Lecture: 9 :CLASS VIII : SCIENCE : Chapter 2: BAD MICRO-ORGANISMS

CLASS VIII   |    SCIENCE    |    CHAPTER 2

      notes prepared by subhankar Karmakar

HARMFUL MICROORGANISMS:

Those microorganisms which cause diseases are harmful to us and called pathogens. Pathogens can be bacteria, viruses, protozoa, fungi etc.

Communicable diseases:

Those microbial diseases which can spread from an infected person to a healthy person through air, water, food or physical contact, etc are called communicable diseases.

Some of the examples of communicable diseases are: Common cold, Cholera, Chicken pox, Tuberculosis (TB), Malaria and AIDS. 

Different ways by which communicable diseases can occur and spread:

Any communicable diseases can occur and spread in the following ways:

1. By breathing of air containing microorganisms,

2. By taking infected food or water,

3. Through insect bites,

4. By sharing infected injection needles,

5. By physical contact with an infected person.

Prevention of communicable diseases: 

Methods for preventing the occurrence and spreading of communicable diseases are as follows: -

1. A person suffering from common cold or influenza should always cover his mouth and nose with a handkerchief while sneezing, so that microorganisms are not being released into the air. We must keep a social distancing too.

2. We should keep our food covered to protect it from getting infected by flies. You should also drink clean and safe water.

3. We should use mosquito nets to protect ourselves from mosquito bites

4. Disposable syringes and needles should we use for injection.

5. A person infected by a communicable disease should be quarantined.

6. We should follow proper vaccination at proper time.

Vectors or carriers of disease causing microorganisms:

The insects or other animals which transmit disease-causing microorganisms to humans without itself suffering from them are called vectors or carriers. 

The most common Carriers of disease causing microorganisms are:

1. Housefly and

2. Mosquito

A. Housefly as the vectors of diseases:

Some of the dangerous diseases spread by housefly are: cholera, tuberculosis (TB), typhoid and diarrhoea.

Prevention of diseases spread by housefly:

The spreading of diseases by houseflies can be prevented in the following ways:

1. Household garbage should be put in garbage bin which should be kept covered. This will prevent the house flies from breeding because they will not be able to lay their eggs on garbage.

2. The food should always be kept covered so that flies cannot sit on it.

3. We should avoid eating uncovered food items from the roadside stalls.

4. The flies should be killed by using insecticide spray.

5. We should take proper vaccination as some of the diseases spread by housefly can be prevented by vaccination.

B. Mosquitoes as the vectors of diseases:

Mosquito spread diseases by transmitting disease causing microorganisms through its bites.

The most common diseases spread by mosquitoes are malaria and dengue fever.

Prevention of diseases spread by mosquitoes:

The spreading of diseases by mosquitoes can be prevented in the following ways:

1. As the mosquitoes breed in stagnant water, we should avoid any pools of stagnant water around the houses and our surroundings should be clean and dry.

2. The windows and doors of the house should have fine iron wire mesh so that mosquitoes cannot enter our house.

3. Insecticides should be spread in houses periodically to kill mosquitoes.

4. Oil should be sprayed on the surface of water in dirty water drains to kill the larvae of mosquitoes.

5. Mosquito net should be used over beds while sleeping to prevent mosquito bites.

Some of the common diseases caused by bacteria:

Tuberculosis, Cholera, Typhoid etc.

Some of the common diseases caused by virus:

Measles, Chicken pox, Polio, Hepatitis B,  Dengue.

Disease causing microorganisms in animals:

Some of the example of diseases caused in animals by the microorganisms are: foot and mouth disease, anthrax, aspergillosis.

1. Foot and mouth disease of animals like cattle is caused by a virus.

2. Anthrax is a dangerous disease of animals like cattle which is caused by a bacterium, known as bacillus anthracis.

3. Aspergillosis is a disease of animals like poultry birds which is caused by fungus.

Disease causing microorganisms in plants:

Several microorganisms cause diseases in plants like Wheat, Rice, Potato, Orange, Apple and others. 

Some of the common plant diseases caused by microorganisms are: rust of wheat, citrus canker and yellow vein mosaic of bhindi.

