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.