LECTURE 7: RESPIRATORY SYSTEM IN HUMANS

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The main organs of human respiratory system are: Nose, Nasal Passage (Nasal Cavity), Trachea, Bronchi, Lungs and Diaphragm.

1. Air for Respiration is drawn into our body through the nostrils (two holes in the nose) present in the nose. This air goes to nasal passage (passage behind the nostrils). 

2. Nasal hair and mucus present in nasal cavity cleans the incoming air. The part of throat between the mouth and wind pipeis called Pharynx. 

3. The wind pipe is known as Trachea. Trachea is reinforced by rings of cartilage, hence it will not collapsedeven when there is no air in it. Upper end of Trachea contains Voice box or Larynx.

4. Trachea is divided into two smaller tubes called. Bronchi. The two bronchi is connected to the two lungs. 

LUNGS: 

5. The lungs lie in the chest cavity or thoracic cavity and separated from abdominal cavity by a muscular partition called diaphragm. The diaphragm is a sheet of muscle below the lungs. It helps in "breathing in" and "breathing out". 

6. The lungs are covered by two thin membranes called pleura and protected by the rib cage made of ribs. 

7. Each bronchus divides in the lungs to form a large number of smaller tubes called bronchioles. 

8. The bronchioles have have tiny air-sacs at their ends called alveoli. The walls of alveoli are very thin and they are surrounded by very thin blood capilaries. Here, oxygen is taken in the body and carbon di oxide is eliminated, i.e. gaseous exchange takes place in alveoli. All the alveoli have a cumulative surface area of around 80 square metres. 

9. Oxygen of air diffuses out from the alveoli walls to the blood and carried by the blood to all the parts of the body and oxygen again diffuses into the individual cells and takes part in the respiration and releases carbon di oxide. 

RATE OF BREATHING

The average breathing rate in an adult man at rest is about 15 to 18 times per minute. The breathing rate increases with increased physical activity. 

HAEMOGLOBIN

Oxygen required for breathing and respiration is carried by haemoglobin present in our blood. The normal range of haemoglobin in the blood of a healthy adult person is from 12 to 18 gm/dL (grams per decilitre) of blood. The deficiency of haemoglobin in the blood of a person reduces the oxygen carrying capacity of blood resulting in breathing problems, tiredness and lack of energy. 

CARBON DI OXIDE POISONING

Haemoglobin has more affinity for carbon monoxide then oxygen. So, if carbon monoxide gas is inhaled by a person then this carbon di oxide binds very strongly with haemoglobin  in the blood and prevents it from carrying oxygen to the brain and other parts of the body and it creates fatal breathing problems. It is known as Carbon dioxide poisoining. 

VENTILATOR

When a patient suffers a serious breathing problem, the patient is put on a machine called "ventilator" in which a tube is inserted directly into the trachea of the patient to help him in breathing comfortably. 

LECTURE -1 : CLASS VIII : SCIENCE : CHAPTER 8 : CELL STRUCTURE & FUNCTIONS

CLASS VIII   |    SCIENCE    |    CHAPTER 8

      notes prepared by subhankar Karmakar

Cell : Cells are the basic units of life. All the living things both plants and animals, are made from cells. Cells are tiny basic unit of structure and function of all living organisms. Cells are the building blocks of plants and animals. Therefore, we can say a cell is the smallest unit of life which has a definite structure and performs specific function.

Microscope: The instrument used to study cells is called microscope.

Discovery of cell: an English scientist named Robert hooke discovered cell in 1665.

In 1838, a German scientist Schleiden first suggested that all plants are made of cells. 

In 1839, another German scientist Schwann suggested that all animals are made of cells too. 

Cell division: all cells arise from pre-existing cells by a method which is called cell division.

Classification of cell: All cells are primarily categorised into two main types. Animal cells and plant cells. 

Structures of a cell: Each cell has a number of smaller parts or internal structures in it. Some of the structures are present in both animal and plant cells, while some structures are only present in plant cells, they are not present in animal cells. They are also called parts of a cell.