Rust of wheat is caused by fungi.

Citrus canker is caused by bacteria.

Yellow vein mosaic of bhindi is caused by virus.

Food poisoning:

The disease caused due to the presence of a large number of microorganisms like bacteria and fungi in the food or due to the presence of toxic substances in food formed by the action of microorganisms is called food poisoning.

The major symptoms of food poisoning are: vomiting, diarrhoea, pain in abdomen, headache and fever.

The most common microorganisms which cause food poisoning are salmonella bacteria, clostridium botulinum bacteria and aspergillus fungus.

Lecture: 8 :CLASS VIII : SCIENCE : Chapter 2: GOOD MICRO-ORGANISMS

Friendly microorganisms/ beneficial microorganism:

Not all microorganisms are bad for human. Some of them are useful too. Beneficial effects of microorganisms are as follows:

1. In the making of card, bread and cake microorganisms are used.

2. In the production of alcohol, wine, acetic acid or vinegar microorganisms are used.

3. Microorganisms are used to produce antibiotics.

4. Microorganisms are used to increase the fertility of the soil by nitrogen fixation.

5. Microorganisms are used to decompose the organic waste matter.

a. Process to make curd:

Milk is is turned into curd by using the bacteria Lactobacillus. 

Milk contains sugar called lactose. Lactobacilli bacteria convert the lactose sugar into lactic acid. This lactic acid then converts milk into curd.

b. Process to make bread:

Yeast is used in the baking industry for making bread. When Yeast is mixed in dough, it reproduces quickly and produces carbon dioxide during respiration. The bubbles of carbon dioxide gas filled the dough and increases volume. This is the secret of increasing the volume of bread. It makes the bread light, soft and spongy.

c. Commercial use of microorganisms:

Microorganism are used for the large scale production of alcohol and acetic acid. Yeast is the microorganism used for the large scale production of alcohol.

The process of conversion of sugar into alcohol by the action of yeast is called fermentation. 

Bacteria can turn alcohol into acetic acid. A dilute solution of acetic acid is called vinegar.

The bacteria which convert alcohol into acetic acid is called Acetobacter.

d. Medicinal use of microorganism:

A medicine which stops the growth of, or kills the disease causing microorganisms is called antibiotic. Antibiotics medicine are made from microorganisms. 

Example: some of the common antibiotics which are made from fungi and bacteria are: penicillin, streptomycin, erythromycin, tetracycline.

Antibiotics are effective for bacteria causing diseases but they are ineffective against the diseases caused by virus.

Precautions that to be observed in the use of antibiotics:

1. Antibiotics should be taken only on the advice of a qualified doctor.

2. A person must complete the full course of antibiotics prescribed by the doctor.

3. The antibiotics should be taken in proper doses as advised by the doctor.

4. Antibiotics should not be taken unnecessarily, if taken unnecessarily it may kill the useful bacteria in the body and harm us.

Vaccine:

A vaccine is a special kind of preparation or medicine which provides immunity or protection against a particular disease.

A vaccine contains the dead or weakened but alive microorganisms of a disease. Find the vaccine containing dead or alive microorganisms introduced into the body of a healthy person either orally or by injection the body of that person responds by producing some substances called antibodies in the blood. These antibodies kill the disease causing microorganism in the body. Thus a vaccine developes the immunity from a disease.

Vaccination: 

Vaccination is the process of giving a vaccine orally or by injection which provides protection against a particular disease.

The diseases which can be prevented by vaccination of children at proper age are: polio, smallpox, cholera, typhoid, hepatitis, tuberculosis, tetanus, measles, rabies, diphtheria and whooping cough.

Polio in India is prevented by giving oral polio vaccine or OPV under the pulse polio programmes of government of India.

e. Increasing soil fertility by microorganisms:

Some bacteria and blue green algae are able to fix nitrogen gas from the atmosphere to enrich the soil with nitrogen compounds and increase its fertility. The nitrogen fixing bacteria and blue green algae are called biological nitrogen fixers. One of the nitrogen fixing bacteria is rhizobium. Rhizobium bacteria present in the root nodules of leguminous plant (like peace, beans etc) also fix atmospheric nitrogen and increase soil fertility.

f. Cleaning the environment by microorganisms:

Some microorganisms decompose the harmful and smelly dead remains of plants and animals and animal wastes (like faeces, urine etc) into harmless materials and thus they clean the environment. In addition to the cleaning the environment, the microorganisms also help in recycling the nutrients present in dead plants, dead animals and animal wastes in nature which can then bi used as food by Green plants.

