CHAPTER-2 

Microorganism: Friend and Foe

Microorganisms:-Those organisms that cannot be seen by the necked eyes are called microorganisms or microbes.

* Microorganisms are only seen through a microscope.

* The study of microorganisms is known as microbiology.

* Father of microbiology is Antonio Van Leeuwenhoek.
Habitat / Occurrence of Microorganisms         

* Microorganisms live almost everywhere on the earth. They are found on land, water and in air.

* They are even found inside and on our body and animal.

* Some microbes are even found in extremely harsh conditions like hot springs, desert soil, saline water, ice-cold water and marsh land.

* Microorganisms live in dead and decaying organic matter.

* Microorganisms like Amoeba may live alone, whereas fungi and bacteria may live in colonies.

Types of microorganisms:-    There are five major groups of microorganism as:
(i) Bacteria (जीवाणु)

(ii) Algae (शैवाल)

(iiii) Protozoa (प्रोटोजोआ)      

(iv) Fungi (कवक)

(v) Viruses (विषाणु)

Bacteria:-Those microscopic organisms which have cell walls but do not have nucleus are called Bacteria.

Examples:- Rhizobium, E. coli, Pseudomonas, Streptococcus, Lactobacillus etc.

* Some bacteria are autotrophs but most are heterotrophs.

* They are mostly single- celled tiny organisms, but they live together in colonies of millions.

* Bacteria are found in different shapes; like rod-shaped, spiral, spherical and comma-shaped.

Algae:-The simple green plant like organisms which are usually aquatic in nature is called algae.

Ex:-   Chlamydomonas, Spirogyra,  Diatoms and Seaweed Etc.

* Algae are autotrophs and some algae are microscopic.                  

* They contain a cell wall and chlorophyll and can make their own food by photosynthesis.

* Algae can be unicellular or multicellular.

Fungi:-Plant -like organisms that have cell wall and nucleus in their cells but do not have chloroplast are called Fungi.

Ex- Yeast, Rhizopus (Bread mould), mushrooms, puffballs, penicillium.

* Fungi may be unicellular (Yeast) or multicellular (Bread mould).

* Fungi are found in warm and moist places.

* Fungi can be heterotrophic, saprophytic or parasitic in nutrition.

* Fungi are saprotrophs, i.e. they feed on dead remains of plants and animals. Almost all fungi are microscopic, except mushrooms.

Ex- yeast, Rhizopus (bread mould), Aspergillus, Penicillium, etc.

Protozoa:-Those unicellular organisms which have no cell wall and chloroplast but they have nucleus are called protozoa.

Ex- Amoeba, paramecium Euglena etc

* They are similar to animals that can move about to capture food.

* They are heterotrophic in nature.

* They are found in moist and aquatic habitats and reproduce by binary and multiple fission. 

Viruses:- Those microorganisms that have the characteristics of both the living and non-living beings are called viruses.

Ex- HIV, Tobacco Mosaic Virus (TMV), etc.

* Viruses are smaller than any known cell.

* Viruses can only be seen with electron microscope.

* Viruses can reproduce and grow only inside the bodies of other organisms, which mean they need a host.

* A virus is like a non- living thing outside the body of other organisms. Therefore, it is a borderline between a living and a non- living thing.

* A virus behaves as non-living when it is outside a host cell, i.e. a virus does not carry on nutrition, respiration or reproduction when it is outside a host.

* A virus behaves like a living being when it is inside a host, i.e. it carries on nutrition, respiration and reproduction when it is inside a host.

* Structure of virus consist of nucleic acid and a protein coat. Nucleic acid can either be DNA or RNA
 USEFUL MICROORGANISMS:-  Microorganisms are useful in the following ways:
1. Preparation of curd, bread, cake, idli, dosa and cheese.

2. In industry- to produce alcohol, wine, and vinegar

3. In agriculture- to increase soil fertility

4. In medicines- to produce antibiotics and vaccines

5. Cleaning the environment

1. Preparation of curd, bread, cake, idli, dosa and cheese

(i) Formation of curd:- Making of curd is a process in which the lactose (milk sugar) of the milk is converted into lactic acid by the action of Lactobacillus bacteria. This curd is further used in the preparation of idli-dosas
Qus:-How does the addition of small amount of curd to milk converts the whole milk into curd?
Ans:-Curd contains several microbes. Out of these, Lactobacillus, promotes the formation of curd. When the curd is added to lukewarm milk, the bacteria, multiplies faster and results in conversion of whole milk into curd.
(ii) In bread making:- When yeast is added to ingredients (dough) of cake, Bread, idle and Dosa. The dough rises due to production of carbon dioxide because of respiration of yeast. Carbon dioxide gas creates bubbles in dough which makes fluffy cakes, breads, idli and dosa.

2. Add flavour:-Some fungi (Aspergillus and penicillum) are added to cheese to give a special flavour.

(i) Commercial use of microorganisms:-In  industry
The wine and beer industry are important industries which use of the yeast. Yeast is grown on natural sugars present in fruit juice and grains like barley and rice.

