Microorganisms : Friend and Foe Class 8 NCERT Notes

Microorganisms

Definition and General Characteristics of Microorganisms-

Microorganisms, often referred to as microbes, are tiny living organisms that are usually too small to be seen with the naked eye. These organisms are diverse, existing in nearly every environment on Earth, from deep sea vents and hot springs to arctic ice and our own bodies.

• Invisibility– Most microorganisms cannot be seen without the aid of a microscope, although some, like the fungus on spoiled bread, might be visible with a magnifying glass.
• Diversity– They vary widely in shape, size and behaviour. Some live independently, while others prefer living in colonies.
• Living Conditions– They can thrive in a range of environments, including extreme conditions not suitable for most other forms of life.

Types of Microorganisms-

Microorganisms are broadly categorised into five major types, each with distinct characteristics and roles in the environment and human life.

Bacteria-

• Structure– Bacteria are single-celled organisms. They lack a nucleus, meaning their DNA is not enclosed within a membrane. Instead, their genetic material floats freely in the cell in a region called the nucleoid. Bacteria also have a cell wall that gives them their shape.
• Shape and Size– Bacteria come in different shapes-
  • Spherical (called cocci).
  • Rod-shaped (called bacilli).
  • Spiral-shaped (called spirilla).
  • Comma-shaped (called vibrios).
• Most bacteria are very small, usually between 0.5 to 5 micrometers, which is much smaller than most other cells.
• Types– There are different types of bacteria, such as aerobic (need oxygen) and anaerobic (can live without oxygen). Some bacteria can even survive extreme conditions like high heat or acidic environments.
• Habitat– Bacteria live everywhere, from soil and water to the human body. Some even thrive in extreme environments like hot springs or icy polar regions.
• Mode of Nutrition– Bacteria can be autotrophic (make their own food) or heterotrophic (depend on other organisms for food). Some bacteria use sunlight to create energy (photosynthetic bacteria), while others break down chemicals (chemosynthetic bacteria).
• Reproduction– Bacteria reproduce very quickly by a process called binary fission. In this process, one bacterial cell divides into two identical cells. This allows bacteria to multiply rapidly under favorable conditions.
• Roles–
  • Bacteria play a role in fermentation, which helps produce foods like yogurt, cheese and bread.
  • They help in nitrogen fixation, converting nitrogen from the air into a form that plants can use.
  • Some bacteria are harmful and cause diseases like tuberculosis and typhoid.

Also Check – Structure ,Habitat, Mode of Nutrition in Bacteria, Reproduction and Functions of Bacteria

Fungi-

• Structure– Fungi can be single-celled, like yeasts, or multicellular, like molds and mushrooms. Their cells have a nucleus and a rigid cell wall made of chitin.
• Shape and Size– Fungi vary in size, from tiny single-celled yeasts to large mushroom structures that can grow several feet.
• Types– There are different types of fungi, including-
  • Yeasts (single-celled, used in baking and fermentation).
  • Molds (multicellular, seen as fuzzy growth on food or damp surfaces).
  • Mushrooms (the visible fruiting bodies of fungi).
• Habitat– Fungi can grow in moist, dark environments. You can find them in soil, on food, in decaying organic matter and even inside the human body.
• Mode of Nutrition– Fungi are heterotrophic, meaning they cannot produce their own food. They absorb nutrients from dead or decaying organic matter. This makes fungi important decomposers in nature.
• Reproduction– Fungi reproduce through spores, which are tiny cells that can grow into new fungi when conditions are right. These spores can be spread by the wind, water, or animals.
• Roles–
  • Fungi are important for breaking down dead plants and animals, recycling nutrients into the environment.
  • Yeasts are used in making bread and alcoholic beverages.
  • Some fungi produce antibiotics like penicillin, while others cause diseases such as athlete’s foot or ringworm.

Protozoa-

• Structure– Protozoa are single-celled organisms. They are more complex than bacteria and have internal structures like a nucleus and other organelles.
• Movement– Many protozoa are motile, meaning they can move around. They use different structures for movement-
  • Cilia (tiny hair-like structures).
  • Flagella (a long whip-like tail).
  • Pseudopodia (temporary “feet” that they extend to move).
• Shape and Size– Protozoa vary in size but are generally larger than bacteria. They come in different shapes depending on the species.
• Types– There are different types of protozoa, some of which live in water, while others live inside other organisms as parasites.
• Habitat– Protozoa are found in moist environments like ponds, lakes, soil and inside the bodies of animals and humans.
• Mode of Nutrition– Protozoa are heterotrophic, meaning they feed on other organisms like bacteria or smaller protozoa. Some protozoa can also feed on dead organic material.
• Reproduction– Most protozoa reproduce by binary fission, but some reproduce by budding or sexual reproduction.
• Roles–
  • Protozoa play a role in the food chain by controlling bacterial populations.
  • Some protozoa, like Plasmodium, cause diseases such as malaria.