CLASS-VIII: SCIENCE: CONSERVATION OF PLANTS AND ANIMALS

CLASS VIII  |   SCIENCE   |  CHAPTER 7

           notes prepared by Subhankar Karmakar

Chapter 7: conservation of plants and animals

Q1) Define biosphere.

Ans: Biosphere is that part of the earth in which living organism exist. It includes land surface of the earth, atmosphere of the earth, as well as water bodies on the earth.

Q2) What do you understand by the term wildlife? 

Ans: The term wildlife means all the animals and plants which are found naturally in the forest and other natural habitats.

Q3) What is biodiversity? 

Ans. Biodiversity refers to the variety of organisms like plants animals and microorganism etc better found in a particular area of habitat.

Q4) What is an ecosystem?

Ans: A system which includes all the living organisms like plants animals and microorganisms of an area and the physical environment like soil air and water in which they live are together called an ecosystem.

Q5) What is deforestation?

Ans: The tearing of forest by cutting down forest trees over a wide area is called deforestation.

Q6) What are the various causes of deforestation?

Ans: The various causes of deforestation are

i) the forest trees are cut down to obtain wood for using as fuel

ii) the forest trees are cut down to obtain doors, windows and furniture.

iii) the forest trees are cut down to obtain wood for making paper.

iv) the forest trees are cut down to obtain more agricultural land for cultivation of crops for the increasing population.

v) the forest trees are cut down to get land for building houses, factories, roads and dams etc.

Q7) What are the consequences of deforestation?

Ans: The consequences of deforestation are 

i) deforestation will lead to a shortage of wood and other forest products

ii) deforestation will cause an increase in temperature of Earth's atmosphere leading to global warming.

iii) deforestation will cause soil erosion making the soil infertile and lead to desertification.

iv) deforestation will cause frequent flooding of rivers leading to loss of life and property.

v) deforestation affects the water cycle leading to decrease in rainfall. The decrease in rainfall lowers  the groundwater level and could cause droughts.

vi) deforestation leads to the extinction of many wild animals and plants.

Q12) Name some biosphere reserves of India.

Ans: There are several biosphere reserves in India. 

These are

1. great nicobar biosphere reserve

2. Kaziranga biosphere reserve

3. Sundarbans biosphere reserve

4. Kanha biosphere reserve

5. Pachmarhi biosphere reserve

Q13) What are the roles of biosphere reserve?

Ans: The biosphere reserves perform the following roles

1. It help in conservation of wildlife of the area

2. It help to maintain the biodiversity of the area.

3. It preserve the natural ecological conditions in the area.

4. It promotes the economic development of the area.

5. It helps to maintain the lifestyle the tribal people living in the area

6. It prevents the commercial exploitation of the area.

7. It provides opportunities for scientific research, environmental education and tourism.

Q14) What do you understand by flora and fauna?

Ans: The plants that grow naturally in a particular area are called Flora of that area and the animals which live naturally in a particular area are called fauna of that area. As an example, Teak, jamun, fern, mango, Arjun are the flora of pachmarhi biosphere reserve and cheetal, wolf, Leopard, chinkara, blue bull, barking deer and wild dog are the examples of fauna of the pachmarhi biosphere reserve.

Q15) What are endemic species of a particular area?

Ans. Endemic species are those species both of plants and animals which are found exclusively in a particular area. The plants and animals which are found only in a particular area are said to be endemic to that area. As an example sal and wild mango are the two examples of the endemic flora of the pachmarhi biosphere reserve and giant squirrel, flying squirrel and bison are the three examples of endemic fauna of the pachmarhi biosphere reserve area.

Q16) Explain biosphere reserve.