The parts of a cell present in both animal and plant cells: 

Cell membrane or plasma membrane, Cytoplasm, Nucleus and Mitochondria. These basic parts are present in in both animal as well as plant cells. 

.                  Parts of a cell

The parts of a cells present in plant cells only:

Cell wall, Chloroplasts, Large vacuole are present in plant cell only. 

.               Parts of a Plant Cell

1. Cell membrane or plasma membrane:

Every cell is covered by a thin sheet of skin which is called cell membrane or plasma membrane. The cytoplasm and nucleus are enclosed within the cell membrane. Therefore we can say, cell membrane encloses the living part of the cell which is known as protoplasm. 

The cell membrane protects the cell and also gives shape to the cell. The cell membrane has tiny pores in it. Through this pores, the cell membrane controls the movement of substances "into the cell" and "out of the cell" like the dissolved glucose and oxygen can enter into the cell whereas the waste products like carbon dioxide can go out from the cell through this pores of the cell membrane. 

Cell membrane separates the cell from other cells as well as from the surrounding medium. The cell membrane or plasma membrane is a living part of the cell.

2. Cytoplasm: 

Cytoplasm is a transparent jelly like material which fills the cell between nucleus and the cell membrane. It acts like a chemical factory of the cell. In cytoplasm, new substances are built from materials taken into the cell and energy is released and stored. It is a place where most of the chemical reactions which keep the cell alive take place. Cytoplasm has many internal structures which are known as organelles. The most prominent internal structure in the cytoplasm is nucleus. It also contains mitochondria, Golgi bodies, ribosomes etc. Cytoplasm for plant cells also contain chloroplast. Cytoplasm and the nucleus taken together is called protoplasm.

3. Nucleus:

Nucleus is a large spherical organelle present in all the cells. In animal cell, nucleus lies in the centre of the cell whereas in plant cells the nucleus maybe on the periphery of the cell.  Nucleus is separated from the cytoplasm by a membrane called nuclear membrane. Nucleus controls all the activities of cell. The transmission of characteristics from the parents to the offsprings is called inheritance and Nucleus plays a role in inheritance.  

Chromosome: Nucleus contains thread like structure called chromosome. The function of chromosomes is to transfer the characteristics from the parents to the offspring through the genes and it is called inheritance. 

Nucleolus: The nucleus also contains a tiny round structure called nucleolus. The nucleus containing chromosomes and nucleolus is bound by a membrane called nuclear membrane. Nuclear membrane has tiny pores for the exchange of materials with cytoplasm. Some cells like red blood cells do not have a nucleus.

Gene: Gene is a unit of inheritance in living organisms, which is transferred from parent to offspring during reproduction and determine some characteristic feature of the offspring. Thus genes control the transfer of hereditary characteristics from parents to offsprings. 

Protoplasm: All the living matter in a cell is called protoplasm. Protoplasm is a liquid substance which is present inside the cell membrane. Protoplasm includes cytoplasm, nucleus and other organelles. Most of the protoplasm is made up of compounds of only 4 elements Carbon, Hydrogen, Nitrogen and Oxygen. It also contains water, carbohydrates, proteins, nucleic acids, fats and mineral salts.

4. Mitochondria: 

Mitochondria are the tiny rod-shaped or spherical organelles which are found in all the cells. Mitochondria provide energy for all the activities of the cell. This energy is produced by the process of respiration in which food such as glucose is broken down by oxygen. Thus mitochondria use glucose and oxygen to produce energy. Mitochondria are found in large numbers in the cytoplasm in all the cells.

5. Cell wall: The plant cells have a thick cell wall around them outside the cell membrane. The cell wall is made of a tough material called cellulose. Cell wall gives shape and support to the plant cell. Cell walls also hold the plant cells together and give plants most of their strength. Plants need protection against high wind speed, variation in temperature and atmospheric moisture etc. Since plants are fixed at a place so they cannot move to protect themselves from the various changes in their surroundings. The tough cell wall present in plant cells provides protection to plants. Cell wall is not there in animal cells. The cell wall is a non living part of the plant cells.

