Microorganisms: Friend and Foe - 8th science

Many microorganisms are harmful for us. These harmful microorganisms are caused for several diseases in animals as well as in plants. Some microorganism spoils even food, clothes, and articles made of leather.

Such disease causing microorganisms are known as PATHOGENS.

Disease causing Microorganisms in Humans

Pathogens make people diseased after entering in their bodies through air, drinking water and food they eat.

Such diseases caused because of pathogens (microorganisms) are transmitted also through direct contact with an infected person or carried through animals.

Microbial diseases that can spread from an infected person to a healthy person through air, water, food or physical contact are called communicable diseases. Cholera, common cold, chicken pox and tuberclulosis, etc. are example of such communicable diseases.

For example when a person sick with common cold sneezes, fine droplets of moisture carrying thousands of viruses spread in the air. The virus spread in the air nearby may enter in the body of a healthy person while breathing and can infect that healthy person. That is why a person should keep cover his mouth while sneezing so that virus coming out because of sneezing could not infect other healthy person.

Pathogens carrying Insects and Animals

There are many insects and animals act as carrier of disease causing microbes. For example housefly, rats, street dogs, cats, etc. are such carriers of pathogens.

Pathogens carrying flies

When flies sit on garbage pathogens present in garbage stick to their legs and bodies. And when these flies sit on food, they may transfer pathogens stick to their bodies to the food. By transferring of pathogens to the food, food gets contaminated. When a person eat those contaminated food, he likely to get sick.

Prevention to get sick because of contaminated food

(a) We should always keep food covered to prevent from contamination.

(b) We should not consume uncovered items of food.

(c) We should always be careful to take food from street food vendors, as some food vendors keep their food uncovered and in unhygienic condition.

Pathogens carrying mosquitoes

Parasite of Malaria Carrying Mosquito – Female Anopheles

Female Anopheles mosquito carries the parasite of malaria. When female Anopheles mosquito bites a person, it transfers the microbes of malaria to his body. Parasite of malaria makes sick a healthy person with malaria. Malaria is a disease and seeks immediate medical treatment.

Dengue carrying Mosquito – Female Aedes

Female Aedes mosquitoes carry the virus of dengue. It transfer dengue virus while biting a person. Dengue is a deadly disease and require immediate medical attention.

 

Prevention from Mosquitoes

Mosquitoes breed in stagnant water and usually bite in night time. However, mosquito bites even in daytime. Female Aedes, carrier of dengue virus, bites in day time, generally in the morning and evening. Thus, we should take following preventive measures to stop breeding of mosquitoes and to avoid get bitten by mosquitoes.

(a) Water should not be allowed to collect anywhere, in collers, tyres, flower pot, etc.

(b) By keeping surroundings dry the breeding of mosquitoes can be controlled.

(c) We should use of mosquitoes repellents to keep the mosquitoes out.

(d) Mosquito net should be used in night.

By taking above preventive measures we can prevent ourselves from getting sick.

Disease causing Microorganisms in animals

Several microorganisms are responsible for disease in animals.

Example: Anthrax is a dangerous human and cattle disease. Certain type of bacterium called Bacillus antracis is responsible for Antrax.

 

 

Bacillus Antracis responsible for Antrax

Referece: Y tambe [CC BY-SA 3.0], via Wikimedia Commons

Bacillus anthracis was the first bacterium to be used to prove that bacteria caused diseases.

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

Rabies is a viral disease that affects animals like dogs, cats, and money, etc. It spread even in human through saliva of animals having rabies.

Disease causing Microorganisms in Plants

There are many microorganisms causing diseases in plants. Plants of wheat, rice, potato, sugarcane, orange, apple and other many plants are destroyed because of diseases causing microorganisms. The disease reduces the yield of crops and sometimes even destroys the crop completely.

Example :

Citrus canker is a lemon plant disease caused by bacteria. Mode of transmission of Citrus canker is air.

Rust of wheat is a wheat plant disease caused by microorganism called Fungi and it spread by air and infected seeds.

Yellow vein mosaic is a disease of plant of lady finger (bhindi or okra) caused by the virus and spread by insect.

Plants diseases can be controlled by using certain chemicals which kill microbes.

Food Poisoning

Microorganisms that grow on our food sometimes produce toxic substances. These types of toxic substances make the food poisonous and causing serious illness and even death.

Illness caused because of taking of poisonous food is called Food Poisoning.

Food Preservation

Microorganisms spoil our food. Spoiled food emits bad smell and has a bad taste and colour change. Spoiled food is harmful also to eat.