Ans: A biosphere reserve is a large, protected area of land meant for the conservation of wildlife, biodiversity, and the traditional lifestyle of the tribal people living in the area. A special feature of the biosphere reserve is that local people or tribals are an integral part of it.

Q17) What are the different zones in a biosphere reserve?

Ans: A biosphere reserve has been divided into 3 zones.

i) The innermost zone of a biosphere reserve is known as core zone. It is devoted to strict protection of wildlife. No human activity e is allowed in the core zone of a biosphere reserve.

ii) The middle zone of a biosphere reserve is called buffer zone. Buffer zones around the core zone and limited human activity  is allowed here.

iii) The outermost zone of a biosphere reserve is called transition zone. In the transition zone several non destructive human activities such as settlements of tribals and cultivation of crops are allowed.

Q18) What are the different types of protected areas which have been established by the government for the conservation of forest and wild animals?

Ans: There are three types of protected areas established by government for the conservation of forest and wild animals. These are

i) biosphere reserves

ii) wildlife sanctuaries

iii) national parks

Q19) Why do we need protected areas forest and wildlife conservation?

Ans: The purpose of establishing several biosphere reserves, wildlife sanctuaries and national parks in India is to conserve wild animals and their natural surroundings so as to maintain a healthy balance in nature and to prevent the extinction of endangered wild animals.

Q20. What is wildlife sanctuary?

Ans. Wildlife sanctuary is a protected area of land who is is created for the protection of wild animals in their natural environment like forests. Therefore a wildlife sanctuary provides protection and suitable living conditions to the wild animals in their natural habitat. In a wildlife sanctuary killing or poaching and capturing of wild animals is strictly prohibited.

Q21. Write the name of some wildlife sanctuaries of India.

Ans. There are more than 500 wildlife sanctuaries in India. The major wildlife sanctuaries are-

1. Sanjay Gandhi wildlife sanctuary in Maharashtra

2. Mudumalai wildlife sanctuary in Tamil Nadu

3. Nagarjun Sagar wildlife sanctuary in Andhra Pradesh

4. Bharatpur Bird sanctuary in Rajasthan

5. Sultanpur lake bird sanctuary in Haryana

6. Dandeli wildlife sanctuary in Karnataka

7. Thattekad Bird sanctuary in Kerala

8. Satkosia Basipalli wildlife sanctuary in West Bengal

9. Lokchao wildlife sanctuary in Manipur

10. Bori wildlife sanctuary in Madhya Pradesh.

Q22. What are the differences between biosphere reserve and wildlife sanctuary?

Ans. The main differences between biosphere reserve and wildlife sanctuary are as follows.

1. A biosphere reserve is spread over a very large area of land, where as a wildlife sanctuary occupies a comparatively smaller area of land.

2. A biosphere reserve is for the conservation of biodiversity of the area as well as the economic development of the area where as a wildlife sanctuary is mainly for the protection of wild animals of the area in their natural habitat.

3. Local tribal people form an integral part biosphere reserve where as local people is not included in a wildlife sanctuary.

4. The human activities such as cultivation of land and building of settlements are allowed in the outermost zone of a biosphere reserve where as the human activities are not allowed in a wildlife sanctuary.

Q23. What is a national park?

Ans. A National Park is a relatively large area of scenic beauty  protected and maintained by the government to preserve flora and fauna landscape history objects of the area and places of of scientific interest. Another purpose of establishing National parks is to provide human recreation and enjoyment.

Q24. Write the name of some prominent National parks of India.

Ans. Name of the some prominent National parks of India are as follows.

1. Corbett national park in uttarakhand

2. Kanha national Park in madhya Pradesh

3. Ranthambore national Park in Rajasthan

4. Gir national Park in Gujarat

5. Kaziranga national Park in Assam.

Q25. What is project tiger?

Ans. Tiger is one of the many wildlife species which are slowly disappearing from our forest. Project tiger is a world life conservation project which was launched by the government of India in 1972 to protect the tigers in the country. There are 28 tiger reserves in India at present which are governed by project tiger.

Q26. What are the main differences between a wildlife sanctuary and a national park?