6. Chloroplasts: Chloroplasts are the green coloured organelles present in the cytoplasm of plant cells. The process of food making by plants known as photosynthesis takes place in chloroplasts. The green colour of chloroplasts is due to the presence of a green pigment called chlorophyll in them. Chlorophyll can absorb sunlight energy. In the chloroplasts, carbon dioxide and water combine in the presence of sunlight energy to produce food such as glucose. And this process of food making is called photosynthesis. 

The organelles containing pigments or colour matter present in the cytoplasm of plant cells are called plastids. Plastids can be of many different colours. The plastids containing green pigment or chlorophyll are known as chloroplasts. Chloroplast are present in the cells of leaves. It makes the leaves green. The plastids are may be of different colour like red colours of tomatoes are due to red plastids. Different colours of flowers are also due to this plastids.

7. Large Vacoule: 

Vacoule is a space in the cytoplasm of a cell which is enclosed by a membrane and is usually contains substances dissolved in water. A vacoule appears as an empty space under the microscope. All the plant cells have a large vacoule. The vacuole is filled with a liquid called "cell sap" , which contains dissolve sugar and salts. The function of vacuole in a cell is to store various substances including waste products of the cell.

* In amoeba vacuoles contain food particles so they are called food vacuoles.

Lecture: 10 :CLASS VIII : SCIENCE : Chapter 2: PRESERVATION OF FOOD & NITROGEN FIXATION

CLASS VIII   |    SCIENCE    |    CHAPTER 2

      notes prepared by subhankar Karmakar

Preservation of food:

The process in which the food materials are given a suitable physical or chemical treatment to prevent their spoilage is called food preservation. Some of the methods for preserving foods are: 

1. Sun drying or dehydration

2. Heating

3. Cooling or refrigeration

4. Deep freezing

5. Addition of common salt

6. Addition of sugar

7. Addition of mustard oil and vinegar

8. Use of special chemical preservatives like sodium meta-bi-sulphite, sodium benzoate and citric acid.

9. Pasteurisation

10. Packing food in airtight packets.

1. Preservation of food by sun drying or dehydration:

Water content of the food is removed by sun drying. It is also known as dehydration.

Vegetables like spinach, methi leaves, cauliflower, peas are preserved in our homes by the sun drying method.

2. Preservation of food by heating:

Microorganisms in the food can be killed by heating the food. We boil milk to prevent it from spoilage.

3. Preservation of food by cooling or refrigeration:

The growth of microorganisms can be inhibited by keeping low temperature. 

The food materials like milk, kneaded flour, cooked food, fresh fruits and vegetables are kept in a cool place like refrigerator to prevent their spoilage.

4. Preservation of food by deep freezing:

At sub zero (below zero degree centigrade) temperature the growth of microorganism are completely stopped. 

Deep freezing method is used for the preservation of foods like meat, fish and their products; fruits and vegetables.

5. Preservation of food by adding common salt:

common salt prevents the growth of food spoilage microorganisms due to which it is used to preserve a number of food materials. It is one of the oldest practice for preservation of food like meat and fish. 

common salt is also used to preserve fruits such as raw mangoes lemon and amla as well as tamarind.

6. Preservation of food by adding sugar:

Sugar is used as a preservative in making jams and jellies from fruits. The fruits which are preserved in the form of jams and jellies by using sugar as preservative are Apple, ripe mango, Orange, strawberry, pineapple and guava etc.

7. Preservation of food by mustard oil and vinegar: 

Mustard oil and vinegar are widely used as preservatives for the preservation of fruits and vegetables in the form of pickles.

Fruits like raw mango, amla and lemon are preserved using mustard oil and vinegar in the form of their pickles.

8. Preservation of food by using special chemicals as preservatives:

Sodium metabisulphite, sodium benzoate and citric acid are used as chemical preservatives. To preserve foods such as jams, jellies, juices and squashes sodium metabisulphite and sodium benzoate are used. To preserve confectionery citric acid is used as a preservative.

