L.No.1 Micro-Organisms: Friend’s & Foe’s Terminologyscholarsschool.com/CMS/Files/Class 8th Science 2017.pdf(a) Immunity: Immunity or disease resistance is the ability of an organism

Science 8th

/ 2016-17 Page 73 Scholar‟s School Srinagar-0194-2437181

--Sir Ishfaq/ssnp

L.No.1 Micro-Organisms: Friend’s & Foe’s

Terminology (1) Microorganisms: Organisms whose size is very small and can not be seen with the help

of naked eyes. They are also known as “microbes”. e.g. bacteria, fungi, protozoa, algae,

etc.

(2) Virus: These are also microorganisms which are living only inside the cells of the host

organisms, i.e. they can reproduce only inside the cells of host. Outside they are non-

living.

(3) Bacteriophages: Viruses that infect/attack bacteria, e.g. lambda-phages, etc.

(4) Lactobacillus: The bacterium that help in the formation of curd.

(5) Antibiotics: Medicines, which kill or stop the growth of disease causing microorganisms,

e.g. streptomycin, tetracycline, erythromycin, etc.

(6) Antibodies: The molecules/proteins which are produced by the body when an antigen

(foreign body) enters in the body of living organisms that may cause infection/diseases.

(7) Pathogens: Disease causing microorganisms are called pathogens.

(8) Communicable diseases: Those diseases which are transferred/transmitted from the

infected person to a healthy person through air, water, food, etc.

(9) Carriers: Organisms (some insects and animals) which carry pathogens to organisms to

cause diseases in them, e.g. female anopheles carry plasmodium malariae to cause

malaria.

(10) Food poisoning: Poisoning which occurs due to consumption of uncovered food

on which bacteria have produced various toxic substances. This is also known as

“Botulism” and caused by clostridium botulinum bacteria.

(11) Preservatives: Those chemical compounds which are added to food items to

check their spoilage and increase their shelf level for longer periods of time, e.g. common

salt, sodium benzoate, sodium metabisulphite, etc.

(12) Pasteurization: It is the method of heating the milk to about 700C for about 15 –

30 seconds and then suddenly cooled at 40C and then stored. This process was discovered

by Louis Pasteur.

Textual questions

Q.1) Can microorganisms be seen with the naked eye? If not, how can they be seen?

Ans. We can not see microorganisms directly with our naked eyes. In order to observe

microorganisms we have to take the aid of a microscope.

Q.2) What are the major groups of micro-organisms?

Ans. Following are the major groups of micro-organisms:

(i) Bacteria (ii) Fungi (iii) Viruses (iv) Protozoa

(v)Algae.

Q.3) Name the microorganisms which can fix atmospheric nitrogen in the soil?

Ans. Following are the names of microorganisms which can fix atmospheric nitrogen in the

soil e.g.,

Rhizobium Leguminosarium, Klebsiella pneumoniae, Azotobacter, blue green algae etc,

can fix atmospheric nitrogen in the soil.

Q.4) Write 10 lines on the uses of microorganisms in our lives?

Ans. Following are the various uses of microorganisms in the life of human beings.

(i) Microorganisms (e.g.; bacteria and fungi) act as decomposers

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(ii) Microorganisms play an important role to maintain the fertility of soil.

(iii) Microorganisms are also used in sewage disposal

(iv) Microorganisms are also used in dairy industry to manufacture various dairy-

products such as curd, butter, ghee, cheese, etc.

(v) Microorganisms are also used in the process of curing and ripening of crude

leaves of tea and tobacco.

(vi) Microorganisms are also used in the production of vitamins.

(vii) Microorganisms are also used in the production of antibiotics.

(viii) Microorganisms are also used on a large scale in the research field of

microbiology.

(ix) It is used as cleaning agents of the environment.

(x) Microbes are used for the production of vaccines, wine, alcohol and Beer.

Q.5) Write a short paragraph on the harms caused by Microorganisms?

Ans. Microorganisms are responsible to cause various harmful effects to human beings e.g.

Many bacterial species, which grow on food stuffs liberate toxins which cause food

poisoning e.g.; Clostridium botulinum causes the rare and fatal type of food poisoning in

human beings and other animals known as botulism, Microorganisms are also

responsible to cause various types of diseases to human beings e.g.; Tuberculosis,

Diptheria, Tetanus, influenza, Small pox, Polio, Pneumonia, cholera, Typhiod, Ringworm

etc.

Q.6) What are antibiotics? What precautions must be taken while taking antibiotics?

Ans. Antibiotics are the substances, primarily produced by certain useful Microorganisms

which in low concentrations inhibit growth of harmful Microorganisms such as

pathogenic bacteria. The property of antibiosis to kill the pathogenic Microorganisms is

called antibiosis. Some medicinally important antibiotics are: penicillin, aureomycin,

erythromycin, neomycin, streptomycin etc. Following precautions must be taken while

consuming antibiotics.

(i) Antibiotics should be taken by consulting a specialist doctor.

(ii) Antibiotics should be taken in less concentrations.

(iii) Antibiotics should not be taken unnecessarily. Antibiotics taken un-necessarily may

kill the beneficial bacteria

Additional questions

Q.1) Define the following terms:

(a) Immunity (b) Vaccination

(a) Immunity: Immunity or disease resistance is the ability of an organism to resist the

development of a disease. Immunity is provided by immune system which forms specific

defense mechanism of an organism. The most peculiar feature of it is that it can

differentiate between “Self” (body‟s own cells) and non-self (foreign microbes)

(b) Vaccination: The process of vaccination was first developed by Dr. Edward Jenner in

1796. He derived the word vaccine from Latin word „Vacca‟ which means cow. He found

that milk maids once attacked by a „cow pox‟ disease (called vaccinia in Latin) were

immune to small pox. Vaccination is the most important method of preventing infection

of microorganisms, especially of bacteria and viruses. In vaccination, a vaccine is

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inoculated inside the body, before the occurrence of a disease, to stimulate the immune

cells to produce antibodies. So a vaccine has antibody generating agents.

Q.2) Explain in detail mechanism of nitrogen cycle?

Ans. Introduction: Nitrogen is essential component of amino acids, proteins, enzymes and

nucleic acids. Reserve pool of nitrogen is atmosphere which contain, about 78% of

nitrogen in gaseous state. But it can not be used directly and is changed into nitrites and

nitrates and then utilized by plants.

Steps of nitrogen cycle: Following are the various steps of nitrogen cycle.

(i) Nitrogen fixation: Nitrogen fixation involves the conversion of atmospheric nitrogen

(molecular nitrogen (N2) into nitrites and nitrates. Nitrogen fixation occurs in

following three ways.

(a) Atmospheric nitrogen fixation in the presence photochemical and electrochemical

reaction induced by thundering and lightening.

(b) Biological nitrogen fixation in the presence of certain living organism e.g.

Rhizobium bacterium in the root nodules of leguminous plants e.g. pea

Azotobacter in the soil

Anabaena (blue green alga) in water in the paddy field.

(ii) Ammonification: Ammonification involves the decomposition of proteins of dead

plants and animals to ammonia in the presence of ammonifying bacteria like Bacillus

ramosus and B. vulgaris

(iii) Nitrification: Nitrification involves the oxidation of ammonia to nitrites (NO-2) and

nitrates (NO-3) in the presence of nitrifying bacteria like nitrosomonas (Ammonia to

nitrite), Nitrobacter (Nitrite to Nitrate) etc; Plants absorb the nitrites and nitrates from

the soil through roots and convert them into organic compounds (e.g.; protein) by the

process called nitrogen assimilation.

(iv) Denitrification:- It involves reduction of ammonium compounds, nitrites and nitrates

to molecular nitrogen in the presence of denitrifying bacteria like thiobacillus

denitrificans, pseudomonas, etc.

Nitrification Ammonification

Atmospheric

nitrogen

Nitrates

NO-3

Green plants

Nitrites

NO-2

Ammonia in

soil

Animals

protoplasm

Absorption by

roots of plants

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Additional questions (Short Answer Type)

1) Define the term virus?

Ans) Latin virus literally means poison or venom. Viruses are defined as infectious

nucleoproteins. Viruses are obligate intracellular parasites, i.e. they depend upon specific hosts

for their reproduction and development.

2) Name the smallest virus?

Ans) Foot and mouth disease virus (FMV)

3) Name the longest virus?

Ans) Citrustristeza

4) Name the largest virus?

Ans) Small pox virus or variola virus.

5) Name the smallest bacterium?

Ans) Dialister pneumosintes.

6) Name the largest bacterium?

Ans) Bacillusbuschlii.

7) Name the biologist who has given the term antibiotics?

Ans) S. Waksman.

8) Write a short note on nitrogen fixation:

Ans) It is the process which involves the conversion of free atmospheric nitrogen into nitrites,

nitrates, ammonia, either by certain living organisms (biological nitrogen fixation) or by a

physical agents (physical nitrogen fixation).

9) What is botulism?

Ans) Botulism is a fatal type of food poisoning caused by the bacterium clostridium botulinum.

10) Write names of various bacterial diseases?

Ans) Following are the names of various bacterial diseases:

(i) Cholera – Vibrio cholerae

(ii) Pneumonia – Diplococcus pneumoniae

(iii) Tuberculosis – Mycobacterium tuberculosis

(iv) Pertussis – Bacillus haemophilus pertusis

11) Write names of various viral diseases and their causative agents?

Ans) (i) Chicken pox – Varicella virus

(ii) Small pox – Variola virus

(iii) Measles – Rubeola virus

(iv) Rabies – Rabies virus or lassa virus

12) What are bacteriophages?

Ans) Virus that attack and eat bacteria is called bacteriophages or simply phages e.g. Lambda

phage.

Some important Points

i) Bawden and Pirie (1936) first of all studied the chemical nature of viruses and said that

these are nucleoproteins (composed of nucleic acid and protein).

ii) Edward Jenner (1796) discovered vaccination against small pox.

iii) Louis Pasture (1880) discovered vaccination against rabies.

iv) I. Salk (1957) invented vaccination against polio.

v) Ioran Klug (1982) described the structure of TMV (Tobacco Mosaic Virus).

vi) Robert Koch discovered the bacterium Bacillus anthracis which causes anthrax disease.

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Science 8th


--Sir Ishfaq/ssnp

L. No.2 Coal and petroleum Terminology

Coal: It is naturally occurring solid black mineral which is a mixture of carbon and its

compounds. It is a fossil fuel

Coaltar: It is a black, thick liquid with unpleasant smell, obtained by the destructive

distillation of coal. It is a mixture of about 200 substances.

Petroleum: It is a dark, viscous and greasy thick liquid derived from rocks (petra) oleum

(oil) and formed as a result of the decomposition of organic materials like fishes etc. The

organic materials were held between the sedimentary rocks and changed into oils.

Petroleum therefore, is fossil fuel with unpleasant smell. It gives other useful by products

after refining (.e.g. kerosene oil, diesel, etc.)

Coke: It is a tough, porous and black substance. It is obtained by destructive distillation

of coal. It is rich in carbon.

Fossil Fuels: The fuels formed over millions of years ago by the burial of plant and

animal remains are called fossil fuels e.g. coal and petroleum.

Natural gas: Natural gas is also a fossil fuel. It is found above the petroleum trapped

under rocks. It is stored under high pressure as compressed natural gas. (CNG)

Text book questions

Q.1) What are the advantages of using C.N.G and L.P.G as fuels?

Ans) The main advantages of using C.N.G and L.P.G as fuels are as follows:

i) Both C.N.G and L.P.G have high calorific value.

ii) They have low ignition temperature.

iii) Both can be used directly as fuels in homes.

iv) They leave no residue after their combustion. Thus, are clean fuels.

v) They are easy to store and transform.

vi) They are readily available.

Q.2) Name the petroleum product used for surfacing of roads

Ans) Bitumen, a product of petroleum is used for surfacing of roads.

Q.3) Describe how coal was formed. What is this process called?

Ans) Coal is believed to be formed from plants which got burried under earth‟s crust due to

earthquakes, volcanoes, floods etc. which occurred about 300 million years ago. Due to high

temperature and high pressure and the absence of air inside the earth, these plants got converted

into coal. This process is known as carbonization. It gives coke, coaltar and coal gas as useful

products.

This process of conversion of plants burried inside the earth under high temperature and

pressure into coal is called carbonization. It is a very slow process and may take thousands of

years.

Q.4) Why fossil fuels are exhaustible in nature?

Ans) Since the deposits of fossil fuels such as coal, petroleum and natural gas in nature are

limited and these resources can‟t be replenished themselves by quick recycling. Also people are

consuming them at a faster rate due which these may extinct sooner or later. Thus are exhaustible

in nature.

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Q.5) Describe characteristics and uses of coke?

Ans) Coke is a destructive distillation product of coal. It is a tough, porous and black substance.

It is rich in carbon and is almost pure form of carbon (98% carbon).

It is used in the manufacture of steel and in the extraction of many metals.

Q.6) Explain the process of formation of petroleum?

Ans) Petroleum was formed from ocean organisms. Those organisms lived in seas millions of

years ago. When those organisms died, they got settled to the bottom of seas and were preserved

in the mud. As time passed (over millions years), the effects of high temperature and high

pressure, absence of air and action of bacteria resulted in the conversion of these organisms into

petroleum. Petroleum occurs deep under the earth‟s crust between two impervious rocks.

Q.7) What are inexhaustible natural resources? Give examples?

Ans) Those resources which are present in unlimited quantity in nature and are not likely to be

exhausted by human activities, e.g. sun light, air, water, rainfall, sand etc.

Q.8) What are inexhaustible materials? Give examples?

Ans) Those resources which are present in limited quantity in nature and can be exhausted by

human activities, e.g. forests, wildlife, coal, petroleum, natural gas etc.

Q.9) Why natural gas is considered as clean fuel?

Ans) Natural gas is an important fossil fuel which can be transported through pipes, stored under

high pressure as compressed natural gas (CNG). It leaves no residue after burning and does not

produce any poisonous gasses i.e. is eco-friendly. Hence is considered a clean fuel.

Q.10) State important uses of coal?

Ans) The important uses of coal are as follows:

i) It is used as a fuel.

ii) It can be converted into other useful forms of energy like coal gas.

iii) It is used to manufacture many organic compounds.

iv) It is used as a reducing agent in industries in the extraction of metals..

Q.11) What is petroleum refining? Name the fraction obtained after petroleum refining.

Ans) The process of separating petroleum into useful fractions and removal of undesirable

impurities is called petroleum refining. Some of the fractions of petroleum are; petrol, naptha,

kerosene, diesel, wax and lubricant oil, bitumen etc.

Q.12) What steps should be followed to preserve petrol/diesel while driving as per (PCRA)?

Ans) The petroleum conservation research association (PCRA) advises people how to save

petrol/diesel while driving. Their suggestions are:

i) Drive at a constant and moderate speed as far as possible.

ii) Switch off the engine at traffic lights or at a place where you have to wait.

iii) Ensure correct tyre pressure.

iv) Ensure regular maintenance of the vehicle.

Some important questions Q.1) What is the process of destructive distillation of coal?

Ans) It is the process of heating coal to a high temperature and in absence of air, in order to

decompose it, to get some useful products such as coke, coal-tar and coal gas.

Q.2) What do you mean by the process of fractional distillation?

Ans) It is the process of separation of a mixture (e.g. petroleum) into its constituents or fractions,

by using difference of their boiling points, by heating them to a temperature at which a specific

fraction of the substance will be vapourised and obtained.

Q.3) What are petrochemicals?

Ans) Many useful substances which are obtained from petroleum and natural gas are called

petrochemicals. They are used in manufacture of synthetic fibres (polyester, nylon, etc)

polythene, synthetic rubber, plastics, perfumes, dyes, drugs, explosives, etc.

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Q.4) Why is petroleum called as „black gold‟?

Ans) Petroleum is also called as „black gold‟ because of its great commercial importance. It is

widely and enormously used as fuel in locomotives.

Q.5) Which fossil fuels is called a „black diamond‟?

Ans) Coal is the fossil fuel, called as „black diamond‟.

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L.No.3 Conservation of plants and animals

Q.2) Differentiate between the following:

Ans)

Wildlife sanctuary Biosphere reserve

1. Areas where animals are protected from any

disturbance to them and their habitat.

1. A multipurpose protected area developed to

conserve biodiversity.

2. Here operations like, cutting of timber trees,

collection of minor forests, products are also

allowed.

2. It often includes one or more than one

national parks along with extended areas that

are open to some economical uses.

3. There are 509 wild life sanctuaries. 3. There are 15 biosphere reserves in India.

Zoo Wildlife sanctuaries

1. In zoo, artificial habitat is provided to

animals & their food is made available by

human beings.

1. In wildlife sanctuary, the animals get their

natural habitat and naturally available food.

2. The animals living in zoo are looked after by

animal doctors in case they fall sick, which is

not possible in the forest.

2. The animals living in sanctuaries are looked

up by the nature.

3.It is the facility in which animals are kept for

public exhibition.

3.It is an area where public visits are generally

prohibited.

Flora Fauna

1. Collection of plants found in a particular

area.

1. Collection of animals found in a particular

area.

2. There are 45,500 plants present in India. 2. There are 91,000 animals present in India.

Endangered species Extinct species

1.These are the species whose number is

diminishing and may face extinction.

1.There are the species which have been

disappeared from the earth.

2. Their habitat is so heavily decreased. 2. Their habitat doesn‟t survive now.

3. They exist in their natural habitat in low

numbers.

3. They are totally extinct from their natural

habitat.

4. Their examples are Asian elephants, blue

whale, sea turtle, etc

4.There examples are dinosaurs, dodo, pink –

headed duck, etc

Q.3) Discuss the effects of deforestation on the following.

Ans) (1)Wild animals: Plants and trees are the habitat and food for wild animals. So cutting of

trees destroy the natural habitat of wild animals and thus they would become endangered species.

(2)Environment:

Deforestation decreases the level of oxygen in the atmosphere. Deforestation also decrease

rainfall and the fertility of soil in. As a result, there is increase in the natural calamities like

floods and droughts..

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(3) Villages (rural areas):

Most of the agriculture is done in rural areas when trees and plants are cut down, it leads to

change in soil properties which disturbs the crop cultivation.

(4)Cities (urban areas):

In cities because of factories and automobiles, smoke & other pollutants are released which do

not get cleansed due to deforested land of cities which leads to pollution & makes life unhealthy

& miserable in urban areas.

(5)Effects of deforestation on earth:

Deforestation leads to increase in temperature of earth which causes global warming, floods, etc.

Less trees result in more soil erosion. Thus the planet earth will loose its greenery.

(6)The next generation:

Because of the deforestation their will be changes in climate and the world environment will be

polluted. So the next generation would not be as prosperous as previous one.

Q.4) What will happen if –

(a) We will go on cutting trees?

Ans) Trees play a very vital role in the world. The benefit and advantages of trees can‟t be

discussed in few lines. The first importance of trees is that they provide the life sustaining gas

called as oxygen gas and receives toxic gas from human body, i.e. CO2. Moreover, they add to

the fertility of soil as they increase amount of nitrogen in it and prevent it from getting eroded. if

we cut the trees that means we cut our life sustaining material. Timber of trees is used for

construction purposes. They add to the beauty of surroundings. They are the parts of food chain.

Deforestation may lead to destruction. So, there should be Afforestation and no deforestation.

(b) The habitat of animals is disturbed

The destruction of the habitat of an animal leads to decrease in the species as some species have

extinct because of no shelter. The benefits of those species/animals will go on declining. Their

destruction leads to decrease of beauty of nature. So, the animal habitat should not be disturbed.

(c) The top layer of soil is exposed?

Top layer of soil is the most fertile layer. This layer is responsible for the growth of crops. Soil

erosion has several disadvantages, it changes soil properties which decreases the production of

crops, washing away of top layer of soil should be regarded as creeping death of earth.

Q.5) Answer in brief.

(a) Why should we conserve biodiversity?

Ans) We need to conserve biodiversity for our survival and to maintain the natural ecological

balance. It will enable us to preserve the rich quality of our environment and also ensure the

continuous availability of useful plants and animals and their products to our future generations.

(b) Protected forests are not completely safe for wild animals. Why?

Ans) Protected forests are not completely safe for wildlife because there are a number of reasons

associated with it. On one hand it is a good move to conserve wildlife and on the other hand it

poses threat to the lives of the animals living in forests. This is because they get a limited habitat

over there for their better living. Their remains threat of hunting, scarcity of food and water etc.

to these animals.

(c) Some tribals depend on jungle.

Ans) Some tribals depend on jungle for the following requirements:

(i) To get firewood for cooking their meals and warming their bodies in cold days.

(ii) To build their houses and other structures/buildings

(iii) To make money by cutting the trees.

(iv) To graze their cattle.

(d) What are the causes and consequences of deforestation?

Ans) The cause of deforestation:

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Procuring land for cultivation

Building houses and factories

Making furniture

Using wood as a fuel

Consequences of deforestation:

Global warming (increase in temperature)

Ground water level also gets lowered

Decrease of rainfall and in fertility of soil

Increased chances/demands of natural calamities like floods and droughts

Desertification (conversion of fertile land into desert)

Decrease in water holding capacity of the soil

(e) What is Red Data Book?

Ans) Red Data Book or RDB is the source book which keeps a record of all endangered animals

and plants. It is also known as (International Union for Conservation of Nature and Natural

resource). IUCN Red list of threatened species.

(f) What do you understand by the term migration?

Ans) Seasonal movement of some birds and animals in large number from one place to another

to overcome unfavourable conditions and to return back to original habitat when conditions

become favourable, is called migration.

Q.6) In order to meet the ever-increasing demand in factories and for shelter, trees are

continually cut. It justified to cut trees for such projects. Prepare a brief report.

Ans) Modern life has totally become dependent on forests. We need to cut trees for building our

homes. We also get several useful materials from trees to run our factories. Some people earn

their living from factories. So, it is the need of modern man to cut trees in order to run factories

and make their homes but it has disadvantages too.

