Microorganisms, Friend and Foe Notes

Major Groups of Microorganisms

Microorganisms (or microbes) are living organisms that are too small to be seen with the naked eye and require a microscope to observe. They include a vast diversity of life forms, which can be broadly grouped into:

A. Bacteria areSingle-celled prokaryotes without a true nucleus Examples: Escherichia coli, Streptococcus species.

B. Viruses are acellular particles composed of genetic material (DNA or RNA) inside a protein coat. They do not possess a proper cell some examples: Influenza virus, bacteriophages.

C. Fungi are eukaryotic organisms that can be unicellular (yeasts) or multicellular (molds, mushrooms). Examples include Saccharomyces cerevisiae (yeast), Penicillium species.

D. Protozoa are single-celled eukaryotes often found in aquatic environments.
Examples: Amoeba, Paramecium.

E. Microscopic Algae ; Photosynthetic eukaryotes, ranging from single cells to simple colonies. Some examples are: Chlorella , Diatoms.

Features of microorganisms:

Feature	Description
Size	Very small (0.2 micron to 100 microns); requires microscope to see
Cell Type	Prokaryotic (no true nucleus: bacteria, archaea) or Eukaryotic (true nucleus: fungi, protozoa, algae)
Organization	Mostly unicellular; some form colonies or simple multicellular structures
Reproduction	Asexual (binary fission, budding, spore formation) and, in some groups, sexual (conjugation, gametes)
Nutrition	Autotrophic (photosynthesis or chemosynthesis) or Heterotrophic (saprophytic, parasitic)
Genetic Material	DNA or RNA (viruses); organized in a single chromosome (prokaryotes) or multiple chromosomes in nucleus (eukaryotes)
Metabolism	Diverse biochemical pathways (aerobic, anaerobic, fermentation, photosynthesis)
Cell Wall	Present in bacteria (peptidoglycan), fungi (chitin), algae (cellulose); absent in animal cells and viruses
Habitat	Ubiquitous: soil, water, air, extreme environments (hot springs, deep sea vents), and host bodies
Mobility	Some have flagella, cilia, or pseudopodia; many are non-motile
Adaptability	Rapid growth and mutation rates enable quick adaptation to changing conditions
Role in Ecosystem	Decomposers, primary producers (algae), symbionts, pathogens

Microorganisms As friends

Preparation of curd, bread, cake, idli, dosa and cheese . Formation of curd (dahi) : Making of curd is a process in which the lactose (milk sugar) of the milk is converted into lactic acid by the action of certain bacteria (mainly Lactobacillus). This curd is further used in the preparation of idli-dosas and bhaturas. In bread making: Yeast is added to the uncooked dough to make the dough "rise". The dough rises due to the production of carbon dioxide (because of respiration of yeast) in the dough. The bread is then baked. Heat of baking drives off the carbon dioxide, making the bread porous and light. Add flavor : Some fungi (Aspergillus and Penicillium) are added to cheese to give a special flavour.

Commercial use of microorganisms

In industry ,The wine and beer (brewery) industries are important industries which make use of the fungus yeast. Yeast is grown on natural sugars present in fruit juices and grains like barley and rice. Yeast brings about conversion of sugars into alcohol and carbon dioxide.

1. Agricultural use of microorganisms

All plants and animals need nitrogen, the gas that makes up 78% of the air. Some bacteria and Blue green algae are the only organisms that can take nitrogen directly from air. These microbes convert atmospheric nitrogen into compounds of nitrogen and so called as biological nitrogen fixers. Thus, they are very useful to agriculture, as they enrich the soil with nitrogen.

2. Nitrogen cycle

Nitrogen is an essential element for all living organisms because it is a principal component of proteins and nucleic acids. The circulation of nitrogen through the living and nonliving components of the biosphere (air, soil, water, plants and animals) is called the nitrogen cycle.

