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Milk is turned into curd by bacteria. Milk contains many microorganisms. Of these, the bacterium Lactobacillus promotes the formation of curd.

When a small amount of pre-made curd is added into warm milk, then lactobacillus bacterium present in curd multiplies in milk and converts it into curd. During this process, lactobacillus bacterium acts on lactose sugar present in milk and converts it into lactic acid. This lactic acid then converts milk into curd.

Fish and meat are often preserved by using oil or vinegar.

Role of microbes in medicine :

We obtain anitbiotics and vaccines from microbes

1. Antibiotic :

It is a substance produced by living organisms which is toxic to other organisms. The antibiotic penicillin got from the fungus Penicillium chrysogenum is used to treat diseases like tetanus, diphtheria. Streptomycin got from streptomyces bacteria is used to cure bacterial infections like plague.

2. Vaccines: 

They are prepared from dead or weakened microbes. When a vaccine is injected into the body of a patient, it produces antibodies to fight the germs. These antibodies protect the body from infections in future. 

Example: MMR vaccine for measles

1. Ciliates – presence of cilia for locomotion (e.g. Paramecium) 

2. Flagellates – presence of flagella for locomotion (e.g. Euglena)

3. Pseudopods – presence of pseudopodia for locomotion (e.g. Amoeba) 

4. Sporozoans – parasites (e.g. Plasmodium)

Flax plants are tied in bundles and kept in water. Bacteria loosen the supporting fibres of the stem by acting on the stem tissues. This process is known as retting.

1. Sewage Treatment: 

Aerobic microbes are allowed to grow in the primary effluent during the secondary stage of waste water treatment. These microbes consume the major part of the organic matter in the effluent example Nitrobacter sps. In the anaerobic treatment of sewage Methanobacterium is used.

2. Production of Biogas: 

Human and animal faecal matter and plant wastes are broken down by anaerobic bacteria to produce methane (biogas) along with carbon dioxide and hydrogen. These bacteria are called as methanogens.

3. Production of Alcohol and Wine: 

Alcoholic drinks are prepared by fermentation process using yeast. Sugars in grapes are fermented by using yeast. Beer is produced by the fermentation of sugars in rice and barley.

4. Microbes in Retting and Tanning Process: 

1. Retting: 

Flax plants are tied in bundles and kept in water. Bacteria loosen the supporting fibres of the stem by acting on the stem tissues. This process is known as retting. Linen thread is made from these fibres example Pseudomonas aeruginosa. 

2. Tanning: 

In Tanning industry bacteria act upon the skin of animals and makes it soft and therefore it becomes pliable.

Microscope is needed to see the micro-organisms.

Viruses differ from other micro-organisms because they are too much smaller in comparison to other micro-organisms. They do not show most of the characteristics of the living organisms like respiration. They just reproduce. They, however, reproduce only inside the cells of the host organism, which may be a bacterium, plant or animal. Hence, viruses differ from other micro-organisms.

The two common insects which act as carriers of disease-causing micro-organisms (or disease-causing microbes) are housefly and mosquito.

D. viruses 

Viruses are too much smaller in comparison to other micro-organisms. They do not show most of the characteristics of the living organisms like respiration. They just reproduce. They, however, reproduce only inside the cells of the host organism, which may be a bacterium, plant or animal.

Female Aedes mosquito acts as a carrier of dengue virus.

(a) female Anopheles mosquito carries the parasite of malaria. 

(b) Female Aedes mosquito acts as carrier of dengue virus.

C. cholera 

Measles, smallpox and polio are caused by viruses while cholera is caused by a bacterium.

Dengue disease is caused by a virus. Female Aedes mosquito acts as carrier of dengue virus.

They were heated to make them bacteria free.

(a) He is suffering from food poisoning. 

(b) Micro-organisms like bacteria and fungi present in the spoilt dish of mutton causes the disease, food poisoning.

The communicable diseases can occur and spread in the following ways: 

• Through air we breathe 

• Through water we drink 

• Through food we eat, and 

• Through carriers such as mosquito.

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 and tuberculosis are examples of communicable diseases.

Yeast is used for commercial production of alcohol and wine. 

B. alcohol

C. fermentation 

The process of conversion of sugar into alcohol is known as fermentation. Louis Pasteur Discovered fermentation in 1857.

B. streptomycein 

Streptomycin, tetracycline and erythromycin are some of the commonly known antibiotics which are made from fungi and bacteria.

D. female anopheles mosquito 

The carrier of malaria causing protozoan called plasmodium is female anopheles mosquito.

B. housefly 

Housefly is most common carrier of communicable diseases. The houseflies feed on garbage, animal excreta and dead organic matter. Diseases cholera and tuberculosis spread by housefly.

Cholera, chickenpox and malaria are communicable disease while cancer is not a communicable disease.