Cutting of trees disturbs the climatic conditions.It also destroys the habitat of wild animals. So, it

may be said that in order to meet the evr-increasing demand in factories and for shelter, trees

may be cut for such purposes but we should plant trees at equal rate so that ecology and

environment does not get disturbed. This will be possible only if rate of aforestation will be

greater than or equal to rate of deforestation.

Q.7) How can you contribute to the maintenance of green wealth of your locality? Make a list

of actions to be taken by you?

Ans) We can contribute to the maintenance of green

wealth of our locality in the following ways:-

1.We can help in maintaining the green wealth of

our locality by taking care of the plants & trees

growing in or around our locality. We can plant

more & more trees .

2. We can also encourage the people in our locality

to plant more trees by informing them about the

importance of growing trees.

3. We can make people especially young children

aware of the effects of deforestation on our

environment & on our planet .

In fact , planting new trees is as important as taking

care of the existing ones. In this way, we can

contribute to the maintenance of green wealth

(plants) of our locality.

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Q.8) Explain how deforestation leads to reduced rainfall.

Ans) We know that plants need CO2 for their photosynthesis. It is obvious that if deforestation

starts everywhere. Only fewer trees would exist. The rate of CO2 will increase because there are

only few trees to utilize it. It is common sense that there will be rise in temperature as CO2 traps

the heat rays reflected by earth. The increase in temperature on the earth disturbs the water cycle

and may reduce the rainfall. In short rainfall is directly or indirectly dependent on the trees

(forests).

Q.9) Find out the information about the national parks in your state. Identify and show their

location on the outline map of India.

Ans) The main national parks and the wildlife sanctuaries are given below in the outline map of

India.

Q.10) Why should paper be saved? Prepare a list by which you can save paper.

Ans) Paper should be saved because it takes around seventeen full grown trees to make one

tonne paper. Trees, as we know, are important to maintain balance in nature.Therefore, in order

to save trees & prevent the impact of their loss on living organisms, we need to save paper.

Ways by which paper can be saved:

i) Collect used paper & recycle it (can be recycled upto 5-7 times for use).

ii) Use paper judiciously.

iii) Spread awareness about the importance of paper.

iv) Not to waste the paper & use both sides of paper for writing.


Q.1) Write about classification of vegetation in J&K.

Ans) In J&K, vegetation is classified as

Dry savanna and scrubs

Sub-tropical forests

Temperature forests

Alpine vegetation

Xerophytic vegetation

Q.2) What is soil erosion? What are the results of soil erosion? Name the places of J&K

where soil erosion takes place.

Ans: Soil erosion: It is the process by which top layer of soil & rocks are removed from earth’s

surface by exogenic processes such as wind or water flow .It is the removal of top soil faster

than the soil forming processes can replace it, due to natural , animal & human activity (like

overgrazing, over-cultivation ,forest-clearing , mechanized farming, etc).

Soil erosion results in:

i) Land infertility.

ii) Desertification.

iii) Devastating floods.

Following areas of the J&K are prone to soil erosion:

Kandhi belth (situated in lower Himalayas called siwalik)

Area located between mansar and surinsar .

Area between Balaul & Basantar.

Kaleeth & Chauki chora of Akhnoor other effected areas are Dansal, Jhajjar, Kotli, Ram

Nagar, Jandial, Amb, Mansar and Suriansar, etc.

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--Sir Ishfaq/ssnp

Q.3) Name the endemic species of animals in J&K state.

Ans)

Himalayan harbour

Yak (Ladakh)

Shaggy horned wild ox

Tibetan antelope

Bharal (blue sheep)

Wild sheep

Kiang (Tibetan wild ass)

Kashmir stag (Hangul)

Red fox

Himalayan libex

Indian wolf

Q.4) Name the wildlife sanctuaries and national parks present in J&K state

Ans) Wildlife sanctuaries

Dachigam wildlife sanctuary

Surinsar mansar wildlife sanctuary

Ramnagar wildlife sanctuary

Overa wildlife sanctuary

Jasrota wildlife sanctuary

Nandni wildlife sanctuary

Trikuta wildlife sanctuary

National parks

Kishtwar High Altitude National Park

Salim Ali National park

Dachigam National park

Q.5) Endangered animals of J&K state

Ans) Due to habitat loss, poaching and over exploitation, many animals have become

endangered

Following birds and animals of J&K state are most endangered at present and need conservation

on war footing.

Monal pheasants – Neel

Koklas pheasants – Makk – Makau

Western horned pheasants – Bindus

Indian panglin

Musk deer

Barking deer

Himalayan brown bear

Himalayan ibex

Kashmir stag (Hangul)

Red fox

Common leopard

Indian wolf

Snow leopard

Q.6) Pen down the brief note on conservation of forests and wildlife

Ans) Conservation of forests and wildlife:

We know that conservation refers to the wise and judicious use of all natural resources.

Conservation means to keep the components of our environment in balance. It is the duty of all

human beings to conserve forests and wildlife. It will enable us preserve of our environment and

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also ensure the continuous availability of useful plants and animals and their products for our

future generations. Government and non-government bodies are involved in the conservation of

biodiversity programmes, framing laws to protect the existing forests and wildlife.

Q) How to conserve our forests and wildlife?

Ans) To protect our forests and wildlife, we have to stop illegal hunting of animals, felling of

trees. There are some areas where our flora and fauna and there habitats are protected, these

protected areas are called sanctuaries, national parks and biosphere reserves have been

earmarked.

Q.7 What is species?

Ans. Species: A species refers to a group of organisms (plants or animals) that have common

characteristic features and can interbreed with each other. In, other words the members of species

have some features unique to their groups that clearly distinguish from other groups. The

members of species can reproduce fertilize offsprings only with the members of their own

species and not with the members of other species.

Q.8) What is Ecosystem?

Ans. Ecosystem:An ecosystem is a “self – sustaining” unit of the living world made up of

various communities of living organisms (like plants & animals) along with the non-living

components like soil, air, water & minerals of that region. The term ecosystem was coined in

1930 by Roy – Clapham to mean the combined physical & biological components of an

environment.

Q.9 Reforestation:

Ans. Reforestation is restocking of the destroyed forests by planting new trees. The planted

trees should generally be of the same species which were found in the forest. We should plant as

many trees as we cut. Reforestration can take place naturally also. If the deforested area is left

undisturbed it re-establishes itself. In natural reforestarion there is no role of human beings.

Government of India has implemented the national forest policy in 1952. It aimed at

forest coverage of one-third of total hand area of the country. On the failure of this policy, Indian

government revised the policy in 1980 at preservation and conservation of natural forests and

meeting the basic needs of the people living in or near the forests.

Some Important points

Total area under forests in J&K. 20,230 sq. kms.

Forest cover in Kashmir division: 50.97%

Forest cover in Jammu division: 45.89%

Forest cover in Ladakh: 3.14%

District Doda is leading in forest cover: Kargil District is very poor in forest wealth.

Global warming: It is the rise in average temperature of the earth‟s atmosphere due to green

house effect caused by greenhouse gases , like CO2.

Desertification: The conversion of fertile land into barren land (less fertile) as result of

deforestation.

IBWL: Indian board of wildlife was formed in 1952.

Since 1995 a wild life week (First week of October) is being celebrate all over the globe.

In 1972, a wildlife protection act was established.

Project tiger: Project tiger was launched by the government to protect the tigers in the country.

The objective of this project was to ensure the survival and maintenance of the tiger population

in the country.

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Science 8th


--Sir Ishfaq/ssnp

L.No.4 Reproduction in animals

Terminology

Reproduction: It is the process by which living organisms produce young ones of their own kind

to continue their existence.

Sperms: These are the sex gametes (sex cells) produced by the testes of males.

Ova/Egg: These are the sex gametes (sex cells) produced by the ovaries of females. Usually one

egg is produced by either of the ovary per month.

Fallopian tube or Oviduct: It is that part of female reproductive system in which fertilization

takes place i.e. fusion of male & female gametes.

Uterus: It is a bag like structure in female reproductive system in which development of

baby/new born takes place.

Fertilization: It is the process in which fusion of male gametes (sperm) & female gametes (egg)

takes place in fallopian tube to form zygote.

Zygote: Zygote is the cell formed as a result of fertilization which marks the beginning of a new

individual.

Invitro fertilization (IVF): It is the fertilization that is done outside the body of a female.

Embryo: It is a structure formed as a result of repeated divisions of zygote to form groups of

cells, tissues & organs like feet, hands , etc inside the uterus.

Q.1 What is reproduction and what are its types?

Ans. Reproduction is the process by which living organisms produce young ones of their own

kind to continue their existence. Reproduction is one of the characteristic feature of living

organisms. Living organisms reproduce by many methods which have been broadly

classified into two types:

i. Sexual reproduction ii. Asexual reproduction.

i. Sexual reproduction:- It is that type of reproduction in which individuals (young ones)

are produced by the fusion of male and female gametes contributed by two parents.

ii. Asexual reproduction:- It is that type of reproduction in which new individuals (young

ones) are formed without the fusion of male and female gametes. In asexual reproduction

only one parent is involved in the formation of new individuals.

Q.2 Explain the importance of reproduction in organisms.

Ans. Reproduction is the fundamental property of the protoplasm exhibited by all living

beings. It must be remembered that the process of reproduction is not essential for the

survival of the individual but for the race or the species because of the following:

1) New members (daughter individuals) are added in population in place of old ones to

maintain the existence of the species, i.e. increase in population.

2) It plays an important part in transmitting the favourable characteristics to the

offsprings, thus becomes a vehicle of organic evolution.

Q. What are the different types of asexual reproduction? Explain fission and budding?

Ans. Asexual reproduction takes place in the following ways:-

i. Fission. (ii) Budding (iii) Spore formation.

(iv) Regeneration or Fragmentation. (v) Vegetative propagation.

i. Fission:- It is the process in which the parent body (cell) divides to form daughter

cells which grow as new individuals. The process of fission is most common in

unicellular organisms such as bacteria and protozoa. The process of fission is of two main

types:

a. Binary fission b. Multiple fission.

Science 8th


--Sir Ishfaq/ssnp

a. Binary fission:- It is a type of asexual reproduction in which the body of a unicellular

organism divides into two daughter cells which grow as new individuals. This type of

reproduction is found in Amoeba, paramecium, Euglena, etc.

In some organisms like amoeba, the splitting of the two cells during division can take

place in any plane. However, in some organisms like leishmania (which have a whip like

structure at one end of the cell) binary fission occurs in a definite orientation in relation to these

structures.

b. Multiple fission:- It is a type of asexual reproduction in which the body of a

unicellular organism divides into many daughter cells. This type of reproduction is found in

plasmodium (a malarial parasite) and in case of Amoeba under unfavorable conditions.

ii. Budding:- In budding, a small bulb like outgrowth develops on the body of an organism

called bud. The bud develops into a tiny individual and when fully mature detaches from the

parent body and becomes a new independent individual. This type of reproduction takes place in

coelenterates (hydra), sponges (scypha) and yeasts.

Q. With the help of diagram describe the structure of male reproductive system in humans.

Ans . The male reproductive system consists of a scrotum, a pair of testis, vasa efferentia, a pair

of epididymes, a pair of vasa deferentia, a pair of ejaculatory ducts, urethra and penis.

Scrotum:- It is a pouch of pigmented skin arising from the lower abdominal wall and

hanging between the legs. The testes originate in the abdominal cavity but later during the

seventh month of development descend into the respective scrotal sacs. The scrotum acts as a

thermoregulatar, maintaing the testes at a temperature 2o lower than that of the body.

Testis:- The testes are soft, smooth, pinkish oval organs about 4-5 cm long, 2.5 cm wide

and 3cm thick. Testes are formed of seminiferous tubules which consists of spermatogenic cells

and sertoli cells. The former becomes sperms while the latter provides nutrient to the sperms.

The semniferous tubules also contain the interstitial or Leydig‟s cells which secrete the male sex

hormone called testosterone.

Epididymis:- The epididymis is a long tube attached to the

hind surface of the testis. Maturation of sperms and their

fertilization capacity occurs in head of the epididymis and are

stored in the tail part of Epidydimis. The sperms not ejaculated

are reabsorbed in the vasa deferens.

Vasa Efferentia:- The vasa efferentia bear cilia to aid in sperm

transport.

Vasa deferentia:- It is about 40 cm long narrow and tubular

structure which starts from epididymis and joins the seminal

vesicles to form ejaculatory duct. Vas deferentia conducts the sperms by peristalsis.

Ejaculatory ducts:- These are about 2cm long thin walled tubes which open in to the urethra.

Urethra:-It is the urinary duct leading from the bladder. It carries urine as well as sperms. It is

about 20 cm long.

Penis:- Penis is a male couplatory organ through which urethra pass. It is used for depositing

semen into the vagina of the female.

Accessory sex glands:- Accessory glands helps in secretion of seminal fluids. In man there

are three types of sex glands namely:

1. Seminal vesicles:- These are a pair of glands present between rectum and urinary

bladder.

2. Prostate glands:-It is a single large sized lobulated gland present just below the urinary

bladder.

3. Cow pars glands:-These are a pair of white pea sized glands present at the base of penis.

Science 8th


--Sir Ishfaq/ssnp

Q. With the help of diagram describe the structure of female reproductive system.

Ans. The female reproductive system consists of a pair of ovaries, a pair of fallopian tubes

(oviducts), uterus and vagina.

Ovaries:- The ovaries are the primary sex organs of the female. They are about the size and

shape of an almond. Each ovary is connected by ovarian ligament to the uterus. The ovaries

remain attached to the body wall by ligament. The ovaries produce female gamete ova and

female sex hormones estrogen and progesterone. The ovaries are externally lined by germinal

epithelium. Ovaries are two in number and each ovary produces eggs alternately.

Fallopian tubes:- These are a pair of elongated, ciliated muscular and tubular

structures extending from just close to ovaries to uterus. The outer part of each fallopian tube

lying close to ovary has a wide aperture called ostium and a number of finger like processes

called fimbriae to receive the ovum released from ovary.

Functions of Fallopian Tube:- Fallopian tube is the

site of fertilization and is also called fertilization canal. It

conducts the Zygote towards uterus by its cilliary action.

Uterus:- It is a muscular pear shaped structure

present between urinary bladder and rectum. Its internal

linings is highly glandular and vascular and is called

endometrium. Its lower and narrow part is called cervix

which opens into vagina.

Function:- It is the site of foetal development.

Vagina:- It is about 7.5cm long and is adopted for

receiving penis, allowing menstrual flow and serves as

the birth canal.

Q In Which female reproductive organ does the embryo get embedded?

Ans. Uterus

Q Give two differences between zygote and foetus?

Ans)

Zygote Foetus

1. The fusion of sperm and egg is

called a zygote

1. The stage of embryo in which

cell body parts are identifiable is

called foetus.

2. It is single celled structure. 2. It is a multicellular structure.

Test tube babies: In some women, oviducts are blocked and they are unable to bear babies

because sperms cannot reach the egg for fertilization. In such cases, doctors collect fresh released

egg and sperms and keep them together for a few hours for IVF or in vitro fertilization

(fertilization outside the body). The zygote is allowed to develop for about a week and is then

placed in the mother‟s uterus for further development. The babies produced through this

technique are called test tube babies.

Q. What are viviparous and oviparous animals?

Ans. Viviparous animals: Those animals which directly give birth to their young ones are

called viviparous animals e.g. mammals

Oviparous animals: Those animals which lay eggs are called oviparous animals e.g. birds.

Q) What is metamorphosis? Give examples?

Ans) Metamorphosis: The transformation of the larva into an adult through gradual changes is

called metamorphosis. A beautiful moth emerging out of the cocoon and the transformation of a

tadpole into an adult frog are the examples of metamorphosis.

Science 8th


--Sir Ishfaq/ssnp

Q2. Describe the process of fertilization in human beings?

Ans: Fertilization in human beings means the fusion of male & female gametes in the fallopian

tube of the female reproductive system .During fertilization , the nuclei of the sperm & the egg

fuse to form a single nucleus. This results in the formation of a fertilized egg or zygote .The male

gametes (sperms) are produced by the father & ova/egg is produced by the mother. So , the new

individual inherits some characteristics from the mother & some from the father. In human

beings fertilization takes place inside the female body is called internal fertilization.

Q9. Differentiate between internal fertilization & external fertilization? Ans:

Internal Fertilization External Fertilization

1. It is the fertilization which takes place inside

the body of a female.

1. It is the fertilization which takes place outside

the body of a female.

2. Example: In humans , birds , Mammals,

Reptiles etc

2. Example: In fishes and Amphibians.

Q) With the help of diagram show; (i)

Life cycle of frog (ii) Budding in hydra

and (iii) Binary fission in amoeba.

Budding in hydra

a)

Cytoplasm

Nucleus

b)

Dividing of

nucleus

c)

Dividing of

cytoplasm

d)

Daughter amoeba Binary fission in amoeba

Cloning: It is a technique by which an exact copy of a

cell, an organ, or a complete organism is produced. This

technique for the first time was successfully performed

by Lan Wilmut and his collegues at the Roslin Institute

in Edinburgh, Scotland in 1996. Q) Write a short note on Dolly and explain that how it was

produced as an exact copy of the Finn Dorsett Sheep.

Ans) Dolly was a clone of a Finn Dorsett Sheep, Dr, Lan

wilmut and his team collected a cell from the mammary

gland of a female Finn Dorsett Sheep and

simultaneously, an egg was obtained from a Scottish

black face Ewe. They removed the nucleus of the egg

and inserted the nucleus of the mammary gland cell of

the Finn Dorsett Sheep into the egg. The egg thus

produced was implanted into the Scottish Blackface ewe

whose nucleus had been removed. Development of this

egg followed normally and finally Dolly was produced.

It was an exact copy of the Finn Dorsett Sheep from

which the nucleus was taken.

Transgenic animal: Transgenic animal is one that

carries a foreign gene that has been deliberately inserted

into its genome.

Life cycle of frog

Eggs early tadpole

Late tadpole Adult frog

Science 8th


--Sir Ishfaq/ssnp

L.No.5 Sound Textbook questions

Q.5) A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.

Ans) Here number of oscillations = 40

Time taken = 4 seconds

Frequency = ?

We know, Frequency = Number of oscillations

Time taken in seconds.

= 40 = 10H2

4

Also, time period = 1 = 1 = 0.1 sec

Freq. 10

Q.6) The sound from a mosquito is produced when it vibrates its wings at an average rate of

500 vibrations per second. What is the time period of the vibrations?

Ans) Here, frequency of wings = 500 vib./sec.

Time period = ?

We know, Time period = 1 = 1 = 0.002

Freq. 500

or 2 = 2 = 2x10–3

sec.

1000 103

Q.7) Identify the part which vibrates to produce sound in the following instruments:

(a) Dholak (b) Sitar (c) Flute.

Ans) Instrument Vibrating part

(a) Dholak Stretched membrane (called head)

(b) Sitar Stretched strings

(c) Flute Air column

Q.8) what is the difference between music and noise/ can music become noise sometimes?

Ans) The main differentiating points between music and noise are:

Noise Music

(1) It is an unpleasant sound. (1) It is a pleasant sound.

(2) It causes discomfort. (2) It has soothing effect.

(3) It can lead to health problems such as, high

blood pressure, heart attack and partly deafness

(3) It does not cause any health problem

(4) It has undesirable frequency. (4) It has desirable frequency.

Yes, music can become noise sometimes, when the musical instrument produce high volume

sounds.

Q.9) List some sources of noise pollution in your surrounds.

Ans) The following are the major sources of noise pollution:

(a) The sound produced by different vehicles.

(b) Sound from high volume of loudspeakers, TVs, radios and other musical instruments.

(c) Sound from kitchen appliances such as pressure cookers.

(d) Sound of generators.

(e) Sound produced by different machines at construction sites.

(f) Sound produced by crackers.

Science 8th


--Sir Ishfaq/ssnp

Q.10) Explain in what way noise pollution is harmful to humans.

Ans) Following are the harmful effects of noise pollution:

(a) Noise pollution can effect our sense organs, nervous system, glandular and

cardiovascular

systems.

(b) Noise pollution causes behavioural alterations in human beings.

(c) Noise pollution can cause high blood pressure.

(d) Noise pollution can also cause loss of memory, anxiety and partial deafness.

(e) Noise pollution can also lead to severe headache.

Q.11) Your parents are going to buy a house. They have been offered one on road side and

another three lanes away from the roadside. Which house would you suggest your parents to

buy? Explain your answer.

Ans) I would suggest my parents to buy a house three lanes away from the road side. This is

because; it would protect our house from: (i) Lot of noise due to passing of vehicles (ii) Smoke

and dust produced due to traffic on road (iii) sound of pressure horns at the time of traffic jams.

Q.12) Sketch the larynx and explain its formation in your own words.

Ans) Larynx is a part of the throat. It is responsible for production of sound and is, therefore,

called as sound box.

Larynx consists of two vocal cords inside it. There is a small gap between them which allows air

to pass through. When we speak, air is forced into this small gap by the lungs. This prompts

vocal cords to vibrate. Since vibrating objects produce sound, sound is produced due to the

vibration of vocal cords.

Q.13) Lightning and thunder take place in the sky at the same time and at the same distance

from us. Lightning is seen earlier and thunder is heard later. Can you explain why?

Ans) Speed of light is 3 x 108m/s, which is far greater than the speed of sound i.e., 330m/s. That

is shy lightening is seen earlier and thunder is heard later.\

ADDITIONAL QUESTIONS

Q.14) What is noise pollution? What are its causes and ill effects. Suggest the steps to control

noise pollution.

Ans) Noise pollution: The unwanted sounds which is not soft and is undesirable to the ear, is

called noise pollution. The presence of loud sound in atmosphere is only noise pollution.

Cause of noise pollution: a) The loud sound produced by machines in factories.

b) Loudspeakers (e) Generators

c) Railway stations (f) Air ports

d) Music programmes (g) Crackers

Effects of noise pollution: a) It causes deafness

b) It raises heart beat

c) It increases blood pressure

d) It causes loss memory

e) It affects nervous system, glandular system and sense organs.

f) Loud music during night disturbs our sleep.

g) It may cause lack of concentration in work or studies.

Control: Following are some of the measures one should adopt to keep noise pollution under

control:

a) Silencers should be used in automobiles.

b) The horns of motor vehicles should not be blown unnecessarily.