Steps involved in nitrogen cycle. Atmospheric nitrogen is fixed into nitrogen compounds by Rhizobium bacteria, Blue green algae. This is called nitrogen fixation. The plants absorb nitrogen compounds from the soil and convert them into plant proteins. The plants are eaten up by animals and thus plant proteins are used for making animal proteins. When the plants and animals die, putrefying bacteria and fungi present in the soil decompose the proteins of dead plants and animals into ammonia. This process is called ammonification. 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. 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.

3. Medicinal use of microorganisms

Microbes are being employed for the production of both antibiotics and vaccines. Antibiotics : Antibiotics are produced by a number of microorganisms and inhibit the growth of other microorganisms even at very low concentrations. Fungi and bacteria are important microbes producing a variety of antibiotics. Antibiotics obtained from bacteria : Streptomycin, aureomycin and chloromycetin. Antibiotics obtained from fungi : Penicillin and Griseofulvin. These antibiotics are used to cure a variety of diseases in humans, plants and animals

4. Cleaning in the environment

Microbes, like bacteria and fungi, bring about the decay of dead plants and animals, both on land and in water. 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. They also help in sewage disposal by putrefaction (incomplete decomposition of dead organic matter).

Microorganisms As Foe

Microorganisms can cause harm in many ways. Many microbes are the causative agents of various diseases that affect plants and animals. While others causes are damage of clothes, leather and spoilage of food.

Disease causing microorganisms

(a) In human - Modes of Transmission of some human diseases caused by microbes

Human Disease	Causative Microorganism	Mode of Transmission	Preventive Measures (General)
Tuberculosis	Bacteria	Air	Keep the patient in complete isolation. Keep the personal belongings of the patient away from those of the others. Vaccination to be given at suitable age.
Measles	Virus	Air
Chicken Pox	Virus	Air/ Contact
Polio	Virus	Air/Water
Cholera	Bacteria	Water/ Food	Maintain personal hygiene and good sanitary habits. Consume properly cooked food and boiled drinking water. Vaccination.
Typhoid	Bacteria	Water
Hepatitis A	Virus	Water	Drink boiled drinking water. Vaccination.
Malaria	Protozoa	Mosquito	Use mosquito net and repellents. Spray insecticides and control breeding of mosquitoes by not allowing water to collect in the surrounding

(b) In animals : Microbes not only cause disease in humans but also in animals. The following table shows the list of microorganisms affecting various animals.

Microorganism	Name of animal diseases
Virus	Foot and mouth disease of cattle, Ranikhet of birds
Bacteria	Anthrax disease of cattle
Protozoa	Sleeping sickness (in cattle, pigs and horses)

(c) In plants : There are several microbes causing diseases in plants. The list of microorganisms affecting plants is shown below in the table.

Plant Diseases	Microorganism	Mode of Transmission
Citrus canker	Bacteria	Air
Rust of wheat	Fungi	Air, seeds
Yellow vein mosaic of bhindi (Okra)	Virus	Insect

The contamination of food by microorganisms results in food spoilage. The consumption of this spoiled food by humans or animals results in food poisoning. Microorganisms like bacteria and fungi are responsible for food poisoning. These microbes when grown on food substances produce toxins. These make the food poisonous causing vomiting, serious illness and even death. Therefore, there is a need to preserve food from being spoiled.

Food preservation

The food that we eat is either in raw or cooked form. All types of food can be targets of microbes which result in food spoilage. This prevents the food from being spoiled by the action of microorganisms. Proper preservation of food increases the storage period of food materials. It helps in obtaining the off-season food materials. It makes the transportation of food materials easier.

Methods of Food Preservation

The process of treating and handling food with an aim to stop or slow down its spoilage while maintaining its nutritional value, texture, and flavor.

Heat and cold treatment

1. Boiling of milk and liquid food products kills many microorganisms. Similarly low temperature inhibits the growth of microbes.

2. Pasteurisation : This method was developed by scientist Louis Pasteur. It is used to store milk and liquid food products. In this the food is heated up to 60°C for 30 minutes or 70°C for 15 to 30 seconds and then is suddenly chilled and stored.

