Where do microorganisms live?

• Microorganisms are present almost everywhere on earth.
• They are observed in all the three habitats i.e. land, water and air.
• They are even observed in harsh conditions such as high-temperature zones (volcano), extremely cold climates, desert and marshy lands.
• Microbes are also being observed inside the body of living organisms including human beings.
• Amoeba lives alone or freely while fungi and bacteria live in colonies.

Friendly microorganisms:

• Some of the microorganisms are much helpful to us.
• Lactobacillus bacteria helps in converting milk into curd.
• Also, many products like cake, bread, antibiotics and beverages are prepared with the help of microorganisms.
• They also help in cleaning our environment by acting as bio-fertilizers and decomposers.
• Sewage treatment also uses microorganisms.
• The organic wastes (vegetable peels, remains of animals, faces, etc.) are broken down into usable and harmless substances by bacteria.
• They are used in agriculture to increase soil fertility by nitrogen fixation.

Commercial use of microorganisms:

Commercially microorganisms are of great use. Several food and beverage industries, as well as many other industries, uses it as:

Making of Curd and Bread:

• Lactobacillus bacteria helps in the formation of curd.
• When a little amount of bacteria is added to the milk it starts multiplying and gets converted to curd.
• Bacteria are also involved in the making of cheese, pickles and many other food items.

Preparation of alcohol:

• From ages alcohol preparation through yeast has been the most viable method.
• Saccharomyces cerevisiae is popularly known as Brewer’s yeast is used for alcohol preparation.

Preparation of different food items:

• Microorganisms are used for the preparation of vinegar (acetic acid).
• Yeast microbe is also used in baking.
• It also plays an important role in fermenting idli/dosa batter (containing urad pulses).

Medicinal use of Microorganisms:

Microorganisms are used on a large scale in the medicinal sector. Several medicines make use of microbes in one way or the other. Some of them are listed below:

• Doctors prescribe us antibiotics, injections or capsules such as penicillin, all these are made of microorganisms.
• Bacteria and fungi are used nowadays to prepare medicines which fight against various disease-causing germs. Such medicines are called antibiotics.
• Streptomycin, erythromycin, tetracycline, amoxicillin, cefotaxime, cefoperazone etc. are made from bacteria and fungi and are some antibiotics.
• Microorganisms are also used to cure diseases in plants.

Vaccine:

• One of the main quality of human body is that it has tendency to fight against diseases.
• A small amount of disease-causing weak microbes (mainly they are dead) is inserted in our body, this makes the antibodies present in our body to fight against the particular microbe.
• Once the antibodies are activated it remembers how to fight with that particular microbe throughout life.
• This is the way how vaccine
• Cholera, TB, hepatitis, smallpox, hepatitis etc. are some diseases which can be prevented by vaccination.

Soil fertility:

• Blue-green algae are the most favourable microorganism which helps in increasing soil fertility.
• They help in nitrogen fixation.
• Leguminous plants contain rhizobium bacteria in its root nodule for nitrogen fixation.
• Plants utilize nitrogen from soil through their roots.

In the cleaning environment:

• Decomposers are the microorganisms which help in converting dead and decaying matters into simpler substances.
• Microbes have the main role in clearing organic waste from our surroundings.

Harmful microorganisms

• Many microbes cause several diseases in plants, animals & human beings.
• That is why we read this chapter as microorganism friend and foe.
• We call such disease-causing organisms as Pathogens.
• Bacteria, viruses, protozoa & fungi are pathogens.
• Typhoid is an example of diseases which is caused pathogen bacteria named as Salmonella typhi. This microorganism enters our body through contaminated food and water.
• Food, clothing, leather and many of our useful items get spoiled by microorganisms.
• Microbial diseases that can spread from an infected person to a healthy person through air, water, food or physical contact are called Communicable diseases.

Food poisoning

• Microbes produce toxic substances in the food and thus it gets poisoned.
• Eating such food makes us ill.
• Microbes do not attack a particular food, only it searches a suitable environment to survive.
• Moisture and warm temperature make it easy to survive thus releases toxic substance in food. Thus food poisoning occurs.

Food preservation

• Prevention of food from getting it spoiled by the action of microorganisms by taking suitable measures are said to be food preservation.
• It is very important to preserve food items so that microbes cannot grow & spoil them.

Methods of food preservation:

There are many methods of food preservation. We will discuss each one by one.

Chemical Methods of food preservation:

• Preservatives are the chemicals which check the growth of microorganisms on the food.
• In pickles, we use salt as preservatives.
• Also, salt is used to preserve meat and fish.
• Sugar is used in jams as a preservative material.
• Vinegar is used as preservative in vegetables.
• Sodium benzoate, oils (edible) and salts are common preservatives.

Heat and cold treatments

• We boil milk to kill microorganisms present in it.
• Milk for commercial use is pasteurized.
• The technique to boil milk at 70⁰C for 15 to 30 sec then suddenly cooled and stored is said to be pasteurization.
• We use refrigerators to preserve fruits, vegetables and edible items.

Proper storage and packing:

• Properly sealed packets or airtight containers are necessary to store some kind of food such as dry fruits.
• Such containers would inhibit the growth of microbes as they need moisture, air etc. for growth.

Nitrogen fixation

• The process of converting Nitrogen (N₂) in the atmosphere into ammonia (NH₃) inside the soil is said to be nitrogen fixation.
• Those bacteria which is involved in such process is said to be nitrogen-fixing bacteria.
• Rhizobium bacteria which lives in the root nodules of leguminous plants (peas and beans) helps in nitrogen fixation.
• Nitrogen also gets fixed through the action of lightning.
• However the atmospheric nitrogen is fixed, it neither decreases nor increases.

Nitrogen cycle

• Our atmosphere contains 78% nitrogen gas and is most essential for living organisms.
• Nitrogen is one of the main constituents of protein, chlorophyll and vitamins.
• Atmospheric nitrogen can’t be utilized directly by living beings.
• Blue-green algae and certain bacteria present in soil fix the nitrogen of atmosphere.
• Nitrogen gets utilised by plants from the soil through their root system then used for the synthesis of plant proteins and other important compounds.
• Heterotrophic animal feeds on plants and get protein and essential nutrients based on nitrogen.
• When plants and animals die, bacteria and fungi present in the soil convert the nitrogenous wastes into nitrogenous compounds.
• Plants use these nitrogenous compounds again.

We will have a detailed study of each topic in higher sections. However, the necessary material is provided in class 8 chapter 2 microorganism friend and foe notes.