Science 8th


--Sir Ishfaq/ssnp

c) We should not play radio, TV and stereo systems too loudly.

d) Airports and factories should be shifted away from residential areas.

e) The use of loud speakers should be banned as far as possible.

Q.15) What is music? Name different kinds of musical instruments?

Ans) Music is the arrangement of sound of different frequencies in a way that it produces

pleasing effect on the ear. Depending upon the part of a musical instrument that vibrates, we

have five main types of musical instruments.

(1) Stringed instruments: The musical instruments in which a string (metal wire) vibrates

are known as stringed instruments, e.g. guitar, veena, sitar, violin.

(2) Wind instruments: These musical instruments are generally made in the form of pipes.

When we blow air into them the column of air inside vibrates producing sound, e.g.

whistle, flute, Sheena.

(3) Percussion instruments: The instruments in which a stretched membrane or skin

produces sound are known as percussion instruments, e.g. drum, dholak, tabla

(4) Reed instruments: These musical instruments contain metal reeds which produce sound

when air is blown through them, e.g. harmonium and mouthorgan.

(5) Ghana Vadya: Musical instruments produce sound while beaten or struck with some

object, e.g. manjira, noot (mud pot)

Q.16) What are the characteristics of sound?

Ans) The characteristics of a sound are: (a) Pitch (b) Loudness (c) Quality

a) Pitch: Pitch is a characteristic of sound which distinguishes a sharp (shrill) sound from a

hoarse (grave) sound. The pitch of a sound depends upon the frequency of vibrations. The

pitch of the sound produced by an object vibrating with low frequency is low and the

sound is described as grave sound.

Low freq. ------ low pitch -------- grave sound

The pitch of a sound produced by an object vibrating with high frequency is high and the

sound is described as shrill sound.

High freq. ---------- high pitch ----------- shrill sound

e.g. the voice of children and ladies is shrill as compared to the voice of men. The sound

produced by the wings of bees and mosquitoes is also shrill in nature.

b) Loudness: It is a characteristic of sound by which a loud sound can be distinguished

from a faint sound. It is measured accurately by amplitude and vibrations of the sound

source. The loudness of sound is directly proportional to the square of amplitude,

i.e. loudness amplitude2.

Am

plit

ud

e

Wave form

Time (s)

Am

plit

ud

e

Time (s)

Science 8th


--Sir Ishfaq/ssnp

If a sound has smaller amplitude it is soft in nature and is represented as in fig. (a):

Fig. (a)

Fig. (b)

The sound having greater amplitude is louder in nature is represented as in fig. (b):

c) Quality: It is the characteristic of sound that enables us to distinguish between two

sounds of same pitch and loudness produced by two different things.

Q 17) Explain the structure and working of human

ear?

Ans) We are able to hear sounds from our surroundings

through our sensory organs called ears. Our ear is divided

into three parts: (1) Outer ear or external ear (2) Middle

ear (3) Inner ear

(1) Outer ear: It consists of a flap like structure called

pinna. The pinna is further connected to ear canal at the

end of which is a circular membrane called ear drum. The

pinna collects the sound waves and then directs them to

the ear drum, through ear canal. The ear drum starts to

vibrate.

(2) Middle ear: It consists of a chain of three bones –the

hammer (mallus), anvil (incus) and stirrup (stapes) –

whose one side is connected to ear drum and the outer side to the inner ear. The function of these

bones is to amplify the vibrations received from ear drum several times in the middle ear.

(3) Inner ear: The inner ear contains cochlea. Cochlea is filled with a fluid and has many hair

cells inside it. The amplified vibration from bones passes to cochlea. The sensitive hair cells

present in cochlea change these vibrations into electrical signals. These signals are then carried

by the auditory nerves to the brain. The brain on receiving the nerve impulses decodes them and

interprets the sound

Q 18) What are the various ways to take care of ears?

Ans) (1) We should never insert any pointed object into the ear. It can damage ear drum. (2) We

should clean our outer ears with soft towels and inner ears with cotton buds. (3) We should not

hit any one hard on his/her ear. (4) We should not listen loud music from music systems.

Q 19) Write a short note on echo.

Ans) An echo is the repetition of the original sound heard after the sound is reflected from a

distant dense and rigid object such as a high building, cliff etc. Echo has many applications in

our day to day life, e.g. in solar system to find the depth of seas in sonography to study the

human physiology in medical sciences.

Q 20) Explain the following terms.

Ans:- (a) Amplitude:- It is defined as the maximum displacement made by a wave in the

direction of propagation of wave. It is denoted by „a‟. Its SI unit is metre.

(b)Time period:- It is defined as the time taken to complete one oscillation. It is denoted by „T‟.

Its SI unit is second. It is the reciprocal of frequency i.e., T = 1/f

(c) Frequency:- Frequency of a medium is defined as the number of oscillations made by a

vibrating body in a second. It is measured in Hertz (Hz).

Am

plit

ud

e

Am

plit

ud

e

Science 8th


--Sir Ishfaq/ssnp

(d) Wavelength:- It is defined as the distance between two consecutive crests or between two

troughs. It is denoted by

„‟ (lamda). Its SI unit is metre.

Amplitude Crest

a

a

Trough

Wavelength

L.No. 6 Food production and management

Textbook questions Q.1) What are the requirements of farming which would lead to high yields of crops?

Ans) The basic requirements of farming which would lead to high yields of crops are:

a) Proper type of soil

b) Use of manures

c) Irrigation

d) Good varieties of seeds

e) Sophisticated agricultural tools

f) Chemicals to prevent diseases of the crop plants.

Q.2) What is tilling? How it is done?

Ans) Tilling is the process of breaking up and stirring soil. It can be done for preparing the area

for plantation to mix in organic matter or to reduce the amount of weeds in the area.

For tilling the soil on a large scale, tractors are used with large tillers. But on a small

scale rototiller is a manageable and affordable way to till the area. Moreover it can also be done

using a spade. In case of the tractors, large tillers are fixed at their back and are then sunk deep

into the soil. After that they are dragged resulting in stirring of the soil.

Q.3) Write a short note on process of sowing?

Ans) The process of putting the seeds in the agricultural field is called sowing. It is done by two

methods:

a) Broadcasting: In this method, seeds are scattered in the field by hand. Depth, to

which the seed is sown and the space between the seeds is not taken into

consideration.

b) Seed drilling: In this type of method, seeds are sown with the help of a mechanical

agricultural implement called „seed drill‟ which is equipped with a long pipe and a

funnel on it. This is connected with a plough. While ploughing seeds are

mechanically broadcasted in the field.

Q.4) What are manures? Discuss their important types.

Ans) Manures are the organic materials which supply the nutrients that a plant needs in small

amount. They are important to increase the fertility of soil.

The important types of manures are farmyard manure (FYM), Green manure, compost

and vermicompost.

a) Farmyard manure (FYM): It is the most valuable organic matter commonly

applied to the soil. This usually consists of straw, leaves and other materials like

excreta of cattle.

Science 8th


--Sir Ishfaq/ssnp

b) Green manuring: The practices of turning or ploughing of green plants into soil for

the purpose of improving physical structure as well as soil fertility is called green

manuring. Leguminous crops, like cluster beans, sunnhemp etc, are green manure

crops.

c) Compost: It consists of all the cattle shed wastes and all the available refuse, which is

allowed for rottening.

Q.5) What is a fertilizer? Explain its importance?

Ans) Fertilizers are the commercially prepared inorganic chemical substances that are rich in

nitrogen, phosphorous,potassium etc and add fertility to the soil.

Importance: Fertilizers are nutrient specific i.e. they are used mainly to increase the essential

elements in the soil.

A fertilizer is soluble in water, so it is readily absorbed by the crop plants

Q.6) What is broadcasting and transplantation?

Ans) Broadcasting: It is a type of sowing of seeds in which seeds are scattered in the field by

hand or by a machine called broadcaster.

Transplantation: It is the process of taking out young plants or saplings from nursery beds and

transferring them to agricultural fields with adequate spacing, water and minerals for adequate

growth.

Q.7) Differentiate between manures and fertilizers?

Ans)

Manure Fertilizer

(1) Manures are partially decayed wastes

and animal residues by microbes.

(1) Fertilizer is an inorganic salt or organic

compound containing essential plant nutrients.

(2) Manures have a very little quantity of

nutrients; therefore they are required in a

very large quantity.

(2) They have a very large quantity of nutrients

in them; therefore they are required in a very

small quantity.

(3) They do not cause water pollution and

are very important

(3) The cause water pollution and decreases the

natural fertility of soil.

(4) Manures are cheap (4) fertilizers are costly

(5) A manure is a natural substance (5) A fertilizer is an inorganic salt

(6) Manure is prepared in fields (6) Fertilizer is prepared in factories

Q.8) Why are weeds harmful? what is used to remove them?

Ans) Weeds are unwanted plants which grow in the agricultural field along with the main crop

plants. They severely reduce crop yields by competing for light, water and nutrients.

There are different methods to control the growth of weeds:

Mechanical methods: Uprooting weeds with khurpi, hand hoeing, ploughing and

interculture can control the growth of weeds.

Cultural method: Proper seed bed preparation, timely sowing of crops and crop rotation can

also control the growth of weeds.

Chemical method: Spraying of some chemicals such as herbicides and weedicides is also

done in case of high infestation.

Biological control: Use of some organisms which consume weeds, can destroy them.

Q.9) What are insecticides? Give examples?

Ans) The special type of chemicals which selectively kill the harmful insects as well as their

eggs and larvae, but do not affect the main crop are called insecticides. e.g. malathion, dimecron,

polythion etc

Science 8th


--Sir Ishfaq/ssnp

Q.10) How do insecticides protect crops?

Ans) Insecticides do not affect the main crop but kill the pests which compete for light, nutrients

and water with the main crop. Insecticides destroy the eggs and larvae of pests.

Q.11) Which are the two main seasons in India for cultivating crops?

Ans) (1) Rabi season (November – April) (2) Kharif season (June – October)

Q.12) Name some harvest festivals of India?

Ans) Following are some harvesting festivals of India:

(1) Pongal (2) Baisakhi (3) Nabanya (4) Bihi

Q.13) Name four factors responsible for improvement of a crop.

Ans) Following are the factors responsible for the improvement of a crop:

a) Plant breeding

b) Soil improvement

c) Protection from pests and weeds

d) Proper storage

Q.14) Write a short note on harvesting.

Ans) Harvesting is the process in which the mature and the ripe crop is cut. The harvested crop

called produce represents crop yield. It is done by using an ordinary sickle in crops like wheat,

paddy and maize.

Q.15) Why does a farmer rotate crops in the fields?

Ans) Farmer rotate crops in the field to maintain the fertility of soil because if the same crop is

grown continuously, soil may be deprived of certain nutrient elements. So in order to maintain

the fertility of soil, two crops are grown alternatively e.g. maize and wheat are grown

alternatively with ground nuts.

Q.16) What do you understand by mixed cropping?

Ans) Mixed cropping can be defined as practice of cultivating two or more crops simultaneously

to economise time and energy. This saves time and labour. It also helps the products and waste

materials of one crop to be utilized by another crop if chosen properly.

Q.17) Why are fields some times allowed to remain fallow?

Ans) Sometimes, the fields may be left as such and crop is not cultivated for one season. During

this period humus of the soil may increase and promote the growth of micro organisms to

replenish the nutrients of soil.

Q.18) List the importance of fish in our life.

Ans) Importance of fish: (1) The oil obtained from fish can be used for various purpose. (2)

Fish wastes can be used as manure for tea, coffee and tobacco plants. (3) Their liver oil is rich

source of vitamin A (4) skin of sharks is used to form handbags, shoes, tobacco pouches etc.

Q.19) What is the nutrient value of honey?

Ans) Honey contains 17% water and 78% sugar with minerals and enzymes which help in the

digestion of food.

Q.20) How are domestic animals useful for us?

Ans) Domestic animals are useful for us in the following ways: (1) Domestic animals are used

for our own work and food. (2) These animals play as significant role in the welfare of mankind.

(3) Hens are used for eggs. (4) Cows and buffaloes are used for milk. (5) Domestic dogs are used

for our home protection.

Additional questions Q.1) What is green revolution? Give its socio economic implications.

Ans) In the mid sixties, a strategy of agricultural development based on irrigation, fertilizers and

seeds were introduced known as “package technology” or the “green revolution”. It refers to the

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adoption of irrigation, chemical fertilizers and high yielding varieties of seeds as basic inputs in

agricultural production.

The stage and pace of development in Indian agriculture has not been the same in all the

regions and among all the farming classes. It has benefited the large and rich farmers much more

than medium and small farmers because these farmers had not the resources to take advantage of

the latest, agricultural technology. States of Punjab, Haryana and western Uttar Pradesh have

witnessed higher levels of agricultural development than the other parts of the country such as

Rajasthan, Gujarat, western Uttar Pradesh, parts of Andhra Pradesh and Karnataka plateau. This

has widened the gap between the rich and poor farmers.

Q.2) Give a short account on agricultural practices in India?

Ans) The word „agriculture‟ has been derived from two Latin words „Ager‟ means field and

„cultura‟ means cultivation. Thus agriculture means field cultivation. It in broader sense includes

raising of crops, animal rearing, forestry, pisciculture and fishing. The following types of

farming are practiced in different parts of the country:

Subsistence agriculture: It is that type of agriculture in which farmers grow the crops for

themselves. As the farmers are poor, they do not use fertilizers and high yielding variety of

seeds and this results into low productivity.

Shifting agriculture: It is a primitive form of agriculture. It is also known as slash farming.

It includes the clearing of forests by cutting or burning the trees and the crops are grown for

two or three years.

Plantation agriculture: It is a type of commercial farming of single cash crop grown on

large estates. It requires a large capital investment, skilled labour and scientific methods.

Intensive agriculture: It is that type of farming in which farmers use fertilizers and

pesticides on large scale. They bring their land under high yielding variety of seeds. It is

capable of raising more than one crop a year.

Q.3) What is the economic importance of saffron for our state?

Ans) Saffron is the cash crop of J & K. It is very important in the economy in the state. It has

great demand outside the market of state. It is sent outside the state or the country and in turn our

state earns a large amount, which adds to our national income.

Besides, it is a big source of income for our people. It gives employment to hundreds of

youth. Efforts are being made to cultivate this crop on large scale to lead the economy of the

state towards the economic growth, development and national prosperity.

Q.4) What is meant by Net Sown Area and Gross Cultivated Area?

Ans) Net Sown Area: The land cultivated in a year. India is top in world in percentage or net

sown area.

Gross Cultivated Area: The Net Sown Area and more than once cultivated land together is

called gross cultivated area.

Q.5) What are geographical conditions required for the cultivation of (a) Rice (b) wheat (c)

sugarcane.

Ans)

Rice: Temperature = more than 250C.

Rainfall: Rice requires 100cm and above of annual rainfall

Soils: Heavy loamy soil and clayey soil is good for rice cultivation. Plains and deltas have such

soil.

Wheat: Temperature : wheat requires cool and moist weather during growth. Ideal temperature

at the time of sowing is 100C to 15

0C and at the time of harvesting 20

0C to 25

0C.

Rainfall: It is usually grown in areas of annual rainfall ranging between 50 – 70cm. Soils: Light

loamy soil is ideal for cultivation. Black and sandy soil is also suitable.

Sugarcane: Temperature: Its cultivation requires temperature of 270C.

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Rainfall: Average rainfall above 100cm is suitable for its cultivation.

Soils: Deep fertile soil and also black soil is suitable for its cultivation.

Q.6) Distinguish between Rabi and Kharif crops

Ans:-

Kharif crop Rabi crop

(1) Kharif crops are those agricultural crops

which are raised from mid June to October.

(1) Rabi crops are those agricultural crops

which are raised from November to April.

(2) Harvesting of such crops is done by the

end of September to early October.

(2) Harvesting of such crops is done by the

end of April – May.

(3) These crops mostly depend on the

monsoon.

(3) These crops mostly depend on subsoil

moisture.

(4) Major Kharif crops are rice, millets,

maize and pulses.

(4) Major Rabi crops are wheat, gram,

oilseeds, barely and mustard.

Q.7) List any three fertilizers rich in potassium.

Ans) (1) Potassium sulphate (2) Potassium chloride (3) Potassium nitrate

Q.8) Briefly explain contribution of Dr. V. Kurien.

Ans) Dr. V. Kurien born on 26th

November, 1921, the founder chairman of National Dairy

development Board, (NDDB), designed and implemented the world‟s largest dairy development

programme. „The operation flood‟, he is also known as „father of white revolution‟.

Q1) Name various sources of food?

Ans: Various sources of food are:- Plants , Animals , Water , etc.

Q2) What are various sources of plant nutrients ?

Ans: Various sources of plant nutrients are:- Soil , micro-organisms, etc.

Q3) Differentiate between farmyard manure and green manure?

Ans:

Farmyard Manure Green Manure

1.It is the most valuable organic matter

commonly applied to the soil.

1.It is the green plants present on the soil

which are turned or ploughed into the soil for

increasing fertility of soil.

2.It usually consists of straw leaves & other

materials like excreta of cattle.

2. Examples include leguminous crops like

cluster beans , sunnhemp , etc.

Q4) What are the advantages of sea manures?

Ans:Advantages of sea manures are:- Sea manures contains complex carbohydrates which

stimulate soil microbes .It assists nutrients uptake of plants .It defends plant against soil borne

diseases.

Q5) What are weeds? How do they affect crops?

Ans: Weeds are unwanted plants that grow besides the main crop.

They compete with the crop plants for nutrients & sun light & thus , grow at the expense of crop

plants.

Q6) Name any two insecticides?

Ans: Malathion & Dimecron.

Q7) Name two harvest festivals?

Ans: Pongal and Baisakhi.

Q8) Name two main crops raised in India .Also mention their time of harvesting?

Ans: Two main crops raised in India are:-

a) Rabi crop and b) Kharif crop

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Rabi crops are raised from November to April & harvested by the end of April – May

while as Kharif crops are raised from mid June to October and harvested by the end of

September to early October.

Q9) Name a machine which is used for harvesting?

Ans: The machine which is used for harvesting are called combines or harvesters.

Q10) Name the cereals grown in India?

Ans: Rice, Wheat , Maize, Barley , Bajra , etc.

Q11) Differentiate between agriculture & horticulture?

Ans:

Agriculture Horticulture

1. The word agriculture is derived from

the latin words ; ager=field & culture =

cultivation.

1.The word horticulture is derived from the

latin words ; Hortus = garden , & culture =

cultivation.

2. Some examples are cereals , fibre

crops , pulses , root crops , etc.

2.Some examples are vegetables , fruits ,

flowers , decorative plants , etc.

Q12) Why is soil ploughed?

Ans: Soil is ploughed for the better penetration & aeration of plants in it.

Q13) Name the methods of sowing?

Ans: There are two methods of sowing:

a) Broadcasting & b) By seed drills.

Q14) Why do farmers raise seedlings in nursery?

Ans: Farmers raise seedlings in nursery under the great care so that they are not damaged & only

after a certain stage they are transferred to the main field.

Q15) What is plant breeding ? And how it is performed?

Ans: It is a technique which involves cross breeding (hybridization) between two varieties of

plants to obtain a new & better adapted variety.

It is done by removing the anthers of one plant by a process called „emasculation‟. Then the

pollen grains of another plant are dusted over to the stigma of this plant to bring about cross-

pollination which results in the production of better & improved variety called stock. This

variety has the desired characters & is resistant to many diseases.

Q16) Name two leguminous crops?

Ans: Mustard and Pulses.

Q17) What is live stock?

Ans: All useful and domesticated animals constitute live stock.

Q18) What is a broody hen?

Ans: An egg laying bird is called broody hen.

Q19)Name any two breeds of :

a) Cows & b) Buffaloes.

Ans: a)Two breeds of cows are Jersy & Desi.

b) Two breeds of buffaloes are Murrah & Nagpuri.

Q20) Name any four fish?

Ans: Catla , Labeo , Hilsa & Rainbow trout.

Q21) Give any two uses of honey?

Ans: a) It helps in the digestion of food.

b) It has many medicinal applications.

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Scholar’s Boarding School Srinagar

Science 8th


--Sir Ishfaq/ssnp

L. No. 7 Combustion and Flame

TERMINOLOGY

1. Fuels: The substance which burn to produce energy in the form of heat and light are

called as fuels e.g. wood, charcoal, coal, kerosene oil, petrol, LPG etc.

2. Combustion: A chemical reaction in which a substance reacts with oxygen to produce

heat and light is called as combustion. e.g.

C + O2 CO2 or CH4 + 2O2 CO2 +H2O Carbon Oxygen carbon dioxide, methane oxygen carbon dioxide water 3. Combustible Substance: The substances which can burn in presence of air are called as

combustible substances e.g. wood, cloth, dry, leaves, paper etc.

4. Non-combustible substances: The substances that do not burn are called as non-

combustible substance. e.g. steel spoon, glass, iron nail, stone piece etc.

5. Ignition temperature: The lowest temperature at which a substance catches fire is called

its Ignition temperature. It is also known as kindling temperature.

6. Global Warming: The rise in average temperature of the atmosphere of the earth is

known as Global warming.

7. Inflammable Substance: The substance which have very low ignition temperature and

can easily catch fire with a flame are called as inflammable substances. e.g. LPG, petrol,

CNG (Compressed Natural Gas), kerosene, paper, straw, alcohol etc.

8. Calorific Value: The amount of heat energy produced on complete combustion of 1 Kg

of a fuel is called its calorific value. It is expressed in kilojoule per kilogram (kj/kg)

9. L.P.G: Liquefied Petroleum Gas.

10. CNG: Compressed Natural Gas.

QUESTIONS

Q.1. What is combustion? Give the various types of combustion?

Ans: Combustion: A chemical process in which a substance reacts with oxygen to produce

energy in the form of heat and light is known as combustion.