3. Low temperature Storage : Microorganisms present in food products cannot be destroyed by low temperature but their metabolic activities can be arrested. So that they can't act on food products at –10°C to –18°C temperature. Fruits, eggs and meat can be stored for a long time.

4. Refrigeration : Fresh fruits, vegetables, fish, meat, eggs, etc. can be stored by keeping the temperature below 5°C.

Chemical Method

1. Chemicals which are used to check the growth of microbes are called preservatives.

2. The commonly used preservatives are sodium benzoate, sodium metabisulfite and potassium metabisulphite.

3. This method is employed in the preservation of fruit juices, jams, squashes, fruits, etc.

Preservation by common salt

1. Common salt has been used to preserve meat and fish for ages.

2. Concentrated solutions of common salt can kill microorganisms due to dehydration. Salting is also used to preserve amla (Indian gooseberry) and raw mangoes.

Preservation by sugar

Sugar reduces the moisture content which inhibits the growth of bacteria. Jams, jellies and squashes are preserved by sugar.

Preservation by oil and vinegar

Use of oil and vinegar prevents spoilage of pickles because bacteria cannot live in this environment. Vegetables, fruits, fish and meat are often preserved by this method.

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.

Question Answers

Question 1. Fill in the blanks:
(a) Microorganisms can be seen with the help of a ___________
(b) Blue green algae fix _________ directly from air to enhance fertility of soil.
(c) Alcohol is produced with the help of a microorganism ___________
(d) Cholera is caused by __________

Answer:
(a) Microscope
(b) Nitrogen
(c) Yeast
(d) Bacteria

Question 2. Tick the correct Answer:
(a) Yeast is used in the production of
(i) sugar
(ii) alcohol
(iii) hydrochloric acid
(iv) oxygen
Answer:(ii) Alcohol

(b) Which one of the following is an antibiotic?
(i) Sodium bicarbonate
(ii) Streptomycin
(iii) Alcohol
(iv) Yeast
Answer:(ii) Streptomyci

(c) Carrier of malaria-causing protozoan is
(i) female Anopheles mosquito
(ii) cockroach
(iii) housefly
(iv) butterfly
Answer: (i) Female Anopheles Mosquito

(d) The most common carrier of communicable diseases is
(i) ant
(ii) housefly
(iii) dragonfly
(iv) spider
Answer: (ii) Housefly

(e) The bread or idli dough rises because of
(i) heat
(ii) grinding
(iii) growth of yeast cells
(iv) kneading
Answer: (iii) growth of yeast cells

(f) The process of conversion of sugar into alcohol is called
(i) nitrogen inflation
(ii) moulding
(iii) fermentation
(iv) infection
Answer: (iii) fermentation

Question 3. Match the organisms in Column A with their action in Column B.

Answer:

Column A	Column B
(i) Bacteria	(e) Causing Cholera
(ii) Rhizobium	(a) Fixing nitrogen
(iii) Lactobacillus	(b) Setting of curd
(iv) Yeast	(c) Baking of bread
(v) A protozoan	(d) Causing malaria
(vi) A Virus	(f) Causing AIDS

Question 4. Can microorganisms be seen with the naked eye? If not, how can they be seen?
Answer: No, we cannot see microorganisms with the naked eye. They can be seen with the help of a microscope.

Question 5. What are the major groups of microorganisms?
Answer:The major groups of microorganisms are bacteria, fungi, algae, and protozoa.

Question 6. Name the microorganisms which can fix atmospheric nitrogen in the soil.
Answer: Bacteria e.g., Rhizobium, Azotobactor, and blue-green algae e.g., Anabaena and Nostoc can fix atmospheric nitrogen in the soil.

Question 7.Write 10 lines on the usefulness of microorganisms in our lives.
Answer: The uses of microorganisms are:

1. Microorganisms are utilized in the preparation of wines, pickles, vinegar, cheese, curds, the aroma in tobacco.

2. They are used in the production of antibiotics.

3. They help in sewage disposal.

4. Some soil bacteria like Rhizobium fix atmospheric nitrogen, which is useful for plants.

5. Some microorganisms are used for the large-scale production of alcohol, wine, and acetic acid.

6. Milk is turned into curd by bacteria.

7. Some bacteria help in tanning leather.

8. Some microorganisms are used to produce vaccines.

9. They clean the environment.

10. Some bacteria tenderize meat by breaking down muscle fibers.

Question 8. Write a short paragraph on the harms caused by microorganisms.
Answer: The harms caused by microorganisms are:

They cause a number of diseases in men, plants, and animals.