Algae-

• Structure– Algae can be single-celled (like Chlamydomonas) or multicellular (like seaweeds). They are similar to plants because they have chlorophyll and perform photosynthesis.
• Shape and Size– Algae vary greatly in size. Some are tiny single-celled organisms, while others form large seaweeds that can grow several meters long.
• Types– There are different types of algae, such as green algae, brown algae and red algae, depending on the pigments they contain.
• Habitat– Algae are mostly found in water—oceans, lakes, ponds and rivers. Some algae also live in moist environments like tree bark or damp soil.
• Mode of Nutrition– Algae are autotrophic, meaning they make their own food through photosynthesis. They use sunlight, carbon dioxide and water to produce energy and release oxygen.
• Reproduction– Algae reproduce both asexually by cell division and sexually through the fusion of gametes (reproductive cells).
• Roles–
  • Algae are important in producing oxygen through photosynthesis, which supports life on Earth.
  • Some algae are used in making products like agar (a substance used in food and scientific research) and biofuels.

Viruses-

• Structure– Viruses are much smaller than bacteria. They are made up of a core of genetic material (either DNA or RNA) enclosed in a protein coat called a capsid. Some viruses also have an outer lipid layer called an envelope.
• Size– Viruses are extremely small, usually between 20 to 400 nanometers. This makes them much smaller than bacteria.
• Types– There are different types of viruses depending on their structure and the organisms they infect. Some viruses infect humans, while others infect plants, animals, or bacteria.
• Habitat– Viruses do not have a habitat of their own. They can only live and reproduce inside a host cell, which can be a bacterium, plant, or animal cell.
• Mode of Nutrition– Viruses do not have a mode of nutrition as they are not living organisms outside a host. They rely entirely on the host cell to reproduce and produce more viruses.
• Reproduction– Viruses cannot reproduce on their own. They need to infect a host cell, where they take control of the cell’s machinery to make more copies of themselves. After making copies, the virus either kills the host cell or leaves it to infect other cells.
• Roles–
  • Viruses cause a variety of diseases in humans, such as the common cold, influenza, polio and more serious illnesses like HIV/AIDS and COVID-19.
  • Some viruses are used in genetic engineering and as tools in scientific research.

Habitats of Microorganisms

Microorganisms are incredibly versatile and can be found thriving in nearly every environment on Earth. Their ability to adapt to various conditions plays a crucial role in maintaining ecological balance and supporting life. Here’s a detailed exploration of the various environments where microorganisms live and their adaptability:

1. Where Microorganisms Are Found:

• Water: Microbes are present in all water bodies, from the deepest oceans to the smallest ponds. They play essential roles in aquatic ecosystems, such as breaking down pollutants and supporting food chains.
• Soil: Soil is rich with microorganisms like bacteria, fungi, and protozoa. They decompose organic matter, recycle nutrients, and help in the nitrogen cycle, which is vital for plant growth.
• Air: Even the air contains microorganisms, including bacteria, viruses, and fungal spores, which can travel long distances driven by air currents.
• Extreme Environments:
  • Hot Springs and Geysers: Certain bacteria and archaea thrive in the boiling temperatures and are capable of surviving in extreme heat.
  • Arctic and Antarctic Regions: Cold-loving microbes, or psychrophiles, inhabit icy waters and frozen soils.
  • Deserts: Some bacteria and fungi can withstand dry, nutrient-poor conditions and can remain dormant until moisture is available.
• Inside Living Organisms: Many microbes live symbiotically within plants and animals. For example, gut bacteria in humans help in digestion and protect against harmful pathogens.

Reasons Why Microorganisms Can Adapt to Various Environments:

1. Simple and Versatile Structure:
   • Microorganisms, like bacteria and viruses, have simple structures that can easily adapt to changes. This simplicity allows them to modify and adjust quickly to new environments without complex biological processes.
2. Rapid Reproduction:
   • Microorganisms reproduce at an incredibly fast rate. This quick reproduction means that they can evolve rapidly, adapting to new environments through genetic changes that occur over several generations in a short time.
3. Genetic Mutations:
   • Mutations can occur during reproduction, and these genetic changes can sometimes lead to new traits that make a microorganism better suited to a particular environment. Beneficial mutations can spread quickly through the population.
4. Horizontal Gene Transfer:
   • Many microorganisms can acquire genes from their environment or from other microbes, even different species. This horizontal gene transfer can include genes that confer advantageous traits, such as antibiotic resistance or the ability to utilize new nutrients.
5. Biofilm Formation:
   • Some microorganisms can form biofilms, which are protective communities where microbes can share nutrients and are better protected from hostile conditions. Biofilms can help microorganisms survive in harsh environments like hot springs or icy conditions.
6. Metabolic Flexibility:
   • Microorganisms often have flexible metabolic pathways that allow them to switch their energy sources based on availability. For example, some microbes can switch between breathing oxygen and fermenting sugars depending on the oxygen levels in their environment.
7. Endospore Formation:
   • Certain bacteria can form endospores when conditions become unfavorable. Endospores are tough, dormant structures that can withstand extreme temperatures, radiation, and desiccation. When conditions improve, the endospore can reactivate into a functional bacterial cell.