9. Preservation of food by pasteurisation:

Pasteurisation involves the process of heating followed by quick cooling. Packaged milk is always pasteurized.

10. Preservation of food by packing and air tight packets:

This days dry fruits and even vegetables are sold in sealed airtight packets to prevent the attack of microorganisms on them. This helps the dry fruits and vegetables to remained unspoiled for a longer time.

NITROGEN FIXATION:

The process of converting nitrogen gas of atmosphere or air into compounds of nitrogen which can be used by the plants is called nitrogen fixation.

The nitrogen gas of atmosphere or air can be fixed or converted into nitrogen compounds-

1. By certain nitrogen fixing bacteria present in the soil,

2. By Rhizobium bacteria present in the root nodules of leguminous plants,

3. Buy blue-green algae,

4. By lightning.

Rhizobium Bacteria:

The nitrogen fixing rhizobium bacteria live in in the root nodules of leguminous plants like peas, beans etc, also known as legumes.

Nitrogen fixation by lightning:

Nitrogen gas of atmosphere also gets fixed through the action of lightning in the sky. When lightning takes place in the sky during thunderstorm, a high temperature is produced in the atmosphere. At this high temperature, nitrogen gas of air combines with oxygen gas of air to form nitrogen compounds. These nitrogen compounds dissolve in rain water, fall to earth with rain water and go to the soil. Nitrogen of atmosphere can also be fixed by artificial methods.

THE NITROGEN CYCLE:

The circulation of nitrogen element through living things like plants and animals and non living environment like air soil and water, is called nitrogen cycle in nature.

"Nitrogen is required by both plants and animals for their growth and development. Nitrogen is an essential component of proteins, which make up the bodies of plant and animals. Nitrogen is also present in chlorophyll, nucleic acids and vitamins. The same nitrogen element is circulated again and again through living things like plants and animals and non living things like air soil and water. This whole process is known as nitrogen cycle."

                  Fig:  Nitrogen Cycle in nature    

The main steps of nitrogen cycle:

I. The atmosphere or air contains nitrogen gas. The nitrogen fixing bacteria present in the soil and in the root nodules of leguminous plants, blue green algae and lightning in the sky fix nitrogen gas from the atmosphere and convert it into compounds of nitrogen which go into soil.

II. The plant take compounds of nitrogen from the soil for their growth. The plants absorb the nitrogen compounds from the soil through their roots. The plants convert the compounds of nitrogen into plant proteins and other organic compounds which make up the body of plants.

III.  The plants are eaten by the animals as food. Animals convert plant proteins into animal proteins and other organic compounds which make up their body. Some animals also eat other animals to obtained nitrogen compound. Thus, animals obtain nitrogen compounds by eating plants as well as other animals.

IV.  When plants and animals die, the complex nitrogen compounds like proteins etc. present in their dead bodies are decomposed and converted into simple compounds of nitrogen by certain bacteria and fungi present in the soil. Animal excretions like urine etc. are also converted into simple compounds of nitrogen. All the simple compounds of nitrogen formed in this way go into the soil. In this way, the compounds of nitrogen which were taken by the plants from the soil during their growth are returned to the soil. From the soil these nitrogen compounds are again absorbed by the new plants for their growth and this part of nitrogen cycle is repeated endlessly.

V. Some of the compounds of nitrogen formed from the decay of dead plants and animals, are decomposed by denitrifying bacteria present in the soil to form nitrogen gas. This nitrogen gas goes back into the atmosphere from where it initially came. This process is the reverse of fixation of nitrogen. In this way the nitrogen gas which was removed from the atmosphere during fixation is put back into the atmosphere.

From the atmosphere nitrogen gas is used again during nitrogen fixation and the nitrogen cycle is repeated in nature again and again. As a result of nitrogen cycle in nature, the percentage of nitrogen gas in the atmosphere or their remains constant.