Some microorganisms spoil milk, pickles, jams, squashes, and other food items.

They damage the crops and thus, reducing productivity.

Question 9. What are antibiotics? What precautions must be taken while taking antibiotics?
Answer: Antibiotics are medicines that kill or stop the growth of disease-causing microorganisms. Antibiotics must be taken only on the advice of a qualified doctor. The course of antibiotics prescribed by the doctor must be finished. Antibiotics must not be taken when not needed, because this helps bacteria in our body to develop resistance to them. Next time when we fall ill and need these antibiotics then there would be less effectiveness.

Additional Questions and Answers

Question 1. What are microorganisms?
Answer: Microorganisms are living organisms which cannot be seen with unaided eyes, they can be seen only through the powerful microscope.

Question 2.What happens to moist bread during the rainy season?
Answer: During the rainy season, moist bread gets spoilt and its surface gets covered with greyish white patches.

Question 3.What are viruses?
Answer: Viruses are disease-causing agents and are very minute particles visible only under an electron microscope. They are smaller than bacteria.

Question 4.Name few diseases caused by virsues.
Answer: Rabies, polio, chickenpox, common cold, influenza (flu), and mosaic of tobacco and potato are the diseases caused by viruses.

Question 5.Where do microorganisms live?
Answer: Microorganisms live in the soil, mud, water, sea, air, plants, animals, food products, various utensils, etc, and on dead weeds, leaves, clothes, books, jams, pickles, dung, shoes, etc. They also live in man and animals. Amoeba lives alone. Fungi and bacteria live in colonies.

Question 6.State some beneficial effects of bacteria.

Answer:

1. The beneficial effects of bacteria are:

2. They bring about the decomposition of wastes in the soil and thus, increase the fertility of the soil.

3. Some of the putrifying bacteria decompose the matter of sewage and help in sewage disposal.

4. Some bacteria help in tanning leather.

5. Bacteria tenderize meat by breaking down muscle fibers.

6. Curd, cheese, etc. are formed by the action of bacteria in the milk.

7. The fermentation activity of bacteria is useful in the preparation of vinegar, wine, palm juice, etc.

8. Filamentous bacteria are used in the production of antibiotics.

9. Some bacteria like Rhizobium can fix the nitrogen of the atmosphere, thus, enriching the soil in the nitrogen contents.

Question 7.Name the bacteria that convert milk into curd.
Answer: Lactobacillus.

Question 8.Name the bacteria used for the production of acetic acid from alcohol.
Answer: Acetobacter acetic.

Question 9.What are yeasts? What is their shape? How do they reproduce?
Answer: Yeasts are (saccharomyces) unicellular and saprophytic fungi. The shape of yeast cells is spherical, elliptical, or cylindrical. Yeast reproduces through asexual mode by budding or by binary fission.

Question 10.Name the gas produced by yeast during respiration.
Answer: Carbon dioxide.

Question 11.Name the antibiotics made from bacteria and fungi.

Answer:Penicillin, Streptomycin, tetracycline, and erythromycin.

Question 12.Who discovered penicillin?
Answer: Alexander Fleming discovered penicillin in 1929.

Question 13.Draw a diagram to show blue-green algae.
Answer:

Question 14. Describe the role of blue-green algae in the fertility of the soil.
Answer: Blue-green algae have the ability to fix atmospheric nitrogen into usable compounds. It increases the humus content of the soil. This improves the water-holding capacity of the soil. Due to these reasons, the fertility of the soil is increased and hence, crop growth is also increased.

Question 15.What are pathogens?
Answer: Microorganisms causing diseases in human beings, plants, and animals are called pathogens.