Beneficial Microorganisms

Role in Food Production-

Microorganisms play a crucial role in the production of various foods and beverages, utilising their natural processes to transform basic ingredients into delicious and nutritious products.

1. Curd and Cheese– Bacteria such as Lactobacillus are involved in making curd from milk. These bacteria ferment the lactose in milk, producing lactic acid, which helps the milk to coagulate and form curd. Similarly, different bacteria are used to produce various types of cheese.
2. Bread– Yeast, a type of fungus, is essential in bread making. Yeast ferments the sugars present in dough, producing carbon dioxide, which causes the dough to rise, making the bread light and fluffy.
3. Alcoholic Beverages– Yeast is also used in the production of alcoholic beverages like beer and wine through the process of fermentation, where yeast converts sugars into alcohol and carbon dioxide.

Environmental Cleanup Through Decomposition-

Microorganisms are nature’s recyclers. They break down organic matter in the environment, which helps in cleaning up waste and returning essential nutrients to the soil.

• Decomposition– Bacteria and fungi decompose dead plants and animals, converting them into simpler forms that can be used as nutrients by other organisms in the ecosystem.

Use in Agriculture for Nitrogen Fixation and Increasing Soil Fertility-

Some microorganisms are directly involved in enhancing soil fertility, making them indispensable in agriculture.

• Nitrogen Fixation– Certain bacteria, such as those in the genus Rhizobium, live in the roots of leguminous plants and convert atmospheric nitrogen into forms that plants can absorb and use. This naturally enriches the soil with nitrogen, reducing the need for chemical fertilisers.

Production of Antibiotics and Vaccines-

Microorganisms are also key players in modern medicine, particularly in the production of antibiotics and vaccines.

• Antibiotics– Microorganisms like molds produce substances that can kill or inhibit the growth of other harmful bacteria. For example, the mold Penicillium produces penicillin, which is used to treat bacterial infections.
• Vaccines– Certain bacteria and viruses are used to create vaccines, which are biological preparations that provide acquired immunity against various infectious diseases.

Use in Scientific Research and Industries-

Microorganisms are vital tools in biotechnology and scientific research, where they are used to study genetic functions and produce a variety of products.

• Genetic Engineering– Microbes are used in genetic engineering to produce insulin, hormones and other important medical substances.
• Bioremediation– Certain microorganisms are employed to clean up pollutants from the environment, such as oil spills and heavy metal contamination in water, through a process called bioremediation.

Harmful Microorganisms

Disease-Causing Microorganisms in Humans

Microorganisms that cause diseases in humans are called pathogens. They enter our body through the air we breathe, the water we drink, or the food we eat. Sometimes, they spread through direct contact with an infected person or through animals. These diseases can be communicable, meaning they spread from one person to another.

Modes of Transmission:

1. Airborne Diseases: Some diseases spread through the air when an infected person sneezes or coughs. Tiny droplets carrying viruses or bacteria get released into the air and can be inhaled by a healthy person. Examples of airborne diseases include:
   • Tuberculosis (caused by bacteria).
   • Common Cold (caused by viruses).
   • Chicken Pox (caused by viruses).
2. Waterborne and Foodborne Diseases: Pathogens can enter our body through contaminated water or food. These microorganisms grow in unclean water or on improperly stored food. Drinking or eating such contaminated items can lead to illnesses like:
   • Cholera (caused by bacteria in contaminated water).
   • Typhoid (caused by bacteria through water or food).
   • Hepatitis A (caused by a virus through contaminated food or water).
3. Direct Contact: Some diseases spread through direct physical contact with an infected person or their belongings. For example:
   • Chicken Pox and Measles spread through direct contact with an infected person’s skin or clothing.
   • Polio can spread through water or food that contains the virus.
4. Animal or Insect Carriers: Some animals and insects carry harmful microorganisms and pass them to humans. These animals are called vectors.
   • Mosquitoes can spread diseases like malaria (caused by protozoa) and dengue (caused by a virus).
   • Houseflies carry pathogens from garbage or animal waste to uncovered food, causing diseases like cholera and typhoid.

How Diseases Spread:

When a person with an infectious disease sneezes or coughs, they release tiny droplets into the air. If someone nearby inhales these droplets, they can catch the disease. Similarly, touching contaminated surfaces, like door handles or shared items, can transfer pathogens to the body.

For example, when houseflies sit on garbage or waste, pathogens stick to their bodies. When these flies land on uncovered food, they transfer the pathogens to the food. Eating such contaminated food can make a person sick.

Mosquitoes spread diseases by biting an infected person and then biting a healthy person, transferring the pathogens from one to the other.

Disease Prevention and Control

Preventing and controlling diseases causedMethods to Control the Spread of Diseases Caused by Microorganisms- by microorganisms involves various strategies focused on hygiene, sanitation and medical interventions. Here are some effective methods-

Personal Hygiene-

• Handwashing– Regularly washing hands with soap and water, especially before eating or after using the restroom, is crucial. This simple action can prevent the spread of many infectious diseases.
• Respiratory Hygiene– Covering the mouth and nose with a tissue or the elbow when sneezing or coughing helps contain the spread of airborne pathogens.