 

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 5: CLASS VIII: SCIENCE: CHAPTER 1: HARVESTING

CLASS-VIII; SCIENCE

Prepared by Subhankar Karmakar

6. HARVESTING:

The cutting and gathering of the matured food crop is called harvesting. 

MANUAL HARVESTING:

In harvesting, the crops like wheat or rice are cut close to the ground by hand using a cutting tool called sickle and this is called manual harvesting.

MACHINE HARVESTING:

In large fields, wheat and paddy crops are cut by a motorised machine called harvester.

THRESHING:

After harvesting the crop, the grains are separated from the harvested crops. The process of beating out the grains from the harvested crops plants is called threshing. It can be done manually as well as with the help of a motorised machine called thresher.

WINNOWING: 

The process of threshing brings out grains from the cut and dried crop plants, but this grain is mixed with chaff ( outer inedible covering of grain) and hay. The process of separating grain from chaff and hay with the help of wind is called winnowing.

COMBINE: 

A combine is a large machine which cuts the standing cereal crop in the fields, threshes it, and separates the chaff from grain in one operation.

Lecture-4: CLASS VIII: SCIENCE: CHAPTER -1: WEEDS

CLASS-VIII; SCIENCE

Prepared by Subhankar Karmakar

5) REMOVING THE WEEDS OR WEEDING

Weeds: The unwanted plants or wild plants which grow along with a cultivated crop are called weeds. Like some of the common weeds found in wheat and rice fields are:

(a) Wild oat 

(b) Grass

(c) Amaranthus

(d) Chenopodium

HARMFUL EFFECTS OF WEEDS:

The growth of weeds in the fields is harmful because 

(i) they consume a lot of fertilisers, water, sunlight and space, meant for the crops plants, 

(ii) weeds reduce the crop yield and lower the quality of food grains,

(iii) some weeds are poisonous for human beings and animals,

(iv) some weeds interfere in harvesting.

WEEDING: 

The process of removing weeds from a crop field is called weeding. 

VARIOUS METHODS OF WEEDING:

(a) Removal of weeds by pulling them out with hand.

(b) Removal of weeds by using a trowel ( khurpa)

(c) Destroying the weeds by spraying special chemicals called weedicides.

WEEDICIDES: 

The poisonous chemicals which are used to kill weeds in the fields are called weedicides.  Some of the common weedicides are: 2,4-D, MCPA, Butachlor. 

Lecture 3: CLASS-VIII: SCIENCE: CHAPTER 1: MANURE & FERTILIZER

CLASS VIII   |    SCIENCE    |    CHAPTER 1

      Notes prepared by Subhankar Karmakar

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Lecture 3: 

ADDING MANURE AND FERTILISERS

1. NEED OF MANURE & FERTILISERS

Repeated growing of crops in the same field removes a lot of precious mineral elements, organic matter and other materials from the soil. The deficiency of plant nutrients and organic matter in the soil is made up by adding manures and fertilisers to the soil.

2. MANURES: 

Manure is a natural fertiliser. A manure is a natural substance obtained by the decomposition of animal wastes like cow-dung, human wastes and plant residues, which supplies essential elements and humus to the soil and makes it more fertile.

3. PREPARATION OF MANURES: 

Manures are prepared from animal wastes, human wastes and plant residues by the action of micro- organisms. In order to prepare manure, farmer dump animal wastes and plant wastes in pits at open places and allow it to decompose slowly. The decomposition is carried out by some micro-organisms. The decomposed animal and plant matter is used as organic manure.

4. FUNCTION OF MANURES:

Manures provide a lot of organic matter like humus to the soil. A manure improves the soil texture for better retention of water and aeration. 

5. CHEMICAL FERTILISERS:

A chemical fertiliser is a salt or an organic compound containing the necessary plant nutrients like nitrogen, phosphorus or potassium, to make the soil more fertile. A chemical fertiliser is rich in a particular plant nutrients such as nitrogen, phosphorus or potassium (NPK). Some examples of chemical fertilisers are Urea, Ammonium sulphate, Superphosphate, Potash and NPK.