Ans. The main differences between a wildlife sanctuary and a national park are as follows

1. A Wildlife sanctuary may or may not be an area of great scenic beauty but a national park is an area of great scenic beauty.

2. A wild life sanctuary protects and preserves the wild animals in their natural environments but a national park protects and preserves wild animals and their environment as well as the scenic beauty e historical objects and habitats of scientific interest in the area.

3. A wildlife sanctuary is not meant for  recreation and enjoyment of the public but in a national park in addition to protection wild animals are kept for recreation enjoyment and educated interests of the public.

4. Wildlife sanctuary is usually does not allow easy access to the visitors but a national park allows easy access for the visitors.

Q27. What is a a extinct species?

Ans. The species who is no longer exist anywhere on the earth are called extinct species. Dinosaur, dodo bird, cave lion, Caspian tiger, Irish deer are examples of extinct species.

Q28. What is an endangered species?

Ans. The species which are facing the risk of extinction are called endangered species. It means that the wild animals whose numbers are are diminishing to such a low level that they might face extinction soon are known as endangered animals. Tiger, snow leopard, great Indian rhinoceros, Asiatic lion, desert cat, lion tailed macaque, namdapha flying squirrel and Kashmir stag are some examples of endangered species.

Q29. What is a red Data book?

Ans. Red Data book is the book which keeps record of all the endangered animals, plants and other species. Some of the endangered species of animals listed in the red Data book of India are: Flying squirrel, Indian giant squirrel, Barasingha, blackbuck, Himalayan musk deer, great Indian rhinoceros, snow leopard and tiger.

Q30. What is migration?

Ans. Thr process of a bird or other animals moving from one place to another according to the season is called migration. Migration of birds for other animals is an adaptation to escape the harsh and cold conditions of their normal habitat in winter so as to survive. 

Q31. What are migratory birds? 

Ans. The birds which move from very cold region to warmer regions in winter and go back after the winter is over are called migratory birds. Migratory birds fly to far away places more than 3000 km every year. 

One of the example of migratory birds  is the Siberian crane.

Q32. What is  Recycling of paper?

Ans. Paper is made from wood pulp that is produced from the wood of the forest trees. And it causes a rapid deforestation. But we already know deforestation harms ecology very much. To save forest trees from deforestation, the used paper can be  reconverted into usable paper and that is called recycling of paper. Paper can be recycled 5 to 7 times for use.

Q33. What are the Advantage of recycled paper?

Ans. The advantages of recycling of paper are as follows.

1. Recycling of paper reduce the amount of deforestation of trees.

2. Recycling of paper saves tremendous amount water which are used in paper making.

3. Recycling of paper also save use amount of energy used in making paper.

4. It reduces the amount of harmful chemicals used in paper making.

Q34. How many full grown trees are needed to make 1 tonne of paper?

Ans. It has been estimated that 17 full grown trees are needed to make 1 tonne of paper.

Q35. What is reforestation? 

Ans. The planting of trees in an area in which forest were destroyed is called reforestation. The planted trees should generally be of the same species which wire cut down from the forest during deforestation.

Q36. What are the advantages of reforestation?

Ans. The advantages of reforestation are as follows-

1. Reforestation producers a large quantity of raw materials for industry like paper industry, timber trade etc.

2. Reforestation will lead to a decrease in global warming by reducing the amount of carbon dioxide gas in the atmosphere.

3. Reforestation increases rainfall in an area. This will raise ground water level and prevent droughts.

4. Reforestation prevents soil erosion and floods.

5. Reforestation increases the area of Earth under forest which is good for the conservation of wildlife.

Lecture-2 : CLASS-X: SCIENCE : Chapter: Electricity Content: numericals

NUMERICAL PROBLEMS ON ELECTRICITY; CLASS 10

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Q1. How much work is done in moving a charge of 3 coulombs from a point at 110 volts to a point at 220 volts?

Soln. We know, 

Potential difference = work done/charge moved

or.          V   =   W/Q

∴   W =  VQ

Here, potential difference, V = 220 - 110 = 110 volts and Charge moved , Q = 3 coulombs

 ∴  W = VQ = 3 x 110 joules = 330 joules

---

Q2. How much energy is given to each coulomb of charge passing through a 6 volt battery?

