Important topics covered From Microorganisms – Friend and Foe Chapter:
- Introduction to microorganisms
- Commercial and Medicinal use of Microorganisms
- Harmful microorganisms
- Food poisoning
- Food preservation
- Nitrogen fixation
- Nitrogen cycle
Introduction to microorganisms:
- Those organisms which are too small to be seen with our naked eye are said to be microorganisms.
- They are also called microbe.
- Generally microbes are unicellular while some other is multicellular.
- They can survive under different types of climatic environment, ranging from hot to ice cold climate.
Types of microorganisms:
Microorganisms are mainly classified into four groups. They are:
- Bacteria are the microorganisms with defined cell wall but cell has no nucleus.
- Some of the bacteria are autotrophs while some other are heterotrophs.
- These are categorized in the plant kingdom.
- The part of it can be the category which can be in the same manner.
- Lactobacillus, Escherichia coli etc. are some examples of bacteria.
- These are multicellular organisms.
- Chlorophyll is absent in fungi so they can’t prepare their own food.
- They are dependent on heterotrophs and dead organic matter for their food.
- These are mainly found in colonies.
- Aspergillus and Penicillium are some of the examples of fungi.
- These are green substances floating on the surface of stagnant water, pond, lake, river, moist soil etc.
- These are either unicellular or multicellular organisms.
- Also, they are mainly autotrophs and contains chlorophyll, thus carry photosynthesis to prepare their own food.
- Chlamydomonas and spirogyra are some examples of algae.
- Protozoa are unicellular organisms.
- Some protozoans are free-living while the others are parasites.
- Protozoa do not have cell wall and chloroplast but they contain a nucleus.
- Some of the parasitic protozoans cause disease in humans.
- Amoeba and Plasmodium are some examples of protozoa.
- Reproduction of viruses takes place in host organism.
- The host organism may be bacteria, plants or animals.
- Viruses are considered as the borderline between living and non-living organisms. As they possess the character of living as well as non-living organisms.
- Outside a host cell, the virus behaves as non-living as when it is outside a host it does not carry on nutrition, respiration or reproduction.
- Inside a host it carries all the essential life processes, thus behaves as living organisms.
- HIV, H1N1, TMV are some examples of virus.
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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.