Combustion process is of following three types;

i) Spontaneous combustion ii) Rapid combustion iii) Slow combustion

i) Spontaneous combustion: When a Combustible substance burns on its own without

the help of any external heating agent, it is called as Spontaneous combustion e.g. the

burning of white phosphorus in air

ii) Rapid combustion: When a combustible substance burns at a rapid rate, with the

help of external heating agent producing a very large amount of heat and light, it is

called as Rapid combustion e.g. burning of candle, fire cackers, LPG etc.

iii) Slow combustion: When a combustible substance burns at a slow rate producing very

little heat but no light, it is called as slow combustion, e.g. rusting of iron, the process

of respiration, etc.

Q.2. List the conditions under which combustion takes place?

Ans: There are three conditions necessary for combustion to take place. These are;

i) The presence of combustible substance.

ii) The presence of supporter of combustion (oxygen).

iii) Attainment of ignition temperature of the combustible substance.

Science 8th


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These three conditions, necessary for combustion to take place are also called as

triangle of fire, a shown below;

Q.3. Explain how the use of CNG in automobiles has reduced pollution in our cities?

Ans: The use of CNG has reduced the pollution in our cities because of the following reasons;

i) CNG produces very less amount of poisonous gases as compared to other fuels

like petrol and disel.

ii) It is comparatively cleaner fuel as it does not liberate any unburent particle upon

its combustion.

Q.4. Compare LPG and wood as fuels?

LPG Wood

i) LPG has low ignition

temperature.

ii) LPG has high calorific value

(55000kj/kg).

iii) It is easy to store and

transport.

iv) It leaves no residue after it

combustion.

i) Wood has high ignition

temperature.

ii) Wood has low calorific

value (17000 to 22000 kj/kg)

iii) Wood is inconvenient to

store and transport.

iv) It leaves residue in the form

of ash after its combustion.

Q.5. Give reasons;

a) Water is not used to control fires involving electrical equipments.

Ans: This is because water obtained from taps, rivers, springs, ponds contain some dissolved

salts. These dissolve salts make water a good conductor of electricity. So when water is poured

over burning electrical wires, it conducts electric current through it and this cause electric shocks

to the people involved in the fire fighting operations. This electric current or electric shock can

even consume the life.

b) LPG (Liquefied Petroleum Gas) is a better domestic fuel than wood.

Ans: LPG is easily available. It is cheaper and has low ignition temperature. It has calorific value

than wood. It does not leave any residue upon its combustion. Hence is a better fuel than wood.

c) Paper by itself catches fire easily where as a piece of paper wrapped around an

aluminum pipe does not?

Ans: When heat is supplied to a piece of paper it raises the temperature of paper to its ignition

temperature and paper catches the fire but when paper is wrapped around an aluminum pipe and

heat is supplied, this heat is absorbed by the pipe (aluminum, being a metal, is a good conductor

of heat). The heat supplied, thus does not raise the temp. of the paper to its ignition temperature

hence the paper does not burn.

Science 8th


--Sir Ishfaq/ssnp

Q.6 Make a labeled diagram of a candle flame.

Q.7. Name the unit in which calorific value of a fuel is expressed.

Ans: The calorified value of a fuel is expressed in kilojules per kilogram (kj/kg)

Q.8 Explain how CO2 is able to control fire.

Ans. Carbon dioxide is the best fire extinguisher even for fires involving electrical equipments

and inflammable materials like petrol, Kerosene oil etc because of the following properties:

(i) CO2 being heavier than oxygen surrounds the burning combustible material like a

blanket. Thus cuts off the contact between the burning substance and oxygen supply.

(ii) CO2 in the liquid form (in cylinders) is good heat absorber, hence lowers the ignition

temperature of the substance. Thus, fire is extinguished.

Q.9 Which zone of a flame does a goldsmith use for melting gold and silver and why?

Ans. The goldsmith uses the outer most zone of a flame with a metallic blow pipe for melting

gold and silver. This is because the flame in the outer most zone has the highest temperature

(18000C) sufficient to melt the gold and silver.

Q.10 In an experiment 4.5kg of fuel was completely burnt. The heat produced was

measured to be 180,000kj. Calculate the calorific value of the fuel.

Ans. Total amount (quantity) of fuel = 4.5kg total amount of heat produced = 180,000kj

Calorific value = ?

We know that

Calorific value = Total amount of heat

Total amount of fuel

= 180000 kj

4.5 kg

= 40000 kj/kg

Therefore, the calorific value of the fuel is 40,000 kj/kg.

Q.11 Can the process of rusting be called combustion? Discuss/

Ans. Yes, the rusting can be called as combustion. This is because like other combustion

processes, rusting also takes place in presence of oxygen and is an exothermic process. During

this process, the heat is released at a very slow rate, thus, is an example of slow combustion.

Q.12 Aabida and Ramesh were doing and experiment in which water was to be heated in

a beaker. Aadida kept the beaker near the wick in the yellow part of the flame while

Ramesh put just above the flame. Whose water will get heated in a shorter time?

Ans. The water in Ramesh‟s beaker will heat up in a shorter time. This is because the

outermost zone of the candle flame is the hottest zone, while the yellow zone, in which Aabida

had kept the beaker, is less hot.

Science 8th


--Sir Ishfaq/ssnp

Other Important questions.

Q.13 What are the characteristics of an ideal fuel?

Ans. Following are the characteristics of an ideal fuel:

(i) It should be cheap and easily available.

(ii) It should be easy to handle, safe to transport and convenient to store.

(iii) It should have high calorific value.

(iv) It should have proper ignition temperature.

(v) It should not leave any residue after burning and should not give out poisonous gases.

Q.14. Give classification of fuels with proper examples?

Ans: Fuels are classified on the basis of physical states in which they occur. These are solid fuels

liquid fuels and gaseous fuels.

i) Solid fuels: Coal, coke, charcoal, wood, paraffin wax, cow dung cakes, etc.

ii) Gaseous fuels: LPG, biogas, compressed natural gas (CNG), etc.

iii) Liquid fuels: Kerosene, petrol, diesel, etc.

Q.15. Write a short note on the zones of a candle flame?

Ans: A typical candle flame consists of three zones depending upon the amount of air it

receives. These zones have different colours and temperatures. These are;

1. The Innermost Zone: This zone lacks oxygen (of air) and hence, no combustion takes

place in this zone. It contains un-burnt wax vapour. It is dark and cooler than the other

two zones.

2. The Middle Zone: This is largest zone of flame. In this zone, there is not enough

oxygen, fuel burns partially and produces carbon particles and carbon monoxide. It is the

luminous (light-giving) zone and is moderately hot.

3. The Outer Zone: This zone is thin and blue in colour. In this zone, there is a plenty of air

around it and complete combustion of fuel takes place producing carbon dioxide and

water vapours. It is the hottest zone of the candle flame (maximum temperature is

1800ºC)

Q.16. Write a short note on flame?

Ans: A flame is region where combustion of a fuel, in its gaseous form, takes place. All the

fuels which vapourise on heating burn with a flame e.g. all the combustible gases like LPG and

solid fuels (like wax and camphor), liquid fuels (like kerosene oil, petrol, mustared oil) which

vapourise on heating burn with a flame.

Q.17. What is meant by fire-fighting?

Ans: Fire-fighting means to control and extinguish the unwanted fire. The fire fighting

operations work mainly on two principles.

a) Bringing down the temperature of the burning substances below their ignition

temperature.

b) Cutting off the air (oxygen) supply to the burning substances.

Q.18. What are the various types of fire extinguishers used?

Ans: Various types of fire extinguishers are used for different types of fires. Some of them are:

1. Water as a fire extinguisher: Water cools the combustible substance below its ignition

temperature and prevents the fire from spreading. Also, the water vapours formed

surround the combustible materials and help in cutting off the supply of air. So, the fire is

extinguished. But water should not be used to extinguish the fires caused by electric short

circuits or by burning of petrol or kerosene oil

2. Carbon dioxides as fire extinguisher: Carbon dioxide being heavier than oxygen,

surrounds the burning combustible substance, cuts off the contact between the burning

substance and oxygen supply and the fire is extinguished. It is the best fire extinguisher

Science 8th


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for fires caused by electrical equipments and inflammable materials like kerosene or

petrol.

3. Dry powder fir extinguisher: The essential constituent of this fire extinguisher is baking

soda, i.e… sodium bicarbonate (NaHCO3). When it is thrown over a burning material, it

decomposes (break down) by the action of hear and carbon dioxide is produced.

2NaHCO3 Heat Na2CO3 + H2O + CO2

Baking Soda washing soda Water Carbon dioxide

(Sodium Carbonate)

4. Foam – type fire extinguisher: It consists of a metallic cylinder which contains a

solution of sodium bicarbonate (NaHCO3). A glass bottle is kept inside the cylinder

which contains sulphuric acid (H2SO4). When the knob of the cylinder is struck against a

hard surface, the acid bottle breaks and H2SO4 comes in contact with NaHCO3 and the

reaction produces a foam of carbon dioxide, which extinguishers the fire.

NaHCO3 + H2SO4 NaHSO4 + H2O + CO2

Sodium bicarbonate Sulphuric acid carbon dioxide

(Foaming)

Q.19 How burning of fuels is hazardous activity?

Ans. Burning of fuels liberates various gases which imbalance the nature in one way or the

other, e.g.

(i) Carbon monoxide: The incomplete combustion of fuels give carbon monoxide gas. It

is a poisonous gas. It interferes the normal functioning of hemoglobin which leads to

suffocation and even death.

(ii) Carbon dioxide: CO2 is the main product of combustion. It is not a poisonous gas.

However, it is responsible for global warming which in turn affects badly the rains,

changes the seasonal pattern, causes excess melting of polar ice and hence a threat of

flooding, etc.

(iii) Sulpur dioxide: Burning of coal and diesel releases SO2 gas. When SO2 dissolves in

rain water, it forms sulphuric acid (H2SO4). This polluted rain containing H2SO4 is

called acid rain and is harmful for crops, soil and monuments such as Taj Mahal.

Ya Allah Increase Me In Knowledge

And Shower On We All The Happiness And Success In This World & Hereafter - - - Aaameen

Scholar’s School Srinagar

Science 8th


--Sir Ishfaq/ssnp

L.No.8 Chemical effects of electric current

Terminology (1) Electrodes: Electrodes are the metal rods or plates through which current enters or leaves

the electrolytes.

(2) Conductors: Materials which allow the electric current to pass through them are called as

conductors, e.g. aluminium, copper, silver, graphite rod etc.

(3) Insulators: Materials which do not allow the electric current to pass through them are

called as insulators, e.g. rubber, wood, plastic etc.

(4) LED: LED stands for “light emitting diode”. It is a bulb like electrical instrument used

for lighting purpose. It runs on very low voltage.

(5) Electric tester: An electric tester consists of a cell, a bulb fitted in a holder and some

connecting copper wires. It is used to check whether a given substance is a good or bad

conductor of electricity. In modified electric testers LED is used instead of ordinary bulb.

Q.1) Fill in the blanks:- (i) Most liquids that conduct electricity are solutions of acids, bases and salts.

(ii) The passage of an electric current through a solution causes chemical effects.

(iii) If you pass current through copper sulphate solution, copper gets deposited on the plate

connected to the negative terminal of the battery.

(iv) The process of depositing a layer of any desired metal on another material by means of

electricity is called electroplating.

Q.2) When the free ends of a tester are dipped into a solution, the magnetic needle shows

deflection. Can you explain the reason?

Ans) This is because the solution conducts electricity. The flow of electric current gives rise to

induced magnetic field which interacts with magnetic needle. Thus deflection is observed.

Q.3) Name the liquids, which when tested in the manner shown in fig. 8.9 (text Book P. No.

99) may cause the magnetic needle to deflect.

Ans.) Liquids like lemon juice, salt water and vinegar allow electricity to pass through them.

Hence, these liquids can be used as in the beaker to show the given effect.

Q.4) The bulb does not glow in the set-up shown in fig. 8.10 (Text book P. 100). List the

possible reasons. Explain your answer.

Ans.) The possible reasons may be:

(i) Liquid in the beaker is non-conducting. In such case, the electric current would

not be able to pass through the liquid. Hence, the circuit is not complete.

(ii) Electric current in the circuit is very weak. This can happen if the material used

for making the circuit is not a good conductor of electricity or the battery does not

have the sufficient energy to generate electricity. Sometimes it is also possible

that the bulb may be fused or the connections may be loose. So, the circuit will

not be properly working and bulb does not glow.

Q.5) A tester is used to check the conduction of electricity through two liquids, labeled A and

B. It is found that the bulb of the tester glows brightly for liquid A while it glows very dimly for

liquid B. You would conclude that

(i) liquid A is a better conductor than liquid B.

(ii) liquid B is a better conductor than liquid A.

(iii) Both liquids are equally conducting.

(iv) conducting properties of liquid cannot be compared in this manner.

Ans:- liquid A is a better conductor than liquid B.

Science 8th


--Sir Ishfaq/ssnp

Q.6) Does pure water conduct electricity? If not what can you do to make it conducting?

Ans.) Pure water does not conduct electricity. It can be made conducting, if acid, base or salt is

dissolved in it.

Q.7) In case of any fire, before the firemen use the water hoses, they shut off the main

electrical supply for the areas. Explain why they do so?

Ans.) The water used to extinguish fire is obtained from rivers, lakes, ponds, etc. This water

contains a lot of minerals and dissolved salts. These dissolved salts make water

conducting. Thus, before the fireman use water hoses, they shut off the main electrical

supply. This prevents the fire men from electric shock.

Q.8) A child staying in the coastal region tests the drinking water and also the sea-water with

his tester. He finds that the compass needle deflect more in case of sea-water. Give the

possible reason.

Ans.) It is observed that the water which contains salts dissolved in it, is a good conductor of

electricity. Since, the sea water contains more salts dissolved in it than drinking water

found in the coastal region, therefore, seawater conducts more electricity than drinking

water. That is why compass needle deflects more in case of sea water.

Q.9) Is it safe for electrician to carry out electrical repairs outdoors during heavy down

pours (raining)? Explain:

Ans.) When it rains heavily, the rain water dissolves many gases like CO2, SO2 from the

atmosphere. This makes rain water impure (acidic) and conductive to electricity. The air

becomes humid with this water. Therefore this humid air also becomes very conductive

to electricity. Due to this reason electricians may get electric shocks. Thus it is not wise

for electricians to do electric repairs when it is raining heavily.

Q.10) Paheli had heard that rainwater is as good as distilled water. So, she collected some

rainwater in a clean glass tumbler and tested it using a tester. To her surprise, needle

showed deflection. What could be the reasons? Ans.) Rain water is as good as distilled water. But when it passes through atmosphere, it

dissolves a lot a gases such as CO2, SO2 to form acid rain. Due to this acidic nature of

rain water, it conducts electricity. Thus, the magnetic needle shows deflection.

Q.11) Prepare a list of objects around you that are electroplated?

Ans.) Some examples of electroplated objects around us are as follows:-

(i) Chromium plating is done on different parts of cars, buses and motor cycles to give them

shiny appearance.

(ii) A fine layer of gold is deposited on the ornaments made of less expensive metals like

silver, and are called gold-plated ornaments.

(iii) Iron objects used for various purposes like constructing buildings are electroplated with

chromium or nickel or zinc to protect them from rusting.

Q.12) The process that you saw in activity 8.7 is used for purification of copper. A thin plate of

pure copper and a thick rod of impure rod are used as electrodes. Copper from impure rod is

sought to be transferred to thin copper plate. Which electrode should be attached to the positive

terminal of the battery and why?

Ans.) Copper ion is positively charged. It is attracted towards the plate which is connected to the

negative terminal of the battery. As copper ions are transferred to the thin copper plate, this thin

pure copper plate must be connected to the negative terminal of the battery. Consequently, impure

copper rod is connected to the positive terminal of the battery.

Science 8th


--Sir Ishfaq/ssnp

Some Important Questions Q.1) Write notes on:

(i) Electrolyte (ii) Non- Electrolyte (iii) Electrolysis.

(i) Electrolyte: Chemical compounds whose molecules ionize into positively and

negatively charged ions in a solution are called electrolytes. Thus, electrolytes are

chemical compounds which conduct electricity when dissolved in water. e.g. Aqueous

solution of soluble salts such as common salt, copper sulphate. Lemon juice, Tap water,

vinegar, also act as electrolytes.

(ii) Non – Electrolyte: Non – electrolyte are chemical compounds which do not conduct

electricity when dissolved in water. e.g aqueous solution of glucose.

(iii) Electrolysis: The process of decomposition (break down) of electrolyte by passing an

electric current through it, is called electrolysis.

Q.2) Write a note on electroplating.

Ans.) The method of coating the metal‟s surface of a given article with a layer of superior metal

with the help of electric current is called electroplating.

Electroplating is done for various purposes e.g.

(i) Decoration: Metals used for making jewellery like gold and silver are used to

electroplate less expensive metals to make them look expensive.

(ii) Protection: More reactive metals are electroplated with less reactive metals to prevent

them from corrosion. e.g Iron articles are electroplated with chromium or zinc

Q.3) Define the following terms:

(a) Cathode (b) Anode (c) Voltameter (d) Ions (e) Cations (f)

Anions

(a) Cathode: The electrode connected to the negative terminal of cell/battery is called as

cathode.

(b) Anode: The electrode connected to the positive terminal of a cell/battery is called as

anode.

(c) Volta meter: A glass or plastic container in which the process of electrolysis is done is

known as voltammeter or electrolytic cell.

(d) Ions: Electrically charged atoms or group of atoms are called ions. Ions are formed

when atoms loose or gain electrons.

(e) Cations: The positively charged ions are called as cations. Cations are formed when

neutral atoms loose electrons e.g Na+, K

+, Ca

2+ , etc.

(d) Anions: The negatively charged ions are called as anions. Anions are formed when

neutral atoms gain electrons e.g., Cl-, O

2- , F

-, etc.

************************************************ **********************************************************************

The Joy of Learning------- At the Right School

Priceless

Scholar’s School Srinagar

Science 8th


--Sir Ishfaq/ssnp

Lesson No. 9

Force and Pressure Terminology

Force: Force is any influence that causes an object to undergo a certain change, either

concerning its movement, direction or geometrical construction. It is denoted by letter „F‟ and its

S.I unit is Newton (N).

Non contact force: It is the force which exists between the two objects/bodies without any

physical contact between them, e.g. magnetic force, gravitational force, etc

Contact force: It is the force which exists between the two objects/bodies when there is definite

physical contact between them, e.g. muscular force, frictional force, etc.

Magnetic force: It is a non contact force which exists between the magnets or between the

magnet and magnetic materials such as iron, etc.

Gravitational force: It is a non contact force which arises between the objects as a result of their

masses. This force can be usually seen between the bodies/objects of large size e.g. between

earth and moon.

Electrostatic force: It is also a non contact force which exists between charged bodies. The

nature of this force can be either attractive or repulsive.

Muscular force: It is a contact force which arises as a result of action of muscles.

Frictional force: It is an opposing force that comes into play when one body tries to move over

the surface of the other body. It is also an example of contact force.

Gravity: It is the force of attraction which is exerted by the earth on all the objects towards itself,

e.g. if a stone is allowed to fall from a height, it moves downwards towards ground because of

gravity.

Pressure: It is the force acting per unit area of an object. It is denoted by „P‟.

Its S.I unit is Pascal (Pa) or N/m2

Pressure = Force

Area

or P = F/A

Atmospheric pressure: It is the force per unit area exerted by the weight of air on the earth‟s

surface.

Lateral pressure: The pressure exerted by the liquids on the walls of container is called lateral

pressure.


Q.1 What is force? Give various effects of force?

Ans. Force is a push or pull acting on a body. The various effects of force are summarized as

follows:

(i) A force can cause motion in a stationary body. e.g. A foot ball lying on the ground

when kicked begins to move.

(ii) A force can stop a moving body e.g. The goalkeeper applies force to stop the ball

from entering the posts.

(iii) A force can change the direction of motion e.g. while riding a bicycle we can change

the direction of moving bicycle by applying the force on its handle.

(iv) A force can change the speed of a moving body e.g. By applying the force on the

accelerator or brake we can increase or decrease the speed of a moving car.

Science 8th


--Sir Ishfaq/ssnp

(v) A force can change the shape and size of a body e.g. we can increase and decrease the

size of spring by compression or stretching it. Similarly we can change the shape of

kneaded flour into desired breads.

Q.2 State units of force.

Ans. The S. I unit of force is Newton. It is denoted by letter “N”

Q.3 What is resultant force? Give example.

Ans. The total force or summation of all forces applied on a body is known as resultant force

e.g. if Sabha applies a force of 40N on a body and Faizan applies a force of 50N in the same

direction. The resultant force is given as:

Resultant force = Force applied by Sabha

+ Force applied by Faizan

= 40 + 50

= 90N

If the forces acting on a body are in same direction, the resultant force is found by adding the

forces.

If the forces acting on a body are in opposite directions the resultants force is found by

subtracting the forces.

Numerical 1: In a bullock- cart, each bullock pulls with a force of 1500N in the same direction.

Find the resultant force. Give reasons.

Solution: In the bullock-cart, bullocks pull in the same direction.

Therefore, the resultant force will be the sum of both the forces (addition of forces).

Resultant force = 1500N + 1500N

= 3000 N

(addition of forces)

Numerical 2: Two boys pull a rope with a force of 250N in opposite direction. What will be the

resultant force? Give reason:

Solution: Since the boys pull the rope in opposite direction. So, the resultant force acting on the

rope is the difference between the two forces.

Resultant force= 250 N – 250 N = 0N

Q.4 Name and discuss the different types of forces.

Ans. Following are the two main types of forces.

(i) Contact forces.

(ii) Non-Contact forces

(i) Contact forces: Contact forces are those forces which act only when objects are in

physical contact with each other and bring about changes

Contact forces are further classified into following types:

(i) Muscular force

(ii) Mechanical force

(iii) Frictional forces

(i) Muscular force: This force is caused by the action of muscles. The force resulting

due to the action of muscles is known as muscular force e.g. We use our muscular

force during walking, running, pushing and lifting certain objects.

(ii) Mechanical force: The force exerted by a machine to do some work is called

mechanical force.

However, the machine does not produce force of its own. So, in order to produce force

we must supply it with some kind of energy e.g. ceiling fan uses electrical energy to

produce mechanical force.

