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.