Food Safety-

• Proper Cooking– Cooking food at the right temperature to kill harmful microorganisms is essential, especially for meat and poultry.
• Safe Storage– Keeping food in clean, sealed containers and refrigerating perishables can prevent contamination and spoilage.

Water Safety-

• Safe Drinking Water– Ensuring the water is clean and safe to drink is vital, as many pathogens spread through contaminated water. Boiling water is one of the most effective methods to purify it.

Environmental Cleanliness-

• Waste Disposal– Proper disposal and management of waste, including human and animal faeces, helps reduce the risk of water and soil contamination.
• Clean Surroundings– Regularly cleaning and disinfecting homes, schools and workplaces reduces the risk of contact with harmful microorganisms.

Vector Control-

• Mosquito Control– Preventing water stagnation, using mosquito nets and applying insect repellents can control mosquito-borne diseases like malaria and dengue.
• Rodent Control– Keeping areas clean and free of food scraps can help prevent rodents, which are carriers of several pathogens.

Vaccination-

• Immunisation– Vaccines are critical in preventing diseases such as measles, polio and hepatitis. Ensuring that vaccination schedules are followed can provide long-lasting protection against specific pathogens.

Education and Awareness-

• Community Education– Informing communities about the risks of infectious diseases and ways to prevent them can significantly reduce the spread of infections.
• School Programs– Schools play a crucial role in teaching children about hygiene practices through programs and practical demonstrations.

Disease-Causing Microorganisms in Animals

Microorganisms also cause diseases in animals, just like they do in humans. These diseases can affect various animals, including domestic pets, livestock, and wildlife. Disease-causing microorganisms in animals are harmful and can sometimes lead to serious health issues or even death. These microorganisms are commonly bacteria, viruses, and fungi.

Common Diseases in Animals Caused by Microorganisms:

1. Anthrax:
   • Causative Organism: Anthrax is caused by a bacterium called Bacillus anthracis.
   • Affected Animals: It mainly affects animals like cattle, sheep, and goats. Humans can also get infected if they come into contact with infected animals or animal products.
   • Symptoms: Animals with anthrax often show symptoms like high fever, difficulty breathing, and sudden death.
   • Transmission: The disease spreads when animals come in contact with contaminated soil, feed, or water. The bacteria form spores that can survive in the soil for many years.
   • Prevention: Vaccination is the most effective way to prevent anthrax in animals.
2. Foot and Mouth Disease (FMD):
   • Causative Organism: This disease is caused by a virus called the Foot and Mouth Virus.
   • Affected Animals: It primarily affects cloven-hoofed animals like cows, pigs, sheep, and goats.
   • Symptoms: The disease causes blisters in the mouth and on the feet of infected animals. This leads to difficulty in eating and walking. Animals may also develop fever and lose weight.
   • Transmission: FMD is highly contagious and spreads through direct contact between animals or through contaminated feed, water, and even the air.
   • Prevention: Regular vaccination and controlling the movement of infected animals can help prevent the spread of this disease.
3. Rabies:
   • Causative Organism: Rabies is caused by a virus known as the Rabies virus.
   • Affected Animals: It affects both domestic animals like dogs and cats and wild animals like bats and foxes. Humans can also get infected through the bite of an infected animal.
   • Symptoms: Animals infected with rabies may show unusual behavior like aggression, foaming at the mouth, and paralysis. The disease affects the brain and nervous system.
   • Transmission: Rabies spreads through the saliva of an infected animal, usually through bites.
   • Prevention: Vaccination of pets, especially dogs, is crucial in preventing rabies. Avoiding contact with wild animals and seeking medical treatment immediately after a bite can also prevent the disease.
4. Ringworm:
   • Causative Organism: This is caused by a type of fungus that affects the skin.
   • Affected Animals: It affects many animals, including dogs, cats, cattle, and horses.
   • Symptoms: Infected animals develop round patches of hair loss, and the skin becomes red and itchy.
   • Transmission: The fungus spreads through direct contact with infected animals or contaminated objects like bedding and grooming tools.
   • Prevention: Regular cleaning and disinfecting of animal shelters, as well as proper grooming of pets, can help prevent ringworm.
5. Avian Influenza (Bird Flu):
   • Causative Organism: This disease is caused by the Avian Influenza Virus.
   • Affected Animals: It primarily affects birds, including chickens, ducks, and turkeys. In some cases, it can also spread to humans.
   • Symptoms: Birds infected with avian influenza may show symptoms like coughing, sneezing, swelling of the head, and sudden death.
   • Transmission: The virus spreads through direct contact with infected birds, contaminated equipment, or feed.
   • Prevention: Controlling the movement of birds, disinfecting birdhouses, and regular monitoring of poultry can help prevent outbreaks of bird flu.