6. DIFFERENCES BETWEEN MANURES AND FERTILISERS: 

1. A manure is a natural substance obtained by the decomposition of animal wastes like cow dung, human waste and plant residue. 

But a fertilizer is a salt or an organic compound.

2. Manure is not very rich in essential plant nutrients like nitrogen, phosphorus and potassium where as fertilizers are very rich in plant nutrients like nitrogen, phosphorus and potassium.

3. A manure provides a lot of organic matter like humus to the soil but a fertilizer does not provide any humus to the soil.

4. A manure is absorbed slowly by the plants because it is not much soluble in water but being soluble in water if fertilizer is readily absorbed by the plants.

5. Menure can be prepared in the field but fertilizers are prepared in factories.

7. ADVANTAGES OF MANURE:

Organic manure is considered better than Fertilisers because of the following reasons:

1. Manure enhances the water holding capacity of the soil.

2. Manure makes the soil porous due to which the exchange of gases becomes easy.

3. Manure increases the number of useful microbes in the soil.

4. Manure improves the texture of the soil.

8. LEGUMINOUS CROPS:

The pulses, peas, beans, groundnut, gram and clover are called leguminous crops. Leguminous crops have the ability to fix atmospheric nitrogen to form nitrogen compounds. The planting of leguminous crops in a field has the same effect as adding nitrogenous fertiliser in the field.

9. CROP ROTATION:

The practice in which different types of crops like leguminous crops and non-leguminous crops are grown in the same field or soil is called crop rotation. In crop rotation, cereal crops like Wheat, Maize, Paddy and Millet are grown alternately with leguminous crops pulses, peas, beans, groundnut and clover etc. in the same field.

10. ADVANTAGES OF CROP ROTATION:

Rotation of crops has the following advantages:

1. Rotation of crops improves the fertility of the soil and hence increases the production.

2. Rotation of crops saves a lot of nitrogenous fertiliser.

QUESTIONS BANK:

21. Why does soil needs manuring?

22. What are manures? Why it is needed?

23. What are the advantages of manures?

24. What are chemical fertilisers? Give examples.

25. Differentiate between manures and fertilisers.

26. What are leguminous plants? What they are being planted in the field?

27. What are crop rotation? What are their advantages?

Lecture 2: CLASS - VIII: SCIENCE: CROPS -2: IRRIGATION

CLASS VIII   |    SCIENCE    |    CHAPTER 1

      Notes prepared by Subhankar Karmakar

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• IRRIGATION

The process of supplying water to crop plants in the fields is called irrigation. 

• Why is Irrigation Necessary: 

1. Irrigation before ploughing the fields makes the soil soft due to which ploughing of fields becomes easier.

2. Irrigation is necessary to provide moisture for the germination of seeds. This is because seeds do not grow in dry soil.

3. Irrigation is necessary to maintain the moisture of soil for healthy crop growth so as to get good yield.

4. Irrigation is necessary for the absorption of nutrient elements by the plants from the soil.

5. Water supplied to the crops during irrigation protects the crop plants from hot air currents as well as frost.

• Factors Affecting Irrigation Requirements of Crops:

The irrigation requirements of crops depend on three factors:

• 1) Nature of the crop
• 2) Nature of the soil, and 
• 3) Season.

• NATURE OF THE CROP: 

Paddy crop is transplanted in standing water and requires continuous irrigation where as other other crops like wheat, gram, cotton etc. do not require so much water. Hence irrigation depends upon the nature of the crops.

• NATURE OF THE SOIL: 

There are two types of soil on which the crops are grown, (a) Sandy soil and (b) Clayey soil. The crops grown in a Sandy soil need irrigation more frequently where as the frequency of irrigation for the crops grown in a Clayey soil is comparatively less.

• SEASON: 

The frequency of irrigation of the crops is higher in summer season.

• SOURCES OF IRRIGATION:

Crops are supplied water for irrigation from different sources like: Rivers, Canals, Wells, Tube-wells, Dams, Ponds and Lakes.