Soln. We know, 

Potential difference = work done/charge moved

or.          V   =   W/Q

∴   W =  VQ

Here, potential difference, V = 6 volts

and charge Q = 1 coulomb ( each coulomb given)

∴   W =  VQ = 6 x 1 joules = 6 joules

---

Q3. What is the potential difference between the terminals of a battery if 500 joules of work is required to transfer 25 coulombs of charge from one terminal of battery to the other?

Soln. We know, 

Potential difference = work done/charge moved

or.          V   =   W/Q

Workdone , W = 500 joules

Charge moved, Q = 25 coulombs

∴  V   =   W/Q = 500/25 = 20 volts

Therefore, the potential difference between the terminals of the battery = 20 volts

---

Q4. A circuit contains a battery of 1.4 V with a resistance of 2 ohms and a resistance of 5 ohms connected in series. Calculate the current flowing through the circuit and the potential difference across the 5 ohm resistance.

Using Ohm's law, we can calculate the current flowing through the circuit as:

I = V / R_total

where V is the voltage of the battery, and R_total is the total resistance of the circuit, which is the sum of the resistance of the 2-ohm resistor and the 5-ohm resistor:

R_total = R₁ + R₂ = 2 ohms + 5 ohms = 7 ohms

So we have:

I = 1.4 V / 7 ohms = 0.2 A

Therefore, the current flowing through the circuit is 0.2 A.

To calculate the potential difference across the 5 ohm resistor, we can use Ohm's law again, using the current we just calculated:

V_5ohm = I * R₂

where R₂ is the resistance of the 5 ohm resistor. Substituting the values we have:

V_5ohm = 0.2 A * 5 ohms = 1 V

Therefore, the potential difference across the 5 ohm resistor is 1 V.

Q5. A parallel circuit contains two resistors, one with a resistance of 10 ohms and the other with a resistance of 20 ohms. If the voltage across the circuit is 12 volts, calculate the total current flowing through the circuit and the current through each resistor.

Q6. An electric motor is rated at 120 volts and draws a current of 5 amperes. Calculate the power consumed by the motor.

Q7. A 220-volt electric heater draws a current of 5 amperes. Calculate the resistance of the heater.

Q8. A circuit contains a 10-ohm resistor, a 5-ohm resistor, and a 12-volt battery. Calculate the total current flowing through the circuit and the potential difference across each resistor.

Q9. An electric power station produces 1000 megawatts of power. If the voltage of the power lines is 100,000 volts, calculate the current flowing through the lines.

Q10. A transformer has a primary coil of 100 turns and a secondary coil of 500 turns. If the primary coil is connected to a 240-volt power source, calculate the voltage across the secondary coil.

Lecture-1 : CLASS-X: SCIENCE : Chapter: Electricity

Class X  |   Science  |  Electricity

             notes prepared by Subhankar Karmakar

CHARGE: 

Charge is a inherent property of a matter.

Types of Electric Charges:

There are two types of electric charges. 

1. Positive Charge

2. Negative Charge

POSITIVE CHARGE:

The charge acquired by a glass rod (rubbed with a silk cloth) is called positive charge.

NEGATIVE CHARGE:  

The charge acquired by an ebonite rod (rubbed with a wooden clock) is called negative charge

Property of electric charge:

1. Opposite charges or unlike charges attract each other

2. Similar charges or like charges repel each other

The SI unit of electric charge:

The SI unit of electric charge is called Coulomb.

It is denoted by the symbol C. 

1 coulomb charge:

1 coulomb charge is that charge which exerts a force of 9 x 10⁹ N force on an equal charge placed at a distance of 1  m from it.