Science 8th


--Sir Ishfaq/ssnp

(iii) Frictional force: The force acting along the two surfaces in contact which opposes

the motion of one body over the other is called the force of friction.

Non – Contact Forces: Non- contact forces are the forces which act when the objects are not in

physical contact with each other and bring about changes.

Non-contact forces are further classified as follows:

(i) Magnetic force

(ii) Electrostatic force

(iii) Gravitational force.

(i) Magnetic force: The force exerted by a magnet over magnetic materials is called as

magnetic force.

(ii) Electrostatic force: The force exerted by a charged body on another charged or

uncharged body is known as electrostatic force. e.g. a charged body (comb) can attract

small pieces of paper.

(iii) Gravitational force: The force with which two objects attract each other is called a force

of gravitation.

Gravity: The force exerted due to the attraction between the earth and an object is called

the force of gravity or just gravity.

Pressure: Pressure is the force acting on a unit area. If P is the Pressure, F is the force and A is

the area of contact then,

Pressure = Force

Area

P = F

A

The standard unit of measuring force is Newton (N) and the standard unit of measuring area is

square

meter (m)2 . Therefore, the standard unit of measuring pressure is Newton per square meter

(N/m2) which is also called as Pascal.

Applications of Pressure: (i) A heavy truck is fitted with six to eight wheels. These wheels increase the area of

contact on which their weight acts hence reduce their pressure on ground.

(ii) Skiers use long flat skies to slide over snow, the longer the area of contact, the lesser

is the pressure on the snow enabling the skier to slide over the snow with out sinking

in the snow.

(iii) The cutting edges of knives, blades, axes; etc are sharpened. As the cutting edge is

sharpened, the area of contact decreases and hence pressure exerted by them

increases. Thus this large pressure cuts the objects easily.

(iv) Foundations of high rise buildings are kept wide so that the pressure due to overlying

weight will decrease.

(v) The tip of a sewing needle is sharp and pointed. This may put the force on a very

small area of the cloth, producing a large pressure sufficient to pierce the cloth being

stitched.

(vi) A wide steel belt is provided over the wheels of army tanks, so that they exert less

pressure on the ground.

Pressure due to liquids: All liquids have weight. So a liquid contained in a vessel exerts

pressure on its walls and bottom. However magnitude of pressure due to liquid varies with

respect to depth which is greater at bottom and lesser at top. Besides pressure exerted by the

liquids on the walls of a container is known as lateral pressure.

Science 8th


--Sir Ishfaq/ssnp

Applications of liquid pressure: 1. The wall of a dam is made thicker at bottom. This is because water pressure increases

with depth, so a thicker wall can withstand a greater pressure exerted by the water at

greater depth.

2. Water supply tank is placed at high place in the building. This is because when the

tanks are placed at a greater height. The pressure of water will be large enough to

force the water to reach the taps of the houses.

Atmospheric pressure:- Atmospheric pressure is the weight of a column of atmosphere upon

one unit area on the earth‟s surface. At sea level, the atmosphere exerts a pressure of 1kg per

1cm2 of land surface.

Applications of Atmospheric Pressure:

Atmospheric pressure is applicable in following situations.

1. Using a drinking straw to suck up fruit juice.

2. Suction of liquid using syringe.

3. Rubber suction pads are used on the walls to hang clothes and calendars.

Barometer: Atmospheric pressure is measured by an instrument called barometer.

Text book questions

Q.1 Give two examples each of situations in which you push or pull to change the state of

motion of objects.

Ans. A small cart moving on road when pulled comes into rest.

A ball rolling on ground is in state of motion. If an obstacle is kept in its way it stops and comes

into rest.

Q.2 Give two examples of situations in which applied force causes change in the shape of

an object.

Ans. The kneaded (wet flour) can be set into different kinds of shapes.

Similarly, an inflated balloon is pressed with two hands, its shape changes from spherical to

oblong.

Q.3 A blacksmith hammers a hot piece of iron which making a tool. How does the force

due to hammering affect the piece of iron?

Ans. The hammer acts as an agent of force which helps it to change the shape of hot iron piece

in to a desired iron tool.

Q.4 An inflated balloon was pressed against a wall after it has been rubbed with a piece of

synthetic cloth. It was found that the balloon sticks to the wall. What force might be

responsible for the attraction between the balloon and the wall?

Ans. This attraction is due to electrostatic force.

Q.5 Name the forces acting on a plastic bucket containing water held above ground level in

your hand. Discuss why the forces acting on the bucket do not bring a change in its state of

motion

Ans. The forces that act on a bucket are muscular force and force of gravity due to earth

Since the force of gravity is overcome by the person carrying bucket in his hands, therefore no

motion is observed.

Q.6 A rocket has been fired upwards to launch a satellite in its orbit. Name the two forces

acting on the rocket immediately after leaving the launching pad.

Ans. The two forces that act on rocket immediately after leaving the pad are:

(i) The force of gravity acting down wards.

(ii) The frictional force forwarded by air particles.

Science 8th


--Sir Ishfaq/ssnp

Lesson No. 10

Reaching the Age of Adolescence Terminology

Adolescence:- The period of life , when the body undergoes some physical & biological changes

leading to reproductive maturity, is called adolescence.

Puberty:- It is the age during adolescence when boys & girls become capable of reproduction.

Adam‟s apple:- It is the protruding voice box usually seen in boys at puberty.

Sebaceous glands:- These are the oil glands present on the skin due to which many young

people get acne & pimples on their faces.

Secondary sexual characters:- These are certain external features developed at puberty which

help to distinguish the males from females e.g. development of breasts in females & appearance

of facial hair i.e. moustaches & beard in males.

Harmones:- These are the chemical substances released by the glands that bring about certain

changes in the body.

Endocrine glands:- These are the glands which pour their secretions/harmones directly into the

blood stream .They have no ducts, hence called as ductless glands. e.g. pituitary gland , thyroid

gland, adrenal gland , testes , ovaries , etc.

Testosterone:- It is the male sex hormone which is produced by the testes at puberty.

Estrogen:- It is the female sex hormone which is produced by the ovaries at puberty.

Pituitary gland:- It is an endocrine gland which is situated in head region & influence the

activity of other endocrine glands.

Menstruation:- It is the bleeding from female reproductive tract due to degeneration of uterus

wall when fertilization of egg does not take place .It occurs once in about 28 to 30 days.

Menarche:- The first menstrual flow which begins at puberty is known as menarche.

Menopause:- Stoppage of menstruation is termed as menopause .It usually stops at the age of 45

to 50 years.

Chromosomes:- These are the thread like structures , present inside the nucleus & are

responsible for the determination of sex of an individual & other characters due to presence of

genes on them.

Thyroxine:- It is as a hormone which is secreted by the thyroid gland & is essential for the

normal growth & development of an organism.

Goitre:- It is an outgrowth of thyroid gland which is produced due to deficiency of Iodine in the

body.

Insulin:- It is a hormone which is secreted by the pancreas & is responsible for the control of

blood sugar level.

Diabetes:- It is a metabolic disorder which results due to increased sugar level in the blood

because of less or no production of insulin in the body.

Adrenalin:- It is an emergency hormone which is released by the adrenal gland at the time of

emergency.

Metamorphosis:- The transformation of the larva into an adult through drastic changes is called

metamorphosis.

Textual Questions Q1) What is the term used for secretions of endocrine glands responsible for changes

taking place in the body?

Ans: Hormones. Q2) Define adolescence?

Ans: Adolescence is the period of life, when the body undergoes some physical & biological

changes leading to reproductive maturity.

Science 8th


--Sir Ishfaq/ssnp

Q3) What is Menstruation? Explain.

Ans: Menstruation is a discharging of blood, secretions & tissue debris from the uterus that

occurs in non-pregnant females every month.

In females, the reproductive phase of life begins at puberty (10 to 12 years of age) & generally

lasts till the age of approximately 45 to 50 years. The ova begin to mature with the onset of

puberty. One ovum matures & is released by one of the ovaries once in about 28 to 30 days.

During this period, the wall of the uterus becomes thick so as to receive the egg, in case it is

fertilised & begins to develop. This results in pregnancy. If fertilization does not occur, the

released egg, and the thickened lining of the uterus along with blood vessels are shed off. This

causes bleeding in women which is called menstruation.

Q4) List changes in the body that take place at puberty?

Ans:- Various changes occurring at puberty are:-

a) Change in body shape:- Males/Boys develop broader shoulder , muscles & wider chest

while as in girls the region below the waist becomes wider.

b) Voice change: The voice of boys become deeper due to better development of voice box

that can be easily seen as a protruding part, called adams apple as compared to girls due

to which they produce a sound of lower pitch than girls.

c) Increased activity of sweat & sebaceous glands:- These glands secrete sweat & oil

respectively which results in a very common problem of acne & pimples.

d) Development of sex organs:- With puberty development of testes & penis takes place in

males & enlargement of ovaries occurs in females .Both testes & ovaries are capable of

producing sperms & eggs respectively.

e) Maturity: Reaching mental , intellectual & emotional maturity.

f) Increase in the height of an individual.

Q5) Prepare a table having two columns depicting names of endocrine glands & harmones

secreted by them.

Endocrine glands Hormones Secreted

1. Thyroid gland 1. Thyroxine , Calcitonin, T3 (Tri-iodothyroxine)

2. Adrenal gland 2. Cortisol , aldosterone, adrenaline, nor adrenaline

3. Pancreas 3. Glucogan, insulin, somatostatin, Pancreatic Polypeptide.

Q6) What are sex hormones? why are they named so? State their function.

Ans: Sex hormones are the hormones which affect the sexual development & maturation of an

organism / individual.

They are named so because they are produced by the sex organs like testes & ovaries .Testes

produce testosterone while as ovaries produce estrogen.

Functions:

Testosterone:

a) It helps in development of facial hair, hair on body, pubic hair, etc.

b) It helps in enlargement of penis & Scrotum

c) It helps in development of shoulder bones & muscles.

Estrogen:

a) It helps in development of breasts & milk secreting glands or mammary glands.

b) It helps in development of bones in the pubic region.

Q8) Write notes on:

a) Adam‟s apple: At puberty, the voice box or the larynx begins to grow .Boys develop

larger voice boxes than girls which can be easily seen as a protruding part of the throat

called Adam‟s apple.

b) Secondary sexual characters:- These are the characters which are developed as a result

of sex hormones , testosterone in boys & estrogen in girls & helps us to distinguish

Science 8th


--Sir Ishfaq/ssnp

X X

XY

XY

X

XX

XY

X

between boys & girls e.g. appearance of facial hair i.e. moustaches & beard in boys &

development of breasts in girls.

c) Sex determination in the unborn baby:- All human beings have 23 pairs of

chromosomes in the nuclei of their cells. Two chromosomes out of these are the sex

chromosomes, named X & Y. A female has two X chromosomes, while a male has one X

& one Y chromosome. The unfertilized egg always has one X chromosome. But sperms

are of two kinds. One kind has an X chromosome, and the other kind has Y

chromosome.

When the sperm containing X chromosome fertilizes the egg, the zygote will be having

two X chromosomes & develop into a female child. If the sperm contributes a Y

chromosome to the egg (ovum) at fertilization, the zygote would develop into a male

child in this way the sex of an unborn baby can be determined.

Sperm Sperm

Y

X

Egg Egg

Zygote Zygote

Male Baby Female Baby

Q9)Show by the block diagram the role of hormones in initiating reproduction function ? Ans:

Q10) What is balanced diet?

Ans: Diet which contains all the essential nutrients such as Carbohydrates, proteins, fats &

vitamins in requisite proportions.

Hormones from pituitary stimulate testes & ovaries to release testosterone (in males) &

estrogen (in females)

Released in the blood stream & reach parts of the body i.e. target site.

They stimulate changes in the body at the onset of puberty.

Science 8th


--Sir Ishfaq/ssnp

Lesson No. 11

Materials-Metals and Non-Metals Terminology

1.Metals :- Elements which are hard ,lustrous ,malleable ,ductile ,sonorous and good conductors of

electricity are known as metals e.g. iron ,Aluminum ,Gold ,Copper, Silver etc.

2.Non-Metals :-Elements which are dull in appearance ,break down into powdery substance, non sonorous

and poor conductors of heat and electricity are known as non-metals .e.g. sulphur ,oxygen,

phosphorous etc

3 Metalloids :-Elements which possess properties of both metals and non-metals are called metalloids .e.g

Bi, Ge, As.

4. Malleability:-The property by virtue of which metals can be drawn into thin sheets or foils is called

malleability such as Copper and Aluminium Sheets.

5.Ductility:-The property by virtue of which metals can be drawn into thin wires is known as ductility e.g

Copper and Iron.

6.Lusture:-The property of metals by virtue of which they possess shiny appearance is known as lusture.

7.Sonority:-The property of producing a sound by metals when struck with a hard material is called

sonority.

Text Book Questions Q. Can you store lemon pickle in an aluminium utensil? Explain.

Ans. Pickles are sour in taste due to the presence of acids. Metals react with acids to produce their

respective salts with the liberation of H2 gas. Aluminum is also a metal. That is why acidic

materials like lemon pickle should not be stored in „Aluminium‟ utensils.

Q. Give reasons for the following:

Ans. a) Aluminum foils are used to wrap food items. It is one of the least reactive metals, so it does

not react with food items and does not alter the taste. Moreover, being a metal, Al is highly

malleable and can be made into very thin foils, which are convenient for wrapping food items.

(b) Immersion rods for heating liquids are made up of metallic substances?

Ans. Metals are good conductors of electricity. Due to this property of metals, they are used for

making immersion rods.

(c) Copper can not displace zinc from its salt solution.

Ans. It is because copper is less reactive than zinc.

(d) Sodium and potassium are stored in kerosene.

Ans. Sodium and potassium are very reactive metals. They react vigorously with oxygen even at room

temp. To keep them away from the atmospheric attack, they are stored in kerosene.

Q. What happens when:

(a) Dilute sulphuric acid is poured on a copper plate.

Ans. When sulphuric acid is poured on copper plate,no reaction will take place as hydrogen is more

reactive than copper.

(b) Iron nail are placed in copper sulphate solution. write word equation of the reaction taking

place.

Ans. When Iron nails are placed in copper sulphate solution, displacement reaction occurs. In this

reaction copper is displaced by iron nails and form iron sulphate.

Iron nails + copper sulphate soln Iron sulphate + copper

Fe + CuSO4 FeSO4 + Cu

Q. Saloni took a piece of burning charcoal and collected the gas in a test tube.

(a) How will we find the nature of gas.

(b) Write down word equations of all the reactions taking place in this process.

Ans. Charcoal is rich form of carbon. Therefore when charcoal is burnt in air carbon dioxide is

formed. This gas when dissolved in water forms carbonic acid. This CO2 solution turns, blue litmus into

red. Hence is acidic is nature.

(b) Carbon + Oxygen Carbon dioxide gas

Science 8th


--Sir Ishfaq/ssnp

C + O2 heat CO2

( CO2 + H2O H2CO3) Carbonic acid , H2CO3 H+

+ HCO3-

Q Why Phosphorus is stored in water?

Ans. Phosphorus is stored in water, so as to prevent it from reacting with oxygen to prevent

combustion.

Q. One day Ritta went to a Jewelers shop with her mother. Her mother gave old gold jewelery

for polishing. Next day when they brought the jewelery back, they found that there was slight loss

in weight. Can you suggest a reason for losing weight?

Ans. There was a slight decrease in the weight of gold jewellery because of polishing. The goldsmith

uses acid in polishing the gold & some part of the gold reacts with the acid as a result of which some

weight is lost due to its reaction with acid.

Additional Questions QNo1:- Give general physical properties of metals?

The general physical properties of metals are stated as follows:-

1. Metals in the pure state possess lustre i.e. shining surface.

2. Metals are generally hard. The hardness varies from metal to metal e.g. Iron, Copper, Aluminium,

Lead are hard metals. They can‟t be cut with a knife. However, Lithium, Sodium and Potassium

are soft metals. They can be cut even with a knife.

3. Metals are malleable i.e. they can be beaten into thin sheets .e.g. Iron, Copper, Aluminium etc.

4. Metals are ductile in nature i.e. they can be drawn into wires. e.g. 1gram of gold can be drawn

into a wire of about 2km length.

5. Metals are good conductors of heat and possess high melting point. Silver is the best conductor of

heat and copper is the second best followed by aluminium. Whereas, lead is the poorest conductor

of heat.

6. Metals are good conductors of electricity. Silver is the best conductor of electricity where as

mercury is very poor conductor of electricity.

7. Metals are sonorous i.e. they produce ringing sound on striking with hard surfaces.

8. Metals generally have high density. Exception is Lithium, Sodium, and Potassium which have

low densities.

9. Metals have high tensile strength i.e. they possess load bearing capacity

QNo2:- General physical properties of non-metals?

Some of the general physical properties of non-metals are as follow:

(1) Non-metals do not possess any lustre except iodine which is non-metallic solid but has lustre.

(2) They are soft and brittle i.e. they break into pieces when hammered. The only exception is

diamond, an allotropic form of carbon which is a non-metal but is the hardest substance known. (3) They are neither malleable nor ductile. (4) They are generally bad conductors of heat and electricity, except graphite which is an allotropic

form of carbon and is a good conductor of electricity. (5) They are non-sonorous i.e. they do not produce any sound when hit with any hard object. (6) They have generally low melting and boiling point except boron, diamond and graphite which are

non-metals but have high melting point. (7) They have low densities i.e. they are light elements. (8) They have low tensile strength i.e. they are easily broken. (9) They may be solids, liquids or gases at room temperature. e.g. Carbon, Sulphur, phosphorus are

solids and iodine is a liquid, while as hydrogen, oxygen, nitrogen and chlorine are gaseous non-

metals.

QNo3:- Differentiate between the physical properties of metals and non-metals?

Ans. The main features that distinguish metals from non-metals are given below:

Metals Non –metals

1. Metals are generally solid in nature at room

temp. (except Hg which is a liquid)

1. Non- metals exist in all the three states i.e.

solid, liquid and gaseous state.

2.Metals possess bright lustre. 2. Non-metals have dull appearance.

Science 8th


--Sir Ishfaq/ssnp

3. Metals have high density (except Na and K

which are lighter than H2O)

3. Non –metals have low densities (except

diamond which has a high density.)

4. Metals are usually malleable (except zinc and

Hg)

4. Non-metals are non-malleable.

5. Metals are usually ductile (except Zn and Hg) 5. Non-metals are not ductile.

6. Metals are hard and have high tensile

strength

6. Non-metals are soft in nature (except

diamond which is hardest substance known)

7. Metals are hard but not brittle 7. Non-metals are brittle in nature

8. Metals are good conductors of heat and

electricity except Bismuth & Tungsten.

8. Non metals are non-conductors of heat and

electricity except carbon (graphite).

9. Generally metals have high melting and

boiling points

9. Non-metals have low melting and boiling

points (except carbon, boron, graphite and

silicon) .

QNo4:- What are the important chemical properties of metals?

(Ans):-Following are the important chemical properties of metals.

1. Reactions of Metals with oxygen:-Metals react with oxygen to form metalic oxides. However, the

vigor of reactivity varies from metal to metal.

Some metals react at rooms temperature, some upon heating and some even do not show any reactivity

e.g.

4Na +O2 2Na2O

2Mg+O2 2MgO

2Zn+O2 2ZnO

Metal oxides are generally basic in nature.

2. Reaction of Metals with water :- Metals react with water to form metallic oxides or metal Hydroxides

However, vigor of reactivity varies from metal to metal .

Some metals react with cold water ,some with hot water and some with steam.

Some of the metals do not show any reactivity even with steam.e.g.

2Na +2H2O 2NaOH +H2

Mg +H2O MgO +H2

Zn +H2O ZnO +H2

Copper , Silver and Gold do not show any reaction with water .

3.Reaction with acids :- Metals react with acids to form their corresponding salts with the liberation of

hydrogen gas .e.g.

Mg +2HCl MgCl2 +H2

Fe +2HCl FeCl2 + H2

How ever ,Ag , and Pt do not react with acids.

4. Reaction with bases :- Metals react with bases to form their salts with the liberation of H2 gas .

5.Displacement reaction :- The displacement reaction is a chemical reaction in which a more reactive

metal displaces a less reactive metal from its salt solution.

Displacement reaction is an important property of metals .e. g.

Zn +Fe SO4 Zn SO4 + Fe

Zinc + Ferrous Sulphate Zinc sulphate + + Iron

Fe +Cu SO4 Fe SO4 +Cu

Iron + copper sulphate Ferrous sulphate + copper

Q No5:- Chemical properties of non-metals .

Following are the important chemical properties of non metals:-

1) Reaction with oxygen:- Non metals upon heating with oxygen give their respective oxides. e.g.

C + O2 Heat CO2

Carbon Oxygen Carbon dioxide

Science 8th


--Sir Ishfaq/ssnp

] S + O2 heat SO2 Sulphur Oxygen Sulphur dioxide

Non – metalic oxides are generally acidic in nature.

CO2 + H2O H2 CO3 Carbonic acid.

(2) Reaction with water: Non- metals do not react with water or steam to liberate H2 gas.

(3) Reaction with Acids: Non – metals do not react with acids to liberate hydrogen gas.

Q. 6 Comparison of chemical properties between metals and non-metals:

Metals Non metals

Metals react with oxygen to form metalic oxides Non-metals react with oxygen to form non-

metallic- oxides.

Metallic oxides are basic in nature. Non-metalic oxides are acidic in nature.

Metals react with water to form metal hydroxides

or metal oxides.

Non – metalls do not react with water.

Metals react with acids to form metal salts and

hydrogen gas

Non-metals do not react with acids.

Q.7 What are the general uses of metals?

Ans. Following are the general uses of metals:

(i) Metals are used for making electrical wires and cables e.g. Al & Cu.

(ii) Metals are used for making cooking utensils e.g Al & Cu. Aluminum foils are also used for

wrapping food items .

(iii) Metals are used for machinery purposes e.g. iron.

(iv) Zinc is used for Galvanization.

(v) Nickle and chromium are used for electroplating.