* The process of conversion of sugar solution into alcohol due to anaerobic respiration by microbes is called fermentation.

3. Agriculture use of microorganisms

All plants and animals need nitrogen.  Some bacteria like Rhizobium and blue green algae like Nostoc, live in the root nodules of plants such as gram, pea etc. These microbes convert atmosphere nitrogen into nitrate (nitrogen compound) which serves as natural fertilizers for plants, hence, enhancing soil fertility.

Nitrogen Fixation

The process of conversion of atmospheric nitrogen gas into nitrogen compound usable (taken up) by plants and animals is called nitrogen fixation.

* Green plants cannot utilize gaseous nitrogen. Gaseous nitrogen needs to be converted into compounds of nitrogen so that plants can utilize nitrogen.

* Nitrogen fixation is conducted by variety of bacteria and in symbiotic association with plants. Ex-The root of leguminous plants like pea, beans, bear certain swollen structures called root nodules. The rhizobium bacteria lives in root nodules. Bacteria fix nitrogen for the plant, while the plant give food and shelter to the bacteria. This type of relationship is called symbiotic association.

* Nitrogen is an essential element for all living organisms because it is a principle component protein and nucleic acids.

Nitrogen Cycle: The cycle/circulation of nitrogen through living and non-living component of the biosphere (air, soil, water, plant and animals) is called nitrogen cycle.

Following steps of nitrogen cycle:

STEPS INVOLVED IN NITROGEN CYCLE

A.  Atmospheric nitrogen is fixed nitrogen compounds by Rhizobium bactria , blue green algae, this is called nitrogen fixation.

B.  The plants absorb nitrogen compounds from the soil and convert them into plant proteins.

C. The plants are eaten up by animals and thus plant proteins are used for making animal proteins.

D.  When the plants and animals die, the putrefying bacteria and fungi present in the soil decompose the proteins of dead plants and animals into ammonia. This process is called ammonification.

E.  Ammonia thus formed is converted first into nitrites and then to nitrates by the action of Nitrosomonas and Nitrobacter bacteria respectively. The process is called nitrification. These nitrates are absorbed by plants.

F.   The soil contains denitrifying bacteria called Pseudomonas which convert nitrate form of nitrogen into free nitrogen which goes back into the atmosphere. The process is called denitrification.

4. Medicinal use of microorganisms :-Making Antibiotic and vaccines

Antibiotic:- These are medicines that kill or stop the growth of the disease-causing microorganisms which are produce by number of microorganisms.

NOTE:- Fungi and bacteria are important microbes producing a variety of antibiotics.

Antibiotics obtained form bacteria:- Streptomycin, aureomycin and chloromycetin.

Antibiotics obtained from fungi:- Penicillin and Griseofulvin.

These antibiotic are used to cure a variety of diseases in humans, plants and animals.

* The first antibiotic to be isolated was Penicillin from penicillium notatum by Alexander Fleming in 1929.

* Antibiotics are not effective against cold and flu as these are caused by viruses.

* Bacteria and Yeast are used in making vitamin B complex tablets.

Precautions that must be taken while using antibiotics-

* Antibiotics must be taken only on the prescription of a doctor.

* Must finish the course prescribed by the doctor.

* Excess dose must not be taken.

* An antibiotic should be taken in the right amount only. Antibiotics taken unnecessarily may kill beneficial bacteria in the body.

Vaccine:-A vaccine is a biological preparation that improve immunity to a particular disease.

A small dose of weakened or killed forms of the microbe needed to immunise the body against a particular diseases is called vaccine.

When a vaccine is inoculated in the body, the body prepares antibodies against it. Thus, the body learns and remembers how to fight with that microbe in future. Thus, vaccination helps in preventing against a particular disease.

* Edward Jenner discovered the first vaccine against small pox in 1798. He observed that people who were rearing cows did not suffer from small pox.

* Vaccines are now available for many diseases; like small pox, tuberculosis, polio, tetanus, diphtheria, whooping cough, hepatitis, mumps etc.
Que Why are children /infants given vaccination? 

Ans:-Vaccination is given to children/infants to activate the defence mechanism of the body against a disease and to protect the body from the disease causing microbes, because the immunity of an infant is low and so is more susceptible to any infection.

5. Cleaning in the environment:

* Microbes, like bacteria and fungi decay the dead plant and animals.

* They act on dead plants and animals and convert various complex organic compounds into simple inorganic substances. Thus, microbes also help in recycling of nutrients.

* Some bacteria decompose sewage and other waste in water. This is nature’s method of keeping the environment free from pollution.

HARMFUL MICROORGANISMS

1. Disease causing microorganisms:-

* In human:- Microorganisms that cause diseases in human, animals and plants are called pathogens or germs.

* Germs may enter the body of living organisms through air, contaminated food and water, from an infected person by direct or indirect contact or by a carrier.

