrocaulus.
It's free distal end is produced into a conical process called oral cone or manubrium or hypostome having a termination and circular mouth.
Oak cone is about one third of total length of zooid.
Arising from the base of Hydranth, there is a ring of 24-30 solid, tapering and fillifo tentacles, each having batteries of stinging cells.
The tentacles are radially arranged to capture the food from all directions.
Hydranth is protected by a cup-shaped and transparent cover called hydrotheca.
So Obelia belongs to sub order Thecata while the hydranths of Bougainvillea and Tubularia have no theca, so placed in sub-order Athecata.
It is formed by the expansion of Perisarc.
Hydrotheca is open at the tip so Hydranth can be protruded.
At its lower end, hydrotheca is produced inward to form a centrally- perforated circular shelplf which keeps a limit on the retraction of polyp.

(b) Coelenteron:-

Mouth of Polyp leads into a small cavity of manubrium, sometimes called gullet, which opens in the Coelenteron of body of Hydranth which in turn is continuous with that of hydrocaulus.

Histologically , living Coenosarc of Hydranth is formed of 2 layers with a non-living and gelatinous mesoglea in between.
So Obelia is a Diploblastic animal.

(A) Epidermis:-

It is outer and thinner layer.
It is formed of 5 types of cells:-

(1) Myoepithelial or epitheliomuscular cells:-

Position and structure:-
These forms the bulk of epidermis.
These are colonial-shaped with their broader side outward.
Their broader sides meet and form a continuous layer except when interrupted by sensory cells and cnidoblasts.

Each Myoepithelial cell is differentiated into 2 parts:-

Epithelial part and muscular part:-

Epithelial part is outer and nucleated part having vacuolated cytoplasm, a layer of secretary granules in its outer part and two supporting fibrils called tonofibrils.
Muscular part is inner and is produced into two or more tail or muscle processes having a contractile myoneme formed of myofilaments.
Myonemes of these cells are arranged along the longitudinal axis so forming a kind of longitudinal muscles which when contract, make the Hydranth small and thick.
Functions:- These are protective, secretory and contractile in function.

(2) Interstitial cells:-

Position and structure:-

These are groups of cells present in the spaces between the inner narrow ends of Myoepithelial cells.
These are mainly present in the basal part tthe polyp.
Each is spherical-shaped, about 5micrometer, with clear cytoplasm and nucleus having 1 to 2 nucleoli.
Position:-
These act as reserve or undifferentiated cells which can differentiate into any type of cell depending upon their requirements, these are called totipotent cells.
So these help in regeneration, budding and reproduction.
Breton showed that these can renew cells within 45 days

(3) Cnidoblasts:-

Position and structure:-

Cnidoblasts ,also called nematoblasts or stinging cells, are present among the Myoepithelial cells on the hypoblast and tentacles.
These are peculiar cell-type of Coelenterates which are also called cnidarians while their study is called Cnidology.
These form ring-like groups called annular batteries on the tentacles.
Each cnidoblast is pear shaped and about 16 micrometer in size.
It has contractile cytoplasm, eccentric nucleus, a sensory trigger hair called cnidocil at it's free distal end and a sac like nematocyst inside.

A namatocyst is differentiated into two parts :-
Capsule and thread tube.
Capsule is oval-shaped, double walled , chitinous sac externally covered by a lid or operculum.
It is filled with a poisonous fluid called hypnotoxic (a mixture of proteins and phenol).
Thread tube is differentiated into basal butt and distal thread tube proper.
Butt is again formed of proximal wider and funnal shaped part with no spines, called shaft, and distal and tapering part with three large-sized stylets or barbs and three spiral rows of spines or barbules, called spinneret.
Thread tube proper is long tube of uniform diameter which ends into a hypodermic needle.
Such nematocyst of Obelia are called penetrants or stenoteles.
On the outer surface of capsule, there are a number of refractile rods, each giving rise to a contractile fibril extending upto the base of cnidoblast.
Another coiled thread, called lasso, also extends the outer surface of the capsule to its base.
These both prevent the protrusion of capsule.