Prevention and Control of Animal Diseases:

• Vaccination: Regular vaccination of animals is the most effective way to prevent many diseases caused by microorganisms.
• Good Hygiene: Keeping animal shelters and farms clean and disinfected reduces the risk of infections.
• Isolating Sick Animals: Animals that show signs of illness should be isolated from healthy animals to prevent the spread of disease.
• Proper Nutrition: Providing animals with a balanced diet and clean water helps strengthen their immune systems, making them less vulnerable to infections.

Disease-Causing Microorganisms in Plants

Microorganisms can also cause diseases in plants, leading to reduced crop yield and quality. These microorganisms are mainly bacteria, fungi, and viruses. They attack plants and damage their leaves, stems, roots, and fruits. This affects not only the growth of the plants but also the economy, as crops are an important source of food and income.

Common Plant Diseases and Their Microorganisms:

1. Citrus Canker:
   • Causative Organism: Citrus canker is caused by a bacterium called Xanthomonas citri.
   • Affected Plants: It affects citrus plants like lemon, orange, and lime.
   • Symptoms: The disease causes yellow-brown spots on the leaves, stems, and fruits. These spots are often surrounded by a raised border, and affected fruits may drop early.
   • Transmission: Citrus canker spreads through air, water, and direct contact with infected plants. It can also spread through insects or contaminated farming tools.
   • Prevention: Farmers can control this disease by spraying antibiotics and by removing and destroying infected parts of the plant.
2. Rust of Wheat:
   • Causative Organism: Rust disease in wheat is caused by fungi, mainly Puccinia species.
   • Affected Plants: This disease affects wheat crops, a staple food.
   • Symptoms: Rust appears as small reddish-brown or black pustules on the leaves and stems of the plant. These pustules release fungal spores that can infect other plants.
   • Transmission: The disease spreads through the air, as the wind carries fungal spores from infected plants to healthy ones.
   • Prevention: Rust can be controlled by spraying fungicides and planting rust-resistant varieties of wheat.
3. Yellow Vein Mosaic of Bhindi (Okra):
   • Causative Organism: This disease is caused by a virus.
   • Affected Plants: It primarily affects okra (bhindi) plants.
   • Symptoms: The leaves of infected plants show yellowing of veins, and the plants become stunted. The fruits are small and deformed, reducing the overall yield.
   • Transmission: The virus is spread by insects, especially whiteflies, which feed on the plant sap.
   • Prevention: Controlling the whitefly population using insecticides or natural predators helps in reducing the spread of this disease.
4. Blight of Rice:
   • Causative Organism: Rice blight is caused by a bacterium called Xanthomonas oryzae.
   • Affected Plants: It affects rice, one of the most important food crops.
   • Symptoms: The disease causes yellowish or brown patches on the leaves. These patches enlarge, leading to the drying of leaves and a significant reduction in the rice yield.
   • Transmission: The bacteria spread through water, soil, and air. They can also be carried by contaminated farming equipment.
   • Prevention: Farmers can control the disease by using resistant varieties of rice and applying appropriate bactericides.
5. Wilt Disease in Plants:
   • Causative Organism: Wilt disease is caused by fungi or bacteria.
   • Affected Plants: This disease affects a wide range of plants, including tomatoes, cotton, and groundnuts.
   • Symptoms: Infected plants show wilting of leaves, even when there is enough water in the soil. The disease affects the plant’s vascular system, preventing water and nutrients from reaching the leaves.
   • Transmission: Wilt disease spreads through soil, water, and infected plant debris. It can also be transmitted through contaminated seeds.
   • Prevention: Using disease-free seeds, crop rotation, and removing infected plants can help control wilt disease.

Prevention and Control of Plant Diseases:

• Use of Resistant Varieties: Farmers can plant disease-resistant varieties of crops that are less likely to be affected by harmful microorganisms.
• Chemical Control: Spraying fungicides, bactericides, and insecticides can help reduce the spread of diseases in plants.
• Good Farming Practices: Keeping the field clean, removing infected plants, and using clean water for irrigation can prevent the spread of plant diseases.
• Insect Control: Many plant diseases spread through insects like whiteflies and aphids. Controlling these insect populations using natural predators or insecticides helps reduce disease transmission.

Role in Food Spoilage and Poisoning-

Microorganisms are responsible for the spoilage of food, which not only leads to a loss of nutritional value but can also cause food poisoning if consumed.

• Spoilage– Microbes like molds and yeast can grow on bread, fruits and other perishable items, especially under warm and moist conditions. This growth results in the food becoming inedible.
• Food Poisoning– Some bacteria produce toxins that are harmful to humans and animals. Consuming such contaminated food can lead to symptoms like vomiting, diarrhoea and even severe dehydration and hospitalisation.

Microorganisms in Food Production

Microorganisms play a vital role in the production of many foods and beverages that we consume daily. They help in transforming basic ingredients into finished products through natural processes like fermentation.