* Diseases that can spread from an infected person to a healthy person through air, water, food, insect and direct contact are called communicable or Infectious disease. Examples: Common cold, chicken pox, AIDS, cholera etc.

Infectious Disease: A disease which is caused by an attack from microbes is called infectious disease.

Carriers/vectors:-Those organisms which help the microbes in the transmission of disease are known as carriers or vectors.

Ex- houseflies, mosquitoes, cockroaches, rats.

Que: sneezing can cause infection to a healthy person.Explain?

Ans:-When a person suffering from common cold sneezes, fine droplets of moisture carrying thousands of viruses are spread in the air. The virus may enter the body of healthy person while breathing.

Pathogen: A microbe which causes disease is called a pathogen.

Modes and transmission of some human diseases caused by microbes:-

Plasmodium	Malaria	Spreads through bite of female Anopheles mosquito.
Dengue virus	Dengue	Spreads through bite of female Aedes mosquito.
Common cold virus	Common cold	Through air; when someone coughs or sneezes.
Many bacteria	Diarrhoea	Through contaminated food and water.
Hepatitis B virus	Hepatitis B	Through exchange body fluids.
HIV	AIDS	Through exchange of body fluids.
Bacteria	Cholera and typhoid	Houseflies

 How to Control Measure of Houseflies and Mosquitoes:

* Food must be kept covered.

* Proper sanitation.

* Garbage should be disposed properly.

* Mosquitoes breed in water. So water must not be allowed to collect anywhere.

* Spraying of kerosene on the surface of water to form a thin film (this blocks oxygen and kills larvae of mosuitoes).                

* Keep the overhead tank covered.

* Use mosquito repellant creams and mosquito nets to prevent mosquito bite.

ii. In animals:-

Microorganism	Name of animal diseases
Virus	Foot and mouth diseases of cattle, Rhikhet in birds
Bacteria	Anthrax disease of cattle
Protozoa	Sleeping sickness(in cattle, pig, and horse)

iii. In plant:-

Diseases caused by microbes in plants
Microbes	Disease	Mode of transmission
Bacteria	Citrus canker	Air
Fungi	Rust of wheat	Air, seeds
Virus	Yellow vein mosaic of Okra (bhindi)	Insects

 

 

 

 

 

 

 

 

 

 

 

 

The diseases in plants result in decrease in crop yield. There for plants have to be treated by chemicals to protect them from disease causing microorganisms.

2. Microbes causing food spoilage:-

* The contamination of food by microorganisms results into food spoilage.

* Consuming spoilage food by humans and animals results in food poisoning.

* Many bacteria and fungi grow on food items and produce certain toxin. These makes the food poisonous cause a serious illness, vomiting.Therefore, there is need to preserve food from being spoiled.                

Food preservation:- Processing of food to prevent their spoilage and to retain their nutritive value for period is called food preservation.

There are many methods to preserve the food:-

(i) Heat and cold treatment

(ii) Pasteurisation

(iii) Cooling

(iv) Chemical Method

(v)Preservation by common salt

(vi) Preservation by sugar

(vii) Preservation by Oil and Vinegar

(viii) Preservation by radiation

(ix) Storage and Packing

(i) Heat and cold treatment: - Boiling of milk and liquid food products kills many microorganisms. Similarly low temperature inhibit the growth of microbes.

(ii) PASTEURISATION:-This method was developed by Louis Pasteur. Heating milk and other liquid food product to 60 to 70   for short duration is called pasteurisation.

(iii) Cooling:-Food can be kept in refrigerator at about 5˚C which delays its spoilage.

(iv) Chemical Method- Chemicals like sodium benzoate and sodium metabisulphite prevent microbial attack and are often use to preserve jams, fruits juice, squashes, sauces & ketchup.

(v)Preservation by common salt:-  Concentrated solutions of common salt can kill microorganisms due to dehydration. Common salt has been used to preserve meat, fish, amla and raw mangoes.

(vi) Preservation by sugar:-Sugar reduces the moisture content which inhibits the growth of bacteria. Jams, jellies and squashed are preserved by sugar.

(vii) Preservation by Oil and Vinegar:- Use of oil and vinegar prevents spoilage of pickle because bacteria cannot live in this environment.

(viii) Preservation by radiation:- In this method air tight packed food substances, are passed through a radiation beam, microorganisms present in food substances get destroyed due to radiation. This method is new and cheaper.

(ix) Storage and Packing:-Dry fruits and vegetables are sold in sealed air tight packet to prevent the attack of microbes.​​​​​​​

Polio:-Polio is a viral disease which damages the nerves in spine. This results in weak muscles and paralysis; especially in legs. Polio is also called infantile paralysis. Polio vaccine can prevent this disease.

* Pulse Polio is a large scale programme to eradicate polio from India. This programme is being run by the United Nations; in coordination with the Government of India. All children under five years of age are given polio drops; under this programme. Pulse Polio has been highly successful against eradication of polio.