Function:-

when the stinging. Cells are undischarged,spines and stylets of the butt are inward directed and thread tube proper is coiled around the butt as a watch spring.
When stimulated, stimulus is first received by cnidocil and is conducted to contractile cytoplasm, the contraction of which causes the eversion of thread tube, so the spines and styles are now outward directed while the hypodermic needle is injected in the prey to release the hypnotoxin, which paralyses or kills the prey.So the stinging cells of Obelia are called penetrants or stenosis.
It is now proposed that discharge of nematoblasts is probably due to rapid increase in Calcium level and intracapsular pressure inside the capsule of these cells.
Their coordinated discharge is controlled by neural connections .
So the nematoblasts are cells for offence and defence and are involved in food capturing and protection.
Nematoblasts are independent effectors.
These are stimulated by partly mechanical and partly Chemical stimuli.
Once discharged, these are never withdrawn so these move in the Coelenteron and are digested.
New nematoblasts are regenerated from interstitial cells in about 48 hours in the basal parts of the polyps .

4) Sensory cells:-

Position and structure:-

These are present among the Myoepithelial cells of epidermis, especially in hypostome and tentacles.
Each is a columnar and neuro-sensonry cell.
It has a sensory hair on other side and a few modulated nerve fibres on inner side which join the nerve fibres of nerve cells.

Functions:-

These are sensitive to externally stimuli like touch, temperature, light , Chemicals tc so also called receptors.

(5) Nerve cells:-.

Position and structure:-

Nerve cells, also called protoneurons, from an epidermal nerve net on outer border of mesoglea .
These are more developed in the tentacles.
Each is an irregular cell and is differentiated into a central nucleated part called cell body and a number of nerve processes called neuritis .
Depending upon the number of neurites, nerve cells may be bipolar or multipolar.
But neurites are not differentiated into axon and dendron so nerve impulse can travel in any direction so form diffuse type nervous system.
Neurites of adjacent nerve cells coil around one another to form a net , so called plexiform nervous system.
But there is no continuity of their cytoplasm and nerve impulses are conducted only through synapses, so called synaptic nervous system.
Function:- These form a part of sensory-neuro-motor system and conduct the nerve impulses.

(B) Gastrodermis:-

It is inner and thicker .
It forms the bulk of body wall and is digestive, circulatory and muscular in function.

It is formed of following five types of cells:-

(1) Myoendothelial or Endothelio-muscular cells:-

Position and structure:-

These form the bulk of Gastrodermis .
Each is long and columnar cell which is differentiated into 2 parts:-
Endothelial part and muscular part.
Endothelial part is inner and nucleated part having vacuolated cytoplasm and either pseudopodia or 2 flagella .
Their inner free ends also have microvilli to absorb the digested food from the coelenteron.
It's muscular part is outer and is produced into a muscle process having contractile fibrils called myonemes.
Their myonemes are arranged perpendicular to longitudinal axis of hydranthand act as circular muscle fibres.
When contract, these make the polyp long and thin .
Around the mouth these muscle processes act as sphincter.
Function:- These are nutritive, absorptive, muscular and circulatory in function.

(2) Gland cells:-

Position and structure:-

These are modified Myoendothelial cells present only on manubrium and body of hydranth while these are absent on the tentacles.
Each is columnar-shaped like the Myoendothelial cell but is smaller in size and lacks the muscle process.

Function:-

These secrete either mucus (those in manubrium and called mucous gland cells) or digestive enzymes ( those in the body and. Called enzymatic gland cells) so help in ingestion and intercellular digestion of food in coelenteron.

(3) Interstitial cells:-

These are present in groups in the spaces between the outer ends of Myoendothelial cells.
These resemble those of epidermis in their structure and function.

(4) Sensory cells:-

These are present between the Myoendothelial cells of Gastrodermis.
These resemble those e epidermis in their structure and function except that are less in number.

(5) Nerve cells:-

These form a gastrodermal nerve net on the inner border of mesoglea.
These also resemble those of epidermis in their structure and function but are less in number
Epidermal and gastrodermal nerve nets are interconnected by nerve fibres.

(C) Mesoglea:-

Mesoglea , also called mesenchyme, is the middle homogeneous, non-cellular and gelatinous layer of uniform thickness.
It is joint secretary product of both epidermis and Gastrodermis.

It helps in following functions:-

It acts as middle lamella and provides binding surface for the attachment of muscle processes of both epidermis and Gastrodermis.
It is elastic in nature and helps in extension of hydranth .
It acts as the skeleton so provides mechanical support to hydranth