• TRADITIONAL METHODS OF IRRIGATION:

The various traditional methods of irrigation are:

i) Most (Pulley system),

ii) Chain pump,

iii) Dhekli, and

iv) Rahat ( Lever system)

• MODERN METHODS OF IRRIGATION:

The two main modern methods of irrigation are:

(a) Sprinkler system, and

(b) Drip System.

• SPRINKLER SYSTEM:

In the sprinkler system of irrigation, a main pipeline is laid in the fields. Perpendicular pipes having rotating nozzles at the top are joined to the main pipeline at regular intervals. When water from a tube- well is allowed to flow through the main pipeline under pressure with the help of a pump, it escapes from the rotating nozzles. This water gets sprinkled on the crop plants. It is more useful for the uneven land where sufficient water is not available. It is also useful for Sandy soil.

• DRIP SYSTEM:

In the drip irrigation system, there is a network of narrow pipes with small holes, in the fields. When water flows through the narrow pipes, it falls drop by drop at the position of roots of the plants. This water is absorbed by the soil in the root zone of the plants and utilised by the plants. There is no wastage of water in this type of Irrigation. Drip system is the best technique for watering fruit plants, trees and gardens.

• ADVANTAGES OF DRIP SYSTEM:

Drip Irrigation system has the following advantages:

(a) Drip system provides water to plants drop by drop. So, water is not wasted.

(b) Drip system minimises the use of water in agriculture. So, drip system of irrigation is very useful in those regions where the availability of water is poor.

Lecture 1: Class VIII: SCIENCE: CROPS AND ITS MANAGEMENT (CBSE)- 1

CLASS VIII   |    SCIENCE    |    CHAPTER 1

      Notes prepared by Subhankar Karmakar

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SCIENCE: CLASS VIII CBSE (CLASS NOTES)

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Chapter: 1

• CROP PRODUCTION AND MANAGEMENT

CROP:  When the same kind of plants are grown in the fields on a large scale to obtain foods like cereals (wheat, rice, maize), pulses, vegetables and fruits, etc., it is called a crop.

(i) Cereals: Wheat, Paddy, Maize, Millet

(ii) Pulses: Gram, Peas, Beans

(iii) Oil Seeds: Mustard, Groundnut

(iv) Vegetables: Tomato, Cabbage, Spinach

(v) Fruits: Banana, Grapes, Guava, Mango

• TYPES OF CROPS:

All the crops are categorised into two main groups:

1. KHARIF CROPS: The crops are sown in the rainy season (from June to September) are called Kharif crops. Some of the examples of Kharif crops are: Paddy, Maize, Millet, Soyabean, Groundnut, and Cotton.
2.  RABI CROPS: The crops grown in the winter season (from October to March) are called Rabi crops. Some of the examples of Rabi crops are: Wheat, Gram, peas, Mustard and Linseed.

• AGRICULTURE: 

The growing of plants or crops in the fields for obtaining food ( like wheat, rice etc) is called agriculture.

• BASIC PRACTICES OF CROP PRODUCTION

The various tasks performed by a farmer to produce a good crop are called agricultural practices.

• 1. Preparation of soil,
• 2. Sowing,
• 3. Adding manure and fertilisers,
• 4. Irrigation,
• 5. Removal of weeds,
• 6. Harvesting and
• 7. Storage of food grains.

Sometimes another practice called Rotation of crops is also undertaken to improve soil fertility and to increase crop yield.

• 1. PREPARATION OF SOIL:

The soil is prepared for sowing the seeds of the crop by 

(i) ploughing (ii) levelling and (iii) manuring.

• (i) PLOUGHING: 

The process of loosening and turning the soil is called ploughing or tilling. 

• (ii) LEVELLING: 

The ploughed soil is levelled by pressing it with a wooden leveller so that the top soil is not blown away by wind or drained off by water and thus soil erosion is prevented.