Proton, Electron and their charge:

By convention, it is taken that electrons are negative charges where as protons are positive charges

Magnitude of a proton and an electron charge is equal to 1.6x10⁻¹⁹ C

Number of electrons in 1 coulomb charge:

Suppose we want to to find out how many  electrons will make 1 C

Formula: 

If q = magnitude of charge

   n = number of of electrons

   e = charge of an electron 

      = 1.6 x 10⁻¹⁹ C

then 

     q = ne

therefore, n = q/e

                      = 1/1.6 x 10⁻¹⁹

                      = 6.25 x 10¹⁸

So, 6.25 x 10¹⁸ electrons together make 1 coulomb charge

Conductors: 

Those substances through which electricity can flow are called conductors. All the metals are conductors. Therefore, copper, silver, aluminium, gold, iron etc are all good conductors. One non metal graphite are also conductor. 

Insulators: 

Those substances through which electricity cannot flow are called insulators. All the nonmetals are  insulators. Glass, ebonite, rubber, most plastics, paper, drywood, cotton, Mica, bakelite, porcelain and dry air examples of insulators. 

Reason behind the flow of electricity through a substance:

Electricity or electric charge can flow through a substance if the substance contains free electron. The electrons which can move from one atom to another atom freely  are called free electron.

Therefore, all the conductors contain free electrons where as all the insulators do not contain any free electron.

Free Electron: The electrons which can easily move from atom to atom are called free electron. They are the the carriers of electricity.

Electric potential: (V)

The electric potential or potential at a point in an electric field is defined as the work done in moving a unit positive charge from infinity to that point.

Explanation: suppose you take an unit positive charge and place it very very large distance which is called infinite distance, from that point if you want to bring/ move the charge against an electric field to a point you have to do a work done, that work done will be called electric potential.

Electric potential is denoted by symbol V.

SI unit of electric potential is called volt. Symbol is V. 

Definition of 1 volt: 

A potential of 1 volt at a point inside an electric field means that 1 Joule of work is done in moving one coulomb of positive charge from infinity to that point.

Electric potential difference or potential difference:

The difference in electric potential between two points is known as potential difference between that two points.

Definition: 

The potential difference between two points in an electric circuit is defined as the amount of work ok done in moving a unit charge from one point to the other point.

Formula:

Potential difference = (workdone)/quantity of charge moved

If W = work done

    Q = quantity of charge moved

    V = potential difference between two points

then, V = W/Q

SI unit of potential difference is also volt (V)

1 Volt potential difference means it needs 1 joule of work to move 1 coulomb electric charge from one point to the other.

1 volt = 1 joule / 1 coulomb

1 V = 1 J/C = 1 JC⁻¹

Voltmeter: 

The instrument by which electric potential difference can be measured is called voltmeter. Voltmeter has high resistance, and it allows only very small current through it. Potential difference is also known by voltage.

Lecture 7: CLASS VIII: SCIENCE: CHAPTER 2: CLASSIFICATION OF MICRO-ORGANISMS

Class VIII: SCIENCE:

                       Notes prepared by Subhankar Karmakar

________________________________________________

Micro-organisms: some of them are bad, but some of them are good too.

Those organisms which are too small to be seen without a microscope are called micro-organisms. Some of the microorganisms are useful to us, but some of the micro-organisms are harmful to us. 

Good micro-organisms:

For example, the microorganisms by certain bacteria help in making food products such as curd and cheese. Microorganisms are are also useful in making bread, cakes, pastries, alcohol, acetic acid or vinegar and medicines called antibiotics. 

Bad Micro-organisms;

On the other hand, the microorganisms like certain bacteria and fungi make our food rotten. The Microorganisms also caused diseases in humans, other animals and plants. The diseases like common cold, malaria, skin infections, typhoid, tuberculosis, tetanus, cholera, measles, chicken pox, smallpox, AIDS and of course covid-19 are all caused by the action of various types microorganisms.

Major groups of microorganisms:

Microorganisms are classified into 5 major groups. This groups are: 

1. Bacteria  

2. Viruses  

3. Protozoa

4. Fungi

5. Algae

Cellular structure of microorganisms: 

Some microorganisms are unicellular or single celled where as many microorganisms are multicellular or multi celled. 

1. Bacteria:

Bacteria are very small, single celled microorganisms which have cell walls but do not have an organised nucleus and other structures. They come in various shapes like spherical bacteria, rod shaped bacteria, and spiral bacteria. 