(vi) Gold and silver are used for jewellery purposes.

(vii) Mercury is used in thermometers and barometers.

Q.8 What are general uses of non-metals?

Ans. Following are the general uses of non-metals:

(i) Oxygen is used for respiration

(ii) Non-metals like nitrogen, phosphorus etc are used for making fertilizers.

(iii) Carbon (Graphite) is used for making electrode in electric cells and in pencil leads.

(iv) Carbon (Diamond) is used in jewellery.

(v) Chlorine is used to disinfect water as it kills germs.

(vi) Iodine (Tincture iodine) is used as an antiseptic.

(vii) Phosphorous is used for making match stick , rat poison and fertilizers.

Q.9 Write a note a reactivity series:

Ans. The arrangement of metals in a vertical column in the order of their decreasing reactivities is

called the reactivity series or the activity series of metals. The reactivity series of common metals is given

below: K,

Na,

Ca,

Mg,

Al,

Zn,

Fe, Reactivity decreases.

Ni,

Sn,

H,

Cu,

Hg,

Ag,

Au,Pt.

Science 8th


--Sir Ishfaq/ssnp

Lesson No 12

Light Terminology

1) Light: Light is a form of energy that gives us sensation of vision (sight), & enables us to see

objects.

2) Plane mirror: A thin, flat and smooth sheet of glass having a shiny coating of silver metal on

one side is called a plane mirror.

3) Reflection of light: The phenomenon of bouncing back of ray of light from a polished surface

is called reflection of light.

4) Incident ray: The ray of light which comes from a source and strikes any surface is called as

incident ray.

5) Reflected ray: The ray of light which is sent back after reflection by a mirror is called the

reflected ray.

6) Normal: Normal is a line drawn at right angles (perpendicular) to the mirror surface at the

point of incidence.

7) Angle of incidence: The angle formed between the incident ray and normal is called as angle

of incidence.

8) Angle of reflection: The angle formed between the reflected ray and the normal is called as

angle of reflection.

9) Real image: An image which are obtained on the screen & are formed by the actual meeting

of the light rays.

The image seen on a projector screen (the source being the LCD projector) and the image

produced on retina of eye are examples of real images.

10) Virtual image: An Image which can‟t be obtained on the screen & is not formed by the

actual meeting of the hight rays as shown in figure.

11) Lateral inversion: The phenomenon of image formation on a mirror when left appears right

and the right appears left is known as lateral inversion.

Image

I

O

Object

(a) Convex mirror showing formation of a real image

O

Object

I Image

(a) Concave mirror showing formation of a real image

O

Object

f I

Image

(b) Formation of a virtual image in

convex mirror

O

Object I

Image F

Science 8th


--Sir Ishfaq/ssnp

12) Regular reflection: The phenomenon due to which a parallel beam of light on striking a

smooth, highly polished surface is reflected back as a parallel beam of light is called regular

reflection.

13) Irregular reflection: The phenomenon due to which a parallel beam of light on striking a

rough surface gets reflected in various directions is called as irregular reflection.

14) Luminous objects: The objects which emit their own light are called as luminous objects,

e.g. sun, burning candle, glowing bulbs, stars, etc.

15) Non-luminous objects: The objects which do not emit their own light but receive light from

luminous objects and reflect it are known as non-luminous objects, e.g. chair, duster, table, birds,

etc.

16) Rectilinear propagation: The property of light by virtue of which it travels in straight lines is

known as rectilinear propagation.

17) Periscope: It is an optical instrument which enables the viewer to see objects which are not

visible directly. It makes use of two plane mirrors set to each other at 45 0

angle .It is used in

submarines, tanks, bankers, etc.

18) Kaleidoscope: It is an optical instrument that uses multiple reflections of light to produce

beautiful patterns. It consists of a cylindrical tube made up plastic or cardboard in which mirrors

are inclined to each other, typically three rectangular mirrors strips at angle 600. The mirrors

form a triangle. In between the triangle of mirrors, loose and coloured objects such as beads,

glass pieces or small pebbles are placed. As the tube (closed on both ends) is rotated, the

tumbling of objects presents varying colours and patterns.

19) Prism: A prism is a transparent refracting medium made of glass. It is bounded by at least

two non-parallel plain surfaces. A prism has five plain faces in which 2 faces are triangular and

three faces are rectangular.

20) Dispersion of light: The phenomenon of splitting of white light into its seven component

colours on passing through a transparent medium like glass prism is called dispersion of light.

Rainbow appears due to the dispersion of light (due to presence of water droplets in the

atmosphere).

21) Spectrum: The band of seven colours formed on a white screen when white light passes

through a prism (or any transparent medium) is called spectrum.

Textbook questions

Q.1) Suppose you are in a dark room. Can you see objects in the room? Can you see objects

outside the room? Explain?

Ans) We can‟t see objects in the dark room. But we can see the objects outside the room during

day time. This is because to see an object, we need light which must reflect from the objects to

the eyes.

Q.2A) Difference between regular and irregular (diffused) reflection.

Ans)

Regular reflection Irregular reflection

1) The reflecting surface is smooth and

highly polished.

1) The reflecting surface is rough and

irregular.

2) All the reflected rays go parallel to one

another.

2) The reflected rays do not go parallel to

one another.

3) Due to regular reflection, images are

formed correctly.

3) Due to irregular reflection, images are not

formed very correctly.

Science 8th


--Sir Ishfaq/ssnp

Rays Reflected from irregular Surface

Regular Reflection

Q.2B) Does diffused reflection mean the failure of the laws of reflection?

Ans) No, diffused reflection is not failure of the laws of reflection. This happens because of the

irregular microscopic surfaces. Parallel incident rays reflect in different directions, however,

each ray obeys the laws of reflection. Q.3) Mention against each of the following whether regular or diffuse reflection will take place when a

beam of light strikes. Justify your answer in each case.

Ans) (a) Polished wooden table: Regular reflection will take place because the surface is polished and

smooth.

(b) Chalk powder: Diffused reflection will take place because it is rough surface (irregular surface).

(c) Cardboard surface: Diffused reflection will take place because it is not polished and has a rough

surface.

(d) Marble floor with water spread cover it: Diffused reflection will take place as water drop will form

prisms on the marble surface.

(e) Piece of paper: A piece of paper has rough surface, so diffused reflection will take place.

Q.4) State laws of reflection?

Ans) There are two laws according to which reflection of light takes place. These are stated as

follows:

1. The angle of incidence is equal to the angle of reflection. In given figure if i is angle of

incidence and r is angle of reflection, then

i = r

2. The incident ray, the normal at the point of incidence and the reflected ray, all lie in the

same plane. In given figure AO represents incident ray, OB reflected ray and ON normal.

O

i r

A N B

Q.5) Describe an activity to show that the incident ray, the reflected ray and the normal at the

point of incidence lie in the same plane.

Ans) Things needed: A plane mirror, a sheet of stiff paper, light box, a pair of scissors.

Method: (1) Take a plane mirror MM and place it on a piece of stiff paper, a little beyond the

edge of table so that its reflecting surface is facing sideways. Mark the position of the mirror on

the sheet of paper with a pencil.

(2) Keep light box at position A in front of plane mirror. When we open the slit of the light box,

a beam of light falls from it on the plane mirror. You can see the beam of light AO strikes the

mirror surface at point O, it gets reflected and goes in another direction OB, this is reflected ray.

Science 8th


--Sir Ishfaq/ssnp

(3) Cut the projecting portion of sheet in middle with the pair of scissors. The reflected ray

extends to the projected portion of the paper.

(4) Bend the part of projected portion on which reflected ray falls.

This time we create a plane different from the plane in which the incident ray and the

normal lie and we do not see the reflected ray. It clearly indicates that the incident ray, the

normal at the point of incidence and the reflected ray all lie in the same plane.

O

i r

A N B

Q.9) Describe the construction of a kaleidoscope.

Ans) Kaleidoscope: It consists of

1. Three retangular mirror strips are joined together at 600 angle to form a prism like structure

(triangle). This prism is fixed in a cylindrical (circular) cardboard or plastic tube, slightly longer

than the prism.

2. The circular tube is closed at one end with a cardboard disc. This disc has hole in the centre

through which we can see in.

3. At the other end of the circular tube, a plane glass plate is fixed. It is important that this glass

plate touches the prism mirrors. On this glass plate, several small and broken coloured glass

pieces are placed. This end is now closed by a round glass plate allowing enough space for the

glasses to move and further allowing the light to fall on the coloured glass pieces. Multiple

reflection of light in Kaleidoscope, thus, results in the beautiful patterns.

.Q.10) Write a note on human eye and draw its labelled sketch. Structure of Human Eye:- The human eye is more or less like a photographic camera. The

essential parts of human eye are Cornea, Iris, Pupil, Eye

lens, Ciliary muscles, retina and optic nerve.

Cornea: The front transparent part of the eye is called

cornea which is bulged outwards. The light coming from

the objects enter the eye through cornea, thus it serves as a

window of the eye.

Iris: The coloured diaphragm behind the cornea is called

as iris.

Pupil: A small hole in the centre of iris is called as pupil. It

appears black as no light is reflected from it.

Eye lens: A double convex lens which is a transparent

and flexible material like a jelly made of proteins.

Ciliary muscles: The special type of muscles which hold

the eye lens in a proper position.

Retina: A screen behind the eye lens and at the back of

the eye ball, on which the image of the object is formed.

It is a delicate membrane consisting of a large number of

light, sensitive cells in the form of rods and cones.

Optic nerve: The optic nerve receives the electric pulses

form retina and passes to the brain.

Science 8th


--Sir Ishfaq/ssnp

Aqueous humour: The space between the cornea and the eye lens is filled with a viscous liquid

called aqueous humour.

Vitreous humour: The space between the eye lens and the retina is filled with a specific fluid

called as vitreous humour.

Blind spot: It is the least sensitive spot on the retina through which the optic nerve enters the

retina.

Q) What are the various defects of vision? Explain?

Ans) There are three defects of vision or defects of eye which can be corrected by using suitable

spectacles. These are:

1. Myopia or short sightedness

2. Hypermetropia or long sightedness.

3. Cataract

Out of these three defects the first two are most common.

1. Myopia: It is that defect due to which an eye can see nearby objects clearly but can not see the

distant objects clearly. In a myopic eye, the image of a distant object is formed in front of retina.

To correct this defect, the person has to use

spectacles with a concave lens.

2. Hypermetropia or long sightedness:- It is that

defect of eye due to which an eye can see the distant

objects clearly but can not see the nearby objects

clearly. In this defect, image is formed behind the

retina.

To correct this defect, the person has to use

spectacles with a convex lens

3. Cataract: It is a leading cause of blindness

among adults of 45 years of age and above. The eye

lens becomes cloudy due to which light does not

pass easily through the lens to focus on retina. As a result things look foggy or cloudy. So the

people with cloudy lens are said to have cataract.

Q.11) Gurmeet wanted to perform activity using a laser torch. Her teacher advised her not to

do so. Can you explain the reasons of teacher‟s advice?

Ans) Laser torch can harm or even damage eyes, because intensity of laser light is very high and

our eyes have convex lens which may converge the laser light at one spot on retina which may

lead to blindness.Thus, her teacher advised her not to do so.

Q.12) How can you take care of your eye?

Ans) We can take care of our eyes by taking following measures:

Always sit straight while reading or writing. Do not read while lying down, it strains the

eyes.

Do not read in a dim light or very bright light. Insufficient light causes eye strain and

headache.

Do not watch television or read for a long time.

Do not read while moving in a bus or a car.

Do not rub your eyes with dirty hands or dirty cloth.

Wash your eyes frequently with clean water.

Do not keep the book too close or too far to eyes .

If you feel strain, get your eyesight checked up. Use spectacles if required.

Include vitamin A in the diet component.

Science 8th


--Sir Ishfaq/ssnp

Q.13) What is the angle of incidence of a ray if the reflected ray is at angle of 900 to the

incident ray?

Ans) If the reflected ray is at an angle of 90 0

to the incident ray, then the angle of incidence is

450. According to the law of reflection, the angle of incidence is equal to the angle of reflection.

Therefore, the angle of incidence and the angle of reflection both are = 900 / 2 = 45

0

Q.14) How many images of candle will be formed if it is placed between two parallel plane

mirrors separated by 40cm.

Ans) No. of images formed = 3600 – 1 360

0 – 1 =

Angle between 0

the two mirrors

Infinite no. of images will be formed.

Q.15) Two mirrors meet at Right angles. A ray of light is incident on one at an angle of 300 as

shown in figure. Draw the reflected ray from the second mirror.

Ans)

Q.16) Yasir stands at A just on the side of a plane mirror as shown in figure. Can he see

himself in the mirror? Also can he see the image of objects situated at P, Q and R?

Yasir P Q

A

R

Ans) A plane mirror forms virtual image behind the mirror. The image is as far behind the mirror

as the object is in front of it. Yasir cannot see his image because the length of mirror is too short

on his side. However, he can see the objects placed at point P and Q but cannot see the object

placed at point R (as shown below).

A P Q

Yasir

R

A` P` Q` R`

I.R

300 N

B 300 N

R.R

60o 60

0 60

0

30o R.R

This is the reflected ray from the 2nd

mirror

Science 8th


--Sir Ishfaq/ssnp

Q.17) (a) Find out the position of the image of an object situated at A in the plane mirror.

(b) Can Saba at B see this image? (c) Can Yasir at C see this image? (d) When Saba moves

from B to C, where does the image of A move?

A B

(Saba)

X

C (Yasir)

Ans) (a) Image of the object placed at A is formed behind the mirror. The distance of the image

from the mirror is equal to the distance of A from the mirror (as shown in the given figure)

A B (Saba)

C (Yasir)

A`

. Image of A

(b) Yes, Saba at B can see this image.

(c) Yes, Yasir at C can see this image.

(d) The image of the object at A will not move. It will remain at the same position when Saba

moves from B to C.

Additional questions Q.1) Give characteristics of the image formed by a plane mirror?

Ans) The characteristics of the image formed by a plane mirror are briefly discussed as follows:

1. The image in a plane mirror is of the same size and shape as the object.

2. The image in a plane mirror is erect.

3. The image formed in a plane mirror is virtual.

4. The image formed in a plane mirror is at the same distance behind the mirror as the

object is in front of it.

M

5cm 4cm 4cm 5cm

Object M` Image

Science 8th


--Sir Ishfaq/ssnp

Q.2) What do you mean by multiple image formation?

Ans) When two mirrors are inclined to each other at an angle, many images of the object are

formed. This is because the image formed in one mirror acts as the object for other. Many

images formed in this manner are called multiple images.

By changing the angle between the two mirrors, we can get any number of images. The

actual number of images (n) formed depends upon the angle () between the mirrors and can be

determined by the following formula.

Number of images (n) = _____3600 __ – 1

Angle between

the mirrors ()

(1) Images formed by a pair of mirrors placed perpendicular to each other

Image in Plane mirror at right angles to each other

By formula,

No. of images (n) = 360 – 1

90

= 4 – 1 = 3 images.

(2) No. of images when mirrors are parallel to each other.

No. of images (n) = 360 – 1

0

= (infinite)

(3) No. of images if angle is 600.

No. of images (n) = 360 – 1 = 6 – 1 = 5 images

60

Q.3) State uses of plane mirrors.

Ans) (1) Plane mirrors are generally used as looking glass.

2) They are used in solar cookers.

3) They are used in schools for experimentation to know more about optical science.

4) They are used in jewelery shops.

5) They are used in saloons or in barber‟s shop for hair dressing.

Science 8th


--Sir Ishfaq/ssnp

Q.4) What is meant by power of accommodation of the eye?

Ans) A normal eye can see near by objects clearly as well as the distant objects. The ability of an

eye to focus the distant objects as well as the near by objects on the retina by changing the focal

length of its lens is called accommodation or power of accommodation of eye. This is done by the

action of ciliary muscles. The maximum accommodation is reached when the object is at a

distance of 25cm from the eye.

Far point of eye:- The most distant point at which an object is seen clearly by an eye is called far

point (F) of the eye. It lies at infinity.

Near point of eye:- The point at the closest distance, at which an object is seen clearly by an eye

is called Near point (N) of the eye. The near point is about 25cm.

Q.5) What is a Braille system?

Ans) The most popular resource for visually challenged persons is known as Braille system.

Louis Braille, himself a visually challenged person, developed a system for visually challenged

persons and published it in 1821. The present system was adopted in 1932. There is Braille code

for common languages, mathematics and scientific notation. Many Indian languages can be read

using the Braille system. Braille system has 63 dot patterns or characters. Each character

represents a letter, a combination of letters, a common word or a grammatical sign. Dots are

arranged in cells of two vertical rows of three dots each.

***********************************************************************

Lesson No. 13

Pollution of Air & Water Terminology

Pollution: Any undesirable change that occurs in the physical, chemical or biological properties

of air, water or soil is called pollution.

Pollutants: These are the unwanted substances which cause pollution and have harmful effect on

both the living and the non living things.

Smog: It is the pollution of air which occurs when smoke (containing oxides of nitrogen and

other pollutants) combines with fog. It causes various respiratory problems like Asthma, Cough

and Wheezing in children.

Chlorofluoro carbons (CFCS): These are the chemical substances which are used as

refrigerants, in air conditioners and aerosol sprays. They damage the ozone layer of the

atmosphere due to the formation of chlorine free radicals.

Carbon monoxide (CO): It is a toxic gas which is released in the atmosphere as a result of

incomplete combustion of fuels such as petrol and diesel. It reduces the oxygen carrying capacity

of the blood.

Acid rain: It is rain which is unusually acidic. It possesses elevated levels of hydrogen ions (low

PH). It is formed as a result of emission of gases in the atmosphere like nitrogen and sulphur

oxides, (SO2), NO2, No3 etc. These gases when combine with water from rain form sulphuric and

nitric acid respectively. Hence makes the rain acidic. It has harmful effect on plants, aquatic

animals and infrastructure.

Green house effect: It is the process by which thermal radiation (infrared rays) from the earth‟s

surface is absorbed by atmospheric green-house gases such as CO2, SO2, N2O, CH4, O3 and

water vapour and is reradiated in all directions. Since part of this re-radiation is back towards

earth‟s surface and lower atmosphere, it results in an increase in average surface temperature. It

plays a vital role in agriculture.

Science 8th


--Sir Ishfaq/ssnp

Global warming: It is the rise in the average temperature of earth‟s atmosphere and oceans due

to elevated levels of CO2 and other green house gases in the atmosphere.

Ganga Action Plan: This was an ambitious plan which was launched in 1985 to save the river

Ganga. This plan aimed to reduce the pollution levels in the river.

Biological oxygen demand (BOD): It is the amount of dissolved oxygen needed by aerobic

biological aquatic organisms to break down organic matter present in a given water sample at

certain temperature over a specific time period.

Text book questions Q.1 What are the different ways in which water gets contaminated?

Ans. The various ways due to which water gets contaminated are:

(a) washing, bathing and other house hold activities.

(b) sewage disposal.

(c) toxic chemicals thrown by the industries.

(d) garbage and dead bodies dumped under water resources.

(e) fertilizers, insecticides, pesticides etc.

Q.2 At an individual level, how can you help reduce air pollution.

Ans. Steps to be taken to reduce air pollution at an individual level are:

(i) Use of automobiles to be reduced.

(ii) Unleaded petrol or diesel must be used.

(iii) Plantation of more and more trees to be done.

(iv) Burning of dried leaves and tyres must be stopped.

Q.3 Clear transparent water is always fit for drinking. Comment.

Ans. No, clear and transparent water even without smell may contain bacteria, viruses etc

which are not visible to eyes. These microorganisms may cause many diseases. Thus, water fit

for drinking must be clean, transparent, odourless and germ free.

Q.4 You are a member of the municipal body of your town. Make a list of measures that

would help your town to ensure the supply of clean water to all its residents.

Ans. 1. Industrial waste must be treated chemically before throwing into the water body.

2. Wastage of water due to leakage at various places must be taken into account.

3. Drinking water should be strictly used for drinking but not for other activities

such as bathing, washing and irrigation.

4. Municipal body should keep ready sufficient number of tankers to meet any

emergency challenging situation.

Q.5 Give the differences between pure air and polluted air.

Polluted air Pure air

1. The air is dirty and translucent.

2. Smoke and dust particles are in high

concentration.

3. It may have foul smelling.

4. Microorganisms are present.

1. The air is clean and transparent

2. No smoke and dust particles can be

seen.

3. It is odourless.

4. Microorganisms are absent

Q.6 Explain circumstances leading to acid rain. How does acid rain effect us?

Ans. When oxides of sulphur such as SO2 and SO3 and oxides of nitrogen such as NO2 and

N2O are produced from the incomplete combustion of fossil fuels, they combine with water

vapours present in atmosphere and form their respective acids, sulphuric acid (H2SO4) and nitric

acid (HNO3) respectively. These acids come down with rain making the rain acidic. This rain is

called as acid rain.

Science 8th


--Sir Ishfaq/ssnp

Acid rain corrodes the monuments, rail tracks and railway bridges. It also

effects/destroys crops, wild plants. It also causes irritation to eyes, nose and throat. This acid rain

is responsible for marble cancer of Taj Mahal.

Q.8 Describe “Green house effect” in your own words.

Ans. The sun‟s rays when fall on the surface of earth, they warm it. Some of the sun‟s rays are

absorbed by the earth‟s surface and left out rays are reflected back into the space. Some of these

rays are trapped by the atmospheric gases such as carbon dioxide, sulphure dioxide, Methane,

etc. This causes heating up of the earth‟s atmosphere. This effect i.e. trapping of sun‟s radiations

is known as greenhouse effect. The name green house is derived from green house in which

green plants are kept.

Q.9 Prepare a brief speech on Global warming. You have to deliver the speech in your own

class.

Ans. Global warming, as the name suggests, is the increase in temperature of the Globe. The

average temperature of the atmosphere has increased. Few gases like CO2, CH4, O2, SO2 are

responsible for it. The quantity of these gases is increasing day by day in the atmosphere. If this

is not checked in time, the temperature will have a big rise and there will be hazards all around

us such as glaciers will melt, rain fall will be affected, sea level will rise, loss in the production

of crops, vanishing of forests, etc. It will also affect the life style of all living organisms. So,

special and immediate measures are to be taken to stop global warming.