Question 16.How do disease-causing microorganisms enter our bodies?
Answer: Disease-causing microorganisms enter our body through the air we breathe, the water we drink, or the food we eat; or transmitted by direct contact with an infected person or through an animal carrier.

Question 17.What are communicable diseases?
Answer: Communicable diseases are those microbial diseases which are spread from an infected person to a healthy person through the air, water, food, or physical contact e.g., malaria, T.B, AIDS, cholera, common cold, chickenpox, etc.

Question 18.How is the plasmodium parasite causing malaria transmission?
Answer: Plasmodium parasite is transmitted by the bite of the female anopheles mosquito. Anopheles mosquito merely acts as a carrier of malaria-causing parasites. It takes them alongwith the blood sucked from an infected person and transmits them to a healthy person.

Question 19.What is a causative microorganism of chickenpox and polio?
Answer: Disease Causative microorganism Chicken Pox is CHICKEN POX Virus and polio is caused by polio virus.

Question 20.What is a mode of transmission of causative microorganisms chickenpox and polio?
Answer: Chicken Pox is caused by Air, contact
Polio is caused by Air, water.

Question 21.What is a causative microorganism of cholera and typhoid?
Answer: Bacteria.

Question 22.What is anthrax?
Answer: Anthrax is a dangerous human and cattle disease caused by a bacterium.

Question 23.Name a disease of cattle caused by a virus.
Answer: Foot and mouth disease of cattle is caused by a virus.

Question 24.Name the bacteria which causes anthrax disease.
Answer: Bacillus anthracis.

Question 25.Who discovered the bacterium which causes anthrax disease?
Answer: Robert Koch (1876).

Question 26.Name a disease in plants caused by bacteria. What is its mode of transmission?
Answer: Citrus canker. Its mode of transmission is air.

Question 27.Name a disease in plants caused by fungi. What is its mode of transmission?
Answer: Rust of wheat. Its mode of transmission is insects and seeds.

Question 28.Name a disease in plants caused by viruses. What is its mode of transmission?
Answer: Yellow vein mosaic of bhindi. Its mode of transmission is insect.

Question 29.How food can become a poison?
Answer: Microorganisms that grow on our food sometimes produce toxic substances. These make the food poisonous causing serious illness and even death.

Question 30. What is food poisoning?
Answer: Food poisoning is due to the consumption of food spoilt by some microorganisms.

Question 31.Is spoiling food a chemical reaction?
Answer: Yes.

Question 32.What happens when food gets spoiled?
Answer: Spoiled food emits a bad smell and has a bad taste and changed colour.

Question 33.What is the role of nodules in the biological fixation of nitrogen?
Answer: The role of nodules in the biological fixation of nitrogen is to fix atmospheric nitrogen into nitrates.

Question 34.Name the bacteria which can fix nitrogen present in the air.
Answer: Rhizobium, Clostridium, and Azotobacter.

Question 35.With the help of a labelled diagram explain the various stages of the nitrogen cycle.
Answer: The various stages of the nitrogen cycle are:

1. In the soil nitrogen is present in the form of nitrates by the following processes:

2. Nitrogen and oxygen combine to form nitric acid at the time of lightning in the atmosphere. This nitric acid forms nitrates which reach the earth with rainwater.

3. Nitrates are formed in the soil from the decay of dead plants and animals.

4. Nitrogen-fixing bacteria present in soil and root nodules of some leguminous plants convert the nitrogen in the air directly into nitrates.

5. The plants absorb nitrates from the soil and convert them into plant proteins and plant protoplasm.

6. The animals eat plants and convert plant proteins into animal proteins.

7. The plant proteins and animal proteins of dead plants and animals are converted into ammonia in the soil by bacterial decomposition.

8. Nitrifying bacteria convert ammonia into nitrites and these nitrates are converted into nitrates in the soil.

9. Some of the nitrates formed in the soil are converted back into free nitrogen gas by
denitrifying bacteria. This free nitrogen gas goes back into the atmosphere and the nitrogen cycle is repeated.