The spreading of diseases by houseflies can be prevented by following ways: 

1. Food should always be kept covered. 

2. Proper sanitation should be maintained in the kitchen.

Acetobactor aceti 

The dilute solution of acetic acid is called vinegar. Alcohol can be converted into vinegar by the action of micro-organisms called bacteria. In this process, first alcohol is produce by using yeast. The acetobacter bacteria is then added to alcohol. Acetobacter bacteria convert alcohol into acetic acid (or vinegar).

Several diseases including tuberculosis, smallpox, cholera and hepatitis can be prevented by vaccination.

Micro-organisms Organisms that can be seen only with the help of a microscope are called micro-organisms.

Micro – organisms are of 6 types. 

1. Virus : They are the minutest structures. They are also called the connecting link between living and non-living because they possess both living as well as non – living characteristics.

2. Micro plasma : It is the smallest cell which can be sieved even through a virus filter. It causes diseases in plants.

3. Bacteria : They are unicellular prokaryotes. Bacteria are found in all places around us.

4. Fungi : They are micro-organisms with simple structure and can be unicellular or multi cellular. Science They lack chlorophyll in their cells. So, they can not prepare their own food.

5. Protozoa : They are unicellular organisms. Example : amoeba, paramecium etc.

6. Algae : They are micro – organisms having simple structure and may be unicellular or multi – cellular. Water in ponds, puddles and drains appear green due to the presence of algae.

Then the food is not edible and we can become sick if we eated.

Yes, it is a chemical reaction.

The process of maintaining the nutrient richness and quality of food and other edible substances is called food preservation. 

Remedies for preventing contamination of food items :

1. Through refrigeration 

2. Through sterilization 

3. With the help of pasteurization 

4. With the help of dehydration 

5. Using boiling method 

6. By using chemicals 

7. By using salt, sugar, oil and vinegar 

8. By using disinfectants 

9. By making water bacteria free.

Alexander Flemming.

The process of converting atmospheric nitrogen into compounds of nitrogen is called nitrogen fixation. 

The two ways in which in which nitrogen gas of the atmosphere can be ‘fixed’ in nature to get nitrogen compounds in the soil are:

(i) Nitrogen fixation by lightning: Lightning also helps in fixing atmospheric nitrogen into the soil. The temperature and pressure during lightning convert atmospheric nitrogen into oxides of nitrogen. These nitrogen compounds combine with rainwater to form nitric and nitrous acid which mix with the soil.

(ii) Nitrogen fixation by certain bacteria and blue-green algae: Certain bacteria and blue-green algae present in the soil fix nitrogen from the atmosphere and convert it into compounds of nitrogen.

Blue green algae fix the atmospheric nitrogen to enrich soil with nitrogen and hence, increase soil fertility.

An antibiotic Penicillin was extracted from fungus (mould) by Alexander Fleming in 1929. This antibiotic was made from the fungus called penicillium.

An antibiotic Penicillin was extracted from fungus (mould) by Alexander Fleming in 1929. This antibiotic was made from the fungus called penicillium.

Yeast is used for the large-scale production of alcohol.

Antibiotics are not effective against ‘common cold’ and ‘flu’ as these are caused by viruses. And the viruses do not have cells but live in the cells of living beings. And the working mechanism of the antibiotics is to break the cell wall and attack on the bacteria.

Streptomycin and erythromycin are two commonly known antibiotics which are made from fungi and bacteria.

Medicines which kill or stop the growth of the disease-causing micro-organisms are called antibiotics. Streptomycin, tetracycline and erythromycin are some of the commonly known antibiotics which are made from fungi and bacteria.

Some of the precautions should be taken while taking antibiotics which are as follows:

• Antibiotics should be taken only on the advice of a qualified doctor. 

• A person must finish the full course of antibiotics prescribed by the doctor. 

• Antibiotics should not be taken unnecessarily.

Leguminous plants can fix atmospheric nitrogen into nitrogen compounds.

Leguminous plants such as beans and peas can fix nitrogen.

Some micro-organisms decompose the organic matter of dead plants and animals and convert them into simple substances which mix up with the soil. These substances are again used by other plants and animals. Thus, micro-organisms decompose the harmful and smelly dead remains of plants and animals into harmless materials and thereby clean up the environment.

Certain bacteria and blue green algae present in the soil fix atmospheric nitrogen and convert it into compounds of nitrogen.

Some bacteria and blue green algae present in the soil and rhizobium present in the root nodules of leguminous plants can fix atmospheric nitrogen.

Some bacteria like rhizobium and blue green algae like Nostoc and Anabaena present in the soil are able to fix nitrogen gas from the atmosphere to enrich soil with nitrogen and increase its fertility. These micro-organisms are commonly called biological nitrogen fixers.

D. B and D 

B and D as these two organisms are able to fix nitrogen gas from atmosphere to enrich soil with nitrogen compounds hence increasing fertility of soil