• (iii) MANURING: 

Manuring means adding manure to the soil. It is done to increase the fertility of the soil before seeds are sown into it. 

Prepared by: Subhankar Karmakar 

• AGRICULTURAL IMPLEMENTS:

(i) PLOUGH: 

It is a large agricultural implement which is used for ploughing the soil and it is made of wood.

                       

 

.                             A wooden plough

The wooden plough consists of a long log of wood which is called plough shaft. There is a handle at one end of the ploughshaft. Below the handle is a strong triangular iron strip called ploughshare. The other end of ploughshaft can be attached to a wooden beam which is fixed at right angles to the ploughshaft. 

(ii) HOE:

Hoe is an agricultural implement or tool which is used for removing weeds, and loosening and turning the soil. It consists of a long rod of wood or iron. There is a handle at one end of the hoe. A strong, broad and bent plate of iron is fixed below the handle and acts like a blade. The other end of hoe has a beam which is put on the neck of bullocks.

Prepared by: Subhankar Karmakar 

(iii) CULTIVATOR:

The cultivator is a tractor driven agricultural implement which is used for loosening and turning the soil in the fields quickly. A cultivator has many ploughshares which can dig into a considerable area of soil at the same time, loosen it and turn it. Due to this, many fields can be ploughed in a short time by using a cultivator.

• 2. SOWING:

The process of scattering seeds or putting seeds in the ground soil for growing the crop plants is called sowing. It is the most important part of crop production.

(i) SELECTION OF SEEDS: Good quality seeds are clean and healthy seeds free from infection and diseases and which will give him yield of food grains.

(ii) METHODS OF SOWING SEEDS: There are two methods of sowing the seeds in the soil. These are

(a) Sowing by hand, and

(b) Sowing with a seed drill.

Prepared by: Subhankar Karmakar

(iii) PRECAUTIONS FOR SOWING SEEDS:

a) The seeds should be sown at right depth in the soil suitable for germination.

b) The seeds should be sown at right intervals or spacings.

c) The seeds should not be sown is dry soil.

d) The seeds should not be sown in a highly wet soil.

(iv) ADVANTAGES OF SOWING WITH A SEED DRILL:

a) By using a seed drill for sowing, the seeds are sown at correct depth and correct intervals.

b) The seeds sown with a seed drill are in regular rows.

c) When the seeds are sown in furrows by a seed drill, the seeds get covered by soil and hence these seeds can not be picked up and eaten by birds. This prevents damaged by birds. 

d) Sowing by using a tractor driven seed drill saves time and labour.

Prepared by: Subhankar Karmakar

(v) TRANSPLANTATION:

The process of transferring the seedlings from the nursery to the main field by hand is called transplantation or transplanting.

The Advantages of Transplantation:

a) It helps us to select the better and healthy seedlings for the cultivation by rejecting the damaged seedlings.

b) It allows better penetration of the roots in the soil.

c) It promotes better development of the shoot system of plants.

The practice of transplantation is used in the cultivation of Paddy (rice) crop and in the cultivation of many vegetables like tomatoes and chillies.

Prepared by: Subhankar Karmakar

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HOME TASKS:

1. What are crops? Give some examples.

2. Classify crops with suitable examples.

3. What are Kharif crops? Give examples.

4. What are Rabi crops? Give examples.

5. Which types of crops are also known as summer crops? 

6. What are the basic practices of crop production? 

7. What are agricultural practices? 

8. What are steps to prepare the soil for cultivation?

9. What are ploughing or tilling?

10. What do you understand by the term "manuring"?

11. Describe a plough with a neat sketch.

12. Describe a hoe with a neat sketch.

13. What are agricultural implements?

14. What is a cultivator?

15. What do you understand by " sowing"?

16. What type of seeds are selected for sowing?

17. What are the methods of sowing? 

18. Describe the precautions taken for sowing seeds.

19. Describe the Advantages of sowing with a seed drill.

20. What is transplantation?  Describe its advantages.

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SCIENCE: CLASS VIII CBSE (CLASS NOTES)