Q.10 Describe the threat to the beauty of the “Taj Mahal”.

Ans. Taj Mahal is one of the Seven Wonders of the World. It is a white building made up of

white marble made in the memory of Mumtaz Mahal in Agra.

The monument is being threatened by air pollution. The area surrounding Taj is

congested with many harmful gases such as sulphur dioxide and nitrogen oxides etc. these gases

are being emitted by burning of fossil fuels by industries established around the Taj. These gases

dissolve in rain water to form acid rain. This acid rain is the main cause of Taj deterioration. In

addition to this, the suspended particulate matter remitted by Mathuras oil refinery has also

contributed to the yellowing of the Taj.

Q.11. Why does the increased level of nutrients in the water effect the survival of aquatic

organisms?

Ans. With the increased quantities of nutrients the algae flourish in water (Eutrophication).

When these algaedie, decomposers decompose them, using oxygen present in water. Thus there

is a decrease in oxygen level in water (Eutrophication) which effects the survival of aquatic

organisms.

Some Additional Questions

Q.1 What do you mean by the term pollution? What is the main cause of pollution?

Ans. The contamination of natural resources like air and water due to addition of harmful

(toxic and poisonous) substances is known as pollution. Pollution brings about the undesirable

changes in the physical, chemical and biological characteristics of natural resources. Any

substance that causes pollution is called as pollutant.

Human activities such as industrial growth, urbanization, increase in population and rapid

changes in the modern technology are largely responsible for pollution.

Q.2 What is air pollution? List the pollutants of air and their respective sources?

Ans. The contamination of air with harmful, unwanted substances like toxic gases, smoke and

dust which have harmful effects on both living and nonliving objects is called air pollution.

The harmful and unwanted substances which contaminate the air and cause air pollution

are called air pollutants.

Science 8th


--Sir Ishfaq/ssnp

Some of the air pollutants and their sources are listed below:

Air Pollutant Source of Air Pollutant

1. Sulphur dioxide

2. Oxides of Nitrogen

3. Excess of CO2

4. Carbon Monoxide

5. Acid fumes

6. Smoke

7. Dust

8. Lead Compounds

9. Chlorofluoro Carbons

(a) Burning of fossil fuels, automobile exhausts,

refining of petroleum, volcanic eruptions

(b) Burning of Fossil fuels, automobile exhausts.

(c) Burning of Fossil Fuels

(d) Automobile exhaust incomplete combustion of fossil fuel.

(e) Fertilizer and chemical Industries

(f) Combustion of fossil fuels.

(g) Stone crushers, wood work, volcanic eruptions

(h) Automobile exhausts.

(i) Leaking refrigerators and A. C‟s.

Q.3 What are the harmful effects of air pollution.

Ans. The harmful effects of air pollution are stated below:

(i) Causes many health problems: (i) Carbon monoxide is a very poisonous gas.

When inhaled in excess, it may cause death. CO has 325 times greater affinity than O2 towards

Haemoglobin. Thus, when inhaled it forms a stable compound HbCO. Due to formation of

HbCO, the blood cannot carry O2 to various body parts, thus leading to first headache, then

suffocation and finally death.

(ii) Oxides of sulphur cause respiratory problems.

(iii) Oxides of Nitrogen cause lung congestion.

(iv) Fumes from industries cause irritation in eyes, nose and throat.

(v) Lead oxide particles effect the brain of children.

(ii) Air pollution can cause acid rain: The oxides such as CO2, SO2 and oxides of nitrogen

present in air reacts in water and produce their respective acids. If the rain drops come down with

these acids, it makes rain acidic. This acid rain increases the acidity of soil and effects the plant

and animal life.

This acid rain makes water bodies acidic, thus, destroys aquatic life. Acid rain destroys

monuments and buildings as well.

(iii) Air pollution causes Global warming: The heating up of earth‟s atmosphere due to the

trapping up of IR radiations by green house gases such as CO2, CH4 and water vapours in the

atmosphere is known as green house effect. Green house effect is responsible for increasing the

average temperature of the atmosphere of earth which is known as global warming. The threat of

global warming is that it can lead to melting of glaciers and thus increasing the water level of

seas and other water bodies. Global warming adversely affects the monsoon rains.

(iv) Air pollution causes depletion of ozone layers: CFCs (Chloroflouro Carbons) when

released in air damage ozone layer of the atmosphere due to the formation of chlorine free

radicals. The depletion of ozone layer may cause various diseases in human beings such as

cataract, skin-cancer, dimming of eye sight, mutation in gene structure, damage to early

developmental stages of fishes, crabs and other animals.

Q.4 Suggest the methods of prevention and control of air pollution.

Ans. Following methods are suggested to prevent and control air pollution:

1. Modern automobile engines should be fitted in the vehicles so as to bring about

complete combustion of fuel.

2. CNG should be preferred over the use of petrol and diesel.

3. Unleaded (Lead free) petrol should be used in automobiles.

4. Regular pollution check on vehicles should be made mandatory

Science 8th


--Sir Ishfaq/ssnp

5. More and more trees should be planted to reduce the increasing green house

effect.

6. Electricity should be produced by using water, solar and wind energy instead of

fossil fuels.

7. Design posters and organize awareness campaigns in your locality to highlight the

need of reduction for pollution.

Q.5 What is water pollution? What are the main causes of water pollution?

Ans. The contamination of water with harmful, unwanted substances like domestic sewage,

toxic industrial waste, pesticides and fertilizers etc is known as water pollution.

The harmful and unwanted substances which contaminate the water and cause water

pollution are called water pollutants.

Causes of the water pollution

The major causes of water pollution are:

1. Industrial sewage thrown directly into water bodies is one of the main causes of water

pollution.

2. Domestic sewage like kitchen refuse and toilet discharge also causes water pollution.

3. Human activities like bathing of human beings and animals in lakes and rivers cause water

pollution.

4. Agricultural wastes in the form of fertilizers, if used in excess are directly and indirectly

responsible for water pollution.

5. Oil spills from huge tankers is one of the major cause of water pollution which affects

both marine plants and animals

Q.6 What are the harmful effects of water pollution? (V. I)

Ans. The harmful effects of water pollution are:

1. Effects on human health: Polluted water can cause many diseases like cholera,

dysentery, typhoid, jaundice, diarrhoea in human beings.

2. Eutrophication: The term „eutrophic‟ means well nourished. Thus „eutrophication‟

refers to natural or artificial addition of nutrients to bodies of water.These nutrients

especially phosphates and nitrates promote excessive growth of algae. As the algae

die and decompose, high levels of organic matter and the decomposing organisms

deplete the water of available oxygen causing the death of other organisms, such as

fish. Eutrophication is a natural slow-ageing process for a water body.

3. Biological Magnification: The increase in concentration of harmful chemical

substances like pesticides in the body of living organisms at each tropic level of food

chain is called biological magnification. This occurs actually due to over use of

pesticides and insecticides in the crop fields

Q.7 Suggest the methods to prevent and control water pollution.

Ans. Following methods are employed to prevent and control water pollution:

1. Washing clothes, cleaning utensils or taking bath near water bodies should be

restricted.

2. Excessive use of fertilizers and pesticides should be discouraged.

3. The domestic sewage should be treated at the sewage treatment plants.

4. Pollution control rules enforced by Govt. should be strictly followed.

5. Dead bodies should not be disposed off in rivers, rather should be buried.

6. People should be educated about ill effects of water pollution.

Q.8 What is potable water? Name various methods by which water can be made potable.

Ans. Water, that is suitable for drinking is called as potable water. The methods applied for

making water fit for drinking purposes are:

Science 8th


--Sir Ishfaq/ssnp

1. Filtration: Any suspended impurity in water can be removed by filtering it through a

fine muslin cloth.

2. Boiling: We can purify water by killing the germs present in it by boiling.

3. Chlorination: It is a chemical method commonly used for purifying water for safe

drinking. It is done by adding specified quantity of chlorine tablets or bleaching

power to water. It also kills germs present in it.

4. Exposing water to UV radiation: The filtered water can be made germ free by

exposing it to UV radiations.

Q.9 What is smog? What are its ill effects?

Ans. The mixture of smoke and fog is known as smog. Smog causes breathing difficulties such

as asthma, cough, and wheezing in children

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Scholar’s School Srinagar Lesson No. 14

Friction

Terminology 1. Friction: It is an opposing force that comes into play when two surfaces in contact move

relative to one other.

2. Irregularities: These are the uneven projections on the surface of a body.

3. Static friction: The force of friction comes into play, which does not allow two surfaces

to slide upon one another. It is a self adjusting force, that is only as much as is necessary

to prevent the motion.

4. Limiting friction: The maximum force of static friction comes into play, when the

surface of one body just slides over the surface of another body.

5. Dynamic friction: The force of friction acting between the surfaces of two bodies sliding

upon one another at a constant speed.

6. Rolling friction: The force of friction experienced by a body, when it is made to move

over bodies like roller or a wheel is called Rolling friction.

7. Streamlining: It is a method of giving a special shape to a body/ object, such that a fluid

(Air, water) flowing past it offers a minimum amount of friction.

8. Lubricant: A material which, when applied between two surfaces in contact, reduce the

force of friction.

9. Ball-Bearing: A device used for reducing rolling friction, by making an axle to move

over metal balls placed around it radially.

Textual Questions Q1) Why are the worn out tyres discarded?

Ans: Worn out tyres are discarded because their friction with road surfaces is less as they

are smooth as compared to, when they were new. Hence to avoid slipping of tyres on

roads (to avoid accidents), worn out tyres are discarded.

Science 8th


--Sir Ishfaq/ssnp

Q2) Why do carrom coins move faster on carrom board when dusted with talcum

powder?

Ans: By dusting talcum-powder on carrom board, smoothness of the surface of board is

increased. Hence carrom coins move faster in presence of talcum powder as compared to,

when it is without it.

Q3) Why is the surface of conveyor belt made rough? Ans: The surface of the conveyor belts used for turning pulleys & wheels in factories are

made rough so that they could provide the necessary reaction, & the wheels could turn

about their axels.

Q4) Why is the sewing machine often oiled?

Ans: Sewing machines are often oiled so that its parts should move easily over one

another so by applying oil on machines, roughness of its parts are reduced for its

comfortable movement.

Q5) Why do new automobile tyres have deep grooves?

Ans: Presence of deep grooves on new automobile tyres means more roughness. They are

usually provided with deep grooves so that they can have better grip on road to avoid

slipping.

Q6) Why does a ball rolling on the ground slows down? Ans: A ball rolling on the ground slows down after some time because of frictional force

acting in the opposite direction.

Q7) Why are the boats and aeroplanes given special shapes?

Ans: Boats and aeroplanes are given special shapes, called streamlined shape so that they

can move easily through water and air respectively, offering minimum resistance to their

movement.

Q8) Why do meteors burn on entering into the atmosphere?

Ans: Meteors are very large sized heavenly bodies and when they enter into the earth‟s

atmosphere at very high speed, because of the large friction between them & air they

catch fire and are burnt.

Q9) Why do painters use sand papers in polishing doors?

Ans: Sand papers have very high rough surfaces. That is why painters use them before

polishing doors because the doors to be polished are rubbed with it (sand paper) so that

they (doors) are made first smooth . Only then effective polishing can be done.

Q10) Why is it easier to tie a knot with cotton string as compared to silk string? Ans: Silk string is much smoother as compared to cotton thread/string. Hence knot in

cotton string is easier to make than silk string as better grip is only possible within rough

surfaces as compared to smooth silk string.

Additional Questions Q1) What is the cause of friction?

Ans: The cause of friction between any two surfaces is their roughness or irregularities.

Irregularities in a surface means presence of valleys & hills. When two surfaces come in

contact with each other, valleys of one surface gets locked in the hills of another surfaces

& vice versa i.e. two surfaces are interlocked . Hence an external force is needed to move

one body over the other.

Surface A

Interlocking irregularities

Surface B

Science 8th


--Sir Ishfaq/ssnp

Q2) What are the laws of limiting friction? Ans: Various laws of limiting friction are:

a) Limiting friction always opposes the motion of a body and acts in the direction

opposite to the direction of applied force.

b) Limiting friction depends upon the nature of surfaces in contact with each other.

c) Limiting friction increases with the increase in the weight of the body and vice versa.

d) Limiting friction is independent of the area of contact between two surfaces, provided

the weight of the body and the nature of surfaces does not change.

Q3) Why is dynamic friction slightly less than limiting friction?

Ans: Limiting friction is slightly greater than the dynamic friction because more force is

required to break the interlocking as compared to the force which is required to keep the

interlocking unlocked during motion. That is the reason why dynamic friction is slightly

less than the limiting friction.Fig-01 shows a graph between the applied force on the

spring balance & the force of friction. The region AB in the graph shows static friction,

which is self adjusting .BC shows the magnitude of limiting friction, DE shows the

magnitude of dynamic friction.

B

D

Force of friction (f)

Magnitude of dynamic friction

Magnitude of limiting friction

A

C E

Applied Force F

Fig.-01

Q4) What are advantages of friction?

Ans: Advantages of friction are as follows:

i) It helps us to work.

ii) It helps in movement of vehicles.

iii) It helps spiked shoes of athletes for better grip.

iv) It helps us in writing work.

v) Application of brakes is possible because of friction.

vi) It helps us in lighting of a match stick.

vii) It helps in holding nuts, nails & screws.

Q5) Write any two disadvantages of friction?

Ans: Two disadvantages of friction are:

i) It causes damage to machines.

ii) It causes wear & tear of moving machine parts & soles of shoes.

Q6) What are the various ways by which friction can be reduced?

Ans: Various ways of reducing friction are:

1) By lubricating , i.e. by applying grease or oil over the rough surfaces.

2) By polishing .

3) By using rollers & wheels.

4) By streamlining.

Science 8th


--Sir Ishfaq/ssnp

Q7) Why friction is called as , “necessary evil” ?

Ans: Friction is called as, “necessary evil” , because in some cases it is useful to us & we

cannot do

any work without it. At the same time, it is an evil in some cases because it results

in the loss of

energy & wear & tear of the surfaces in contact i.e. machine parts, soles of shoes,

etc.

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Lesson No. 15

Stars and The Solar System

Terminology

Solar System: The collection of planets & their moons in orbits around the sun together with

smaller bodies such as asteroids, meteors, meteorites, comets etc constitutes solar system.

Celestial body: A celestial body is an astronomical object which exists naturally in the outer

space .It includes stars , planets , nebulae or entire galaxies.

Universe: The vast unimaginable space which encompasses most distant stars, planets &

anything else , which exists is called universe.

Conestellations: These are group of stars which resemble a particular shape of already existing

objects/things in the sky. There are 88 constellations present in sky .e.g.; Ursa Major, Ursa Minor

, Orion etc.

Astronomy: The branch of science which deals with the study of universe i.e. astronomical

objects is called astronomy.

Light year: It is the unit of length which is used to measure the distance between the stars. It is

defined as the distance traveled by the light at a speed of 300,000 km/s in one year (365 days) is

called light year.

1 light year = speed of light x 365 days

= 300,000 km/s x 365 x 24 x 60 x 60 sec

= 9,460,000,000,000 km

= 9.46 x 1012

km

Light minute: The distance traveled by the light at a speed of 3 x 105 km/s in one minute .

1 light minute = 18 x 106 km.

Alpha centauri: It is third brightest star in the sky in the constellation centaurus. It is the nearest

bright star to the solar system(distance 4.34 light years). It is also called Rigil Kentaurus.

North star/Pole star: It is the star which is situated in the direction that is directly above the

geographic north-pole of the earth‟s axis. Thus its position relative to earth does not change &

hence, it appears stationary .It is also called as Polaris or Dhruva tara.

Planets: These are heavenly bodies which revolve around the sun in the solar system. There are

eight planets in solar system.

Satellites: These are heavenly bodies which revolve around the planets in the solar system.

Asteroids: The small pieces of rocks or metal which revolve around the sun, in between the

orbits of Mars & Jupiter are called asteroids e.g. Ceres (Largest), Vesta (brightest), etc.

Science 8th


--Sir Ishfaq/ssnp

Comets: The bright “star like” , objects with a long tail , approaching the sun in a highly

elliptical orbit are called comets.

Halley’s comet: It is a periodic comet which is visible once in 76 years . It was sighted in 1910

& then in 1986 . Now it is expected to sight in the year 2062.

Meteors: The bright star like objects which appear suddenly in the sky for some time with a

brilliant white flash of light falling towards the earth & finally disappear are called Meteors.

Meteorite: The unburnt piece of a meteor which reaches the surface of earth is called Meteorite.

Stars: Gaint balls of fusing hydrogen or helium which emit huge amount of heat & light.

Orbit: The path along which celestial bodies revolve around the sun or other celestial bodies.

Text Book Questions Q.1 Define “Universe”. Give its composition.

Ans. The vast space that includes every thing that exists on the earth and around it, is called

the universe. The universe includes the celestial bodies like the stars, the planets and their moons

(satellites), meteorites, asteroids etc.

Q.2 Define solar system. Name all the planets in the solar system in order of their distance

from the sun.

Ans. The solar system consists of the sun, the eight planets and their satellites and thousands of

other smaller heavenly bodies such as asteroids, comets and meteors.

The eight planets in their order of distance form the sun are:

(i) Mercury (ii) Venus (iii) Earth (iv) Mars (v) Jupiter (vi) Saturn

(vii) Uranus and (viii) Neptune. ( MV – EMJ – SUN).

Q.3 How many moons Mars has? Name these moons.

Ans. Mars has two moons. These are Phobos and Deimos

Q.4 What is a comet? Why does a comet develop a tail while approaching the sun.

Ans. The bright “Star” like objects with a longer tail, approaching the sun in a highly elliptical

orbit are called comets. Because of the pressure of solar radiations the tail of the comet

consisting of gaseous matter always points away from the sun.

Q.5 What is star? What makes the star give out vast amount of energy?

Ans. Stars are the huge glowing balls of hot gases mainly hydrogen, helium and some dust. In

the core of stars, hydrogen atoms fuse together to form helium atoms with the liberation of large

amount of energy in the form of heat and light.

Stars have life in billions of years. They travel in the sky from east to west. Stars are

classified according to size.

Q.6 Difference between meteors and stars.

Ans. Stars Meteors ( Shooting star)

(i) Stars mostly consist of

hydrogen and helium.

(ii) Stars produce heat and light

energy due to fusion of

hydrogen into helium.

(iii) Stars are very big in size

(iv) Star‟s life span is billions of

years.

(i) Meteors are mostly made up of

rocks, metals and dust.

(ii) Meteors produce heat and light

due to friction of air when they

enter into the atmosphere.

(iii) Meteors are comparatively

extremely small in size.

(iv) Meteors last for short period

Science 8th


--Sir Ishfaq/ssnp

Q.7 Write short notes on:

(a) Meteor (b) Meteorite

(a) Meteor: Meteors are the rocky pieces of planets which exploded and broke up long ago

and are now seen floating in space. As soon as they enter the earth‟s atmosphere, they catch fire

due to heat of friction between air and the rocky pieces. These burning pieces move with great

speed and look like streaks of light and are known as meteors. Meteors burn completely before

they reach the earth‟s surface.

(b) Meteorites: Some times meteors are big in size. When these meteors enter the earth‟s

atmosphere, they do not burn completely and reach the surface of earth. These unburnt pieces of

meteors reaching the earth‟s surface are called meteorites.

Additional Questions Q.1 What is moon? Name the phases of Moon.

Ans. A celestial body revolving around a planet is known as satellite. All planets except

Mercury and Venus have natural satellites. The satellite that revolves round the earth is known as

moon.

The day-to-day changes in the size and shape of the moon as seen from the earth are

called the phases of the moon.

There are six phases during which moon completes it revolution around the earth. These

are:

(i) New moon (ii) Crescent moon (iii) First Quarter (iv) Gibbous moon

(v) Full moon (vi) Wanning moon.

Q.2 Give a detailed account of “the Sun”.

Ans. The sun is the nearest star to the earth. It is the star around which the earth and other

planets of our solar system and celestial bodies revolve. The sun is the main source of heat and

light for all the planets. The distance of the sun from the earth is 150x 106 km.

It is 109 times bigger in size than the earth. Diameter of the sun is 14 x105 km. Its mass is

332900 times than the earth.

The temp. on the surface of the sun is about 6000oC and in its center is 20 million

0C

Q.3 What is a constellation? How does the constellation differ from a star?

Ans. A group of stars which forms a recognizable shape or pattern resembling some person or

known object is called constellation.

Constellation is a group of many stars and more over it has some familiar shape of a

person or object which a single star does not have.

Q.4 Name a star which appears stationary from the earth. In which constellation is it

situated?

Ans. The pole star appears stationary because it is situated directly above the geographic north

pole of the earth‟s axis and it is situated at the tail of constellation named Ursa Minor.

Q.5 What is a “light minute”? How many light minutes is earth from the sun? Express this

distance in Kilometers.

Ans. The distance traveled by light at a speed 3x105m/s in one minute is called a light minute.

1 light minute = 300000 km/s x 1 minute

= 18000000 km

= 18 x 106 km.

Q.6 What are Asteroids?

Ans. Asteroids are the small, heavenly bodies of rocks and metals which revolve around the

sun in the gap between the orbits of Mars and Jupiter. The number of Asteroids between Mars

and Jupiter is so large that they appear as a belt in this region. Asteroids can be seen through

large telescopes. There are as many as 100,000 asteroids.

Science 8th


--Sir Ishfaq/ssnp

Q.7 What are artificial satellites? Name some artificial satellites. Gives their uses?

Ans. An artificial satellite is a man –made object that has been purposely placed into the orbit

around the earth or other planets to perform specific functions. They are launched from the

earth. First artificial satellite called Sputnik – I was launched by USSR in 1957. Some other are:

Aryabatta (1975 1st Indian satellite)

INSAT (Indian National Satellite)

IRS ( Indian Remote sensing)

Kalpana – I etc.

Functions/Uses: 1. They are used for weather forecasting.