Example: Beneficial bacteria: 

Lactobacillus bacteria, which are useful for making foods like curd and Rhizobium bacteria which help in nitrogen fixation and decomposition of organic waste matter.

Harmful bacteria: Diseases like cholera, typhoid, tuberculosis or TB, diphtheria, whooping cough and food poisoning all are caused by actions of bacteria.

2. Viruses: 

Viruses are the smallest microorganisms which can develop only inside the cells of the host organisms. They are neither alive nor dead. They are not exactly living things.

Viruses can reproduce and multiply only inside the cells of other organisms like animal cells plant cells or bacteria cells.

Viruses are the agents of disease. The human diseases such as common cold, influenza, measles, polio, chicken pox, HIV, smallpox and covid-19 are all caused by viruses.

3. Protozoa: 

Protozoa are a group of single celled microorganisms which are classified as animals.

They are found in lakes, ponds, dirty water drains, sea water and damp soil. 

Some common examples of protozoa are:

Paramecium, Entamoeba and Plasmodium. 

Protozoa can be parasites also. 

Diseases caused by protozoa: 

• Entamoeba is a protozoan which causes a disease known as amoebic dysentery. 

• Plasmodium is a protozoan which causes a disease called malaria. Plasmodium is also known as Malarial Parasite.

4. Algae: 

Algae is a large group of simple plant like organisms. Like plants, they contain chlorophyll and produce food by photosynthesis.

Example:  Chlamydomonas, Spirogyra, blue green algae, Diatoms are example of algae.

Blue green algae have the ability to fix nitrogen gas of atmosphere.

5. Fungi:

Fungi are a  large group of organisms which do not have chlorophyll and do not photosynthesize. 

Some examples of fungi are: Yeast, Moulds like penicillium and aspergillus, mushrooms, toadstools, puffballs.

All fungi are made up of fine threads called hyphae except Yeast. 

Some of the human diseases caused by fungi are ringworm and athlete's foot. 

Lecture- 6: CLASS VIII : SCIENCE: CHAPTER- 1 : STORAGE

VIII-SCIENCE

Prepared By Subhankar Karmakar

7. STORAGE OF FOOD GRAINS

The fresh food grains (like wheat) obtained by the harvesting of crops contain more moisture than required for their safe storage. So, the food grains (like wheat) obtained by harvesting the crops are dried in the sunshine before storing, to reduce their moisture. It is necessary to reduce the moisture content of grains before storing to prevent their spoilage during storage.

 This is because the higher moisture content in food grains promotes the growth of fungus and mould on the stored grains which damages them (and makes them lose their germination capacity). 

The farmers store the dried food grains at home in metal bins (metal drums) and jute bags (called gunny bags). Dried neem leaves are used for storing food grains at home. For example, when wheat is stored at home in iron drums, then some dried been leaves are put on it. Dry been leaves protect the stored food grains from pests such as insects and micro-organisms. 

The large scale storage of food grains ( like wheat and rice) is done in two ways:

(a) in gunny bags, and

(b) in grain silos ( bulk storage of food grains)

FOOD FROM ANIMALS:

The food provided by animals consists of Milk, Eggs and Meat.

The animals which provide us food are mainly of two types:

(a) Milk yielding animals,

(b) Meat and Egg yielding animals.

Examples of milk yielding animals:

Cow, Buffalo and Goat

Examples of meat and egg yielding animals are: Goat, Sheep, Fish and Poultry.

ANIMAL HUSBANDRY:

The branch of agriculture which deals with the feeding, shelter, health and breeding of domestic animals is called animal husbandry.

The various practices necessary for raising animals for food and other purposes (or the elements of animal husbandry) are :

1. Proper feeding of animals,

2. Proper shelter for animals,

3. Prevention and cure of animal diseases, and

4. Proper breeding of animals.

FISH AS FOOD:

Fish is an important source of animal food. Many people living in the coastal areas (sea-side areas) consume fish as a major part of their diet. Fish is rich in proteins. It is a highly nutritious and easily digestible food. Fish liver oil is rich in vitamin A and vitamin D. For example, Cod liver oil (or Cod fish liver oil) is rich in vitamin A and vitamin D.