Foods are preserved for ancient times to keep food usable for long time. Keeping of food for long time edible, is called Food Preservation. There are many methods to preserve food.

Chemical Methods to Preserve Food

Salt and edible oil are capable to stop the growth of microorganisms, thus salt and edible oils are called Preservatives. So, salt and edible oils are used to preserve foods.

In pickling salt, edible oils and edible acids are used. These preservatives stop the growth of microorganisms.

Sodium Benzoate and Sodium Metabisalphite are also used as preservatives. These chemicals are used in making of jam, jelly and squash. Using these chemicals jam, jelly and squash stop the growth of microbes and keep these food items usable for long time.

Preservation of Food by Common Salt

Common salt is a natural preservative. Covering of foods, such as meat and fish by dry common salt stops the growth of microorganisms. Salt absorbs the moisture present in foods. Microorganisms do not grow in the absence of moisture as they require moisture to grow.

Salting is also used to preserve amla, raw mangoes, tamarind, meat, fish, and egg, etc. for ancient time.

Preservation of food by Sugar

Sugar also absorbs the moisture and check the growth of microorganisms which spoil foods. Jams, jellies and squashes are preserved by using sugar.

Preservation of Food by Oil and Vinegar

Microorganisms like bacteria and fungi cannot live in oil and vinegar, and thus edible oil and vinegar are used to preserve foods. Vegetables, fruits, fish and meat are often preserved by using edible oil and vinegar.

Preservation of food by Heat and Cold Treatments

Heat kills many microorganisms and cold stops the growth of microorganisms. Thus, food items are preserved by heat and cold treatments.

Boiling of milk kill many microorganisms and is stored for some long times.

In similar way cold environment stops the growth of microbes. Thus milk and other food items are refrigerated to preserve them for long hours.

Pasteurization

Pasteurization is a method to keep milk usable for long time. In the process of Pasteurization milk is heated to about 70^o C for 15 to 30 second and suddenly chilled and stored. This process prevents the growth of microbes. Pasteurized milk can be consumed without boiling as it is free from harmful microbes.

Louis Pasteur, a French scientist, discovered the process of Pasteurization. This process got its name as Pasteurization in the honour of its discoverer.

These days pasteurized milk is available in market easily. Pasteurized milk can be consumed without boiling as it is free from harmful microbes.

Storage and Packing

In the absence of air growth of microbes is checked. Thus, food items can be preserved for long time by keeping them in the absence of air.

Vegetables, fruits, dry fruits, potatoes chips, wafers, sweets, etc. are sold in sealed air tight packets and cans to prevent the attack of microbes. In the absence of oxygen in sealed packets microbes do not grow as they require oxygen for their survival. This keeps the food items long time usable.

Nitrogen filled food packets

Sometimes nitrogen is filled in the sealed air tight packet. Nitrogen and absence of oxygen stop the growth of microbes which keep the food usable for long time.

Nitrogen Fixation

Nitrogen is essential for all living organisms. Nitrogen is one of the most important constituents of proteins, chlorophyll, nucleic acid and vitamins which are essential for living organism. So, it becomes essential that our atmosphere should have adequate amount nitrogen.

Our atmosphere contains about 78% of nitrogen gas. And this percent of nitrogen gas is fixed in the atmosphere.

Some microorganisms keep the nitrogen fixed in the atmosphere. Such microorganisms may be called nitrogen fixers or nitrogen fixing microorganisms.

Inspite of presence of adequate amount of nitrogen in the atmosphere, plants and animals cannot take nitrogen directly in that form.

Nitrogen Cycle

Plants take nitrogen from soil only. There are certain bacteria and blue green algae present in the soil fix nitrogen from the atmosphere and convert it into compound of nitrogen which is usable form for plants.

A bacterum called Rhizobium lives in the root nodules of leguminous plants, such as beans and peas, which it has a symbiotic relationship. The Rhizobium takes nitrogen from atmosphere and convert it into usable form and makes available in the soil. Plants absorb the usable form of nitrogen from soil through their root system. Nitrogen is then used for the synthesis of plant proteins and other compounds.

Animals feeding on plants ge these proteins and other nitrogen compounds.

When plants and animal die, bacteria and fungi present in the soil covert the nitrogenous wastes into nitrogen compounds to be used by plants again.

Certain bacteria convert some part of nitrogenous compounds present in dead animals and plants into nitrogen gas, which goes back into the atmosphere.

Sometimes action of lightning also fixes nitrogen in the atmosphere.

As a result the percentage of nitrogen in the atmosphere remains contestant.

 

 

Ref: Image is taken from NCERT Science Book, class 8, page number: 27