Use of Microorganisms in the Preparation of Various Foods and Beverages

1. Curd and Cheese–
   • Lactobacillus bacteria are responsible for turning milk into curd. These bacteria multiply and convert the lactose in milk into lactic acid, which gives curd its sour taste and thick texture.
   • Similarly, cheese is made using different types of bacteria and fungi that help in coagulating the milk, forming different varieties of cheese with unique flavours.
2. Bread and Cakes–
   • Yeast, a type of fungus, is widely used in baking. When added to dough, yeast ferments the sugars present, releasing carbon dioxide gas. This gas gets trapped in the dough, causing it to rise, making the bread soft and fluffy.
   • The same process is applied in making cakes and pastries, giving them their light and airy texture.
3. Alcoholic Beverages–
   • Yeast is also essential in the production of alcoholic beverages like wine, beer and whiskey. In these beverages, yeast ferments the sugars in grains or fruits, converting them into alcohol and carbon dioxide.
   • For example, in the making of wine, yeast ferments the sugars in grape juice, producing wine. In beer, yeast ferments the sugars in barley.

Fermentation Processes and Their Applications

Fermentation is the process where microorganisms like bacteria and yeast break down sugars to produce alcohol, gases, or acids. This natural process is not only essential for food production but also has industrial and medical applications.

1. Bread Making–
   • During fermentation, yeast converts the sugar in the dough into carbon dioxide and alcohol. The carbon dioxide forms bubbles in the dough, causing it to expand and rise. The alcohol evaporates during baking, leaving the bread fluffy and soft.
2. Alcohol Production–
   • In alcoholic beverages like wine, beer and whiskey, yeast ferments sugars to produce alcohol. The fermentation process varies depending on the beverage, but yeast remains the key component in converting sugars into ethanol (alcohol).
3. Pickling–
   • In pickling, vegetables and fruits are preserved through fermentation. Lactic acid bacteria ferment the sugars in the food, producing lactic acid. This acid prevents the growth of harmful bacteria, preserving the food and giving it a tangy flavour.
4. Fermented Dairy Products–
   • Microorganisms are also used to ferment milk into products like yoghurt and kefir. The bacteria involved in fermentation break down lactose, the sugar in milk, into lactic acid, which gives these products their sour taste.

Antibiotics and Vaccines

Development and Use of Antibiotics to Combat Microbial Infections-

Antibiotics are medicines that help fight infections caused by harmful microorganisms, particularly bacteria. They work by either killing the bacteria or stopping them from multiplying.

Discovery of Antibiotics-

• The first antibiotic, penicillin, was discovered by Alexander Fleming in 1929. He noticed that a mold, Penicillium, was able to kill bacteria in a petri dish. This discovery revolutionised medicine and led to the development of many other antibiotics.

How Antibiotics Work-

• Antibiotics target specific parts of bacterial cells, such as the cell wall or proteins needed for survival, causing the bacteria to die or stop growing. For example, penicillin destroys the cell walls of bacteria, leading to their death.
• Different antibiotics are used to treat different infections. For example, streptomycin, tetracycline and erythromycin are common antibiotics used to treat bacterial infections like tuberculosis or pneumonia.

Precautions with Antibiotics-

• Antibiotics should only be taken when prescribed by a doctor. Overuse or misuse of antibiotics can lead to antibiotic resistance, where bacteria evolve and become immune to the effects of antibiotics. This makes infections harder to treat in the future.
• It is essential to complete the full course of antibiotics, even if the symptoms improve, to ensure that all bacteria are killed and to prevent the development of resistant strains.

Importance of Vaccines in Preventing Diseases-

Vaccines play a crucial role in preventing diseases caused by microorganisms, particularly viruses and some bacteria. They protect individuals and communities from outbreaks of infectious diseases.

How Vaccines Work-

• Vaccines contain weakened or dead microbes, or parts of them, that do not cause the disease but stimulate the body’s immune system to produce antibodies. These antibodies help the body recognize and fight the real pathogen if it encounters it in the future.
• Once vaccinated, the body “remembers” how to fight the disease-causing microbes, providing immunity and preventing future infections.

Examples of Vaccines-

• Vaccines have been developed for many serious diseases, including polio, measles, tuberculosis and hepatitis. For example, the polio vaccine has been instrumental in nearly eradicating the disease worldwide.
• The smallpox vaccine, discovered by Edward Jenner in 1798, was the first successful vaccine and led to the complete eradication of smallpox.

Importance of Vaccination-

• Vaccines not only protect the individual who receives them but also help protect the community by reducing the spread of infectious diseases. This is known as “herd immunity.”
• Vaccination programs, such as the Pulse Polio Program in India, have been crucial in preventing diseases from spreading and saving millions of lives.

Nitrogen Cycle

The nitrogen cycle is a natural process in which nitrogen is converted into different forms and made available for use by plants and animals. Microorganisms play a crucial role in this cycle by helping to convert nitrogen into usable forms.

Role of Microorganisms in the Nitrogen Cycle-

Nitrogen Fixation–

• Nitrogen gas (N₂) makes up 78% of the Earth’s atmosphere, but plants and animals cannot directly use nitrogen in this form.
• Certain bacteria, such as Rhizobium, live in the root nodules of leguminous plants (like peas and beans). These bacteria convert nitrogen gas from the air into a usable form called ammonia (NH₃), which can be absorbed by plants.
• This process is called nitrogen fixation. The bacteria benefit by receiving nutrients from the plant and in return, they help the plant by providing nitrogen. This symbiotic relationship improves soil fertility.