2. They are used in transmitting radio and television signals.

3. They are used in telecommunication such as in cellular phones and long distance

telephones, Fax etc.

4. They are used in Remote sensing for locating mineral resources, underground water and

for land mapping.

5. They are used for collecting the information about other planets and about the outer

space.

Q.8 Define the following terms:

(a) Light years (b) Great bear (c) Orion (d) Sirius (e) Period of revolution

(f) Period of rotation.

Ans: (a) Light Years: It is the distance traveled by light in one year.

(b) Great bear: It is one of the most famous constellation, which can be seen in the summer

seasons in the early part of the night. It also called as Saptarishi.

(c) Orion: It is also a well known constellation that can be seen during winter in the late

evening. It is also called as Hunter.

(d) Sirius: It is the brightest star in the sky and is located close to Orion.

(e) Period of revolution: The time taken by a planet to complete one revolution around the

sun.

(f) Period of Rotation: The time taken by a planet to complete one rotation about its own

axis.

Q.9 What do you understand by the following terms.

(a) New moon (b) Full moon

Ans. (a) New Moon When the moon is between the sun and the earth and the reflected

light from the moon does not reach the earth and hence it is not visible. This phase of

moon is called new moon.

(c) Full moon: When the earth is between the sun and the moon and the full bright face of

moon is visible as the night side of the earth is facing the day side of moon. This phase of

moon is called full moon.

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Scholar’s School

Badshahnagar, Natipora, Srinagar

Science 8th


--Sir Ishfaq/ssnp

Lesson No. 16

The Cell Test Book Questions

Q1) Define a cell.

Ans: The cell is the basic structural and functional unit of all known living organisms. It is the smallest

unit of life that is classified as a living thing (except virus), and is often called the building block of life.

Q2) Who discovered the cell?

Ans: The cell was discovered by Robert Hooke in 1665.

Q3) Give three examples of unicellular organisms.

Ans: Three examples of unicellular organisms are:-

i) Amoeba ii) Euglena iii) Paramecium.

Q4). (i) Why cells could not be observed before 17th

century?

Ans. Cells could not be observed before 17th century because of the non-availability of the microscope.

Cells are microscopic in nature. A. V Leeuwen Hock (1674) first studied the living cell.

(ii) Why cork could not be observed as such by Hook?

Ans. Robert Hooke could not observe the cork as such because it is a solid structure.

(iii) Where did Hook demonstrate his observations on cork slice?

Ans. Robert Hook demonstrated his observations on cork slice to scientist at Royal Society of London.

(iv) Name the outermost layer of an animal cell?

Ans. The outermost layer of an animal cell is the plasma membrane.

(v) Name the layer which is present outside the plasma membrane in plant cell? Ans. Cell wall is present outside the plasma membrane in the plant cell.

(vi) Where are chromosomes present in a cell?

Ans. Chromosomes are present in the nucleus of a cell.

(vii) Name the cell part that has tiny holes?

Ans. Cell membrane (plasma membrane) is the part of a cell that has tiny holes.

(viii) Name the cell having organelles which are found in the plant cell?

Ans. The cell organelles found in a plant cell are:-

(i) Mitochondria (ii) Plastids (iii) Endoplasmic reticulum

(iv) Golgi complex. (v) Vacuoles (vi) Lysosomes

(vii) Ribosomes (viii) Cell wall.

(ix) Name the cells having branched structure?

Ans. Nerve cells ( neurons) & osteocytes (bone cells) have branched structure.

(x) Which cell can be observed with unaided eye?

Ans. Ostrich egg (170mm x 135 mm) can be observed with the unaided eye.

Q5) Mention the functions of the following:

(a) Cell membrane (b) Chromosomes

(a) Cell membrane

Ans. (i) It provides shape to the cell

(ii) It protects the cell from injury.

(iii) It regulates the flow of material into and out of cell.

(iv) It keeps the cell contents in place.

(b) Chromosomes

(i) They govern the morphology of the cell.

(ii) They are responsible for passing genetic characters from parents to the off springs as

chromosomes are composed of DNA which contains genes.

Q6) Why are the following important to a plant cell?

(i) Cell wall (ii) Chloroplast (iii) Mitochondria (iv) Nucleus

(i) Cell Wall

(a) It provides shape and rigidity to the cell

(b) It protects the protoplast

Science 8th


--Sir Ishfaq/ssnp

(c) It increases the size of cell by continuous absorption.

(d) It prevents over expansion when water enters into the cell, acting as pressure vessel of

the cell.

(ii) Chloroplast.

(a) Chloroplasts are the site of photosynthesis, so called as kitchen of the cell.

(b) Chloroplasts provide colour to the leaf due to a green pigment called chlorophyll.

(iii) Mitochondria

(a) These are sites of aerobic oxidization (cellular respiration) of glucose to produce ATP

molecules, there by providing the cell with energy.

(b) They provide biological intermediates for synthesis of various biomolecular substances

like amino acids etc.

(iv) Nucleus

(a) It controls all metabolic activities of the cells hence called “the director of cell”

(b) It is responsible for passing genetic characters from parents to off springs because

chromosomes lie within nucleus.

(c) Nucleus governs the morphology of the cell.

(d) Cell division initiation and regulation is done by the nucleus.

Q7) Draw an outline diagram of Plant cell and animal cell. Label the different parts?

Q8) Give the differences between an animal cell and a plant cell?

Animal Cell Plant Cell 1. Animal cells are generally small in size. 1. Plant cells are generally larger than

animal cells.

2. Only cell membrane is present around the cell. 2. It is enclosed by a thick dead cell wall in

addition to cell membrane.

3. Plastids are absent. 3. Plastids are present.

4. Vacuoles are many but small sized. 4. Vacuoles are fewer but large sized.

5. Nucleus is generally near the centre of the cell. 5. Nucleus is often pushed to the outside of

peripheral cytoplasm by central vacuole

containing cell sap.

6. Reserve food material is in the form of glycogen. 6. Reserve food material is in the form of starch.

7. Centrosome is present. 7. Centrosome is absent.

Q9) What features are possessed by both plant cells and animal cells?

(i) Both Plant cell and Animal cell posses nucleus, Cytoplasm, Cell membrane, Chromosomes,

Mitochondria, endoplasmic reticulum, gogli complex, lysosomes & ribosomes.

(ii) Cell division is shown both by Plant and Animal Cell.

(iii) Cell differentiation is the feature of both Plant cell and Animal Cell.

Endoplasmic reticulum Cell wall Chloroplast

Ribosomes Golgi apparatus

Mitochondrion

Nucleus Nucleolus

Large vacuole Containing sap Cell membrane

Plant cell

Endoplasmic reticulum Centrosome Mitochondria Nucleolus Golgi Apparatus Nucleus Ribosomes (tiny dots) Cell membrane Nuclear envelope

Animal cell

Science 8th


--Sir Ishfaq/ssnp

Q10) Why are nerve cells long? Why do these cells have projections?

Ans. The shape of the cell is related to its function. A nerve cell clearly exhibits this relationship.

Nerve cell is long, branched and has thread like projections as it receives and transfers messages

thereby helping to control and coordinate the working of different parts of the body.

Q11) Why are mitochondria known as the power house of the cell?

Ans. Mitochondria are the main site of cell respiration. During the cellular respiration, oxygen brings

about the oxidation of food & energy gets released & this energy is then used to perform different life

processes. For this reason, mitochondria are called as „the Power house‟ of the cell. Some of this energy is

stored in the form of ATP molecules. So, Mitochondria are also known as “ATP Mills”, or “ATP plants”

or “Storage batteries”.

Q12) Which four basic elements constitute more than 90% of protoplasm?

Ans. Ninety nine percent of protoplasm by weight is made up of four elements namely carbon, hydrogen,

nitrogen and oxygen.

Q13) Write in brief about the variation in shape and size of cells?

Ans. Cell shape : Following are the different shapes of the cells in different organisms.

* Spherical (eggs of many animals).

* Spindle shaped (smooth muscle fibre).

* Elongated and branched (nerve cell).

* Oval shaped ( R.B.C‟s).

However, some cells may not have definite shape e.g. Amoeba, W.B.C‟s etc.

Cell Size: Most of the cells are microscopic in nature. The size of the cell varies from the very small cells

of bacteria (0.1 – 0.5 micrometer) to the very large eggs of ostrich (170mm x 130mm). In humans, R.B.C

(7mm) is the smallest and nerve cell (about 100cm) is the largest cell.

Q14) Name the different cell organelles and the functions of these organelles?

Ans. A number of organelles occur in the cytoplasm these are:

(i) Mitochondria (ii) Chloroplast (iii) Endoplasmic reticulum (iv) Golgi complex

(v) Lysosomes (vi) Ribosomes

The functions of the cell organelles are as:

(i) Mitochondria: (a) These are sites of aerobic oxidation (cellular respiration) of glucose to produce ATP molecules.

(b) They provide biological intermediates for synthesis of various biomolecular substances like

amino acids etc.

(ii) Chloroplast.

(c) Chloroplasts are the site of photosynthesis, so called as kitchen of the cell.

(d) Chloroplasts provide colour to the leaf due to a green pigment called chlorophyll.

(iii) Endoplasmic Reticulum:

(a) It provides surface area for various enzymatic reactions.

(b) It forms new muscular membrane after each cell division.

(c) S-ER is concerned with the metabolism of phospholipids and steroids.

(d) R-ER is concerned with synthesis of proteins which are used outside the cell.

(iv) Golgi complex: (a) They help in condensation, package and storage of material.

(b) They form the acrosome of the sperm.

(c) In plants they are called dictyosomes where they help in formation of cell wall.

(v) Lysosomes: (a) They bring about intercellular digestion in unicellular organisms.

(b) They help in cell division.

(vi) Ribosomes:

(a) Ribosomes are responsible for protein synthesis as translation takes place in it.

(b) Many ribosomes remain attached to a single m-RNA molecule during protein synthesis to

form polysomes.

Science 8th


--Sir Ishfaq/ssnp

Some Additional Questions Q15) Who discovered cell and how?

Ans. Robert Hook (1665), an English scientist discovered the cell for the first time. He examined a thin

slice of cork under his self designed crude microscope. He observed that cork resembled the structure of a

honey comb consisting of many hexagonal compartments. He coined the term “Cell” for each box which

in Latin means little room.

Q16) What is staining? Give example of stains.

Ans. The process of colouring (dyeing) of the cell organelles to observe the fine structure of the cell is

called as staining. Safranine; eosin, methylene blue and crystal violet are some common stains.

Q17) What is a micron?

Ans. The cells and their organells are measured by fraction of a millimeter (mm). One

thousandth(1/1000) of a millimeter is called a micron or micrometer. 1 micron = 103 millimeters.

Q18) Point out the difference between the prokaryotes and eukaryotes.

Prokaryotic cell Eukaryotic cell

1. These are generally small in size (1-10um). 1. These are generally larger in size

(5-100um)

2. Genetic material is not surrounded by 2. Distinct nucleus is present and

a nuclear membrane and is in direct contact is surrounded by a nuclear

with cytoplasm Membrane and is not in direct

contact with cytoplasm.

3. Single chromosome present. 3. Contains more than one

chromosomes.

4. Membrane bounded cell organelles are 4. Membrane bound cell organelles

absent. are present.

5. Cell division occurs by binary fission or 5. Cell division occurs by mitosis

budding or meiosis Q19) Why lysosomes are known as „suicidal bags?

Ans. Lysosomes contain hydrolytic enzymes and these enzymes may even digest their own

contents if burst. They carry out autolysis (auto –self; lysis; breakdown) hence called suicidal

bags.

Q20) Explain the process of ingestion in the unicellular organisms?

Ans. The process by which the food is taken inside the body of an organism is called ingestion.

Some unicellular organisms ingest the food in the following ways:

Amoeba: Uses its false feet called pseudopodia to engulf tiny food particles

Paramecium: Has fine hair-like structures called cilia all over its body. The cilia pushes the

food particles along with the water current into its mouth.

Hydra: In hydra there are a large number of tentacles around its mouth which catch small

aquatic animals and kill them with their sting cells. Then the food is pushed inside the mouth. Define Plasma membrane? Give the detailed structure of Plasma membrane with the help of fluid

Mosaic Model:-

Ans:-Plasma membrane:- Plasma membrane is a thin lining selectively permeable membrane that

surrounds all the prokaryotic as well as eukaryotic cells. It is also present around the most cell organelles

in eukaryotic cells. It has the same structure every where, hence it is also called as unit membrane.

Molecular structure of plasma membrane

Fluid Mosaic Model given by Nicolson and Singer in 1972 fully explains the molecular structure

of plasma membrane, According to this model, the plasma membrane is a bilamellar structure i.e.

it is made of two layers of Phospholipids in which are embedded the proteins molecules. The

protein molecules in the plasma membrane have been compared as „the protein ice bergs floating

in the sea of lipids‟. The proteins present inside the membrane between the Phospholipids

molecules are known as intrinsic proteins and those on the outer surface of the membrane are

Science 8th


--Sir Ishfaq/ssnp

known as extrinsic proteins. There are some intrinsic proteins seen through out the both lipid

layers these are known as channel proteins. On the outer surface of membrane there are present

Glycogen molecules, if these molecules are attached with lipid molecules they form Glycolipid

complex and if to the proteins they form Glycoprotein complex, each lipid molecule has a

hydrophobic tail directed inwards and hydrophilic head directed out wards.

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Lesson No. 17

Some natural phenomenon Terminology

Static Electricity: A stationary electric charge, typically produced by friction that causes sparks or

crackling or the attraction of dust or hair constitute static electricity.

Earthing: The process of transferring charges from a charged body to the earth is called earthing.

Thunderstorm: A loud noise produced across the sky during a rainy day is thunderstorm.

Lightning: A bright light produced across sky between the two clouds or between the cloud & earth

is lightning.

Earthquake: The disturbance deep inside the earth‟s crust which causes trembling & shaking of

earth is called an earthquake.

Lightning Rod: It is a device used to secure tall buildings from the effect of lightning.

Discharge: The phenomenon when negative charge from the cloud comes in contact with the

positive charge on the ground or another cloud, a huge amount of energy is produced in the form of

light & sound.

Earthquake: The disturbances deep inside the earth‟s crust which causes trembling and shaking of

earth is called an earthquake.

Epicentre: The point on the earth‟s surface, directly above the seismic focus.

Seismic focus: A place of origin of an earthquake inside the earth is called seismic focus, from this

point, shock waves spread in all directions.

Seismic waves: The waves generated inside the earth‟s surface due to earthquake are called seismic

waves or shock waves.

Seismograph:- The instrument which detects and records the intensity of seismic waves generated

by an earthquake is called seismograph.

Richter scale: It is used to describe the magnitude of an earthquake.

Electroscope:- The device which can be used to test whether an object is carrying a charge or not.

Science 8th


--Sir Ishfaq/ssnp

(Textual Questions) Very short answer questions

Q.1) What is meant by electrostatic force?

Ans) The force of attraction or repulsion exerted on the small objects which is developed due to

rubbing a comb against dry hair or rubbing a balloon against a woolen material is called as

electrostatic force.

Q.2) What is meant by lightning?

Ans) A bright light produced across sky between the two clouds or between the cloud and earth

is called lightning.

Short answer type – 1 questions

Q.1) What is meant by charging by friction?

Ans) Charging an object by rubbing it with another object is called charging by friction.

Q.2) When does a body is said to be charged?

Ans) A body when rubbed with another suitable body and capable of exerting an electrostatic force

over other bodies is said to be charged.

Short answer type – 2 questions

Q1) List any three causes of earthquake?

Ans) Three causes of earthquake are:

(a) Movement of the tectonic plates (b) Volcanic eruption (c) Dislocation (or faults) of the crust Q.2) What are harmful effects of lightning?

Ans) Various harmful effects of lightning are:

a) It can cause fire and shatter buildings resulting in lot of destruction and damage to the

property.

b) It can burn trees and also cause forest fires.

c) It causes injuries or sometimes even kills animals and people instantly. Long answer questions

Q1) Write an activity to show that a charged body attracts tiny bits of paper towards itself?

Ans) Bring a plastic comb and small bits of paper. Rub a plastic comb against your dry hair and bring

it close to small bits of paper. We will see that small bits of paper are attracted towards plastic comb

because rubbing a comb against dry hair produces a kind of force in it, that attract small paper bits

due to development of charge on it. Therefore, comb when rubbed is said to be electrically charged

and the force due to which it attracts small bits of paper is known as electrostatic force.

Q.2) What is a volcano? How do volcanoes cause earthquakes?

Ans) Volcano is a hole in the earth‟s crust through which the molten rocks and hot gases under

high pressure rushes out.

The energy released during volcanic eruption causes vibrations in the crust. These

vibrations cause earthquakes in the area around. Such earthquakes occur at the time of volcanic

eruption or before it.

(Additional Questions) Q1) Sometimes, a cracking sound is heard while taking off sweater during winters. Explain.

Ans: Woolen clothes get electrically charged when they get rubbed. Due to rubbing, attraction or

repulsion occurs between their loose particles which results in cracking sound.

Q2) Explain why a charged body loses its charge if we touch it with our hand?

Ans: Human body is a conductor of electricity. Therefore, when a charged body is touched with

hand, the electric current of charged body passes to the earth through the body & charged body loses

its charge.

Q3) Name a scale on which the destructive energy of an earthquake is measured .An earthquake

measures three on this scale .Would it be recorded by a seismograph? Is it likely to cause much

damage?

2

Science 8th


--Sir Ishfaq/ssnp

Ans: Scale used to measure earthquake is Richter scale .Earthquake with value 3 can be recorded on

seismograph but this earthquake is very feeble in its intensity & very less destructive.

Q4) Suggest three measures to protect ourselves from lightning?

Ans: Measures of protection:-

a) On hearing thunder, go in closed areas such as houses, buildings, etc.

b) In bus /car, close all the doors and windows.

c) In open, sit on floor with your head in knees & arms.

Q5) Explain why a charged balloon is repelled by other

charged balloon whereas an uncharged balloon is attracted by

another charged balloon.

Ans: Same materials get same charges on rubbing & like

charges repel each other whereas unlike charges attract.

Therefore , balloon on rubbing get same charges & thus repel

each other while a charged balloon & an uncharged balloon

attract each other because of opposite charge induction.

Q6) Describe with the help of diagram an instrument which

can be used to detect a charged body.

Ans: Electroscope is used to detect electric charges or kind of

charge on a body.

It consists of a glass jar, which is covered by a wooden or

cardboard disc fixed with an aluminum foil on a paper clip in the vertical position attached at the

centre of the cardboard disc as shown in figure.

When a charged body is brought near the paper clip, two aluminum foils repel each other.

Q7) List three states in India where earthquakes are more likely to strike.

Ans: States of India highly susceptible to earthquake are:-

a) Rann of Kutch (b) Rajasthan & (c) J&K

Q8) Suppose you are outside your home & an earthquake strikes. What precautions would you

take to protect yourself?

Ans: Protection against earthquake outside the house are:-

a) Lie down in open far from buildings, trees & electric poles.

b) Do not step out from car or bus.

c) Take car or bus towards open areas.

Q9) The weather department has predicted that a thunderstorm is likely to occur on a certain day

.Suppose you have to go out on that day. Would you carry an umbrella? Explain.

Ans: To go out during thunderstorm is not safe and with umbrella it is fatal because high buildings,

electric wires, black materials, etc all attract thunderstorm / lightning .So, it is advisable to stay away

from them.

Q1) Why does paper strip open up when touched with a charged rod?

Ans: When we touch one side of the paper strip with a charged rod, it opens up because the two sides

of the strip get the same type of charge from the charged rod & thus repel each other .With the result

, the paper strip opens up (diverges).

Q2) Why are we advised not to be under a tree , if we are in open during a thunderstorm?

Ans: A highly charged cloud when comes near the tree can induce a powerful opposite charge on the

top of tree .This can cause lightning between the cloud & the earth through the tree. It can damage

the tree & can cause fire.

Q3) Why are tall buildings provided with metallic rods running from the top of building to the ground?

Ans: Since metals are good conductors of electricity, they carry the charges from lightning directly

to the ground & the building is thereby saved from the corresponding damage.

Q4) What do you mean when we say that a body is electrically charged or electrified?

Ans: A body like plastic comb, pen, etc when rubbed with another body gets the property of

attracting small pieces of paper, etc. Then, such a body is called electrically charged or electrified.

Science 8th


--Sir Ishfaq/ssnp

Q5) What do you mean by Tsunami? Give examples what are its effects?

Ans: Tsunami is a long & high wave which rises under sea due to earthquakes. It is usually a high

speed wave, which rises in sea. It is also known as harbour wave.

Examples:- In 1819 on Hawain Islands & in 2004 in Tamil Nadu.

Effects of Tsunami:-

a) Loss of lives. b) Loss of aquatic life. c)Physical damage of human life & property.

d) Uprooting of plants on the banks of sea or at coastal regions.

Very Short Answer Type Q1) What is amber?

Ans: It is a type of resin.

Q2) Who established that spark & lightning wave same phenomenon?

Ans: Benjamin Franklin, an American scientist.

Q3) What happens when two balloons rubbed with woolen cloth are brought together?

Ans: They repel each other.

Q4) Which type of charges attract each other?

Ans: Unlike or opposite charges attracts each other.

Q5) How many types of charges are there?

Ans: There are two types of charges positive & negative.

Q6) Why does a plastic comb rubbed in hair attract small bits of paper?

Ans: Because it gets charged.

Q7) Is human body a conductor or Insulator?

Ans: A conductor.

Q8) What happens when glass rod is rubbed with silk cloth?

Ans: Glass rod gets positive charge & silk cloth gets negative charge.

Q9) Name the device which is used for testing the presence of charge on a body?

Ans: Electroscope.

Q10) What is the magnitude of destructive earthquake on Richter scale?

Ans: 7 or above 7

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Science 8th


--Sir Ishfaq/ssnp

Documents

L.No.1 Micro-Organisms: Friend’s & Foe’s Terminologyscholarsschool.com/CMS/Files/Class 8th Science 2017.pdf(a) Immunity: Immunity or disease resistance is the ability of an organism