Nitrification–

• After nitrogen is fixed into ammonia, it is converted into nitrites (NO₂⁻) and then into nitrates (NO₃⁻) by nitrifying bacteria like Nitrosomonas and Nitrobacter.
• Nitrates are the form of nitrogen that plants can easily absorb through their roots. Once absorbed, the nitrogen is used to make proteins, enzymes and other essential compounds.

Assimilation–

• Plants absorb nitrates from the soil through their roots and convert them into proteins and other nitrogen-containing compounds. Animals then eat these plants and use the nitrogen to build their own proteins and other important molecules.

Ammonification–

• When plants and animals die or release waste products, the nitrogen in their bodies returns to the soil in the form of ammonia. Decomposing bacteria break down the proteins and other compounds, releasing ammonia back into the soil.
• This process is called ammonification.

Denitrification-

• Some bacteria, called denitrifying bacteria, convert nitrates back into nitrogen gas, releasing it into the atmosphere. These bacteria, such as Pseudomonas and Clostridium, live in oxygen-poor environments, like waterlogged soils.
• Denitrification is important because it completes the nitrogen cycle by returning nitrogen to the atmosphere, ensuring the balance of nitrogen in the environment remains constant.

Importance of the Nitrogen Cycle-

• Essential for Life– Nitrogen is a key element for all living organisms. It is needed to make proteins, DNA and other vital molecules.
• Soil Fertility– Nitrogen fixation helps enrich the soil with nitrogen compounds, which promotes plant growth and improves crop yields.
• Natural Recycling– The nitrogen cycle ensures that nitrogen is constantly recycled between the atmosphere, soil, plants and animals, maintaining ecological balance.

Practical Activities and Experiments

Microorganisms are tiny, so we cannot see them with the naked eye. To understand them better, practical activities and experiments help us observe and learn how they work in various processes, especially in food preparation and environmental roles.

Observations of Microorganisms Under a Microscope-

Activity- Observing Microorganisms in Soil-

• Materials Needed– A small sample of moist soil, water, a beaker and a microscope.
• Procedure– Collect a bit of moist soil and add it to a beaker with water. Let the soil settle for a few minutes. Take a drop of the water and place it on a glass slide. Now, observe it under the microscope.
• Observation– You will see tiny microorganisms moving in the water. These could be bacteria or protozoa. Although you can’t see them with your naked eye, a microscope reveals the large variety of microorganisms present in soil.

Activity- Observing Microorganisms in Pond Water-

• Materials Needed– A few drops of pond water, a glass slide and a microscope.
• Procedure– Place a few drops of pond water on a glass slide and observe it under the microscope.
• Observation– You will find tiny organisms swimming around. These are microorganisms like protozoa or algae, which live in water bodies.

These activities help us understand that microorganisms are everywhere, even in places we don’t expect, like water and soil.

Experiments Demonstrating the Roles of Microorganisms in Food Preparation-

Activity- Making Dough Rise with Yeast-

• Materials Needed– Flour (atta or maida), sugar, water and yeast powder.
• Procedure– Mix a small amount of yeast powder with the flour, sugar and water to form soft dough. Leave the dough covered in a warm place for about two hours.
• Observation– After two hours, the dough will rise and become larger in size. This happens because yeast ferments the sugars in the dough, producing carbon dioxide. The bubbles of carbon dioxide cause the dough to expand. This is why yeast is used in baking bread and cakes.

Activity- Curd Formation-

• Materials Needed– Warm milk and a spoon of curd.
• Procedure– Add a spoonful of curd to warm milk and leave it in a warm place overnight.
• Observation– By the next day, the milk will have turned into curd. The Lactobacillus bacteria present in curd multiply in the milk and convert lactose (milk sugar) into lactic acid, giving the milk its thick and sour form known as curd. This demonstrates how bacteria are essential for preparing curd.

Experiments Demonstrating the Role of Microorganisms in Environmental Processes-

Activity- Decomposition of Organic Waste-

• Materials Needed– Plant waste (like vegetable peels) and two pots (A and B).
• Procedure– Fill both pots halfway with soil. In pot A, add plant waste. In pot B, add non-biodegradable items like plastic or glass. Leave the pots undisturbed for three to four weeks.
• Observation– In pot A, the plant waste will decompose, turning into manure, thanks to the microorganisms breaking down the organic material. In pot B, no change will be observed because plastic and glass are non-biodegradable. This experiment shows how microorganisms play a crucial role in breaking down organic waste and recycling nutrients in the environment.

Microorganisms and Biotechnology

Microorganisms are extensively used in biotechnology for their ability to carry out essential processes that benefit humans. Two key areas where microorganisms play a crucial role are genetic engineering and bioremediation.

Genetic Engineering-

Genetic engineering involves modifying the genetic material of an organism to achieve specific outcomes. Microorganisms, especially bacteria, are commonly used in genetic engineering because they are easy to manipulate and grow rapidly.

1. Use of Microorganisms in Genetic Engineering–
   • Bacteria like Escherichia coli (E. coli) are frequently used in genetic engineering. Scientists can insert a gene from another organism into a bacterium’s DNA, allowing the bacterium to produce a desired product, like insulin.
   • For example, human insulin is now produced using genetically engineered bacteria. Scientists have inserted the human gene responsible for insulin production into E. coli bacteria. The bacteria then produce insulin, which can be harvested and used as a medication for diabetic patients.
2. Applications of Genetic Engineering–
   • Medicine– Genetic engineering is used to produce medicines, including vaccines and hormones like insulin and human growth hormone.
   • Agriculture– Genetically modified (GM) crops are developed using microorganisms to introduce traits like pest resistance or improved nutritional content. For example, Bt cotton is a genetically modified crop that produces a toxin harmful to pests, reducing the need for chemical pesticides.

Bioremediation-

Bioremediation is the use of microorganisms to remove pollutants from the environment. Microorganisms can break down harmful substances into less toxic or non-toxic substances, making them essential for cleaning up environmental contamination.

1. Role of Microorganisms in Bioremediation-
   • Certain bacteria and fungi are capable of breaking down hazardous substances like oil spills, heavy metals and industrial waste. These microorganisms use the pollutants as a source of food and energy, transforming them into harmless compounds like water and carbon dioxide.
   • For example, bacteria such as Pseudomonas are used in cleaning up oil spills. These bacteria consume the oil, breaking it down into simpler, non-toxic substances, thereby reducing environmental damage.
2. Applications of Bioremediation-
   • Oil Spill Cleanup– When oil spills occur in oceans or lakes, microorganisms are introduced to break down the oil and minimise the environmental impact.
   • Waste Treatment– In sewage treatment plants, bacteria are used to break down organic waste, making water safe for discharge back into rivers or for reuse.
   • Land Reclamation– Microorganisms are used to clean up contaminated land, such as former industrial sites, by breaking down pollutants like heavy metals and pesticides.

Economic Importance of Microorganisms

Microorganisms contribute significantly to various fields, including biotechnology, medicine and agriculture. Their applications help improve the economy by boosting productivity, health and sustainability in these sectors.

Contributions to Biotechnology-

Production of Enzymes and Chemicals-

• Microorganisms are used in the production of enzymes like amylase and protease, which are important for industries such as textiles, detergents and food processing.
• They also help produce important chemicals like ethanol and acetic acid through fermentation. These chemicals are widely used in the production of biofuels, alcoholic beverages and vinegar.

Fermentation Processes-

• Microorganisms like yeast and bacteria are essential in the fermentation process, which is used to make products like bread, yoghurt and beer. These fermentation processes generate income in the food and beverage industry.
• The use of genetically modified microorganisms in biotechnology has enhanced the efficiency of these processes, making the production faster and more cost-effective.

Biotechnology and Genetic Engineering-

• Bacteria, like Escherichia coli (E. coli), are used in genetic engineering to produce human insulin, growth hormones and other medicines. This helps the pharmaceutical industry manufacture life-saving drugs at a large scale.

Contributions to Medicine-

Production of Antibiotics–

• Microorganisms, particularly bacteria and fungi, produce antibiotics like penicillin, streptomycin and tetracycline. These antibiotics are used to treat bacterial infections in humans and animals, making them essential for public health.
• The discovery of antibiotics has revolutionised medicine, allowing doctors to treat infections that were once fatal, thus improving human life expectancy and reducing medical costs.

Vaccine Production–

• Microorganisms are used to develop vaccines for various diseases. Weakened or dead forms of bacteria and viruses are used in vaccines to stimulate the immune system, protecting people from diseases like tuberculosis, hepatitis and polio.
• Vaccines produced using microorganisms help prevent the spread of infectious diseases, reducing healthcare costs and increasing productivity in society by keeping people healthy.

Probiotics and Health Supplements–

• Certain beneficial bacteria, like Lactobacillus and Bifidobacterium, are used as probiotics in health supplements. These microorganisms help in improving digestion, boosting immunity and maintaining gut health, contributing to the wellness industry.

Contributions to Agriculture-

Nitrogen Fixation-

• Some bacteria, such as Rhizobium, live in the root nodules of leguminous plants and help fix atmospheric nitrogen into the soil. This natural process improves soil fertility, reducing the need for chemical fertilisers.
• This process supports sustainable agriculture, increasing crop yields while lowering costs for farmers.

Composting and Waste Decomposition-

• Microorganisms like bacteria and fungi are used in composting organic waste. They break down plant and animal waste into simple nutrients, producing manure that is rich in nutrients and beneficial for soil health.
• This method of natural waste recycling not only enhances soil fertility but also helps reduce environmental pollution.

Biopesticides-

Some microorganisms, such as Bacillus thuringiensis (Bt), are used as biopesticides to protect crops from pests without harming the environment. These biopesticides are natural and safer alternatives to chemical pesticides, reducing the environmental impact and improving crop safety.